Effect of Acute Hypoxia on Heart Rate Variability at Rest and During Exercise

Abstract

The purpose of this study was to investigate sympathovagal balance as inferred from heart rate variability (HRV) responses to acute hypoxia at rest and during exercise. HRV was evaluated in 12 healthy subjects during a standardized hypoxic tolerance test which consists of four periods alternating rest and moderate exercise (50 % V·O₂max) in normoxic and hypoxic conditions. Ventilatory responses were determined and HRV indexes were calculated for the last 5 min of each period. In well-tolerant subjects, hypoxia at rest induced a decrease of root-mean-square of successive normal R-R interval differences (RMSSD) (p < 0.05) and of absolute high frequency (HF) power (p < 0.001). All absolute HRV indexes were strongly reduced during exercise (p < 0.001) with no further changes under the additional stimulus of hypoxia. A significant increase (p < 0.05) in the HF/(LF+HF) ratio (where LF is low frequency power) was found during exercise in hypoxia compared to exercise in normoxia, associated with similar mean changes in ventilation and tidal volume. These results indicate a vagal control withdrawal under hypoxia at rest. During exercise at 50 % V·O₂max, HRV indexes cannot adequately represent cardiac autonomic adaptation to acute hypoxia, or possibly to other additional stimuli, due to the dominant effect of exercise and the eventual influence of confounding factors.

Key words

Hypoxic test - high altitude adaptation - HRV indexes - autonomic nervous system

References

• 1 Arai Y, Saul J P, Albrecht P, Hartley L H, Lilly L S, Cohen R J, Colucci W S. Modulation of cardiac autonomic activity during and immediately after exercise.  Am J Physiol. 1989;  256 H132-H141
• 2 Bernardi L, Passino C, Spadacini G, Calciati A, Robergs R, Greene R, Martignoni E, Anand I, Appenzeller O. Cardiovascular autonomic modulation and activity of carotid baroreceptors at altitude.  Clin Sci. 1998;  95 565-573
• 3 Bernardi L, Passino C, Wilmerding V, Dallam G M, Parker D L, Robergs R A, Appenzeller O. Breathing patterns and cardiovascular autonomic modulation during hypoxia induced by simulated altitude.  J Hypertens. 2001;  19 947-958
• 4 Bernardi L, Salvucci F, Suardi R, Solda P L, Calciati A, Perlini S, Falcone C, Ricciardi L. Evidence for an intrinsic mechanism regulating heart rate variability in the transplanted and the intact heart during submaximal dynamic exercise?.  Cardiovasc Res. 1990;  24 969-981
• 5 Brenner IK, Thomas S, Shephard R J. Autonomic regulation of the circulation during exercise and heat exposure. Inferences from heart rate variability.  Sports Med. 1998;  26 85-99
• 6 Brenner I K, Thomas S, Shephard R J. Spectral analysis of heart rate variability during heat exposure and repeated exercise.  Eur J Appl Physiol Occup Physiol. 1997;  76 145-156
• 7 Brown T E, Beightol L A, Koh J, Eckberg D L. Important influence of respiration on human R-R interval power spectra is largely ignored.  J Appl Physiol. 1993;  75 2310-2317
• 8 Carrasco Sosa S, Gonzalez Camarena S, Roman Ramos R, Medina Banuelos V, Azpiroz Leehan J. The effects of body position, controlled breathing and exercise on the heart rate variability parameters in healthy subjects.  Arch Inst Cardiol Mex. 1999;  69 511-525
• 9 Casadei B, Cochrane S, Johnston J, Conway J, Sleight P. Pitfalls in the interpretation of spectral analysis of the heart rate variability during exercise in humans.  Acta Physiol Scand. 1995;  153 125-131
• 10 Cottin F, Papelier Y, Escourrou P. Effects of exercise load and breathing frequency on heart rate and blood pressure variability during dynamic exercise.  Int J Sports Med. 1999;  20 232-238
• 11 de Meersman R E, Reisman S S, Daum M, Zorowitz R, Leifer M, Findley T. Influence of respiration on metabolic, hemodynamic, psychometric, and R-R interval power spectral parameters.  Am J Physiol. 1995;  269 H1437-H1440
• 12 Eckberg D L. Sympathovagal balance: a critical appraisal.   Reply Circulation. 1997;  96 3224-3232
• 13 Hackett P H, Roach R C. High-altitude illness.  N Engl J Med. 2001;  345 107-114
• 14 Hayano J, Taylor J A, Mukai S, Okada A, Watanabe Y, Takata K, Fujinami T. Assessment of frequency shifts in R-R interval variability and respiration with complex demodulation.  J Appl Physiol. 1994;  77 2879-2888
• 15 Houle M S, Billman G E. Low-frequency component of the heart rate variability spectrum: a poor marker of sympathetic activity.  Am J Physiol. 1999;  276 H215-H223
• 16 Kamath M V, Fallen E L, McKelvie R. Effects of steady state exercise on the power spectrum of heart rate variability.  Med Sci Sports Exerc. 1991;  23 428-434
• 17 Kanai M, Nishihara F, Shiga T, Shimada H, Saito S. Alterations in autonomic nervous control of heart rate among tourists at 2 700 and 3 700 m above sea level.  Wilderness Environ Med. 2001;  12 8-12
• 18 Liu X X, Lu L L, Zhong C F, Cheng Z H, Yuan Q, Ren H R. Analysis of heart rate variability during acute exposure to hypoxia.  Space Med Med Eng. 2001;  14 328-331
• 19 Mathew L, Gopinathan P M, Purkayastha S S, Sen Gupta J, Nayar H S. Chemoreceptor sensitivity and maladaptation to high altitude in man.  Eur J Appl Physiol Occup Physiol. 1983;  51 137-144
• 20 Moore L G, Harrison G L, McCullough R E, McCullough R G, Micco A J, Tucker A, Weil J V, Reeves J T. Low acute hypoxic ventilatory response and hypoxic depression in acute altitude sickness.  J Appl Physiol. 1985;  60 1407-1412
• 21 Nakamura Y, Yamamoto Y, Muraoka I. Autonomic control of heart rate during physical exercise and fractal dimension of heart rate variability.  J Appl Physiol. 1993;  74 875-881
• 22 Pagani M, Montano N, Porta A, Malliani A, Abboud F M, Birkett C, Somers V K. Relationship between spectral components of cardiovascular variabilities and direct measures of muscle sympathetic nerve activity in humans.  Circulation. 1997;  95 1441-1448
• 23 Patwardhan A R, Vallurupalli S, Evans J M, Bruce E N, Knapp C F. Override of spontaneous respiratory pattern generator reduces cardiovascular parasympathetic influence.  J Appl Physiol. 1995;  79 1048-1054
• 24 Perini R, Orizio C, Baselli G, Cerutti S, Veicsteinas A. The influence of exercise intensity on the power spectrum of heart rate variability.  Eur J Appl Physiol Occup Physiol. 1990;  61 143-148
• 25 Physick-Sheard P W, Marlin D J, Thornhill R, Schroter R C. Frequency domain analysis of heart rate variability in horses at rest and during exercise.  Equine Vet J. 2000;  32 253-262
• 26 Pichot V, Gaspoz J M, Molliex S, Antoniadis A, Busso T, Roche F, Costes F, Quintin L, Lacour J R, Barthelemy J C. Wavelet transform to quantify heart rate variability and to assess its instantaneous changes.  J Appl Physiol. 1999;  86 1081-1091
• 27 Rathat C, Richalet J P, Herry J P, Larmignat P. Detection of high-risk subjects for high altitude diseases.  Int J Sports Med. 1992;  13 S76-S78
• 28 Roach R C, Maes D, Sandoval D, Robergs R A, Icenogle M, Hinghofer-Szalkay H, Lium D, Loeppky J A. Exercise exacerbates acute mountain sickness at simulated high altitude.  J Appl Physiol. 2000;  88 581-585
• 29 Seals D R, Johnson D G, Fregosi R F. Hypoxia potentiates exercise-induced sympathetic neural activation in humans.  J Appl Physiol. 1991;  71 1032-1040
• 30 Shin K, Minamitani H, Onishi S, Yamazaki H, Lee M. The power spectral analysis of heart rate variability in athletes during dynamic exercise-Part I.  Clin Cardiol. 1995;  18 583-586
• 31 Somers V K, Mark A L, Abboud F M. Potentiation of sympathetic nerve responses to hypoxia in borderline hypertensive subjects.  Hypertension. 1988;  11 608-612
• 32 Somers V K, Mark A L, Zavala D C, Abboud F M. Contrasting effects of hypoxia and hypercapnia on ventilation and sympathetic activity in humans.  J Appl Physiol. 1989;  67 2101-2106
• 33 Somers V K, Mark A L, Zavala D C, Abboud F M. Influence of ventilation and hypocapnia on sympathetic nerve responses to hypoxia in normal humans.  J Appl Physiol. 1989;  67 2095-2100
• 34 Task Force . Heart rate variability: standards of measurement, physiological interpretation and clinical use. Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology.  Circulation. 1996;  93 1043-1065
• 35 Tulppo M P, Makikallio T H, Laukkanen R T, Huikuri H V. Differences in autonomic modulation of heart rate during arm and leg exercise.  Clin Physiol. 1999;  19 294-299
• 36 Tulppo M P, Makikallio T H, Seppanen T, Laukkanen R T, Huikuri H V. Vagal modulation of heart rate during exercise: effects of age and physical fitness.  Am J Physiol. 1998;  274 H424-H429
• 37 Tulppo M P, Makikallio T H, Takala T E, Seppanen T, Huikuri H V. Quantitative beat-to-beat analysis of heart rate dynamics during exercise.  Am J Physiol. 1996;  271 H244-H252
• 38 Yamamoto Y, Hoshikawa Y, Miyashita M. Effects of acute exposure to simulated altitude on heart rate variability during exercise.  J Appl Physiol. 1996;  81 1223-1229
• 39 Yamamoto Y, Hughson R L, Nakamura Y. Autonomic nervous system responses to exercise in relation to ventilatory threshold.  Chest. 1992;  101 206S-210S
• 40 Zuzewicz K, Biernat B, Kempa G, Kwarecki K. Heart rate variability in exposure to high altitude hypoxia of short duration.  Int J Occup Saf Ergon. 1999;  5 337-346