title: Autonomic cardiovascular response to acute hypoxia and passive head-up tilting in humans.
abstract: Acute hypoxia may alter autonomic cardiovascular reflexes during orthostasis. Heart rate variability (HRV), arterial blood pressure (MAP), and respiratory sinus arrhythmia (RSA) were recorded during supine (SUP) and passive head up tilt (HUT) in eight healthy humans, spontaneously breathing either room air or 10% O₂ in N₂. In the time domain, heart rate increased and variability decreased with HUT in both trials, with no difference between trials. In the frequency domain, normalized low frequency HRV increased, and normalized high frequency HRV decreased with HUT in both trials, with no difference between trials. MAP was 74.9 (8.6) and 77.5 (11.7) mmHg when SUP in the room air and hypoxia trials, respectively. A significant increase in MAP occurred with HUT in the room air trial but not in the hypoxia trial. In both trials, end tidal CO₂ decreased with HUT, with no difference between trials. In the room air trial, end tidal O₂ increased with HUT, whereas during the hypoxia trial, end tidal O₂ decreased with HUT. The distribution of heart beats relative to the phase of ventilation (%HBIN and %HBOUT) was similar in both trials: the %HBIN was 43.5 (3.3) % and %HBOUT was 56.5 (4.2) % breathing room air when SUP, and 45.5 (3.0) and 54.5 (3.2) when hypoxic and SUP. For both trials, this distribution did not change with HUT. As both HRV and RSA showed similar responses to HUT when spontaneously breathing either room air or 10% O₂ in N₂, we suggest that autonomic cardiovascular reflexes are preserved during acute hypoxia.
authors: School of Health Sciences, University of Ballarat, University Drive, Mount Helen, Ballarat, VIC 3350, Australia. bahrainstephen@gmail.com
authors: S J
authors: SJ
authors: Brown
authors: A
authors: A
authors: Raman
authors: M J
authors: MJ
authors: Barnes
authors: T
authors: T
authors: Mündel
mesh_terms: D000328:Adult; D001341:Autonomic Nervous System / Q000502:physiology; D001794:Blood Pressure; D002319:Cardiovascular System / Q000294:innervation; D005260:Female; D019416:Head Movements; D006339:Heart Rate; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D012123:Pulmonary Ventilation; D013990:Tidal Volume
references: J Appl Physiol (1985). 1994 Dec;77(6):2537-42
references: 7896588
references: J Physiol Sci. 2007 Dec;57(6):337-42
references: 17996126
references: Circulation. 1996 Aug 15;94(4):842-7
references: 8772709
references: Int J Cardiol. 1998 Apr 1;64(2):185-94
references: 9688438
references: Intern Med. 2008;47(19):1681-7
references: 18827416
references: Am J Physiol Heart Circ Physiol. 2005 Oct;289(4):H1758-69
references: 15937091
references: Am J Emerg Med. 2005 Jan;23(1):8-12
references: 15672330
references: Aviat Space Environ Med. 2002 May;73(5):460-5
references: 12014605
references: J Appl Physiol Respir Environ Exerc Physiol. 1982 Mar;52(3):570-7
references: 7068472
references: Am J Physiol. 1981 Oct;241(4):H620-9
references: 7315987
references: Acta Physiol Scand. 1986 Jun;127(2):171-5
references: 3728050
references: J Physiol Pharmacol. 2008 Dec;59(4):771-80
references: 19212010
references: Eur Heart J. 1994 Nov;15(11):1463-9
references: 7835360
references: Acta Physiol Scand. 2001 Dec;173(4):409-17
references: 11903133
references: Chest. 2004 Feb;125(2):683-90
references: 14769752
references: Biol Psychol. 2007 Feb;74(2):263-85
references: 17081672
references: J Physiol. 1999 Jun 1;517 ( Pt 2):617-28
references: 10332107
references: J Physiol Sci. 2009 Jan;59(1):31-6
references: 19340559
references: Int J Cardiol. 1995 Jun 30;50(2):117-24
references: 7591322
references: Aviat Space Environ Med. 2008 Feb;79(2):99-104
references: 18309906
references: Stroke. 1998 Jan;29(1):104-11
references: 9445337
references: J Neurosurg. 1986 Nov;65(5):636-41
references: 3772451
references: J Appl Physiol (1985). 2004 Sep;97(3):935-40
references: 15145924
references: Clin Sci (Lond). 1998 Nov;95(5):565-73
references: 9791042
references: J Hum Hypertens. 2010 Jul;24(7):458-66
references: 20016525
references: Eur J Appl Physiol Occup Physiol. 1996;73(6):521-8
references: 8817122
references: Physiol Rev. 1994 Jul;74(3):543-94
references: 8036247
references: Am J Physiol Heart Circ Physiol. 2007 May;292(5):H2397-407
references: 17220187
references: J Appl Physiol (1985). 1998 Apr;84(4):1151-7
references: 9516178
references: Adv Exp Med Biol. 2008;605:361-5
references: 18085300
references: J Clin Invest. 1991 Jun;87(6):1953-7
references: 2040688
references: Clin Auton Res. 2007 Feb;17(1):13-9
references: 17264976
references: Aviat Space Environ Med. 2006 Oct;77(10):1015-9
references: 17042245
references: Clin Exp Pharmacol Physiol. 2005 May-Jun;32(5-6):447-9
references: 15854156
references: J Appl Physiol (1985). 2002 Apr;92(4):1671-6
references: 11896036