Maja Elstad

• Graff, Beata; Pilarczyk, Paweł; Elstad, Maja; Narkiewicz, Krzysztof & Graff, Grzegorz (2026). Ordinal patterns with ties and tolerance provide a physiology-driven method to quantify cardiorespiratory interactions. Biomedical Signal Processing and Control. ISSN 1746-8094. 129(A), s. 1–17. doi: 10.1016/j.bspc.2026.111312. Fulltekst i vitenarkiv
• Skytioti, Maria; Holme, Nathalie; Kousis, Ilias; Søvik, Signe & Elstad, Maja (2026). Impeding respiratory venous return fluctuations alters cardiorespiratory autonomic and mechanical interactions. Journal of applied physiology. ISSN 8750-7587. 140(5), s. 1203–1217. doi: 10.1152/japplphysiol.00113.2025. Fulltekst i vitenarkiv
• Skytioti, Maria; Wiedmann, Markus; Sorteberg, Angelika; Romundstad, Luis Georg; Hassan, Yasin Ali & Ayoubi, Atiq Mohammad [Vis alle 8 forfattere av denne artikkelen] (2024). Dynamic cerebral autoregulation is preserved during orthostasis and intrathoracic pressure regulation in healthy subjects: A pilot study. Physiological Reports. 12(9). doi: 10.14814/phy2.16027. Fulltekst i vitenarkiv Vis sammendrag

  Resistance breathing may restore cardiac output (CO) and cerebral blood flow (CBF) during hypovolemia. We assessed CBF and cerebral autoregulation (CA) during tilt, resistance breathing, and paced breathing in 10 healthy subjects. Blood velocities in the internal carotid artery (ICA), middle cerebral arteries (MCA, four subjects), and aorta were measured by Doppler ultrasound in 30° and 60° semi-recumbent positions. ICA blood flow and CO were calculated. Arterial blood pressure (ABP, Finometer), and end-tidal CO2 (ETCO2) were recorded. ICA blood flow response was assessed by mixed-models regression analysis. The synchronization index (SI) for the variable pairs ABP–ICA blood velocity, ABP–MCA velocities in 0.005–0.08 Hz frequency interval was calculated as a measure of CA. Passive tilting from 30° to 60° resulted in 12% decrease in CO (p = 0.001); ICA blood flow tended to fall (p = 0.04); Resistance breathing restored CO and ICA blood flow despite a 10% ETCO2 drop. ETCO2 and CO contributed to ICA blood flow variance (adjusted R2: 0.9, p < 0.0001). The median SI was low (<0.2) indicating intact CA, confirmed by surrogate date testing. The peak SI was transiently elevated during resistance breathing in the 60° position. Resistance breathing may transiently reduce CA efficiency. Paced breathing did not restore CO or ICA blood flow.

• Skytioti, Maria & Elstad, Maja (2022). Respiratory Sinus Arrhythmia is Mainly Driven by Central Feedforward Mechanisms in Healthy Humans. Frontiers in Physiology. 13. doi: 10.3389/fphys.2022.768465. Fulltekst i vitenarkiv Vis sammendrag

  Heart rate variability (HRV) has prognostic and diagnostic potential, however, the mechanisms behind respiratory sinus arrhythmia (RSA), a main short-term HRV, are still not well understood. We investigated if the central feedforward mechanism or pulmonary stretch reflex contributed most to RSA in healthy humans. Ventilatory support reduces the centrally mediated respiratory effort but remains the inspiratory stretch of the pulmonary receptors. We aimed to quantify the difference in RSA between spontaneous breathing and ventilatory support. Nineteen healthy, young subjects underwent spontaneous breathing and non-invasive intermittent positive pressure ventilation (NIV) while we recorded heart rate (HR, from ECG), mean arterial pressure (MAP) and stroke volume (SV) estimated from the non-invasive finger arterial pressure curve, end-tidal CO 2 (capnograph), and respiratory frequency (RF) with a stretch band. Variability was quantified by an integral between 0.15–0.4 Hz calculated from the power spectra. Median and 95% confidence intervals (95%CI) were calculated as Hodges–Lehmann’s one-sample estimator. Statistical difference was calculated by the Wilcoxon matched-pairs signed-rank test. RF and end-tidal CO 2 were unchanged by NIV. NIV reduced HR by 2 bpm, while MAP and SV were unchanged in comparison to spontaneous breathing. Variability in both HR and SV was reduced by 60% and 75%, respectively, during NIV as compared to spontaneous breathing, but their interrelationship with respiration was maintained. NIV reduced RSA through a less central respiratory drive, and pulmonary stretch reflex contributed little to RSA. RSA is mainly driven by a central feedforward mechanism in healthy humans. Peripheral reflexes may contribute as modifiers of RSA.

• Holme, Nathalie; Zilakos, Ilias; Elstad, Maja & Skytioti, Maria (2022). Cerebral blood flow response to cardiorespiratory oscillations in healthy humans. Autonomic Neuroscience: Basic & Clinical. ISSN 1566-0702. 245. doi: 10.1016/j.autneu.2022.103069. Fulltekst i vitenarkiv Vis sammendrag

  Dynamic cerebral autoregulation (CA) characterizes the cerebral blood flow (CBF) response to abrupt changes in arterial blood pressure (ABP). CA operates at frequencies below 0.15 Hz. ABP regulation and probably CA are modified by autonomic nervous activity. We investigated the CBF response and CA dynamics to mild increase in sympathetic activity. Twelve healthy volunteers underwent oscillatory lower body negative pressure (oLBNP), which induced respiratory-related ABP oscillations at an average of 0.22 Hz. We recorded blood velocity in the internal carotid artery (ICA) by Doppler ultrasound and ABP. We quantified variability and peak wavelet power of ABP and ICA blood velocity by wavelet analysis at low frequency (LF, 0.05-0.15 Hz) and Mayer waves (0.08-0.12 Hz), respectively. CA was quantified by calculation of the wavelet synchronization gamma index for the pair ABP-ICA blood velocity in the LF and Mayer wave band. oLBNP increased ABP peak wavelet power at the Mayer wave frequency. At the Mayer wave, ABP peak wavelet power increased by >70 % from rest to oLBNP (p

• Noreen, Shumaila; Ben-Tal, Alona; Elstad, Maja; Sweatman, Winston L.; Ramchandra, Rohit & Paton, Julian (2022). Mathematical modelling of atrial and ventricular pressure–volume dynamics and their change with heart rate. Mathematical Biosciences. ISSN 0025-5564. 344. doi: 10.1016/j.mbs.2021.108766. Fulltekst i vitenarkiv
• Lin, Aihua; Kousis, Ilias; Ugland, Nora; Andersen, Marian Berge; Bergersen, Tone Kristin & Stankovski, Tomislav [Vis alle 8 forfattere av denne artikkelen] (2020). Cardiorespiratory interactions during three different temperatures - a case report. 2020 11th Conference of the European Study Group on Cardiovascular Oscillations (ESGCO). doi: 10.1109/ESGCO49734.2020.9158146. Fulltekst i vitenarkiv
• Skytioti, Maria; Elstad, Maja & Søvik, Signe (2019). Internal Carotid Artery Blood Flow Response to Anesthesia, Pneumoperitoneum, and Head-up Tilt during Laparoscopic Cholecystectomy. Anesthesiology. ISSN 0003-3022. 131, s. 512–520. doi: 10.1097/ALN.0000000000002838. Fulltekst i vitenarkiv
• Skytioti, Maria; Søvik, Signe & Elstad, Maja (2018). Dynamic cerebral autoregulation is preserved during isometric handgrip and head-down tilt in healthy volunteers. Physiological Reports. 6(6). doi: 10.14814/phy2.13656. Fulltekst i vitenarkiv Vis sammendrag

  In healthy humans, cerebral blood flow (CBF) is autoregulated against changes in arterial blood pressure. Spontaneous fluctuations in mean arterial pressure (MAP) and CBF can be used to assess cerebral autoregulation. We hypothesized that dynamic cerebral autoregulation is affected by changes in autonomic activity, MAP, and cardiac output (CO) induced by handgrip (HG), head-down tilt (HDT), and their combination. In thirteen healthy volunteers, we recorded blood velocity by ultrasound in the internal carotid artery (ICA), HR, MAP and CO-estimates from continuous finger blood pressure, and endtidal CO2. Instantaneous ICA beat volume (ICABV, mL) and ICA blood flow (ICABF, mL/min) were calculated. Wavelet synchronization index c (0–1) was calculated for the pairs: MAP–ICABF, CO–ICABF and HR–ICABV in the low (0.05–0.15 Hz; LF) and high (0.15–0.4 Hz; HF) frequency bands. ICABF did not change between experimental states. MAP and CO were increased during HG (+16% and +15%, respectively, P < 0.001) and during HDT + HG (+12% and +23%, respectively, P < 0.001). In the LF interval, median c for the MAP–ICABF pair (baseline: 0.23 [0.12–0.28]) and the CO–ICABF pair (baseline: 0.22 [0.15–0.28]) did not change with HG, HDT, or their combination. High c was observed for the HR–ICABV pair at the respiratory frequency, the oscillations in these variables being in inverse phase. The unaltered ICABF and the low synchronization between MAP and ICABF in the LF interval suggest intact dynamic cerebral autoregulation during HG, HDT, and their combination.

• Skytioti, Maria; Søvik, Signe & Elstad, Maja (2018). Respiratory pump maintains cardiac stroke volume during hypovolemia in young, healthy volunteers. Journal of applied physiology. ISSN 8750-7587. 124(5), s. 1319–1325. doi: 10.1152/japplphysiol.01009.2017. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Spontaneous breathing has beneficial effects on the circulation, since negative intrathoracic pressure enhances venous return and increases cardiac stroke volume. We quantified the contribution of the respiratory pump to preserve stroke volume during hypovolemia in awake, young, healthy subjects. Noninvasive stroke volume, cardiac output, heart rate, and mean arterial pressure (Finometer) were recorded in 31 volunteers (19 women), 19–30 yr old, during normovolemia and hypovolemia (approximating 450- to 500-ml reduction in central blood volume) induced by lower-body negative pressure. Control-mode noninvasive positive-pressure ventilation was employed to reduce the effect of the respiratory pump. The ventilator settings were matched to each subject’s spontaneous respiratory pattern. Stroke volume estimates during positive-pressure ventilation and spontaneous breathing were compared with Wilcoxon matched-pairs signed-rank test. Values are overall medians. During normovolemia, positive-pressure ventilation did not affect stroke volume or cardiac output. Hypovolemia resulted in an 18% decrease in stroke volume and a 9% decrease in cardiac output (P < 0.001). Employing positive-pressure ventilation during hypovolemia decreased stroke volume further by 8% (P < 0.001). Overall, hypovolemia and positive-pressure ventilation resulted in a reduction of 26% in stroke volume (P < 0.001) and 13% in cardiac output (P < 0.001) compared with baseline. Compared with the situation with control-mode positive-pressure ventilation, spontaneous breathing attenuated the reduction in stroke volume induced by moderate hypovolemia by 30% (i.e., −26 vs. −18%). In the patient who is critically ill with hypovolemia or uncontrolled hemorrhage, spontaneous breathing may contribute to hemodynamic stability, whereas controlled positive-pressure ventilation may result in circulatory decompensation. NEW & NOTEWORTHY Maintaining spontaneous respiration has beneficial effects on hemodynamic compensation, which is clinically relevant for patients in intensive care. We have quantified the contribution of the respiratory pump to cardiac stroke volume and cardiac output in healthy volunteers during normovolemia and central hypovolemia. The positive hemodynamic effect of the respiratory pump was abolished by noninvasive, low-level positive-pressure ventilation. Compared with control-mode positive-pressure ventilation, spontaneous negative-pressure ventilation attenuated the fall in stroke volume by 30%.

• Elstad, Maja; O'Callaghan, Erin L.; Smith, Alex J.; Ben-Tal, Alona & Ramchandra, Rohit (2018). Cardiorespiratory interactions in humans and animals: rhythms for life. American Journal of Physiology. Heart and Circulatory Physiology. ISSN 0363-6135. 315(1), s. H6–H17. doi: 10.1152/ajpheart.00701.2017. Fulltekst i vitenarkiv Vis sammendrag

  The cardiorespiratory system exhibits oscillations from a range of sources. One of the most studied oscillations is heart rate variability, which is thought to be beneficial and can serve as an index of a healthy cardiovascular system. Heart rate variability is dampened in many diseases including depression, autoimmune diseases, hypertension, and heart failure. Thus, understanding the interactions that lead to heart rate variability, and its physiological role, could help with prevention, diagnosis, and treatment of cardiovascular diseases. In this review, we consider three types of cardiorespiratory interactions: respiratory sinus arrhythmia (variability in heart rate at the frequency of breathing), cardioventilatory coupling (synchronization between the heart beat and the onset of inspiration), and respiratory stroke volume synchronization (the constant phase difference between the right and the left stroke volumes over one respiratory cycle). While the exact physiological role of these oscillations continues to be debated, the redundancies in the mechanisms responsible for its generation and its strong evolutionary conservation point to the importance of cardiorespiratory interactions. The putative mechanisms driving cardiorespiratory oscillations as well as the physiological significance of these oscillations will be reviewed. We suggest that cardiorespiratory interactions have the capacity to both dampen the variability in systemic blood flow as well as improve the efficiency of work done by the heart while maintaining physiological levels of arterial CO2. Given that reduction in variability is a prognostic indicator of disease, we argue that restoration of this variability via pharmaceutical or device-based approaches may be beneficial in prolonging life.

• Bergersen, Tone Kristin; Skytioti, Maria & Elstad, Maja (2017). Cold-induced sympathetic tone modifies the impact of endothelium-dependent vasodilation in the finger pulp. Autonomic Neuroscience: Basic & Clinical. ISSN 1566-0702. 203, s. 97–102. doi: 10.1016/j.autneu.2016.11.004. Fulltekst i vitenarkiv
• Skytioti, Maria; Søvik, Signe & Elstad, Maja (2017). Respiration-related cerebral blood flow variability increases during control-mode non-invasive ventilation in normovolemia and hypovolemia. European Journal of Applied Physiology. ISSN 1439-6319. 117(11), s. 2237–2249. doi: 10.1007/s00421-017-3711-0. Fulltekst i vitenarkiv Vis sammendrag

  Purpose: Increased variability in cerebral blood flow (CBF) predisposes to adverse cerebrovascular events. Oscillations in arterial blood pressure and PaCO2 induce CBF variability. Less is known about how heart rate (HR) variability affects CBF. We experimentally reduced respiration-induced HR variability in healthy subjects, hypothesizing that CBF variability would increase. Methods: Internal carotid artery (ICA) blood velocity was recorded by Doppler ultrasound in ten healthy subjects during baseline, control-mode, non-invasive mechanical ventilation (NIV), i.e., with fixed respiratory rate, hypovolemia induced by lower body negative pressure, and combinations of these. ICA beat volume (ICABV) and ICA blood flow (ICABF) were calculated. HR, mean arterial blood pressure (MAP), respiratory frequency (RF), and end-tidal CO2 were recorded. Integrals of power spectra at each subject’s RF ± 0.03 Hz were used to measure variability. Phase angle/coherence measured coupling between cardiovascular variables. Results: Control-mode NIV reduced HR variability (−56%, p = 0.002) and ICABV variability (−64%, p = 0.006) and increased ICABF variability (+140%, p = 0.002) around RF. NIV + hypovolemia reduced variability in HR and ICABV by 70–80% (p = 0.002) and doubled ICABF variability (p = 0.03). MAP variability was unchanged in either condition. Respiration-induced HR and ICABV oscillations were in inverse phase and highly coherent (coherence >0.9) during baseline, but this coherence decreased during NIV, in normovolemia and hypovolemia (p = 0.01). Conclusion: Controlling respiration in awake healthy humans reduced HR variability and increased CBF variability in hypovolemia and normovolemia. We suggest respiration-induced HR variability to be a mechanism in CBF regulation. Maintaining spontaneous respiration in patients receiving ventilatory support may be beneficial also for cerebral circulatory purposes. The final version of this research has been published in European Journal of Applied Physiology. © 2017 Springer Verlag

• Elstad, Maja; Zilakos, Ilias & Bergersen, Tone Kristin (2017). Oscillatory pattern of acral skin blood flow within thermoneutral zone in healthy humans. Physiological Measurement. ISSN 0967-3334. 38(5), s. 848–859. doi: 10.1088/1361-6579/aa5fee. Fulltekst i vitenarkiv Vis sammendrag

  The acral skin contains arteriovenous anastomoses, which probably is the main part of skin microcirculation for blood flow adjustments and thermoregulation in the thermoneutral zone. The objective was to investigate if an increase in sympathetic activation during cooling influences the oscillatory pattern of acral skin blood flow. We had measurements of bilateral acral skin blood flow (n??=??12) during lowering of ambient temperature from 32 °C to 18 °C. We quantified the oscillatory pattern as the time averaged wavelet spectral powers, coherence and phase angles in three frequency intervals (0.01–0.02 Hz, 0.02–0.05 Hz and 0.05–0.08 Hz). The differences were tested by Wilcoxon signed rank sum method between adjacent intervals. The absolute fluctuations in laser Doppler flux at 0.01–0.02 Hz, 0.02–0.05 Hz and 0.05–0.08 Hz were similar at 32 °C and 25 °C, and decreased at 18 °C (p??<??0.001). The relative fluctuations (amplitude of the fluctuations relative to median flux value) in laser Doppler flux at 0.01–0.02 Hz, 0.02–0.05 Hz and 0.05–0.08 Hz were higher at 25 °C and 18 °C as compared to 32 °C (p??<??0.002). The coherence between the oscillations of signals from right and left finger tips was highest (median coherence??>??0.89) at 25 °C, and lower at 32 °C and at 18 °C.The median phase angles between the flux signals from right and left finger tips were close to 0 radians. We found that the relative fluctuations in acral skin blood flow increased during vasoconstriction due to cooling. Wavelet analysis of acral skin blood flow oscillations could serve as a future clinical tool. © 2017 IOP Publishing

• Elstad, Maja; Liu, Xun & Thoresen, Marianne (2016). Heart rate response to therapeutic hypothermia in infants with hypoxic–ischaemic encephalopathy. Resuscitation. ISSN 0300-9572. 106, s. 53–57. doi: 10.1016/j.resuscitation.2016.06.023. Fulltekst i vitenarkiv
• Wood, Thomas Ragnar; Smit, Elisa; Maes, Elke; Osredkar, Damjan; Falck, Mari & Elstad, Maja [Vis alle 7 forfattere av denne artikkelen] (2016). Monitoring of cerebral blood flow during hypoxia-ischemia and resuscitation in the neonatal rat using laser speckle imaging. Physiological Reports. 4(7), s. 1–14. doi: 10.14814/phy2.12749. Fulltekst i vitenarkiv Vis sammendrag

  Neonatal hypoxic‐ischemic encephalopathy (HIE) is associated with alterations in cerebral blood flow (CBF) as a result of perinatal asphyxia. The extent to which CBF changes contribute to injury, and whether treatments that ameliorate these changes might be neuroprotective, is still unknown. Higher throughput techniques to monitor CBF changes in rodent models of HIE can help elucidate the underlying pathophysiology. We developed a laser speckle imaging (LSI) technique to continuously monitor CBF in six postnatal‐day 10 (P10) rats simultaneously before, during, and after unilateral hypoxia‐ischemia (HI, ligation of the left carotid artery followed by hypoxia in 8% oxygen). After ligation, CBF to the ligated side fell by 30% compared to the unligated side (P < 0.0001). Hypoxia induced a bilateral 55% reduction in CBF, which was partially restored by resuscitation. Compared to resuscitation in air, resuscitation in 100% oxygen increased CBF to the ligated side by 45% (P = 0.033). Individual variability in CBF response to hypoxia between animals accounted for up to 24% of the variability in hemispheric area loss to the ligated side. In both P10 and P7 models of unilateral HI, resuscitation in 100% oxygen did not affect hemispheric area loss, or hippocampal CA1 pyramidal neuron counts, after 1‐week survival. Continuous CBF monitoring using LSI in multiple rodents simultaneously can screen potential treatment modalities that affect CBF, and provide insight into the pathophysiology of HI.

• Holme, Nathalie Linn Anikken; Rein, Erling Bekkestad & Elstad, Maja (2016). Cardiac stroke volume variability measured non-invasively by three methods for detection of central hypovolemia in healthy humans. European Journal of Applied Physiology. ISSN 1439-6319. s. 1–10. doi: 10.1007/s00421-016-3471-2. Fulltekst i vitenarkiv
• Skytioti, Maria; Søvik, Signe & Elstad, Maja (2016). Internal carotid artery blood flow in healthy awake subjects is reduced by simulated hypovolemia and noninvasive mechanical ventilation. Physiological Reports. 4(19). doi: 10.14814/phy2.12969. Fulltekst i vitenarkiv
• Quintana, Daniel; Elstad, Maja; Kaufmann, Tobias; Brandt, Christine Lycke; Haatveit, Beathe Christin & Haram, Marit [Vis alle 9 forfattere av denne artikkelen] (2016). Resting-state heart rate variability is related to respiratory frequency in individuals with severe mental illness but not healthy controls. Scientific Reports. 6:37212, s. 1–8. doi: 10.1038/srep37212. Fulltekst i vitenarkiv Vis sammendrag

  Heart rate variability (HRV) has become central to biobehavioral models of self-regulation and interpersonal interaction. While research on healthy populations suggests changes in respiratory frequency do not affect short-term HRV, thus negating the need to include respiratory frequency as a HRV covariate, the nature of the relationship between these two variables in psychiatric illness is poorly understood. Therefore, the aim of this study was to investigate the association between HRV and respiratory frequency in a sample of individuals with severe psychiatric illness (n = 55) and a healthy control comparison group (n = 149). While there was no significant correlation between HF-HRV and respiration in the control group, we observed a significant negative correlation in the psychiatric illness group, with a 94.1% probability that these two relationships are different. Thus, we provide preliminary evidence suggesting that HF-HRV is related to respiratory frequency in severe mental illness, but not in healthy controls, suggesting that HRV research in this population may need to account for respiratory frequency. Future work is required to better understand the complex relationship between respiration and HRV in other clinical samples with psychiatric diseases.

• Elstad, Maja & Walløe, Lars (2015). Heart rate variability and stroke volume variability to detect central hypovolemia during spontaneous breathing and supported ventilation in young, healthy volunteers. Physiological Measurement. ISSN 0967-3334. 36(4), s. 671–681. doi: 10.1088/0967-3334/36/4/671. Fulltekst i vitenarkiv
• Osredkar, Damjan; Thoresen, Marianne; Maes, Elke; Flatebø, Torun; Elstad, Maja & Sabir, Hemmen (2014). Hypothermia is not neuroprotective after infection-sensitized neonatal hypoxic-ischemic brain injury. Resuscitation. ISSN 0300-9572. 85(4), s. 567–572. doi: 10.1016/j.resuscitation.2013.12.006. Fulltekst i vitenarkiv
• Hannah, Gill; Thoresen, Marianne; Smit, Elisa; Davis, Jonathan; Liu, Xun & Dingley, John [Vis alle 7 forfattere av denne artikkelen] (2014). Sedation management during therapeutic hypothermia for neonatal encephalopathy: Atropine premedication for endotracheal intubation causes a prolonged increase in heart rate. Resuscitation. ISSN 0300-9572. 85(10), s. 1394–1398. doi: 10.1016/j.resuscitation.2014.07.002. Fulltekst i vitenarkiv
• Elstad, Maja; Vanggaard, Leif; Lossius, Astrid Haaskjold; Walløe, Lars & Bergersen, Tone Kristin (2014). Responses in acral and non-acral skin vasomotion and temperature during lowering of ambient temperature. Journal of Thermal Biology. ISSN 0306-4565. 45, s. 168–174. doi: 10.1016/j.jtherbio.2014.09.003. Fulltekst i vitenarkiv
• Elstad, Maja; Walløe, Lars; Holme, Nathalie; Maes, Elke & Thoresen, Marianne (2014). Respiratory sinus arrhythmia stabilizes mean arterial blood pressure at high-frequency interval in healthy humans. European Journal of Applied Physiology. ISSN 1439-6319. 115(3), s. 521–530. doi: 10.1007/s00421-014-3042-3. Fulltekst i vitenarkiv
• Dingley, John; Tooley, James; Liu, Xun; Scull-Brown, Emma; Elstad, Maja & Chakkarapani, Elavazhagan [Vis alle 8 forfattere av denne artikkelen] (2014). Xenon Ventilation During Therapeutic Hypothermia in Neonatal Encephalopathy: A Feasibility Study. Pediatrics. ISSN 0031-4005. 133(5), s. 809–818. doi: 10.1542/peds.2013-0787. Fulltekst i vitenarkiv
• Skranes, Janne Helen; Elstad, Maja; Thoresen, Marianne; Cowan, Frances; Stiris, Tom & Fugelseth, Drude (2014). Hypothermia Makes Cerebral Resistance Index a Poor Prognostic Tool in Encephalopathic Newborns. Neonatology. ISSN 1661-7800. 106(1), s. 17–23. doi: 10.1159/000358229. Fulltekst i vitenarkiv
• Bergersen, Tone Kristin; Hoffmann-Vold, Anna-Maria; Midtvedt, Øyvind; Gran, Jan Tore; Mørk, Cato & Toska, Karin [Vis alle 7 forfattere av denne artikkelen] (2014). Dysfunctional arteriovenous anastomoses in hands of systemic sclerosis patients with digital ulcers. Clinical and Experimental Rheumatology. ISSN 0392-856X. 32(6 Suppl 86), s. 53–59. Fulltekst i vitenarkiv
• Liu, X; Dingley, John; Elstad, Maja; Brown, EL; Steen, Petter Andreas & Thoresen, Marianne (2013). Minimum Alveolar Concentration (MAC) for Sevoflurane and Xenon at Normothermia and Hypothermia in newborn pigs. Acta Anaesthesiologica Scandinavica. ISSN 0001-5172. doi: 10.1111/aas.12055. Fulltekst i vitenarkiv
• Dalen, Marit Lunde; Liu, Xun; Elstad, Maja; Løberg, Else Marit; Saugstad, Ola Didrik & Rootwelt, Terje [Vis alle 7 forfattere av denne artikkelen] (2012). Resuscitation with 100% oxygen increases injury and counteracts the neuroprotective effect of therapeutic hypothermia in the neonatal rat. Pediatric Research. ISSN 0031-3998. 71(3), s. 247–252. doi: 10.1038/pr.2011.43. Fulltekst i vitenarkiv
• Elstad, Maja (2012). Respiratory variations in pulmonary and systemic blood flow in healthy humans. Acta Physiologica. ISSN 1748-1708. 205(3), s. 341–348. doi: 10.1111/j.1748-1716.2012.02419.x. Fulltekst i vitenarkiv
• Elstad, Maja; Walløe, Lars; Chon, Ki H. & Toska, Karin (2011). Low-frequency fluctuations in heart rate, cardiac output and mean arterial pressure in humans: what are the physiological relationships? Journal of Hypertension. ISSN 0263-6352. 29(7), s. 1327–1336. doi: 10.1097/HJH.0b013e328347a17a. Fulltekst i vitenarkiv
• Elstad, Maja; Whitelaw, Andrew & Thoresen, Marianne (2011). Cerebral Resistance Index is less predictive in hypothermic encephalopathic newborns. Acta Paediatrica. ISSN 0803-5253. 100(10), s. 1344–1349. doi: 10.1111/j.1651-2227.2011.02327.x. Fulltekst i vitenarkiv
• Elstad, Maja; Nådland, Inger Helene; Toska, Karin & Walløe, Lars (2009). Stroke volume decreases during mild dynamic and static exercise in supine humans. Acta Physiologica. ISSN 1748-1708. 195(2), s. 289–300. doi: 10.1111/j.1748-1716.2008.01887.x. Fulltekst i vitenarkiv
• Elstad, Maja; Toska, Karin & Walløe, Lars (2002). Model simulations of cardiovascular changes at the onset of moderate exercise in humans. Journal of Physiology. ISSN 0022-3751. 543(2), s. 719–728. Fulltekst i vitenarkiv Vis sammendrag

  We have tested whether the cardiovascular changes at the onset of exercise could be simulated only by an increase in the baroreflex set point and locally induced vasodilation in the exercising muscles. The mathematical model consists of a heart, a linear elastic arterial reservoir, and two parallel resistive vascular beds. The arterial baroreflex loop is modelled by three separate time domain processing objects, each with its own gain, time constant, and delay. These are intended to simulate the action of a sympathetic signal to the peripheral vascular bed, a parasympathetic signal to the heart and a sympathetic signal to the heart. We used this model with previously published experimental data to estimate the unknown parameters in the reflex control loop. In all 10 subjects and in the global averaged response, the short-term cardiovascular responses were adequately simulated by using individual sets of parameters in the model. An increase in the baroreflex set point and locally induced vasodilation in the exercising muscles can explain almost all of the cardiovascular changes in the recorded variables (mean arterial pressure, RR interval and stroke volume) at the onset of exercise.

• Elstad, Maja; Toska, Karin; Chon, Ki H.; Raeder, Ernst A. & Cohen, Richard J. (2001). Respiratory sinus arrhythmia: opposite effects on systolic and mean arterial pressure in supine humans. Journal of Physiology. ISSN 0022-3751. 536(1), s. 251–259. Fulltekst i vitenarkiv Vis sammendrag

  Are arterial blood pressure fluctuations buffered or reinforced by respiratory sinus arrhythmia (RSA)? There is still considerable debate about this simple question. Different results have been obtained, triggering a discussion as to whether or not the baroreflexes are responsible for RSA. We suspected that the measurements of different aspects of arterial pressure (mean arterial pressure (MAP) and systolic pressure (SP)) can explain the conflicting results. Simultaneous recordings of beat-to-beat MAP, SP, left cardiac stroke volume (SV, pulsed ultrasound Doppler), heart rate (HR) and respiration (RE) were obtained in ten healthy young adults during spontaneous respiration. In order to eliminate HR variations at respiratory frequency we used propranolol and atropine administration in the supine and tilted positions. Respiration-synchronous variation in the recorded variables was quantified by spectral analysis of the recordings of each of these variables, and the phase relations between them were determined by cross-spectral analysis. MAP fluctuations increased after removing heart rate variations in both supine and tilted position, whereas SP fluctuations decreased in the supine position and increased in the head-up tilted position. RSA buffers respiration-synchronous fluctuations in MAP in both positions. However, fluctuations in SP were reinforced by RSA in the supine and buffered in the tilted position.

Se alle arbeider i NVA

• Elstad, Maja & Zilakos, Ilias (2024). Dynamic cerebral autoregulation quantified with wavelets analysis is preserved during augmented negative intrathoracic pressure and slow, paced breathing in healthy subjects. Fulltekst i vitenarkiv
• Skytioti, Maria; Tveit, Lars Hansen; Sorteberg, Angelika; Elstad, Maja; Romundstad, Luis & Wiedmann, Markus [Vis alle 8 forfattere av denne artikkelen] (2024). ASYMMETRY OF CEREBRAL AUTOREGULATION QUANTIFIED BY WAVELET ANALYSIS IN PATIENTS SUFFERING FROM SPONTANEOUS SUBARACHNOID HAEMORRHAGE. Fulltekst i vitenarkiv
• Tveit, Lars H.; Sorteberg, Angelika; Wiedmann, Markus K. H.; Romundstad, Luis Georg; Elstad, Maja & Zilakos, Ilias [Vis alle 7 forfattere av denne artikkelen] (2024). ASYMMETRY OF CEREBRAL AUTOREGULATION QUANTIFIED BY WAVELET ANALYSIS IN PATIENTS SUFFERING FROM SPONTANEOUS SUBARACHNOID HAEMORRHAGE. Fulltekst i vitenarkiv
• Elstad, Maja (2023). Reductions in cardiac stroke volume are associated with reductions in cerebral blood flow in healthy subjects despite maintained arterial blood pressure. Acta Anaesthesiologica Scandinavica. ISSN 0001-5172. Fulltekst i vitenarkiv
• Elstad, Maja; Holme, Natalie & Zilakos, Ilias (2022). Wavelet analysis to quantify cerebral autoregulation during rapid arterial blood pressure oscillations. Acta Anaesthesiologica Scandinavica. ISSN 0001-5172. Fulltekst i vitenarkiv
• Holme, Nathalie Linn Anikken; Skytioti, Maria; Søvik, Signe & Elstad, Maja (2020). Induced respiratory variability in arterial blood pressure lowers cerebral blood flow in healthy humans. Fulltekst i vitenarkiv Vis sammendrag

  In this study we examined the effect of respiratory oscillations in arterial blood pressure and cardiac output, induced by oscillatory lower body negative pressure, on cerebral blood flow in healthy humans. We found that respiratory oscillations in arterial blood pressure and cardiac output lowered the median cerebral blood flow. In addition, as oscillations in cerebral blood flow increased during oscillatory lower body negative pressure, we conclude that respiratory oscillations in arterial blood pressure and cardiac output are transferred to the cerebral circulation. Induced respiratory oscillations in arterial blood pressure and in flow therefore lower cerebral blood flow in healthy humans.

• Porta, Alberto & Elstad, Maja (2020). Editorial: Probing the Cardiac Arm of the Baroreflex and Complementary Branches. Frontiers in Neuroscience. ISSN 1662-4548. 13. doi: 10.3389/fnins.2019.01422. Fulltekst i vitenarkiv
• Elstad, Maja; Holme, Nathalie Linn Anikken & Skytioti, Maria (2019). Respiratory sinus arrhythmia and its contribution from the central feedforward command, the arterial baroreflex and the pulmonary stretch reflex in healthy humans. Fulltekst i vitenarkiv
• Noreen, Shumaila; Ben-Tal, Alona; Elstad, Maja; Sweatman, Winston; Ramchandra, Rohit & Paton, Julian (2019). Mathematical Modelling of the Cardiovascular System to Study the Effects of Respiratory Sinus Arrhythmia on Cardiac Output. Fulltekst i vitenarkiv
• Skytioti, Maria; Elstad, Maja & Søvik, Signe (2019). Blodflow i arteria carotis interna faller parallelt med cardiac index under laparoskopisk cholecystectomi, uavhengig av blodtrykket. Fulltekst i vitenarkiv
• Elstad, Maja (2019). Cardiorespiratory interactions promote human cardiovascular control. Fulltekst i vitenarkiv
• Elstad, Maja; Skytioti, Maria; Holme, Nathalie Linn Anikken; Zilakos, Ilias & Lin, Aihua (2019). Cardiorespiratory interactions promote the human cardiovascular control. Fulltekst i vitenarkiv
• Ugland, Nora; Lin, Aihua; Bergersen, Tone Kristin; Andersen, Marian Berge; Holme, Nathalie Linn Anikken & Zilakos, Ilias [Vis alle 7 forfattere av denne artikkelen] (2019). The hemodynamic effects of skin blood flow in human thermoneutral zone. Fulltekst i vitenarkiv
• Holme, Nathalie Linn Anikken; Lehre, Martin Andreas; Søvik, Signe; Skytioti, Maria & Elstad, Maja (2019). Cerebral Autoregulation Fails to Maintain Cerebral Blood Flow During Arterial Blood Pressure Oscillations at Respiratory Frequency. Fulltekst i vitenarkiv
• Elstad, Maja; Holme, Nathalie Linn Anikken & Skytioti, Maria (2018). The role of the arterial baroreflex in respiratory sinus arrhythmia in healthy humans. Fulltekst i vitenarkiv
• Skytioti, Maria; Søvik, Signe & Elstad, Maja (2018). Differential response of internal carotid artery blood flow to cardiac output changes. Fulltekst i vitenarkiv
• Elstad, Maja; Skytioti, Maria; Holme, Nathalie Linn Anikken & Reitan, Harald (2018). Pustepumpen. [Radio]. NRK P2 Ekko. Fulltekst i vitenarkiv
• Holme, Nathalie Linn Anikken; Lehre, Martin Andreas; Søvik, Signe; Elstad, Maja & Skytioti, Maria (2018). Responses in cardiac stroke volume index and cardiac index do not differ between genders during moderate central hypovolemia. Fulltekst i vitenarkiv
• Skytioti, Maria; Søvik, Signe & Elstad, Maja (2017). Den respiratoriske sirkulasjonspumpen opprettholder hjertets slagvolum ved hypovolemi hos friske individer. Fulltekst i vitenarkiv
• Elstad, Maja (2017). Cardiorespiratory interactions are responsible for both mechanical and nervous cardiovascular oscillations. Fulltekst i vitenarkiv
• Elstad, Maja (2017). Cardiorespiratory interactions in humans. Fulltekst i vitenarkiv
• Skytioti, Maria; Søvik, Signe & Elstad, Maja (2017). Internal carotid artery blood flow response to isometric handgrip and head down tilt in healthy volunteers. Fulltekst i vitenarkiv
• Elstad, Maja (2017). Hva får din indre klokke til å tikke? Tidsskrift for Den norske legeforening (Tidsskriftet). ISSN 0029-2001. 137(22), s. 1758–1758. doi: 10.4045/tidsskr.17.0901. Fulltekst i vitenarkiv
• Smit, Elisa; Wood, Thomas Ragnar; Elstad, Maja; Liu, Xun & Thoresen, Marianne (2016). The effect of resuscitation in 100% Oxygen on cerebral blood flow and neuropathology in a newborn rat model of hypoxia-ischaemia. Fulltekst i vitenarkiv
• Elstad, Maja; Zilakos, Ilias & Bergersen, Tone Kristin (2016). Oscillatory pattern of arteriovenous anastomoses and skin blood flow within thermoneutral zone. Fulltekst i vitenarkiv
• Skytioti, Maria; Søvik, Signe & Elstad, Maja (2016). Respiratory sinus arrhythmia buffers variability in cerebral blood flow. Fulltekst i vitenarkiv
• Elstad, Maja (2016). Respiratory sinus arrhythmia as buffer of systemic blood flow oscillations. Fulltekst i vitenarkiv
• Elstad, Maja (2015). Disse svingningene kan gi oss bedre helse. Aftenposten Viten. ISSN 2464-3033. Fulltekst i vitenarkiv
• Elstad, Maja (2015). Ujevn hjerterytme stabiliserer blodflyten. [Internet]. http://unikard.org/respiratorisk-sinusarytmi-stabiliserer-bl. Fulltekst i vitenarkiv
• Elstad, Maja (2015). Kan avsløre skjult blodtap på vei til sykehus. [Internet]. http://unikard.org/kan-avslore-skjult-blodtap-pa-vei-til-syk. Fulltekst i vitenarkiv
• Bergersen, Tone Kristin; Skytioti, Maria & Elstad, Maja (2015). Sympathetic tonus modifies endothelial dependent vasodilation in finger pulp of healthy subjects. Fulltekst i vitenarkiv
• Skytioti, Maria; Søvik, Signe & Elstad, Maja (2015). CEREBRAL BLOOD FLOW CHANGES IN RESPONSE TO MILD HYPOVOLEMIA AND POSITIVE PRESSURE VENTILATION. Fulltekst i vitenarkiv
• Osredkar, Damjan; Thoresen, Marianne; Maes, Elke; Flatebo, Torun; Elstad, Maja & Sabir, Hemmen (2014). Hypothermia Is Not Neuroprotective after Infection-Sensitized Neonatal Hypoxic-Ischemic Brain Injury. Fulltekst i vitenarkiv
• Gill, Hannah; Thoresen, Marianne; Smit, Elisa; Davis, Jonathan; Liu, Xun & Dingley, John [Vis alle 7 forfattere av denne artikkelen] (2014). Is Atropine Before Intubation of Term Neonates Justified? An Observation from the CoolXe2 Trial. Fulltekst i vitenarkiv
• Elstad, Maja (2014). The respiratory pump improves cardiac stroke volume during central hypovolemia in healthy subjects. Fulltekst i vitenarkiv
• Holme, Nathalie; Rein, Erling Bekkestad; Walløe, Lars & Elstad, Maja (2014). Cardiothoracic impedance does not reflect beat-to-beat changes in cardiac stroke volume during mild lower body negative pressure. Fulltekst i vitenarkiv
• Elstad, Maja & Walløe, Lars (2014). Left cardiac stroke volume variations during spontaneous breathing and central hypovolemia in healthy subjects. Fulltekst i vitenarkiv
• Elstad, Maja (2013). Forplantning er grunnlaget for nytt liv. I Nicolaysen, Gunnar & Holck, Per (Red.), Kroppens funksjon og oppbygning. Gyldendal Akademisk. ISSN 9788205323629. s. 257–282. Fulltekst i vitenarkiv
• Skranes, Janne Helen; Thoresen, Marianne; Stiris, Tom; Cowan, Frances; Server, Andres Alonso & Fugelseth, Drude [Vis alle 7 forfattere av denne artikkelen] (2013). Changes in Cerebral Resistance Index (RI) after rewarming from day three of cooling predicts good but not poor outcome in infants undergoing therapeutic hypothermia. Fulltekst i vitenarkiv
• Elstad, Maja; Walløe, Lars; Holme, Nathalie; Maes, Elke & Thoresen, Marianne (2013). Respiratory sinus arrhythmia stabilises mean arterial blood pressure. Fulltekst i vitenarkiv
• Elstad, Maja; Walløe, Lars; Holme, Nathalie; Maes, Elke & Thoresen, Marianne (2013). Respiratory sinus arrhythmia stabilises mean arterial blood pressure in healthy humans. Fulltekst i vitenarkiv
• Elstad, Maja (2013). Sats på grunnforskning –ellers vet vi ikke hva vi går glipp av. Aftenposten Viten. ISSN 2464-3033. Fulltekst i vitenarkiv
• Holme, Nathalie; Rein, Erling Bekkestad; Walloe, Lars; Thoresen, Marianne & Elstad, Maja (2013). Cardiac stroke volume predicts progressive central hypovolemia by three different non-invasive methods. The FASEB Journal. ISSN 0892-6638. 27. Fulltekst i vitenarkiv
• Holme, Nathalie; Rein, Erling Bekkestad; Walløe, Lars; Thoresen, Marianne & Elstad, Maja (2013). Cardiac stroke volume predicts progressive central hypovolemia by three different non-invasive methods. Fulltekst i vitenarkiv
• Elstad, Maja (2013). Når bølgene i blodet møtes. Forskning.no. ISSN 1891-635X. Fulltekst i vitenarkiv
• Elstad, Maja & Walløe, Lars (2012). Respiratory variations in pulmonary and systemic blood flow in healthy humans. Fulltekst i vitenarkiv
• Elstad, Maja; Whitelaw, Andrew & Thoresen, Marianne (2010). Cerebral Doppler Resistance Index in Hypoxic-Ischaemic Encephalopathy: Is it still valid in the cooling era? Fulltekst i vitenarkiv
• Liu, Xun; Suleiman, M.Saadeh M.; Elstad, Maja; Potter, Helen & Thoresen, Marianne (2010). Effect of Hypothermia on Cardiac Troponin I after Global Hypoxica-ischemia with Brain Injury in Newborn Pigs. Fulltekst i vitenarkiv
• Dingley, John; Liu, Xun; Tooley, James; Chakkarapani, Ela; Elstad, Maja & Thoresen, Marianne (2010). First human use of 50% Xenon inhalation during cooling therapy for neonatal hypoxic-ischaemic encephalopathy (HIE): The "CoolXenon" clinical feasibility study. Fulltekst i vitenarkiv
• Opdahl, Anders; Remme, Espen W.; Helle-Valle, Thomas; Vartdal, Trond; Pettersen, Eirik & Elstad, Maja [Vis alle 9 forfattere av denne artikkelen] (2007). Load-dependency of early-diastolic mitral annulus velocity: the role of systolic function. Fulltekst i vitenarkiv
• Opdahl, Anders; Remme, Espen W.; Helle-Valle, Thomas; Vartdal, Trond; Pettersen, Eirik & Elstad, Maja [Vis alle 9 forfattere av denne artikkelen] (2007). Early Diastolic Mitral Annulus Lengthening Velocity Reflects Coupling between Systolic and Diastolic Function. Fulltekst i vitenarkiv
• Opdahl, Anders; Remme, Espen W.; Helle-Valle, Thomas; Vartdal, Trond; Pettersen, Eirik & Elstad, Maja [Vis alle 9 forfattere av denne artikkelen] (2006). Mitral Annulus Velocity at Onset of Filling - a New Marker of Diastolic Suction. Fulltekst i vitenarkiv
• Elstad, Maja & Toska, Karin (2006). Point: Counterpoint: Cardiovascular variability is/is not an index of autonomic control of circulation. Journal of applied physiology. ISSN 8750-7587. 101, s. 687–687. Fulltekst i vitenarkiv
• Opdahl, Anders; Remme, Espen W.; Helle-Valle, Thomas; Vartdal, Trond; Pettersen, Eirik & Elstad, Maja [Vis alle 8 forfattere av denne artikkelen] (2006). Early diastolic mitral annulus velocity at onset of filling a new marker for cardiac suction. Fulltekst i vitenarkiv
• Wilhelmsen, Cathrine Monrad & Elstad, Maja (2000). Krise i medisinsk forskning. Aftenposten (morgenutg. : trykt utg.). ISSN 0804-3116. Fulltekst i vitenarkiv Vis sammendrag

  Krisen i medisinsk forskning er et faktum! Vi vil med dette innlegget peke på enkle tiltak som kan bedre denne situasjonen. Vi er studentstipendiater ved Det medisinske fakultet i Oslo og ønsker at interessen for forskning blant medisinstudentene skal øke. Økt satsning på dette feltet vil rekruttere flere medisinstudenter, og dermed kommende leger, inn i forskningen. KUF vil i løpet av høsten behandle noe av dette, og ut fra det vi kjenner til har Norges Forskningsråd (NFR) og Lånekassen anbefalt at det gjøres endringer! NFRs studentstipendiatordning gir studenter en mulighet til å forske. Studentstipendiatordningen er viktig for å rekruttere studenter, og senere leger, til medisinsk forskning. Evaluering av studentstipendiatordningen viser at de som har hatt studentstipend, i mye større grad har gått inn i forskningsstillinger etter endt studie. St.meld.nr. 39 "Forskning ved et tidsskille" viser at det er lysere tider i vente for den medisinske forskningen. Det kreves imidlertid strakstiltak for å gjøre noe med den sviktende rekrutteringen! Sats på studenter som ønsker å forske! Det vil gi viktige langsiktige virkninger. ....

• Skytioti, Maria & Elstad, Maja (2019). Regulation of cerebral blood flow and systemic cardiovascular control. Universitetet i Oslo. ISSN 9788283773828. Fulltekst i vitenarkiv
• Elstad, Maja (2009). Stroke volume variations : Mild exercise and cardiovascular variability. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  Variations in left ventricular stroke volume (SV) is an important cardiovascular variable seldom investigated. This thesis in cardiovascular physiology studied the variations in SV in healthy, young volunteers. The focus was the role of SV variations in short-term regulation of the circulation. The circulatory changes that occur during mild exercise were investigated as were the spontaneous cardiovascular oscillations. The main protocols were experimental studies on humans, and a mathematical simulation model tested a hypothesis of cardiovascular adaptations at the onset of exercise. SV was measured by ultrasound Doppler allowing a high time resolution, and every cardiovascular variable was recorded beat by beat. Thus, short term regulations have been investigated by these methods with a time resolution down to one heart beat. <br> During mild supine exercise SV decreases due to an increase in blood pressure, and there is a redistribution of blood flow even when heart rate is below 90 beats per min. In addition, baroreflex resetting and local vasodilation are sufficient to produce the cardiovascular adaptations observed at the onset of exercise. Cardiovascular rhythms are cyclic fluctuations in cardiovascular variables such as heart rate and blood pressure. We studied cardiovascular oscillations related to respiration (related to respiratory sinus arrhythmia) and the ten second rhythm in blood pressure (Mayer waves). We found that respiratory sinus arrhythmia buffer blood pressure oscillations. We also suggest that blood pressure oscillations are replaced by heart rate oscillations in a healthy cardiovascular system.<br> In conclusion, SV is an important variable, and SV is highly sensitive to blood pressure changes. The combination of variations in heart rate and SV reduces fluctuations in cardiac output. This thesis sheds new light on SV variations, and measurements of SV variations may represent an important tool for evaluation of the circulatory system in the future.

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