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
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
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
