Per Steinar Halvorsen

• Frostelid, Vetle Christoffer; Wajdan, Ali; Villegas-Martinez, Manuel; Hammersbøen, Lars Egil Reine; Espinoza, Andreas & Grymyr, Ole-Johannes Holm Nielsen [Vis alle 9 forfattere av denne artikkelen] (2025). Continuous and Autonomous Monitoring of Changes in Left Ventricular dP/dt<inf>max</inf>Using an Epicardial Accelerometer. Annals of Biomedical Engineering. ISSN 0090-6964. 53(11), s. 2783–2794. doi: 10.1007/s10439-025-03828-6. Fulltekst i vitenarkiv
• Nesaragi, Naimahmed; Qadir, Hemin Ali; Høiseth, Lars Øivind; Rosseland, Leiv Arne; Halvorsen, Per Steinar & Balasingham, Ilangko (2025). Decoding Blood Volume Loss: Can Non-Invasive Signals Match the Gold Standard? I Redaktørkomite (Red.), 2025 47th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC). IEEE (Institute of Electrical and Electronics Engineers). ISSN 9798331586188. s. 1–6. doi: 10.1109/embc58623.2025.11252812. Fulltekst i vitenarkiv Vis sammendrag

  The potential of advanced waveform analysis of physiological signals to diagnose varying levels of hypovolemia has not been fully explored. This study extends previous work by comparing the discriminative ability of invasive and noninvasive signals to classify levels of ongoing hypovolemia using a deep learning (DL) framework. Hypovolemia was simulated via a dynamic lower body negative pressure (LBNP) model among healthy volunteers, allowing for real-life-like fluctuations in intravascular blood volume caused by bleeding and resuscitation. The analysis incorporated photoplethysmography (PPG) as a non-invasive signal and invasive arterial blood pressure (ABP) waveforms, processed using the same DLbased framework. A supervised DL model was developed to perform ternary classification, segmenting the signals and labeling them with corresponding LBNP target levels: Mild (Class 1), Moderate (Class 2), and Severe (Class 3) blood volume loss. The model utilized time-frequency representations of the waveform segments and late fusion of latent space features to enhance classification performance. Results revealed that while both PPG and ABP demonstrated the ability to detect hypovolemia levels, the PPG signal showed comparable or superior performance in classification accuracy with AUROC 0.8861 and F1 0.7216, offering a non-invasive alternative with high diagnostic potential.

• Sævik, Marte; Andersen, Marit Helen; Beitnes, Jan Otto; Aaberge, Lars & Halvorsen, Per Steinar (2025). Health Related Quality of Life (HRQoL) after transcatheter aortic valve implantation in aortic stenosis patients: exploring a novel threshold for clinically significant improvement after 12 months. Journal of Patient-Reported Outcomes. doi: 10.1186/s41687-025-00894-1. Fulltekst i vitenarkiv Vis sammendrag

  Aim The study aimed to determine the proportion of patients with significant improvements in Health-Related Quality of Life (HRQoL) 12 months after Transcatheter Aortic Valve Implantation (TAVI), using a threshold for physical function (PF) and physical role (RP) domains of the SF-36 questionnaire. Additionally, we explored shared baseline characteristics of patients reporting these improvements. Methodology In this prospective observational study, 88 patients with symptomatic, severe aortic stenosis (AS) and preserved ejection fraction were enrolled between April 2017 and February 2020. Exclusion criteria were clinical instability, pacemaker, chronic AF, comorbidities with life expectancy < 1 year. HRQoL was evaluated before and 12 months after transfemoral TAVI using the Norwegian version 2.0 of SF-36, and presented as mean (95% confidence interval). Other outcome measures were 6-minute walking test and NYHA- classification. Independent samples t-test or Mann-Whitney U test was used for between-group comparisons as appropriate. Logistic regression or Chi2-test were used to explore associations between changes in PF and RP and clinical parameters. Statistical significance was set at p ≤ 0.05, and clinically significant changes in HRQoL were defined as increase of ≥ 15 points in the PF and RP categories. Results Mean age of the cohort was 80 ± 6 years. 44 (50%) patients reported clinically significant improvement in PF, and 46 (52%) in the RP domain. Baseline scores were significantly lower in patients reporting clinical improvement after TAVI, with PF scores pre intervention 43.07 (37.37–48.78) vs. 65.34 (59.01–71.68), p < 0.001, and RP 36.01 (29.56–42.46) vs. 59.92 (50.91–68.92), p < 0.001. No significant associations were found between improvement in domain scores and parameters from the routine baseline examination, but having ≥ 15-point improvement correlated to baseline PF and RP scores. Conclusion Our study highlights the importance of defining a uniform threshold for clinically significant improvement in the SF-36 HRQoL questionnaire for patients undergoing TAVI. Half of the patients reported favorable long-term outcome for PF and RP aspects of SF-36. This emphasizes the importance of HRQoL assessment in the preoperative work up for patients undergoing TAVI. Trial registration https://www.clinicaltrials.gov/ 05.04.2017 with ID NCT03107923.

• Antonsen, Lars; Landsverk, Svein A.; Halvorsen, Per Steinar; Thiara, Amrit Paul Singh; Lilja, Didrik & Nesaragi, Naimahmed [Vis alle 7 forfattere av denne artikkelen] (2025). Accelerometer-based vibration analysis and oxygenator thrombosis in venovenous ECMO: an experimental porcine model. Intensive Care Medicine Experimental. 13(1). doi: 10.1186/s40635-025-00763-7. Fulltekst i vitenarkiv Vis sammendrag

  Background Oxygenator thrombosis is a potentially life-threatening complication during venovenous extracorporeal membrane oxygenation (VV ECMO). It can cause blood flow obstruction, impaired gas exchange, hematologic abnormalities, or sudden ECMO flow cessation. Early detection and timely circuit exchange is critical yet challenging. Acute clot formation necessitates immediate circuit replacement, while premature replacement risks unnecessary procedural harm and increased costs. No reliable method exists to detect early oxygenator thrombosis. Strategies include visual inspection, monitoring the pressure difference across the oxygenator (ΔPoxy), gas exchange evaluation, and blood tests. In the present animal study, we aimed to evaluate the feasibility of accelerometer-based vibration analysis as a real-time and non-invasive method for detecting oxygenator thrombosis during VV ECMO. We hypothesized that accelerometer signals would change concurrently with or precede increases in ΔPoxy. Methods The study was performed on anesthetized and mechanically ventilated pigs (n = 7) on VV ECMO. Hemodynamic parameters, ECMO circuit pressures, and signals from an accelerometer attached to the ECMO oxygenator were continuously recorded at different pump speeds, and after anticoagulation reversal to promote thrombosis within the ECMO oxygenator. Results The primary finding of this study was a significant increase in the accelerometer signal's Root Mean Squared (RMSoxy) 15 min after anticoagulation reversal, with no rpm adjustment and without corresponding changes in ΔPoxy. Variations in RMSoxy associated with high ECMO pump speed and circuit flow were discernible from those observed following anticoagulation reversal. Conclusion The present animal study demonstrates the feasibility of accelerometer-based vibration analysis as a real-time and non-invasive method for detecting vibrations associated with reversal of anticoagulation and potential oxygenator thrombosis during VV ECMO.

• Wajdan, Ali; Frostelid, Vetle Christoffer; Villegas-Martinez, Manuel; Halvorsen, Per Steinar; Krogh, Magnus Reinsfelt & Elle, Ole Jakob [Vis alle 7 forfattere av denne artikkelen] (2025). Deep neural network valve detection for accelerometer based cardiac monitoring. Scientific Reports. 15(1). doi: 10.1038/s41598-025-00845-2. Fulltekst i vitenarkiv Vis sammendrag

  Miniaturized accelerometers incorporated in pacing leads attached directly onto the heart provide a means for continuous monitoring of cardiac function. Several functional accelerometer indices first require detection of valve events. We previously developed a deep neural network to detect timing of aortic valve closure and opening. In this study we trained and tested the performance of the network to detect timing of mitral valve closure (MVC) and opening (MVO). Furthermore, we extracted four different functional indices based on the detected valve events and investigated how these indices reflected changes in cardiac function. The neural network was tested on approximately 5900 heartbeats from 289 recordings in a total of 46 animals with a cardiac accelerometer attached to the heart during various interventions that altered function. The neural network correctly detected MVO and MVC in 89.6% and 87.5% of the beats, respectively, with a mean absolute error of 13 ms between the detected values and the annotated targets for both. The functional indices correlated well with measured left ventricular stroke work (0.67 < r < 0.84) and showed expected changes for the different interventions. Hence, automatic detection of valve events is feasible and facilitates improved cardiac monitoring when using implanted cardiac accelerometers.

• Sævik, Marte; Beitnes, Jan Otto; Aaberge, Lars & Halvorsen, Per Steinar (2025). Flow Reserve Does Not Predict Long-Term Outcomes After Transaortic Valve Implantation in Patients With Preserved Left Ventricular Ejection Fraction. Journal of Clinical Ultrasound. ISSN 0091-2751. 53(7), s. 1479–1487. doi: 10.1002/jcu.24034. Fulltekst i vitenarkiv
• Antonsen, Lars; Espinoza, Andreas; Halvorsen, Per Steinar; Schalit, Itai; Bergan, Harald & Lilja, Didrik [Vis alle 7 forfattere av denne artikkelen] (2024). The impact of hypovolemia and PEEP on recirculation in venovenous ECMO: an experimental porcine model. Intensive Care Medicine Experimental. 12(1). doi: 10.1186/s40635-024-00636-5. Fulltekst i vitenarkiv Vis sammendrag

  Background Recirculation is a common problem in venovenous extracorporeal membrane oxygenation (VV ECMO) and may limit the effect of ECMO treatment due to less efficient blood oxygenation or unfavorable ECMO and ventilator settings. The impact of hypovolemia and positive end expiratory pressure (PEEP) on recirculation is unclear and poorly described in guidelines, despite clinical importance. The aim of this study was to investigate how hypovolemia, autotransfusion and PEEP affect recirculation in comparison to ECMO cannula distance and circuit flow. Methods In anesthetized and mechanically ventilated pigs (n = 6) on VV ECMO, we measured recirculation fraction (RF), changes in recirculation fraction (∆RF), hemodynamics and ECMO circuit pressures during alterations in PEEP (5 cmH2O vs 15 cmH2O), ECMO flow (3.5 L/min vs 5.0 L/min), cannula distance (10–14 cm vs 20–26 cm intravascular distance), hypovolemia (1000 mL blood loss) and autotransfusion (1000 mL blood transfusion). Results Recirculation increased during hypovolemia (median ∆RF 43%), high PEEP (∆RF 28% and 12% with long and short cannula distance, respectively), high ECMO flow (∆RF 49% and 28% with long and short cannula distance, respectively) and with short cannula distance (∆RF 16%). Recirculation decreased after autotransfusion (∆RF − 45%). Conclusions In the present animal study, hypovolemia, PEEP and autotransfusion were important determinants of recirculation. The alterations were comparable to other well-known factors, such as ECMO circuit flow and intravascular cannula distance. Interestingly, hypovolemia increased recirculation without significant change in ECMO drainage pressure, whereas high PEEP increased recirculation with less negative ECMO drainage pressure. Autotransfusion decreased recirculation. The findings are interesting for clinical studies.

• Nesaragi, Naimahmed; Høiseth, Lars Øivind; Qadir, Hemin Ali; Rosseland, Leiv Arne; Halvorsen, Per Steinar & Balasingham, Ilangko (2023). Non-invasive waveform analysis for emergency triage via simulated hemorrhage: An experimental study using novel dynamic lower body negative pressure model. Biocybernetics and Biomedical Engineering (BBE). ISSN 0208-5216. 43(3), s. 551–567. doi: 10.1016/j.bbe.2023.06.002. Fulltekst i vitenarkiv Vis sammendrag

  The extent to which advanced waveform analysis of non-invasive physiological signals can diagnose levels of hypovolemia remains insufficiently explored. The present study explores the discriminative ability of a deep learning (DL) framework to classify levels of ongoing hypovolemia, simulated via novel dynamic lower body negative pressure (LBNP) model among healthy volunteers. We used a dynamic LBNP protocol as opposed to the traditional model, where LBNP is applied in a predictable step-wise, progressively descending manner. This dynamic LBNP version assists in circumventing the problem posed in terms of time dependency, as in real-life pre-hospital settings intravascular blood volume may fluctuate due to volume resuscitation. A supervised DL-based framework for ternary classification was realized by segmenting the underlying noninvasive signal and labeling segments with corresponding LBNP target levels. The proposed DL model with two inputs was trained with respective time–frequency representations extracted on waveform segments to classify each of them into blood volume loss: Class 1 (mild); Class 2 (moderate); or Class 3 (severe). At the outset, the latent space derived at the end of the DL model via late fusion among both inputs assists in enhanced classification performance. When evaluated in a 3-fold cross-validation setup with stratified subjects, the experimental findings demonstrated PPG to be a potential surrogate for variations in blood volume with average classification performance, AUROC: 0.8861, AUPRC: 0.8141,

• Lilja, Didrik; Schalit, Itai; Espinoza, Andreas; Nilsen-Hoel, Tom; Larsen, Guttorm & Pettersen, Fred-Johan [Vis alle 7 forfattere av denne artikkelen] (2023). Extracorporeal driveline vibrations to detect left ventricular assist device thrombosis – A porcine model study. The Journal of Heart and Lung Transplantation. ISSN 1053-2498. s. 1–9. doi: 10.1016/j.healun.2023.08.022. Fulltekst i vitenarkiv Vis sammendrag

  Background Pump thrombosis (PT) and related adverse complications contributed to the HeartWare Ventricular Assist Device (HVAD) market withdrawal. Many patients still receive lifelong support, with deficient PT surveillance based on pump power trends. Analysis of pump vibrations is better for detecting PT. Here, we investigated the feasibility of an extracorporeal accelerometer to detect PT from pump vibrations propagated out on the driveline. Methods In a porcine HVAD model (n = 6), an accelerometer was attached to the pump as a reference and another to the driveline for comparisons of signals. In total, 59 thrombi were injected into the heart to induce PT, followed by intermittent thrombus washout maneuvers. Signals were compared visually in spectrograms and quantitatively in third harmonic saliences (S3H) by correlation analysis. Receiver operating characteristic curves expressed the method’s outcome in sensitivity vs specificity, with the overall diagnostic performance in the area under the curve (AUC) score. Results Five experiments had good driveline signal strength, with clear spectrographic relationships between the 2 accelerometers. Third harmonic driveline vibrations were visible 20 vs 30 times in the reference. The comparison in S3H showed a strong correlation and yielded an AUC of 0.85. Notably, S3H proved robust regarding noise and false PT detections. Conclusions An extracorporeal accelerometer on the driveline can be a readily available method for accurate HVAD PT detection before an accelerometer integration with left ventricular assist device is feasible.

• Lilja, Didrik; Schalit, Itai; Espinoza, Andreas; Fiane, Arnt Eltvedt; Dahle, Gry & Sandbu, Helen Littorin [Vis alle 11 forfattere av denne artikkelen] (2023). Detection of inflow obstruction in left ventricular assist devices by accelerometer: A porcine model study. The Journal of Heart and Lung Transplantation. ISSN 1053-2498. 42(8), s. 1005–1014. doi: 10.1016/j.healun.2023.03.017. Fulltekst i vitenarkiv Vis sammendrag

  Background Left ventricular assist devices (LVAD) provide circulatory blood pump support for severe heart failure patients. Pump inflow obstructions may lead to stroke and pump malfunction. We aimed to verify in vivo that gradual inflow obstructions, representing prepump thrombosis, are detectable by a pump-attached accelerometer, where the routine use of pump power (PLVAD) is deficient. Method In a porcine model (n = 8), balloon-tipped catheters obstructed HVAD inflow conduits by 34% to 94% in 5 levels. Afterload increases and speed alterations were conducted as controls. We computed nonharmonic amplitudes (NHA) of pump vibrations captured by the accelerometer for the analysis. Changes in NHA and PLVAD were tested by a pairwise nonparametric statistical test. Detection sensitivities and specificities were investigated by receiver operating characteristics with areas under the curves (AUC). Results NHA remained marginally affected during control interventions, unlike PLVAD. NHA elevated during obstructions within 52-83%, while mass pendulation was most pronounced. Meanwhile, PLVAD changed far less. Increased pump speeds tended to amplify the NHA elevations. The corresponding AUC was 0.85-1.00 for NHA and 0.35-0.73 for PLVAD. Conclusion Elevated NHA provides a reliable indication of subclinical gradual inflow obstructions. The accelerometer can potentially supplement PLVAD for earlier warnings and localization of pump.

• Qadir, Hemin Ali; Nesaragi, Naimahmed; Halvorsen, Per Steinar & Balasingham, Ilangko (2023). A Multi-channel EEG Data Analysis for Poor Neuro-prognostication in Comatose Patients with Self and Cross-channel Attention Mechanism. I Young, Rosanna Degani (Red.), 2023 Computing in Cardiology. IEEE (Institute of Electrical and Electronics Engineers). ISSN 9781665459259. s. 1–4. doi: 10.22489/CinC.2023.251. Fulltekst i vitenarkiv Vis sammendrag

  This work is part of the ’Predicting Neurological Recovery from Coma After Cardiac Arrest: The George B. Moody PhysioNet Challenge 2023’ to investigate the predictive potential of bipolar electroencephalogram (EEG) recordings towards efficient prediction of poor neurological outcomes. A retrospective design using a hybrid deep learning approach is utilized to optimize an objective function aiming for high specificity, i.e., true positive rate (TPR) with reduced false positives (≤ 0.05). A multichannel EEG array of 18 bipolar channel pairs from a randomly selected 5-minute segment in an hour is kept. In order to determine the outcome prediction, a combination of a feature encoder with 1-D convolutional layers, learnable position encoding, a context network with attention mechanisms, and finally, a regressor and classifier blocks are used. The feature encoder extricates local temporal and spatial features, while the following position encoding and attention mechanisms attempt to capture global temporal dependencies. Results: The proposed framework by our team, OUS IVS, when validated on the challenge hidden test data, exhibited an unofficial score (not ranked) of 0.416 at 72 hours after the return of spontaneous circulation. The code for this paper is available on GitHub: https://github.com/HeminQadir/ PhysioNet_OUS_IVS.

• Wisløff-Aase, Kristin; Skulstad, Helge; Beitnes, Jan Otto; Lundblad, Runar; Halvorsen, Per Steinar & Fiane, Arnt Eltvedt [Vis alle 7 forfattere av denne artikkelen] (2022). Left Ventricular Function Changes Induced by Moderate Hypothermia Are Rapidly Reversed after Rewarming - A Clinical Study. Critical Care Medicine. ISSN 0090-3493. 50(1), s. E52–E60. doi: 10.1097/CCM.0000000000005170. Fulltekst i vitenarkiv
• Lilja, Didrik; Schalit, Itai; Espinoza, Andreas Westenvik; Pettersen, Fred-Johan; Elle, Ole Jakob & Halvorsen, Per Steinar (2022). Detection of inflow obstruction in left ventricular assist devices by accelerometer: An in vitro study. Medical Engineering and Physics. ISSN 1350-4533. 110. doi: 10.1016/j.medengphy.2022.103917. Fulltekst i vitenarkiv Vis sammendrag

  Inflow obstruction in left ventricular assist devices (LVAD) may lead to embolic stroke and pump malfunction. We investigated if an accelerometer detected graded LVAD inflow obstructions. Detection performances were compared to the current continuous surveillance routine based on the pump power consumption (PLVAD). In ten mock circuit experiments, four different-sized pendulating balloons obstructed HVAD™ inflow conduits cross-section areas by 14%-75%. Nonharmonic amplitudes (NHA) of continuous signals from a triaxial accelerometer attached to the LVAD were compared against single-point PLVAD values, using load and speed alterations as control interventions. We analyzed the NHA band power with a pairwise nonparametric statistical test. The detection performances were analyzed by receiver operating characteristics with areas under the curves (AUC). The NHA remained unaffected during load alterations. In contrast, NHA increased significantly from the 27% obstruction level (AUC≥0.82), an effect amplified by increased pump speed. PLVAD did not change significantly below the maximal 75% obstruction level (AUC≤0.36). In conclusion, NHA detected the inflow obstructions much better than PLVAD. The technique may provide a future monitoring modality of any pendulating obstructive inflow pathology.

• Wisløff-Aase, Kristin; Skulstad, Helge; Haugaa, Kristina Ingrid Helena Hermann; Lingaas, Per Snorre; Beitnes, Jan Otto & Halvorsen, Per Steinar [Vis alle 7 forfattere av denne artikkelen] (2022). Myocardial electrophysiological and mechanical changes caused by moderate hypothermia—A clinical study. Physiological Reports. 10:e15259(8), s. 1–10. doi: 10.14814/phy2.15259. Fulltekst i vitenarkiv Vis sammendrag

  Moderate hypothermia has been used to improve outcomes in comatose out-of-hospital cardiac arrest survivors during the past two decades, although the effects remain controversial. We have recently shown in an experimental study that myocardial electrophysiological and mechanical relationships were altered during moderate hypothermia. Electromechanical window positivity increased, and electrical dispersion of repolarization decreased, both of which are changes associated with decreased arrhythmogenicity in clinical conditions. Mechanical dispersion, a parameter also linked to arrhythmic risk, remained unaltered. Whether corresponding electrophysiological and mechanical changes occur in humans during moderate hypothermia, has not been previously explored. Twenty patients with normal left ventricular function were included. Measurements were obtained at 36 and 32°C prior to ascending aortic repair while on partial cardiopulmonary bypass and at 36°C after repair. Registrations were performed in the presence of both spontaneous and comparable paced heart rate during standardized loading conditions. The following electrical and mechanical parameters were explored: (1) Electromechanical window, measured as time difference between mechanical and electrical systole, (2) dispersion of repolarization from ECG T-wave, and (3) mechanical dispersion, measured as segmental variation in time to peak echocardiographic strain. At moderate hypothermia, mechanical systolic prolongation (425 ± 43–588 ± 67 ms, p < 0.001) exceeded electrical systolic prolongation (397 ± 49–497 ± 79 ms, p < 0.001), whereby, electromechanical window positivity increased (29 ± 30–86 ± 50 ms, p < 0.001). Dispersion of repolarization and mechanical dispersion remained unchanged. Corresponding electrophysiological and mechanical relationships were present at comparable paced heart rates. After rewarming, the increased electromechanical window was reversed in the presence of both spontaneous and paced heart rates. Moderate hypothermia increased electromechanical window positivity, while dispersion of repolarization and mechanical dispersion remained unchanged. This impact of hypothermia may be clinically relevant for selected groups of patients after cardiac arrest.

• Schalit, Itai; Espinoza, Andreas Westenvik; Pettersen, Fred-Johan; Skulstad, Helge; Fosse, Erik & Fiane, Arnt Eltvedt [Vis alle 7 forfattere av denne artikkelen] (2022). Improved Detection of Thromboembolic Complications in Left Ventricular Assist Device by Novel Accelerometer-Based Analysis. ASAIO journal (1992). ISSN 1058-2916. 68(9), s. 1117–1125. doi: 10.1097/MAT.0000000000001654. Fulltekst i vitenarkiv
• Wajdan, Ali; Jahren, Tollef Struksnes; Villegas-Martinez, Manuel; Khan, Faraz Hameed; Halvorsen, Per Steinar & Odland, Hans Henrik [Vis alle 9 forfattere av denne artikkelen] (2022). Automatic Detection of Aortic Valve Events Using Deep Neural Networks on Cardiac Signals From Epicardially Placed Accelerometer. IEEE Journal of Biomedical and Health Informatics. ISSN 2168-2194. 26(9), s. 4450–4461. doi: 10.1109/JBHI.2022.3181148. Fulltekst i vitenarkiv Vis sammendrag

  Background: Miniaturized accelerometers incorporated in pacing leads attached to the myocardium, are used to monitor cardiac function. For this purpose functional indices must be extracted from the acceleration signal. A method that automatically detects the time of aortic valve opening (AVO) and aortic valve closure (AVC) will be helpful for such extraction. We tested if deep learning can be used to detect these valve events from epicardially attached accelerometers, using high fidelity pressure measurements to establish ground truth for these valve events. Method: A deep neural network consisting of a CNN, an RNN, and a multi-head attention module was trained and tested on 130 recordings from 19 canines and 159 recordings from 27 porcines covering different interventions. Due to limited data, nested cross-validation was used to assess the accuracy of the method. Result: The correct detection rates were 98.9% and 97.1% for AVO and AVC in canines and 98.2% and 96.7% in porcines when defining a correct detection as a prediction closer than 40 ms to the ground truth. The incorrect detection rates were 0.7% and 2.3% for AVO and AVC in canines and 1.1% and 2.3% in porcines. The mean absolute error between correct detections and their ground truth was 8.4 ms and 7.2 ms for AVO and AVC in canines, and 8.9 ms and 10.1 ms in porcines. Conclusion: Deep neural networks can be used on signals from epicardially attached accelerometers for robust and accurate detection of the opening and closing of the aortic valve.

• Krogh, Magnus Reinsfelt; Halvorsen, Per Steinar; Grymyr, Ole-Johannes Holm Nielsen; Bergsland, Jacob; Elle, Ole Jakob & Fosse, Erik [Vis alle 7 forfattere av denne artikkelen] (2021). Continuous Estimation of Acute Changes in Preload Using Epicardially Attached Accelerometers. IEEE Transactions on Biomedical Engineering. ISSN 0018-9294. 68(7), s. 2067–2075. doi: 10.1109/TBME.2020.3020358. Fulltekst i vitenarkiv
• Storm, Benjamin; Halvorsen, Per Steinar; Skulstad, Helge; Dybwik, Knut Gustav; Schjalm, Camilla & Christiansen, Dorte [Vis alle 11 forfattere av denne artikkelen] (2021). Open chest and pericardium facilitate transpulmonary passage of venous air emboli. Acta Anaesthesiologica Scandinavica. ISSN 0001-5172. 65(5), s. 648–655. doi: 10.1111/aas.13796. Fulltekst i vitenarkiv Vis sammendrag

  Background Transpulmonary passage of air emboli can lead to fatal brain- and myocardial infarctions. We studied whether pigs with open chest and pericardium had a greater transpulmonary passage of venous air emboli than pigs with closed thorax. Methods We allocated pigs with verified closed foramen ovale to venous air infusion with either open chest with sternotomy and opening of the pleura and pericardium (n = 8) or closed thorax (n = 16). All pigs received a five-hour intravenous infusion of ambient air, starting at 4-6 mL/kg/h and increased by 2 mL/kg/h each hour. We assessed transpulmonary air passage by transesophageal M-mode echocardiography and present the results as median with inter-quartile range (IQR). Results Transpulmonary air passage occurred in all pigs with open chest and pericardium and in nine pigs with closed thorax (56%). Compared to pigs with closed thorax, pigs with open chest and pericardium had a shorter to air passage (10 minutes (5-16) vs. 120 minutes (44-212), P < .0001), a smaller volume of infused air at the time of transpulmonary passage (12 mL (10-23) vs.170 mL (107-494), P < .0001), shorter time to death (122 minutes (48-185) vs 263 minutes (248-300, P = .0005) and a smaller volume of infused air at the time of death (264 mL (53-466) vs 727 mL (564-968), P = .001). In pigs with open chest and, infused air and time to death correlated strongly (r = 0.95, P = .001). Conclusion Open chest and pericardium facilitated the transpulmonary passage of intravenously infused air in pigs.

• Wajdan, Ali; Krogh, Magnus Reinsfelt; Villegas-Martinez, Manuel; Halvorsen, Per Steinar; Elle, Ole Jacob & Remme, Espen W. (2020). Automatic detection of valve events by epicardial accelerometer allows estimation of the left ventricular pressure trace and pressure–displacement loop area. Scientific Reports. 10. doi: 10.1038/s41598-020-76637-7. Fulltekst i vitenarkiv Vis sammendrag

  Measurements of the left ventricular (LV) pressure trace are rarely performed despite high clinical interest. We estimated the LV pressure trace for an individual heart by scaling the isovolumic, ejection and filling phases of a normalized, averaged LV pressure trace to the time-points of opening and closing of the aortic and mitral valves detected in the individual heart. We developed a signal processing algorithm that automatically detected the time-points of these valve events from the motion signal of a miniaturized accelerometer attached to the heart surface. Furthermore, the pressure trace was used in combination with measured displacement from the accelerometer to calculate the pressure–displacement loop area. The method was tested on data from 34 animals during different interventions. The accuracy of the accelerometer-detected valve events was very good with a median difference of 2 ms compared to valve events defined from hemodynamic reference recordings acquired simultaneously with the accelerometer. The average correlation coefficient between the estimated and measured LV pressure traces was r = 0.98. Finally, the LV pressure–displacement loop areas calculated using the estimated and measured pressure traces showed very good correlation (r = 0.98). Hence, the pressure–displacement loop area can be assessed solely from accelerometer recordings with very good accuracy.

• Wisløff-Aase, Kristin; Kerans, Viesturs; Haugaa, Kristina; Halvorsen, Per Steinar; Skulstad, Helge & Espinoza, Andreas Westenvik (2020). Changes in left ventricular electromechanical relations during targeted hypothermia. Intensive Care Medicine Experimental. 8(1). doi: 10.1186/s40635-020-00363-7. Fulltekst i vitenarkiv Vis sammendrag

  Background Targeted hypothermia, as used after cardiac arrest, increases electrical and mechanical systolic duration. Differences in duration of electrical and mechanical systole are correlated to ventricular arrhythmias. The electromechanical window (EMW) becomes negative when the electrical systole outlasts the mechanical systole. Prolonged electrical systole corresponds to prolonged QT interval, and is associated with increased dispersion of repolarization and mechanical dispersion. These three factors predispose for arrhythmias. The electromechanical relations during targeted hypothermia are unknown. We wanted to explore the electromechanical relations during hypothermia at 33 °C. We hypothesized that targeted hypothermia would increase electrical and mechanical systolic duration without more profound EMW negativity, nor an increase in dispersion of repolarization and mechanical dispersion. Methods In a porcine model (n = 14), we registered electrocardiogram (ECG) and echocardiographic recordings during 38 °C and 33 °C, at spontaneous and atrial paced heart rate 100 beats/min. EMW was calculated by subtracting electrical systole; QT interval, from the corresponding mechanical systole; QRS onset to aortic valve closure. Dispersion of repolarization was measured as time from peak to end of the ECG T wave. Mechanical dispersion was calculated by strain echocardiography as standard deviation of time to peak strain. Results Electrical systole increased during hypothermia at spontaneous heart rate (p < 0.001) and heart rate 100 beats/min (p = 0.005). Mechanical systolic duration was prolonged and outlasted electrical systole independently of heart rate (p < 0.001). EMW changed from negative to positive value (− 20 ± 19 to 27 ± 34 ms, p = 0.001). The positivity was even more pronounced at heart rate 100 beats/min (− 25 ± 26 to 41 ± 18 ms, p < 0.001). Dispersion of repolarization decreased (p = 0.027 and p = 0.003), while mechanical dispersion did not differ (p = 0.078 and p = 0.297). Conclusion Targeted hypothermia increased electrical and mechanical systolic duration, the electromechanical window became positive, dispersion of repolarization was slightly reduced and mechanical dispersion was unchanged. These alterations may have clinical importance. Further clinical studies are required to clarify whether corresponding electromechanical alterations are accommodating in humans.

• Espinoza, Andreas Westenvik; Kerans, Viesturs; Bugge, Jan F; Skulstad, Helge & Halvorsen, Per Steinar (2020). Left Ventricular Function During Epinephrine Stimulation and Hypothermia: Effects at Spontaneous and Paced Heart Rates in a Porcine Model. Therapeutic Hypothermia and Temperature Management. ISSN 2153-7658. s. 35–44. doi: 10.1089/ther.2019.0035. Fulltekst i vitenarkiv
• Sævik, Marte; Beitnes, Jan Otto; Aaberge, Lars & Halvorsen, Per Steinar (2020). Safety and feasibility of dobutamine stress echocardiography in symptomatic high gradient aortic stenosis patients scheduled for transcatheter aortic valve implantation. Journal of Clinical Ultrasound. ISSN 0091-2751. doi: 10.1002/jcu.22915. Fulltekst i vitenarkiv Vis sammendrag

  Purpose We aimed to study the safety and feasibility of low‐dose dobutamine stress echocardiography in a symptomatic high gradient aortic stenosis population scheduled for transfemoral transcatheter aortic valve implantation (TAVI) and to quantify left ventricular (LV) flow reserve. Methods Fifty patients underwent dobutamine stress echocardiography with 5 minutes increments of 5 μg/kg/min up to 20 μg/kg/min until the heart rate increased ≥20 beats/min from baseline or exceeded 100 beats/min. Other criteria for discontinuing the infusion were major adverse events: ventricular arrhythmia, persistent supraventricular arrhythmia, pulmonary edema, chest pain with significant ST‐changes, or minor events: ST‐changes, drop in systolic blood pressure >30 mmHg, mild chest pain, and/or dyspnea. LV flow reserve was defined as an increase in stroke volume ≥20% during the test. Results Of 50 patients, 45 completed the test according to protocol. No patient had major adverse event. Five patients experienced minor side effects: mild chest pain/dyspnea in three, self‐terminating atrial flutter in one, and decrease in blood pressure in one. Significant LV flow reserve was observed in 20 patients (40%). Conclusion Low‐dose dobutamine stress test appeared safe and feasible patients with high gradient aortic stenosis, and showed LV flow reserve in a minority of them.

• El-Ganainy, Noha; Balasingham, Ilangko; Halvorsen, Per Steinar & Rosseland, Leiv Arne (2020). A New Real Time Clinical Decision Support System Using Machine Learning for Critical Care Units. IEEE Access. 8. doi: 10.1109/ACCESS.2020.3030031. Fulltekst i vitenarkiv Vis sammendrag

  Mean arterial pressure (MAP) is an important clinical parameter to evaluate the health of critically ill patients in intensive care units. Thus, the real time clinical decision support systems detecting anomalies and deviations in MAP enable early interventions and prevent serious complications. The state-of-the-art decision support systems are based on a three-phase method that applies offline training, transfer learning, and retraining at the bedside. Their applicability in critical care units is challenging with delay and inaccuracy. In this article, we propose a real time clinical decision support system forecasting the MAP status at the bedside using a new machine learning structure. The proposed system works in real time at the bedside without requiring the offline phase for training using large datasets. It thereby enables timely interventions and improved healthcare services. The proposed machine learning structure includes two stages. Stage I applies online learning using hierarchical temporal memory (HTM) to enable real time stream processing and provides unsupervised predictions. To the best of our knowledge, this is the first time it is applied to medical signals. Stage II is a long short-term memory (LSTM) classifier that forecasts the status of the patient's MAP ahead of time based on Stage I stream predictions. We perform a thorough performance evaluation of the proposed system and compare it with the state-of-the-art systems employing logistic regression (LR). The comparison shows the proposed system outperforms LR in terms of the classification accuracy, recall, precision, and area under the receiver operation curve (AUROC).

• Schalit, Itai; Espinoza, Andreas Westenvik; Pettersen, Fred-Johan; Snartland, Steinar; Ringdal, Mari-Anne I Lindstein & Nilsen-Hoel, Tom [Vis alle 10 forfattere av denne artikkelen] (2020). Detection of thromboembolic events and pump thrombosis in heartware HVAD using accelerometer in a porcine model. ASAIO journal (1992). ISSN 1058-2916. s. 38–48. doi: 10.1097/MAT.0000000000000954. Fulltekst i vitenarkiv
• Pischke, Søren; Hestenes, Siv Merete; Johansen, Harald Thidemann; Fure, Hilde; Bugge, Jan F & Espinoza, Andreas Westenvik [Vis alle 12 forfattere av denne artikkelen] (2019). Sepsis causes right ventricular myocardial inflammation independent of pulmonary hypertension in a porcine sepsis model. PLOS ONE. 14:e0218624(6). doi: 10.1371/journal.pone.0218624. Fulltekst i vitenarkiv Vis sammendrag

  Introduction Right ventricular (RV) myocardial dysfunction is a common feature in septic shock. It can worsen outcome, but the etiology is poorly understood. Pulmonary artery hypertension (PAH) plays a part in the pathogenesis of the right heart dysfunction in sepsis but its importance is unknown. In pigs, PAH in sepsis is substantial and the translational value of porcine sepsis models therefore questioned. We hypothesized that porcine sepsis causes a myocardial inflammatory response which leads to myocardial dysfunction independent of PAH. Materials and methods Sepsis was induced by Escherichia coli-infusion in 10 pigs resulting in PAH and increased right ventricular pressure (RVP). The same degree of RVP was achieved by external pulmonary artery banding (PAB) in a consecutive series of 6 animals. Results Sepsis, but not PAB, led to increase in endothelial damage marker PAI-1 and cytokines TNF and IL-6 (all p<0.05) in plasma. In myocardium, TNF and IL-6 were significantly elevated in sepsis, TNF in both ventricles and IL-6 mostly in RV, while IL-1β, IL-18 and C5a were significantly higher in RV compared to LV after PAB (all p<0.05). Myocardial mRNA levels of IL-1β, IL-6, IL-18, IP-10, E-selectin and PAI-1 were significantly elevated in RV and LV during sepsis compared to PAB, while Caspase-1 was decreased in septic compared to PAB animals (all p<0.05). Cathepsin L activity was increased in RV by PAB, while sepsis inhibited this response. Escherichia coli-induced sepsis caused myocardial inflammation independent of PAH. Conclusion Prominent PAH should therefore not exclude porcine sepsis models to further our understanding of human sepsis.

• Wajdan, Ali; Krogh, Magnus Reinsfelt; Villegas-Martinez, Manuel; Halvorsen, Per Steinar; Grymyr, Ole-Johannes Holm Nielsen & Elle, Ole Jacob [Vis alle 7 forfattere av denne artikkelen] (2019). Monitoring cardiac function by accelerometer -Detecting start systole from the acceleration signal makes additional ECG recordings for R-peak detection redundant. IEEE Engineering in Medicine and Biology Society. Conference Proceedings. ISSN 1557-170X. s. 4922–4925. doi: 10.1109/EMBC.2019.8856417. Fulltekst i vitenarkiv Vis sammendrag

  A miniaturized accelerometer attached to the heart has been used for monitoring functional parameters such as early systolic velocity and displacement. Currently, processing of the accelerometer signal for derival of these functional parameters depends on determining start systole by detecting the ECG R-peaks. This study proposes an alternative method using only the accelerometer signal to detect start systole, making additional ECG recordings for this purpose redundant. A signal processing method for automatic detection of start systole by accelerometer alone was developed and compared with detected R-peaks in 15 pigs during 5 different interventions showing a difference of 30 ± 17 ms. Furthermore, the derived early systolic velocity and displacement using only accelerometer measurements correlated well (r 2 =0.91 and 0.82, respectively) with minor differences compared to the current method using ECG R-peaks as time reference. The results show that an accelerometer can be used to monitor cardiac function without the need to measure ECG which can simplify the monitoring system.

• Dahle, Gry; Helle-Valle, Thomas Michael; Beitnes, Jan Otto; Espinoza, Andreas Westenvik; Halvorsen, Per Steinar & Rein, Kjell Arne (2019). Single-centre first experience with transapical transcatheter mitral valve replacement with an apical tether: Factors influencing screening outcomes. Interactive Cardiovascular and Thoracic Surgery. ISSN 1569-9293. 28(5), s. 695–703. doi: 10.1093/icvts/ivy343. Fulltekst i vitenarkiv
• Krogh, Magnus Reinsfelt; Halvorsen, Per Steinar; Elle, Ole Jacob; Bergsland, Jacob & Remme, Espen W. (2019). Dynamic gravity compensation does not increase detection of myocardial ischemia in combined accelerometer and gyro sensor measurements. Scientific Reports. 9(1). doi: 10.1038/s41598-018-35630-x. Fulltekst i vitenarkiv Vis sammendrag

  Previous studies have shown that miniaturised accelerometers can be used to monitor cardiac function and automatically detect ischemic events. However, accelerometers cannot differentiate between acceleration due to motion and acceleration due to gravity. Gravity filtering is essential for accurate integration of acceleration to yield velocity and displacement. Heart motion is cyclic and mean acceleration over time is zero. Thus, static gravity filtering is performed by subtracting mean acceleration. However, the heart rotates during the cycle, the gravity component is therefore not constant, resulting in overestimation of motion by static filtering. Accurate motion can be calculated using dynamic gravity filtering by a combined gyro and accelerometer. In an animal model, we investigated whether increased accuracy using dynamic filtering, compared to using static filtering, would enhance the ability to detect ischemia. Additionally, we investigated how well the gyro alone could detect ischemia based on the heart’s rotation. Dynamic filtering tended towards lower sensitivity and specificity, using receiver operating characteristics analysis, for ischemia-detection compared to static filtering (area under the curve (AUC): 0.83 vs 0.93, p = 0.125). The time-varying gravity component indirectly reflects the heart’s rotation. Hence, static filtering has the advantage of indirectly including rotation, which alone demonstrated excellent sensitivity to ischemia (AUC = 0.98).

• Lu, Pengfei; Veletic, Mladen; Laasmaa, Martin; Vendelin, Marko; Louch, William Edward & Halvorsen, Per Steinar [Vis alle 8 forfattere av denne artikkelen] (2019). Multi-nodal nano-actuator pacemaker for energy-efficient stimulation of cardiomyocytes. Nano Communication Networks. ISSN 1878-7789. 22:100270, s. 1–11. doi: 10.1016/j.nancom.2019.100270. Fulltekst i vitenarkiv Vis sammendrag

  There is continuous interest in maximizing the longevity of implantable pacemakers, which are effective in remedying and managing patients with arrhythmic heart disease. This paper accordingly first proposes miniature actuating nanomachines that inter-connect with individual cardiomyocytes and then deeply explores their energy expenditure when performing basic cardiomyocyte stimulation tasks. Since evoked electrical impulses from a number of actuated cardiomyocytes could coordinate contraction throughout the remaining heart muscle and lead to a heart beat, the miniature actuating nanomachines acting synchronously form a conceptual multi-nodal nano-actuator pacemaker network. Rectangular-, sine-, half-sine-, and sawtooth stimulation pulses with varying configurations are considered for actuation of a single isolated in-silico cardiomyocyte by each of the nanomachines. Computer optimization methods with energy consumption as a cost function are utilized to configure preferable stimulation signals in terms of numbers of stimulation sessions/pulses, pulse amplitudes, and duration. In addition, the simulation data are compared with experimental data obtained using in-vitro mouse cardiomyocytes. Among the considered waveforms, half-sine pulses that lead to actuation of a single cardiomyocyte consume minimum energy. None of the used sequences with multiple stimulation pulses reduces the overall energy expenditure of cell stimulation when compared to a single pulse stimulation.

• El-Ganainy, Noha; Balasingham, Ilangko; Halvorsen, Per Steinar & Rosseland, Leiv Arne (2019). On the performance of hierarchical temporal memory predictions of medical streams in real time. International Symposium on Medical Information and Communication Technology. ISSN 2326-828X. 2019-May:8743902. doi: 10.1109/ISMICT.2019.8743902. Fulltekst i vitenarkiv Vis sammendrag

  Machine learning is widely used on stored data, recently it is developed to model real time streams. Applying machine learning on medical streams might lead to a breakthrough on emergency and critical care through online predictions. Modeling real time streams implies limitations to the current state-of-the-art of machine learning and requires different learning paradigm. In this paper, we investigate and evaluate two different machine learning paradigms for real time predictions of medical streams. Both the hierarchical temporal memory (HTM) and long short-term memory (LSTM) are employed. The performance assessment using both algorithms is provided in terms of the root mean square error (RMS) and mean absolute percentage error (MAPE). HTM is found advantageous as it provides efficient unsupervised predictions compared to the semi-supervised learning supported by LSTM in terms of the error measures.

• Batat, Mohammad al; Bergsland, Jacob; Arevalo, Hermenegild; Odland, Hans Henrik; Bose, Pritam & Halvorsen, Per Steinar [Vis alle 7 forfattere av denne artikkelen] (2019). Technological and clinical challenges in lead placement for cardiac rhythm management devices. Annals of Biomedical Engineering. ISSN 0090-6964. 48, s. 26–46. doi: 10.1007/s10439-019-02376-0. Fulltekst i vitenarkiv Vis sammendrag

  CardiacCardiacdisease is aleading cause of death worldwide. Disturbance in the conduction system of the heart may trigger or aggravate heart dysfunction, affecting the efficiency of the heart, and lead to heart failure or cardiac arrest. Patients mayrequire implantable cardiac rhythm management devices (ICRMDs) to maintain or restore the heart rhythm. ICRMDs have undergone important improvements, yet limitations still exist, presentingimportant technological challenges. Most ICRMDs consist of a subcutaneous control unit and intracardiac electrodes. The leads, which connect the electrodes to the control unit, are usually placed transvenously through the subclavian veins. Various locations inside the heart areusedfor placement of electrodes, depending on the specific condition. Some of the limitationsto effective pacemaker therapyare associated with placement and location of the leads. Various approaches have been developed to overcome these challenges, such as multi-site pacing and leadless solutions.This paper aims to review the state of the art for the selection of placement sites for pacemakers, implantable cardioverter defibrillator (ICD)and cardiac resynchronization therapy devices (CRT)devices and discuss potential technological advancements to improve the results of ICRMD-therapyincluding development av leadless technology

• Karlsen, Hilde; Bergan, Harald Arne; Halvorsen, Per Steinar; Sunde, Kjetil; Qvigstad, Eirik & Andersen, Geir Øystein [Vis alle 8 forfattere av denne artikkelen] (2019). Esmolol for cardioprotection during resuscitation with adrenaline in an ischaemic porcine cardiac arrest model. Intensive Care Medicine Experimental. 7(65), s. 1–14. doi: 10.1186/s40635-019-0279-5. Fulltekst i vitenarkiv Vis sammendrag

  Background The effectiveness of adrenaline during resuscitation continues to be debated despite being recommended in international guidelines. There is evidence that the β-adrenergic receptor (AR) effects of adrenaline are harmful due to increased myocardial oxygen consumption, post-defibrillation ventricular arrhythmias and increased severity of post-arrest myocardial dysfunction. Esmolol may counteract these unfavourable β-AR effects and thus preserve post-arrest myocardial function. We evaluated whether a single dose of esmolol administered prior to adrenaline preserves post-arrest cardiac output among successfully resuscitated animals in a novel, ischaemic cardiac arrest porcine model. Methods Myocardial infarction was induced in 20 anaesthetized pigs by inflating a percutaneous coronary intervention (PCI) balloon in the circumflex artery 15 min prior to induction of ventricular fibrillation. After 10 min of untreated VF, resuscitation with veno-arterial extracorporeal membrane oxygenation (VA-ECMO) was initiated and the animals were randomized to receive an injection of either 1 mg/kg esmolol or 9 mg/ml NaCl, prior to adrenaline. Investigators were blinded to allocation. Successful defibrillation was followed by a 1-h high-flow VA-ECMO before weaning and an additional 1-h stabilization period. The PCI-balloon was deflated 40 min after inflation. Cardiac function pre- and post-arrest (including cardiac output) was assessed by magnetic resonance imaging (MRI) and invasive pressure measurements. Myocardial injury was estimated with MRI, triphenyl tetrazolium chloride (TTC) staining and serum concentrations of cardiac troponin T. Results Only seven esmolol and five placebo-treated pigs were successfully resuscitated and available for post-arrest measurements (p = 0.7). MRI revealed severe but similar reductions in post-arrest cardiac function with cardiac output 3.5 (3.3, 3.7) and 3.3 (3.2, 3.9) l/min for esmolol and control (placebo) groups, respectively (p = 0.7). The control group had larger left ventricular end-systolic and end-diastolic ventricular volumes compared to the esmolol group (75 (65, 100) vs. 62 (53, 70) ml, p = 0.03 and 103 (86, 124) vs. 87 (72, 91) ml, p = 0.03 for control and esmolol groups, respectively). There were no other significant differences in MRI characteristics, myocardial infarct size or other haemodynamic measurements between the two groups. Conclusions We observed similar post-arrest cardiac output with and without a single dose of esmolol prior to adrenaline administration during low-flow VA-ECMO in an ischaemic cardiac arrest pig model.

• Carling, Johan Ulrik; Barkhatov, Leonid; Reims, Henrik Mikael; Storås, Tryggve; Courivaud, Fredric A A & Kazaryan, Airazat M. [Vis alle 10 forfattere av denne artikkelen] (2019). Can we ablate liver lesions close to large portal and hepatic veins with MR-guided HIFU? An experimental study in a porcine model. European Radiology. ISSN 0938-7994. 29(9), s. 5013–5021. doi: 10.1007/s00330-018-5996-8. Fulltekst i vitenarkiv
• Bugge, Jan F; Kerans, Viesturs; Nyrerød, Hans Christian & Halvorsen, Per Steinar (2018). Haemodynamic evaluation and optimisation of brain-dead donors with oesophageal Doppler during organ harvesting: A feasibility study. European Journal of Anaesthesiology. ISSN 0265-0215. 35(11), s. 893–895. doi: 10.1097/EJA.0000000000000876. Fulltekst i vitenarkiv
• Schalit, Itai; Espinoza, Andreas Westenvik; Pettersen, Fred-Johan; Thiara, Amrit Paul Singh; Karlsen, Hilde & Sørensen, Gro [Vis alle 9 forfattere av denne artikkelen] (2018). Accelerometer Detects Pump Thrombosis and Thromboembolic Events in an In vitro HVAD Circuit. ASAIO journal (1992). ISSN 1058-2916. 64(5), s. 601–609. doi: 10.1097/MAT.0000000000000699. Fulltekst i vitenarkiv
• Bergan, Harald Arne; Halvorsen, Per Steinar; Espinoza, Andreas Westenvik; Kerans, Viesturs; Skulstad, Helge & Fosse, Erik [Vis alle 7 forfattere av denne artikkelen] (2018). Left ventricle function during therapeutic hypothermia with beta&lt;sub&gt;1&lt;/sub&gt;-adrenergic receptor blockade. Therapeutic Hypothermia and Temperature Management. ISSN 2153-7658. 8(3), s. 156–164. doi: 10.1089/ther.2017.0051. Fulltekst i vitenarkiv
• Hauge, Karoline Kråkmo; Dahle, Gry; Bendz, Bjørn; Halvorsen, Per Steinar; Abdelnoor, Michael & Mollnes, Tom Eirik [Vis alle 7 forfattere av denne artikkelen] (2018). Reduced inflammatory response by transcatheter, as compared to surgical aortic valve replacement. Scandinavian Cardiovascular Journal. ISSN 1401-7431. 52(1), s. 43–50. doi: 10.1080/14017431.2017.1416157. Fulltekst i vitenarkiv Vis sammendrag

  Objectives. The inflammatory response to on-pump cardiac surgery is well known. Systemic inflammatory response syndrome after transcatheter valve implantation (TAVI) has been reported. The objective of this study was to study the inflammatory response during TAVI, and compare with the response during surgical aortic valve replacement. Methods. Eighteen patients undergoing transcatheter implantation, either by a transfemoral (n = 9) or transaortal (n = 9) approach were compared with eighteen patients admitted for surgical replacement. Blood samples per- and postoperatively were analysed for C3bc, terminal complement complex, myeloperoxidase, macrophage inflammatory protein-1β, monocyte chemo-attractant peptide-1, eotaxin, IL-6 and troponin-T. All markers were measured at defined time points and the areas under the curve were compared. Results. Activation of complement, granulocytes, monocytes and eosinophils were significantly lower in the transcatheter group as compared to the surgical group (<0.01). There was no difference in generation of troponin T and IL-6. A small difference in complement activation was observed between the transfemoral and transaortal placement of TAVI. There was no significant difference in clinical outcomes between the TAVI and surgical groups. Discussion. Activation and release of inflammatory markers was significantly less during with TAVI as compared to SAVR, particularly for markers associated with extracorporeal circulation. TAVI and SAVR generated the same degree of IL-6 and troponin T, indicating that the burden on the myocardial tissue was the same.

• Hyler, Stefan; Espinoza, Andreas Westenvik; Skulstad, Helge; Fosse, Erik & Halvorsen, Per Steinar (2018). Corrigendum to ‘Left ventricular function can be continuously monitored with an epicardially attached accelerometer sensor’ [Eur J Cardiothorac Surg 2014;46:313–20]. European Journal of Cardio-Thoracic Surgery. ISSN 1010-7940. 54(5), s. 968–968. doi: 10.1093/ejcts/ezy340. Fulltekst i vitenarkiv
• Høiseth, Gudrun; Gottås, André; Berg, Thomas; Arnestad, Marianne; Halvorsen, Per Steinar & Bachs, Liliana Casulleras (2017). Urinary kinetics of heroin metabolites in pigs shortly after intake. Journal of Analytical Toxicology. ISSN 0146-4760. 41(5), s. 451–454. doi: 10.1093/jat/bkx017. Fulltekst i vitenarkiv
• Krogh, Magnus Reinsfelt; Nghiem, Giang Minh; Halvorsen, Per Steinar; Elle, Ole Jakob; Grymyr, Ole-Johannes & Hoff, Lars [Vis alle 7 forfattere av denne artikkelen] (2017). Gravity compensation method for combined accelerometer and gyro sensors used in cardiac motion measurements. Annals of Biomedical Engineering. ISSN 0090-6964. 45(5), s. 1292–1304. doi: 10.1007/s10439-017-1798-4. Fulltekst i vitenarkiv Vis sammendrag

  A miniaturized accelerometer fixed to the heart can be used for monitoring of cardiac function. However, an accelerometer cannot differentiate between acceleration caused by motion and acceleration due to gravity. The accuracy of motion measurements is therefore dependent on how well the gravity component can be estimated and filtered from the measured signal. In this study we propose a new method for estimating the gravity, based on strapdown inertial navigation, using a combined accelerometer and gyro. The gyro was used to estimate the orientation of the gravity field and thereby remove it. We compared this method with two previously proposed gravity filtering methods in three experimental models using: (1) in silico computer simulated heart motion; (2) robot mimicked heart motion; and (3) in vivo measured motion on the heart in an animal model. The new method correlated excellently with the reference (r2 > 0.93) and had a deviation from reference peak systolic displacement (6.3 ± 3.9 mm) below 0.2 ± 0.5 mm for the robot experiment model. The new method performed significantly better than the two previously proposed methods (p < 0.001). The results show that the proposed method using gyro can measure cardiac motion with high accuracy and performs better than existing methods for filtering the gravity component from the accelerometer signal.

• Grymyr, Ole-Johannes; Beitnes, Jan Otto; Eidet, Jo; Tølløfsrud, Stein G.; Fiane, Arnt E & Skulstad, Helge [Vis alle 8 forfattere av denne artikkelen] (2017). Detection of intraoperative myocardial dysfunction by accelerometer during aortic valve replacement. Interactive Cardiovascular and Thoracic Surgery. ISSN 1569-9293. 24(2), s. 188–195. doi: 10.1093/icvts/ivw326. Fulltekst i vitenarkiv
• Eidet, Jo; Dahle, Gry; Bugge, Jan F; Bendz, Bjørn; Rein, Kjell Arne & Aaberge, Lars [Vis alle 10 forfattere av denne artikkelen] (2016). Intraoperative improvement in left ventricular peak systolic velocity predicts better short-term outcome after transcatheter aortic valve implantation. Interactive Cardiovascular and Thoracic Surgery. ISSN 1569-9293. 22(1), s. 5–12. doi: 10.1093/icvts/ivv277. Fulltekst i vitenarkiv
• Secerbegovic, Alma; Bergsland, Jacob; Halvorsen, Per Steinar; Suljanović, Nermin; Mujčić, Aljo & Balasingham, Ilangko (2016). Blood pressure estimation using video plethysmography. IEEE International Symposium on Biomedical Imaging. ISSN 1945-7928. 2016-June, s. 461–464. doi: 10.1109/ISBI.2016.7493307. Fulltekst i vitenarkiv
• Bergan, Harald Arne; Halvorsen, Per Steinar; Skulstad, Helge; Fosse, Erik & Bugge, Jan F (2016). Does therapeutic hypothermia during extracorporeal cardiopulmonary resuscitation preserve cardiac function? Journal of Translational Medicine. 14(1). doi: 10.1186/s12967-016-1099-y. Fulltekst i vitenarkiv Vis sammendrag

  Background Extracorporeal cardiopulmonary resuscitation (E-CPR) is increasingly used as a rescue method in the management of cardiac arrest and provides the opportunity to rapidly induce therapeutic hypothermia. The survival after a cardiac arrest is related to post-arrest cardiac function, and the application of therapeutic hypothermia post-arrest is hypothesized to improve cardiac outcome. The present animal study compares normothermic and hypothermic E-CPR considering resuscitation success, post-arrest left ventricular function and magnitude of myocardial injury. Methods After a 15-min untreated ventricular fibrillation, the pigs (n = 20) were randomized to either normothermic (38 °C) or hypothermic (32–33 °C) E-CPR. Defibrillation terminated ventricular fibrillation after 5 min of E-CPR, and extracorporeal support continued for 2 h, followed by warming, weaning and a stabilization period. Magnetic resonance imaging and left ventricle pressure measurements were used to assess left ventricular function pre-arrest and 5 h post-arrest. Myocardial injury was estimated by serum concentrations of cardiac TroponinT and Aspartate transaminase (ASAT). Results E-CPR resuscitated all animals and the hypothermic strategy induced therapeutic hypothermia within minutes without impairment of the resuscitation success rate. All animals suffered a severe global systolic left ventricular dysfunction post-arrest with 50–70% reductions in stroke volume, ejection fraction, wall thickening, strain and mitral annular plane systolic excursion. Serum concentrations of cardiac TroponinT and ASAT increased considerably post-arrest. No significant differences were found between the two groups. Conclusions Two-hour therapeutic hypothermia during E-CPR offers an equal resuscitation success rate, but does not preserve the post-arrest cardiac function nor reduce the magnitude of myocardial injury, compared to normothermic E-CPR. Trial registration FOTS 4611/13 registered 25 October 2012

• Tjulkins, Fjodors; Thai, Anh Tuan Nguyen; Andreassen, Erik; Hoff, Lars; Grymyr, Ole-Johannes & Halvorsen, Per Steinar [Vis alle 7 forfattere av denne artikkelen] (2016). An Implantable Accelerometer-based Heart Monitoring Device with Improved Positional Stability. Journal of Medical Devices. ISSN 1932-6181. 10(4). doi: 10.1115/1.4034574. Fulltekst i vitenarkiv Vis sammendrag

  This paper reports recent results from an ongoing effort to develop an implantable accelerometer-based heart-monitoring device for ischemia monitoring. The latest device prototype utilizes a new and more compact accelerometer (1.2 × 1.5 × 0.8 mm3), a prototype device from Bosch SensorTec, Reutlingen, Germany. This paper presents the fabrication and testing of the device, including an explorative study of the effect of the capsule shape on the stability of the implanted device in the heart tissue. The stability study indicated sufficient stability of the device and a higher resistance to retraction for one of the capsule designs. The device was able to carry out acceleration monitoring and it meets the leakage current requirements of the IEC60601 standard.

• Eidet, Jo; Dahle, Gry; Bugge, Jan F; Bendz, Bjørn; Rein, Kjell Arne & Aaberge, Lars [Vis alle 10 forfattere av denne artikkelen] (2016). Long-term outcomes after transcatheter aortic valve implantation: The impact of intraoperative tissue Doppler echocardiography. Interactive Cardiovascular and Thoracic Surgery. ISSN 1569-9293. 23(3), s. 403–409. doi: 10.1093/icvts/ivw159. Fulltekst i vitenarkiv
• Gottås, André; Arnestad, Marianne; Halvorsen, Per Steinar; Bachs, Liliana Casulleras & Høiseth, Gudrun (2016). Pharmacokinetics of heroin and its metabolites in vitreous humor and blood in a living pig model. Forensic Toxicology. ISSN 1860-8965. 34, s. 277–285. doi: 10.1007/s11419-016-0315-z. Fulltekst i vitenarkiv
• Thai, Anh Tuan Nguyen; Tjulkins, Fjodors; Aasmundtveit, Knut Eilif; Hoivik, Nils; Hoff, Lars & Grymyr, Ole-Johannes [Vis alle 8 forfattere av denne artikkelen] (2015). Development of a Multifunctional Implantable Heart Monitoring Device. Journal of Microelectronics and Electronic Packaging. ISSN 1551-4897. 12(4), s. 171–180. doi: 10.4071/imaps.476. Fulltekst i vitenarkiv Vis sammendrag

  Early detection of cardiac complications after heart surgery is a crucial demand in clinical surveillance facilities. The use of accelerometer devices fixated to the heart has been demonstrated as a promising method for the detection of myocardial ischemia with high sensitivity and specificity. One of the most important challenges in developing heart implantable accelerometer devices is to minimize any tissue trauma. In this study, a new approach in making a heart muscle implantable accelerometer sensor is described. An overall diameter of 2 mm is achieved by encapsulating a miniaturized three-axis MEMS accelerometer (similar to the BMA355) from Bosch Sensortec GmbH, Germany. The design of the sensor features a simple implantation procedure, which aims to be similar to the medical procedure of temporary pacing wire attachment. The device remained in place in the heart muscle without the need for additional attachment or fixation. The essential clinical requirements for implantable devices, especially heart implantable sensors, are also taken into account in this study. Additional safety enhancement is realized by adding a galvanic isolator, which ensures electrical safety.

• Eidet, Jo; Dahle, Gry; Bugge, Jan F; Bendz, Bjørn; Rein, Kjell Arne & Fosse, Erik [Vis alle 8 forfattere av denne artikkelen] (2015). Transcatheter aortic valve implantation and intraoperative left ventricular function: A myocardial tissue Doppler imaging study. Journal of Cardiothoracic and Vascular Anesthesia. ISSN 1053-0770. 29(1), s. 115–120. doi: 10.1053/j.jvca.2014.10.016. Fulltekst i vitenarkiv
• Pischke, Søren Erik; Hyler, Stefan; Tronstad, Christian; Bergsland, Jacob; Fosse, Erik & Halvorsen, Per Steinar [Vis alle 8 forfattere av denne artikkelen] (2015). Myocardial tissue CO2 tension detects coronary blood flow reduction after coronary artery bypass in real-time. British Journal of Anaesthesia. ISSN 0007-0912. 114(3), s. 414–422. doi: 10.1093/bja/aeu381. Fulltekst i vitenarkiv
• Kerans, Viesturs; Espinoza, Andreas Westenvik; Skulstad, Helge; Halvorsen, Per Steinar; Edvardsen, Thor & Bugge, Jan F (2015). Systolic left ventricular function is preserved during therapeutic hypothermia, also during increases in heart rate with impaired diastolic filling. Intensive Care Medicine Experimental. 3(1), s. 1–17. doi: 10.1186/s40635-015-0041-6. Fulltekst i vitenarkiv Vis sammendrag

  Background Systolic left ventricular function during therapeutic hypothermia is found both to improve and to decline. We hypothesized that this discrepancy would depend on the heart rate and the variables used to assess systolic function. Methods In 16 pigs, cardiac performance was assessed by measurements of invasive pressures and thermodilution cardiac output and with 2D strain echocardiography. Left ventricle (LV) volumes, ejection fraction (EF), transmitral flow, and circumferential and longitudinal systolic strain were measured. Miniaturized ultrasonic transducers were attached to the epicardium of the LV to obtain M-mode images, systolic thickening, and diastolic thinning velocities and to determine LV pressure-wall dimension relationships. Preload recruitable stroke work (PRSW) was calculated. Measurements were performed at 38 and 33°C at spontaneous and paced heart rates, successively increased in steps of 20 up to the toleration limit. Effects of temperature and heart rate were compared in a mixed model analysis. Results Hypothermia reduced heart rate from 87 ± 10 (SD) to 76 ± 11 beats/min without any changes in LV stroke volume, end-diastolic volume, EF, strain values, or PRSW. Systolic wall thickening velocity (S′) and early diastolic wall thinning velocity decreased by approximately 30%, making systolic duration longer through a prolonged and slow contraction and changing the diastolic filling pattern from predominantly early towards late. Pacing reduced diastolic duration much more during hypo- than during normothermia, and combined with slow myocardial relaxation, incomplete relaxation occurred with all pacing rates. Pacing did not affect S′ or PRSW at physiological heart rates, but stroke volume, end-diastolic volume, and strain were reduced as a consequence of reduced diastolic filling and much more accentuated during hypothermia. At the ultimate tolerable heart rate during hypothermia, S′ decreased, probably as a consequence of myocardial hypoperfusion due to sustained ventricular contraction throughout a very short diastole. Conclusions Systolic function was maintained at physiological heart rates during therapeutic hypothermia. Reduced tolerance to increases in heart rate was caused by lack of ventricular filling due to diastolic dysfunction and shorter diastolic duration.

• Grymyr, Ole-Johannes; Remme, Espen W.; Espinoza, Andreas Westenvik; Skulstad, Helge; Elle, Ole Jakob & Fosse, Erik [Vis alle 7 forfattere av denne artikkelen] (2015). Assessment of 3D motion increases the applicability of accelerometers for monitoring left ventricular function. Interactive Cardiovascular and Thoracic Surgery. ISSN 1569-9293. 20(3), s. 329–337. doi: 10.1093/icvts/ivu404. Fulltekst i vitenarkiv
• Espinoza, Andreas Westenvik; Neumann, Kirill; Halvorsen, Per Steinar; Sundset, Arve; Kongerud, Johny & Fosse, Erik (2015). Critical airway obstruction: Challenges in airway management and ventilation during therapeutic bronchoscopy. Journal of Bronchology & Interventional Pulmonology. ISSN 1944-6586. 22(1), s. 41–47. doi: 10.1097/LBR.0000000000000127. Fulltekst i vitenarkiv
• Hyler, Stefan; Pischke, Søren Erik; Halvorsen, Per Steinar; Espinoza, Andreas Westenvik; Bergsland, Jacob & Tønnessen, Tor Inge [Vis alle 8 forfattere av denne artikkelen] (2015). Continuous monitoring of regional function by a miniaturized ultrasound transducer allows early quantification of low-grade myocardial ischemia. Journal of the American Society of Echocardiography. ISSN 0894-7317. 28(4), s. 486–494. doi: 10.1016/j.echo.2014.12.014. Fulltekst i vitenarkiv
• Tjulkins, Fjodors; Thai, Anh Tuan Nguyen; Andreassen, Erik; Aasmundtveit, Knut Eilif; Høivik, Nils Deneke & Hoff, Lars [Vis alle 9 forfattere av denne artikkelen] (2015). Fabrication and assembly of MEMS accelerometer-based heart monitoring device with simplified, one step placement. Journal of Medical Engineering & Technology. ISSN 0309-1902. 39(1), s. 69–74. doi: 10.3109/03091902.2014.981307. Fulltekst i vitenarkiv Vis sammendrag

  An accelerometer-based heart monitoring system has been developed for real-time evaluation of heart wall movement. In this paper, assembly and fabrication of an improved device is presented along with system characterization and test data from an animal experiment. The new device is smaller and has simplified the implantation procedure compared to earlier prototypes. Leakage current recordings were well below those set by the corresponding standards.

• Grymyr, Ole-Johannes; Thai, Anh Tuan Nguyen; Tjulkins, Fjodors; Espinoza, Andreas Westenvik; Remme, Espen W. & Skulstad, Helge [Vis alle 9 forfattere av denne artikkelen] (2015). Continuous monitoring of cardiac function by 3-dimensional accelerometers in a closed-chest pig model. Interactive Cardiovascular and Thoracic Surgery. ISSN 1569-9293. 21(5), s. 573–582. doi: 10.1093/icvts/ivv191. Fulltekst i vitenarkiv Vis sammendrag

  OBJECTIVES Cardiac wall motions reflect systolic and diastolic function. We have previously demonstrated the ability of a miniaturized three-axis (3D) accelerometer to monitor left ventricular function in experimental models and in patients. The main aim of this study was to investigate the clinical utility of the method for monitoring the left and right ventricular function during changes in global and regional cardiac function in a postoperative closed-chest situation. METHODS In 13 closed-chest pigs, miniaturized 3D accelerometers were placed on the left ventricle in the apical and basal regions and in the basal region of the right ventricle. An epicardial 3D motion vector was calculated from the acceleration signals in each heart region. Peak systolic velocity along this 3D vector (3D Vsys) was compared with the positive time derivative of the left and right ventricular pressure and with cardiac index during changes in global LV function (unloading, fluid loading, esmolol, dobutamine) and with ultrasound during regional left ventricular dysfunction (3-min occlusion of the left anterior descending coronary artery). RESULTS Significant and typical changes in accelerometer 3D Vsys were seen in all heart regions during changes in global cardiac function. 3D Vsys reflected the left and right ventricular contractility via significant correlations with the positive time derivative of the left and right ventricular pressure, r = 0.86 and r = 0.72, and with cardiac index r = 0.82 and r = 0.73 (all P < 0.001), respectively. The miniaturized accelerometers also detected regional dysfunction, but showed reduced ability to localize ischaemia as the 3D Vsys in all heart regions showed similar reductions during coronary artery occlusion. CONCLUSIONS Miniaturized 3D accelerometers placed on the heart can assess global and regional function in a closed-chest model. The technique may be used for continuous postoperative monitoring after cardiac surgery.

• Bergan, Harald Arne; Halvorsen, Per Steinar; Skulstad, Helge; Edvardsen, Thor; Fosse, Erik & Bugge, Jan F (2015). Successful ECMO-cardiopulmonary resuscitation with the associated post-arrest cardiac dysfunction as demonstrated by MRI. Intensive Care Medicine Experimental. 3. doi: 10.1186/s40635-015-0061-2. Fulltekst i vitenarkiv Vis sammendrag

  Background Veno-arterial extracorporeal membrane oxygenation (ECMO-CPR) is a life-saving rescue for selected patients when standard cardiopulmonary resuscitation fails. The use is increasing although the treatment modality is not fully established. Resuscitated patients typically develop a detrimental early post-arrest cardiac dysfunction that also deserves main emphasis. The present study investigates an ECMO-CPR strategy in pigs and assesses early post-arrest left ventricular function in detail. We hypothesised that a significant dysfunction could be demonstrated with this model using magnetic resonance imaging (MRI), not previously used early post-arrest. Methods In eight anaesthetised pigs, a 15-min ventricular fibrillation was resuscitated by an ECMO-CPR strategy of 150-min veno-arterial ECMO aiming at high blood flow rate and pharmacologically sustained aortic blood pressure and pulse pressure of 50 and 15 mmHg, respectively. Pre-arrest cardiac MRI and haemodynamic measurements of left ventricular function were compared to measurements performed 300-min post-arrest. Results All animals were successfully resuscitated, weaned from the ECMO circuit, and haemodynamically stabilised post-arrest. Cardiac output was maintained by an increased heart rate post-arrest, but left ventricular ejection fraction and stroke volume were decreased by approximately 50 %. Systolic circumferential strain and mitral annular plane systolic excursion as well as the left ventricular wall thickening were reduced by approximately 50–70 % post-arrest. The diastolic function variables measured were unchanged. Conclusions The present animal study demonstrates a successful ECMO-CPR strategy resuscitating long-lasting cardiac arrest with adequate post-arrest haemodynamic stability. The associated severe systolic left ventricular dysfunction could be charted in detail by MRI, a valuable tool for future cardiac outcome assessments in resuscitation research.

• Floor, Pål Anders; Chavez-Santiago, Raul; Brovoll, Sverre; Aardal, Øyvind; Bergsland, Jacob & Grymyr, Ole-Johannes [Vis alle 12 forfattere av denne artikkelen] (2015). In-Body to On-Body Ultrawideband Propagation Model Derived from Measurements in Living Animals. IEEE Journal of Biomedical and Health Informatics. ISSN 2168-2194. 19(3). doi: 10.1109/JBHI.2015.2417805. Fulltekst i vitenarkiv Vis sammendrag

  Ultra wideband (UWB) radio technology for wireless implants has gained significant attention. UWB enables the fabrication of faster and smaller transceivers with ultra low power consumption, which may be integrated into more sophisticated implantable biomedical sensors and actuators. Nevertheless, the large path loss suffered by UWB signals propagating through inhomogeneous layers of biological tissues is a major hindering factor. For the optimal design of implantable transceivers, the accurate characterization of the UWB radio propagation in living biological tissues is indispensable. Channel measurements in phantoms and numerical simulations with digital anatomical models provide good initial insight into the expected path loss in complex propagation media like the human body, but they often fail to capture the effects of blood circulation, respiration, and temperature gradients of a living subject. Therefore, we performed UWB channel measurements within 1-6 GHz on two living porcine subjects because of the anatomical resemblance with an average human torso. We present for the first time a path loss model derived from these invivo measurements, which includes the frequency-dependent attenuation. The use of multiple on-body receiving antennas to combat the high propagation losses in implant radio channels was also investigated.

• Hestenes, Siv Merete; Halvorsen, Per Steinar; Skulstad, Helge; Remme, Espen; Espinoza, Andreas Westenvik & Hyler, Stefan [Vis alle 10 forfattere av denne artikkelen] (2014). Advantages of strain echocardiography in assessment of myocardial function in severe sepsis: An experimental study. Critical Care Medicine. ISSN 0090-3493. 42(6), s. e432–e440. doi: 10.1097/CCM.0000000000000310. Fulltekst i vitenarkiv
• Hyler, Stefan; Espinoza, Andreas Westenvik; Skulstad, Helge; Fosse, Erik & Halvorsen, Per Steinar (2014). Left ventricular function can be continuously monitored with an epicardially attached accelerometer sensor. European Journal of Cardio-Thoracic Surgery. ISSN 1010-7940. 46(2), s. 313–320. doi: 10.1093/ejcts/ezt653. Fulltekst i vitenarkiv
• Courivaud, Fredric A A; Kazaryan, Airazat M.; Lund, Alice; Orszagh, Vivian C; Svindland, Aud & Marangos, Irina Pavlik [Vis alle 11 forfattere av denne artikkelen] (2014). Thermal fixation of swine liver tissue after magnetic resonance-guided high-intensity focused ultrasound ablation. Ultrasound in Medicine and Biology. ISSN 0301-5629. 40(7), s. 1564–1577. doi: 10.1016/j.ultrasmedbio.2014.02.007. Fulltekst i vitenarkiv
• Thai, Anh Tuan Nguyen; Tjulkins, Fjodors; Aasmundtveit, Knut Eilif; Hoivik, Nils; Hoff, Lars & Grymyr, Ole-Johannes [Vis alle 8 forfattere av denne artikkelen] (2014). Packaging of a Multifunctional Implantable Heart Monitoring Device. I Courtois, Bernard; Karam, Jean Michel; Marcelli, Romolo; Megherbi, Souhil; Mita, Yoshio; Nouet, Pascal & Yeh, J. Andrew (Red.), Symposium on Design, test, Integration & Packaging of MEMS/MOEMS, Cannes, France, 1-4 April, 2014. EDA Publishing Association. ISSN 9782355000287. s. 322–327. doi: 10.1109/dtip.2014.7056657. Fulltekst i vitenarkiv
• Tjulkins, Fjodors; Thai, Anh Tuan Nguyen; Andreassen, Erik; Hoivik, Nils; Aasmundtveit, Knut Eilif & Hoff, Lars [Vis alle 9 forfattere av denne artikkelen] (2014). MEMS-based implantable heart monitoring system with integrated pacing function, 2014 IEEE 64th Electronic Components and Technology Conference (ECTC), 27-30 May 2014, Florida, USA. IEEE (Institute of Electrical and Electronics Engineers). ISSN 9781479924066. s. 139–144. doi: 10.1109/ECTC.2014.6897279. Fulltekst i vitenarkiv Vis sammendrag

  Miniaturized accelerometer-based implantable heart monitoring systems may increase safety during cardiac surgery. Such systems can provide sustained monitoring compared to imaging techniques. During ischemia, changes in acceleration occur instantly and before changes can be observed by electrocardiography. This may allow earlier detection of adverse events like graft occlusion. Recent designs have been made to meet requirements for postoperative use by easy and safe removal. However, the implantation procedure has been too complicated. The system presented in this paper is a reworked package in which a 3-axis accelerometer is placed inside a stainless steel capsule fabricated by additive manufacturing (3D printing). A needle attached to the package allows for easy implantation. In addition, the metallic capsule makes it possible to use the device as a pacing lead. The system demonstrates easy implantation. Furthermore, in conjunction with a second electrode, pacing and electrical potential sensing functionality is demonstrated.

• Espinoza, Andreas Westenvik; Kerans, Viesturs; Opdahl, Anders; Skulstad, Helge; Halvorsen, Per Steinar & Bugge, Jan F [Vis alle 8 forfattere av denne artikkelen] (2013). Effects of Therapeutic Hypothermia on Left Ventricular Function Assessed by Ultrasound Imaging. Journal of the American Society of Echocardiography. ISSN 0894-7317. 26(11), s. 1353–1363. doi: 10.1016/j.echo.2013.06.021. Fulltekst i vitenarkiv
• Pischke, Søren Erik; Tronstad, Christian; Holhjem, Lars; Halvorsen, Per Steinar & Tønnessen, Tor Inge (2012). Perioperative detection of myocardial ischaemia/reperfusion with a novel tissue CO2 monitoring technology. European Journal of Cardio-Thoracic Surgery. ISSN 1010-7940. 42(1), s. 157–163. doi: 10.1093/ejcts/ezr278. Fulltekst i vitenarkiv
• Remme, Espen W.; Hoff, Lars; Halvorsen, Per Steinar; Opdahl, Anders; Fosse, Erik & Elle, Ole Jakob (2012). Simulation model of cardiac three dimensional accelerometer measurements. Medical Engineering and Physics. ISSN 1350-4533. 34(7), s. 990–998. doi: 10.1016/j.medengphy.2012.04.015. Fulltekst i vitenarkiv Vis sammendrag

  A miniaturized accelerometer sensor attached to the heart may be applied for monitoring cardiac motion. Proper understanding of the sensor measurements is required for successful development of algorithms to process the signal and extract clinical information. In vivo testing of such sensors is limited by the invasive nature of the procedure. In this study we have developed a mathematical simulation model of an accelerometer attached to the heart so that testing initially may be performed on realistic, simulated measurements. Previously recorded cardiac motion by sonomicrometric crystals was used as input to the model. The three dimensional motion of a crystal attached to the heart served as the simulated motion of the accelerometer, providing the translational acceleration components. A component of gravity is also measured by the accelerometer and fused with the translational acceleration. The component of gravity along an accelerometer axis varies when the axis direction slightly rotates as the accelerometer moves during the cardiac cycle. This time-varying gravity component has substantial effects on the accelerometer measurements and was included in the simulation model by converting the motion to prolate spheroidal coordinates where the axis rotation could be found. The simulated accelerometer signal was filtered and integrated to velocity and displacement. The resulting simulated motion was consistent with previous accelerometer recordings during normal and ischemic conditions as well as for alterations of accelerometer orientation and patient positions. This suggests that the model could potentially be useful in future testing of algorithms to filter and process accelerometer measurements.

• Johansson, Martin L.; Thomsen, Peter; Hultén, Leif; Halvorsen, Per Steinar; Fosse, Erik & Edwin, Bjørn (2011). Integration between a percutaneous implant and the porcine small bowel. Journal of Biomedical Materials Research. Part B - Applied biomaterials. ISSN 1552-4973. 98B(1), s. 101–109. doi: 10.1002/jbm.b.31838. Fulltekst i vitenarkiv
• Wester, Torjus; Häggblad, Erik; Ahmed, Zaheer; Barratt-Due, Andreas; Kvernebo, Mari Skylstad & Halvorsen, Per Steinar [Vis alle 8 forfattere av denne artikkelen] (2011). Assessments of skin and tongue microcirculation reveals major changes in porcine sepsis. Clinical Physiology and Functional Imaging. ISSN 1475-0961. 31(2), s. 151–158. doi: 10.1111/j.1475-097X.2010.00994.x. Fulltekst i vitenarkiv
• Ahmed, Zaheer; Häggblad, Erik; Wester, Torjus; Kvernebo, Mari Skylstad; Halvorsen, Per Steinar & Kvernebo, Knut (2011). Diffuse reflectance spectroscopy: Systemic and microvascular oxygen saturation is linearly correlated and hypoxia leads to increased spatial heterogeneity of microvascular saturation. Microvascular Research. ISSN 0026-2862. 81(3), s. 245–251. doi: 10.1016/j.mvr.2011.02.004. Fulltekst i vitenarkiv
• Espinoza, Andreas Westenvik; Halvorsen, Per Steinar; Skulstad, Helge; Lundblad, Runar; Bugge, Jan Frederik & Hoff, Lars [Vis alle 8 forfattere av denne artikkelen] (2011). Automated detection of myocardial ischaemia by epicardial miniature ultrasound transducers - a novel tool for patient monitoring during cardiac surgery. European Journal of Cardio-Thoracic Surgery. ISSN 1010-7940. 39(1), s. 53–59. doi: 10.1016/j.ejcts.2010.03.067. Fulltekst i vitenarkiv Vis sammendrag

  Objectives: Early detection of myocardial ischaemia in cardiac surgery is important. We have developed an ultrasonic system for continuous myocardial monitoring by use of miniature transducers. The aim of this study was to investigate the system's ability to detect ischaemia in patients undergoing off-pump coronary artery bypass grafting (CABG), and whether automated signal analysis could detect ischaemia. Methods: In 10 patients scheduled for CABG, ultrasound transducers were fixed to the epicardium in the area supplied by left anterior descending artery (LAD), and in a remote area for control. M-mode images with measurements of wall-thickening velocities were presented in real time and systolic (S?) and post-systolic velocities (PSVs) were recorded. An automated algorithm for ischaemia detection was developed, using end-systolic wall thickening as a fraction of total wall thickening. Registrations were made at baseline and during LAD occlusion. Echocardiographic strain was used as reference. Results: Nine of 10 patients developed ischaemia during LAD occlusion, with resulting decrease in systolic and increase in post-systolic wall-thickening velocities (P < 0.001). In these nine patients, Vdiff shifted below zero with no overlap between baseline and LAD occlusion (P < 0.001). The automated wall-thickening fraction was reduced from 0.93 ± 0.05 to 0.57 ± 0.15 (P = 0.001). A cut-off value of 0.85 could completely separate normal from ischaemic myocardium in all patients. Conclusion: The ultrasonic system detected regional ischaemia during LAD occlusion. An automated analysis algorithm demonstrated excellent ability to detect ischaemia. This technology can develop into a useful tool to detect ischaemia in cardiac surgery.

• Espinoza, Andreas Westenvik; Halvorsen, Per Steinar; Hoff, Lars; Skulstad, Helge; Fosse, Erik & Ihlen, Halfdan [Vis alle 7 forfattere av denne artikkelen] (2010). Detecting myocardial ischaemia using miniature ultrasonic transducers - a feasibility study in a porcine model. European Journal of Cardio-Thoracic Surgery. ISSN 1010-7940. 37(1), s. 119–126. doi: 10.1016/j.ejcts.2009.05.013. Fulltekst i vitenarkiv Vis sammendrag

  Background: Detection of myocardial ischaemia during and after cardiac surgery remains a challenge. Echocardiography is more sensitive in ischaemia detection than echocardiography (ECG) and haemodynamic monitoring, but demands repeated examinations for monitoring over time. We have developed and validated an ultrasonic system that permits continuous real-time assessment of myocardial ischaemia using miniature epicardial ultrasound transducers. Methods: In an open-chest porcine model (n = 8), prototype ultrasound transducers were fixed on the epicardium in the left anterior descending and circumflex coronary artery supply regions, providing continuous measurement of transmural myocardial velocities. Peak systolic velocity and post-systolic velocity were recorded simultaneously with ECG, left ventricular pressure and arterial pressure. Two-dimensional (2D) echocardiographic strain was used as a reference. Global changes were induced by infusing fluid, epinephrine, nitroprusside and esmolol. Regional changes were induced by occluding the left anterior descending coronary artery (LAD). Subsequent LAD stenosis was performed in a subgroup, with flow reduction to 50% of baseline level and further to occlusion. Results: Systolic velocity in the LAD region decreased during LAD occlusion (0.9 +/- 0.1 to 0.1 +/- 0.1 cm s¯¹, P < 0.01), whereas post-systolic velocity increased (0.3 +/- 0.1 to 2.3 +/- 0.1 cm s¯¹, P < 0.01). No changes occurred in the circumflex coronary artery (CX) region. Severe ischaemia was confirmed by reduction in 2D echocardiography strain calculations. Changes in myocardial velocities assessed by miniature transducer during ischaemia differed from changes during all global interventions. Significant reduction in systolic velocity occurred at 50% LAD flow (0.9 +/- 0.1 to 0.5 +/- 0.1 cm s¯¹, P = 0.02) with further decrease on following occlusion (0.0 +/- 0.0 cm s¯¹, P < 0.01). Post-systolic velocity increased both from baseline to 50% LAD flow, and further to occlusion. Conclusion: The epicardial transducers provided continuous assessment of regional myocardial function and detected ischaemia with high sensitivity and specificity. Further development of this system may provide a useful tool for myocardial monitoring during and after cardiac surgery. (C) 2009 European Association for Cardio-Thoracic Surgery. Published by Elsevier B.V. All rights reserved.

• Halvorsen, Per Steinar; Remme, Espen W.; Espinoza, Andreas Westenvik; Skulstad, Helge; Lundblad, Runar & Bergsland, Jacob [Vis alle 11 forfattere av denne artikkelen] (2010). Automatic real-time detection of myocardial ischemia by epicardial accelerometer. Journal of Thoracic and Cardiovascular Surgery. ISSN 0022-5223. 139(4), s. 1026–1032. doi: 10.1016/j.jtcvs.2009.05.031. Fulltekst i vitenarkiv Vis sammendrag

  Objective: Myocardial ischemia may be detected with epicardial accelerometers. We developed and tested automated algorithms for real-time detection of myocardial ischemia by accelerometer measurements in both experimental and clinical settings. Methods: In 10 pigs, an accelerometer was fixed to the epicardium in the area perfused by left anterior descending coronary artery. Acceleration and electrocardiogram were simultaneously recorded, and the QRS complex was automatically detected for exact timing of systole. Peak circumferential velocity and displacement were automatically calculated from epicardial acceleration signal within 150 milliseconds after peak R on electrocardiography. Global myocardial function was reduced by esmolol infusion, and regional function was altered by temporary left anterior descending occlusion. Automated ischemia detection analyses were tested in 7 patients during off-pump coronary artery bypass grafting. Left anterior descending coronary artery was occluded for 3 minutes before grafting. In both models, echocardiographic myocardial circumferential strain was used to confirm ischemia. Results: Systolic displacement changed most during left anterior descending occlusion. Negative displacement during ischemia was found in pigs (11.5 ± 2.3 to ?1.2 ± 2.8 mm, P < .01); regional hypokinesia was found in clinical study (12.8 ± 8.1 to 3.5 ± 4.4 mm, P < .01). Ischemia was confirmed by echocardiography in both settings. Esmolol infusion induced smaller changes in automated accelerometer measurements than did left anterior descending occlusion (P < .01). Conclusions: Automatic real-time detection of myocardial ischemia with epicardial accelerometer was feasible. Automated ischemia detection analysis may be used for continuous monitoring of myocardial ischemia during cardiac surgery.

• Wester, Torjus; Häggblad, Erik; Ahmed, Zaheer; Barratt-Due, Andreas; Kvernebo, Mari Skylstad & Halvorsen, Per Steinar [Vis alle 8 forfattere av denne artikkelen] (2010). Assessments of skin and tongue microcirculation reveals major changes in porcine sepsis. Clinical Physiology and Functional Imaging. ISSN 1475-0961. doi: 10.1111/j.1475-097X.2010.00994.x. Fulltekst i vitenarkiv
• Halvorsen, Per Steinar; Fleischer, Lars Albert; Espinoza, Andreas; Elle, Ole Jakob; Hoff, Lars & Skulstad, Helge [Vis alle 8 forfattere av denne artikkelen] (2009). Detection of myocardial ischaemia by epicardial accelerometers in the pig. British Journal of Anaesthesia. ISSN 0007-0912. 102(1), s. 29–37. Fulltekst i vitenarkiv Vis sammendrag

  Conclusions. Myocardial ischaemia can be detected with epicardial three-axis accelerometers. The accelerometer had the ability to distinguish ischaemia from interventions altering global myocardial function. This novel technique may be used for continuous real-time monitoring of myocardial ischaemia during and after cardiac surgery.

• Espinoza, Andreas Westenvik; Halvorsen, Per Steinar; Hoff, Lars; Skulstad, Helge; Fosse, Erik & Ihlen, Halfdan [Vis alle 7 forfattere av denne artikkelen] (2009). Detecting myocardial ischaemia using miniature ultrasonic transducers - a feasibility study in a porcine model. European Journal of Cardio-Thoracic Surgery. ISSN 1010-7940. 37, s. 119–126. doi: 10.1016/j.ejcts.2009.05.013. Fulltekst i vitenarkiv
• Bergsland, Jacob; Lingaas, Per Snorre; Skulstad, Helge; Hol, Per Kristian; Halvorsen, Per Steinar & Andersen, Rune [Vis alle 11 forfattere av denne artikkelen] (2009). Intracoronary Shunt Prevents Ischemia in Off-Pump Coronary Artery Bypass Surgery. Annals of Thoracic Surgery. ISSN 0003-4975. 87(1), s. 54–60. doi: 10.1016/j.athoracsur.2008.08.032. Fulltekst i vitenarkiv
• Remme, Espen; Hoff, Lars; Halvorsen, Per Steinar; Nærum, Edvard; Skulstad, Helge & Fleischer, Lars Albert [Vis alle 8 forfattere av denne artikkelen] (2009). Validation of cardiac accelerometer sensor measurements. Physiological Measurement. ISSN 0967-3334. 30(12), s. 14291444–14291444. Fulltekst i vitenarkiv Vis sammendrag

  In this study we have investigated the accuracy of an accelerometer sensor designed for the measurement of cardiac motion and automatic detection of motion abnormalities caused by myocardial ischaemia. The accelerometer, attached to the left ventricular wall, changed its orientation relative to the direction of gravity during the cardiac cycle. This caused a varying gravity component in the measured acceleration signal that introduced an error in the calculation of myocardial motion. Circumferential displacement, velocity and rotation of the left ventricular apical region were calculated from the measured acceleration signal. We developed a mathematical method to separate translational and gravitational acceleration components based on a priori assumptions of myocardial motion. The accuracy of the measured motion was investigated by comparison with known motion of a robot arm programmed to move like the heart wall. The accuracy was also investigated in an animal study. The sensor measurementswere compared with simultaneously recorded motion from a robot arm attached next to the sensor on the heart and with measured motion by echocardiography and a video camera. The developed compensation method for the varying gravity component improved the accuracy of the calculated velocity and displacement traces, giving very good agreement with the reference methods.

• Remme, Espen W.; Hoff, Lars; Halvorsen, Per Steinar; Nærum, Edvard; Skulstad, Helge & Fleischer, Lars Albert [Vis alle 8 forfattere av denne artikkelen] (2009). Validation of Cardiac Accelerometer Sensor Measurements. Physiological Measurement. ISSN 0967-3334. 30(12), s. 1429–1444. doi: 10.1088/0967-3334/30/12/010. Fulltekst i vitenarkiv
• Fleischer, Lars Albert; Halvorsen, Per Steinar; Hoff, Lars; Fosse, Erik & Elle, Ole Jakob (2008). Epicardial acceleration signal measured using a single chip 3-axis accelerometer, Proceedings of 14th Nordic-Baltic Conference on Biomedical Engineering and Medical Physics. Springer. s. 221–224. Fulltekst i vitenarkiv
• Halvorsen, Per Steinar; Espinoza, Andreas; Fleischer, Lars Albert; Elle, Ole Jakob; Hoff, Lars & Lundblad, Runar [Vis alle 10 forfattere av denne artikkelen] (2008). Feasibility of a three-axis epicardial accelerometer in detecting myocardial ischemia in cardiac surgical patients. Journal of Thoracic and Cardiovascular Surgery. ISSN 0022-5223. 136(6), s. 1496–1502. Fulltekst i vitenarkiv Vis sammendrag

  Conclusions: The epicardial accelerometer detects myocardial ischemia with great accuracy. This novel technique has potential to improve monitoring of myocardial ischemia during cardiac surgery.

• Imenes, Kristin; Aasmundtveit, K; Husa, EM; Høgetveit, Jan Olav; Halvorsen, Steinar & Elle, Ole Jakob [Vis alle 9 forfattere av denne artikkelen] (2007). Assembly and packaging of a three-axis micro accelerometer used for detection of heart infarction. Biomedical microdevices. ISSN 1387-2176. 9, s. 951–957. doi: 10.1007/s10544-007-9082-2. Fulltekst i vitenarkiv
• Elle, Ole Jakob; Halvorsen, Steinar; Gulbrandsen, Martin Gunnar; Aurdal, Lars; Bakken, Andre & Samset, Eigil [Vis alle 8 forfattere av denne artikkelen] (2005). Early recognition of regional cardiac ischemia using a 3-axis accelerometer sensor. Physiological Measurement. ISSN 0967-3334. 26, s. 429–440. Fulltekst i vitenarkiv
• Skjelland, Mona; Bergsland, Jacob; Lundblad, Runar; Lingaas, Per Snorre; Rein, Kjell Arne & Halvorsen, Steinar [Vis alle 10 forfattere av denne artikkelen] (2005). Cerebral microembolization during off-pump coronary artery bypass surgery with the Symmetry aortic connector device. Journal of Thoracic and Cardiovascular Surgery. ISSN 0022-5223. 130(6), s. 1581–1585. doi: 10.1016/j.jtcvs.2005.08.015. Fulltekst i vitenarkiv
• Mathisen, Lars; Andersen, Marit Helen; Hol, Per Kristian; Tennøe, Bjørn; Lund, Christian & Russell, David [Vis alle 11 forfattere av denne artikkelen] (2005). Preoperative cerebral ischemic lesions predict physical health status after on-pump coronary artery bypass surgery. Journal of Thoracic and Cardiovascular Surgery. ISSN 0022-5223. 130(6), s. 1691–1697. doi: 10.1016/j.jtcvs.2005.08.008. Fulltekst i vitenarkiv
• Bergsland, Jacob; Hol, Per Kristian; Lingås, Per Snorre; Lundblad, Runar; Rein, Kjell Arne & Andersen, Rune [Vis alle 12 forfattere av denne artikkelen] (2004). Intraoperative and intermediate-term angiographic results of coronary artery bypass surgery with Symmetry proximal anastomotic device. Journal of Thoracic and Cardiovascular Surgery. ISSN 0022-5223. 128(5), s. 718–724. Fulltekst i vitenarkiv

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• Hansen, Ingrid Schrøder; Hårvig, Karina Roheim; Brudvik, Kristoffer Watten; Røsok, Bård Ingvald; Bjørk, Ida Torunn & Østergaard, Daniel [Vis alle 15 forfattere av denne artikkelen] (2025). A Randomized Controlled Trial of Resection Versus Thermal Ablation of Colorectal Cancer Liver Metastases (New Comet): Study Protocol. doi: 10.1245/s10434-025-17984-5. Fulltekst i vitenarkiv Vis sammendrag

  Background. The use of thermal ablation of liver tumors is rapidly increasing. This is despite a lack of high-level evidence of the oncologic efficacy of ablation. Ablation is most often used in cases where resection is not possible, but as the technique has improved it is increasingly used as a substitute for resection. Patients and Methods. New Comet is an international multicenter randomized controlled double-blinded, non inferiority trial comparing thermal ablation to resection of colorectal liver metastases. It will include 230 patients with colorectal liver metastases (up to 5 lesions, tumor size up to 3 cm) where thermal ablation and resection both are considered suitable treatment options for all lesions. The patients are randomized to either resection or ablation, and all lesions in each patient are treated with the same modaliity. Complete ablation will be verified with intraoperative computed tomography and ablation confirmation software. Conclusions. The primary endpoint is local tumor recurrence at 12 months. Secondary endpoints include overall survival, disease-free survival, time to surgical failure, health-related quality of life, complications, and cost-effectiveness (trial registration no.: NCT05129787).

• Bugge, Jan F; Espinoza, Andreas & Halvorsen, Per Steinar (2016). Hypothermia Is Not an Inotropic Drug. Critical Care Medicine. ISSN 0090-3493. 44(12). doi: 10.1097/CCM.0000000000002048. Fulltekst i vitenarkiv
• Halvorsen, Per Steinar; Espinoza, Andreas Westenvik; Fiane, Arnt E & Fosse, Erik (2013). Continuous Monitoring of Right Ventricular Function with a 3-Axis Accelerometer during Left Ventricular Assist Device Implantation. The Journal of Heart and Lung Transplantation. ISSN 1053-2498. 32(4), s. S161–S162. Fulltekst i vitenarkiv
• Mørk, Bjørn Erik; Aanestad, Margunn; Hoholm, Thomas & Halvorsen, Per Steinar (2013). "Høyteknologisk innovasjon, tverrfaglighet og ekspertise". Fulltekst i vitenarkiv
• Espinoza, Andreas Westenvik; Kerans, Viesturs; Halvorsen, Per Steinar; Opdahl, Anders; Bugge, Jan F & Skulstad, Helge [Vis alle 7 forfattere av denne artikkelen] (2010). Impaired diastolic filling reduces the frequency force reserve during therapeutic hypothermia in an experimental model. European Heart Journal. ISSN 0195-668X. 31, s. 724–724. Fulltekst i vitenarkiv
• Halvorsen, Per Steinar; Espinoza, Andreas Westenvik; Skulstad, Helge; Bugge, Jan Frederik; Elle, Ole Jakob & Fosse, Erik (2010). EPICARDIAL DISPLACEMENTS BY A 3-AXIS ACCELEROMETER SENSOR DETECT LEFT VENTRICULAR DYSFUNCTION DURING CORONARY ARTERY OCCLUSION. Intensive Care Medicine. ISSN 0342-4642. 36, s. S351–S351. Fulltekst i vitenarkiv
• Hyler, Stefan; Pischke, Søren Erik; Halvorsen, Per Steinar; Espinoza, Andreas Westenvik; Hestenes, Siv Merete & Bergsland, Jacob [Vis alle 8 forfattere av denne artikkelen] (2010). Systolic and postsystolic velocities quantify low grade myocardial ischaemia by a miniaturized epicardial ultrasonic sensor. European Heart Journal. ISSN 0195-668X. 31, s. 45–45. Fulltekst i vitenarkiv
• Hoff, Lars; Imenes, Kristin; Fleischer, Lars Albert; Halvorsen, Per Steinar; Espinoza, Andreas & Remme, Espen [Vis alle 8 forfattere av denne artikkelen] (2010). Microsensors for continuous monitoring of heart function. Fulltekst i vitenarkiv
• Hestenes, Siv Merete; Halvorsen, Per Steinar; Skulstad, Helge; Espinoza, Andreas Westenvik; Hyler, Stefan & Bugge, Jan F [Vis alle 9 forfattere av denne artikkelen] (2010). Right ventricular strain reduction in an experimental model of sepsis is closely related to increasing afterload conditions. European Heart Journal. ISSN 0195-668X. 31, s. 747–748. Fulltekst i vitenarkiv
• Espinoza, Andreas Westenvik; Skulstad, Helge; Kerans, Viesturs; Halvorsen, Per Steinar; Opdahl, Anders & Bugge, Jan F [Vis alle 7 forfattere av denne artikkelen] (2010). Moderate hypothermia causes increased left ventricular wall stiffness and delayed filling in a porcine model. European Heart Journal. ISSN 0195-668X. 31, s. 123–123. Fulltekst i vitenarkiv
• Hyler, Stefan; Halvorsen, Per Steinar; Espinoza, Andreas Westenvik; Hoff, L; Edvardsen, Thor & Skulstad, Helge [Vis alle 7 forfattere av denne artikkelen] (2009). REAL TIME MONITORING OF LEFT VENTRICULAR PERFORMANCE WITH AN EPICARDIAL ACCELEROMETER SENSOR. Intensive Care Medicine. ISSN 0342-4642. 35, s. 236–236. Fulltekst i vitenarkiv
• Hyler, S; Halvorsen, Per Steinar; Espinoza, Andreas; Hoff, Lars; Edvardsen, T. & Skulstad, Helge [Vis alle 7 forfattere av denne artikkelen] (2009). REAL TIME MONITORING OF LEFT VENTRICULAR PERFORMANCE WITH AN EPICARDIAL ACCELEROMETER SENSOR. Intensive Care Medicine. ISSN 0342-4642. s. 236–236. Fulltekst i vitenarkiv Vis sammendrag

  INTRODUCTION. Left ventricular stroke work (LVSW) measured with a pulmonary artery catheter is considered the clinical gold standard method for assessment of global cardiac function. However, only intermittent measurements are achievable by the use of this technique. A miniaturized accelerometer sensor provides continuous real time information of myocardial movement and has shown excellent ability for continuous detection of myocardial ischemia. The aim of this study was to evaluate whether measures from an epicardial accelerometer sensor could represent LVSW. CONCLUSION. Alterations in circumferential peak systolic velocities measured by an epicardial accelerometer were closely correlated to changes in LVSW during interventions affecting global cardiac function. Peak systolic velocity generated from an epicardial accelerometer sensor could therefore be used to quantify LV performance continuously and in real time. This technique may be a powerful tool for continuous monitoring of myocardial contraction during and after cardiac surgery.

• Espinoza, Andreas Westenvik; Kerans, Viesturs; Opdahl, Anders; Halvorsen, Per Steinar; Skulstad, Helge & Hoff, L [Vis alle 8 forfattere av denne artikkelen] (2009). Moderate hypothermia induces severe diastolic changes in a porcine model. Fulltekst i vitenarkiv
• Mathisen, Lars; Andersen, Marit Helen; Hol, Per Kristian; Tennøe, Bjørn; Lund, Christian & Russell, David [Vis alle 11 forfattere av denne artikkelen] (2005). Pre- and postoperative cerebral lesions as predictors of health status after coronary artery bypass surgery. Fulltekst i vitenarkiv
• Halvorsen, Per Steinar & Fosse, Erik (2010). Continuous monitoring of left ventricular function by epicardial 3-axis accelerometers. Universitetet i Oslo. ISSN 9788280723642. Fulltekst i vitenarkiv

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