Breathing patterns and cardiovascular autonomic modulation during hypoxia induced by simulated altitude

Objective To assess the influence of different breathing patterns on autonomic cardiovascular modulation during acute exposure to altitude-induced hypoxia. Design We measured relative changes in minute ventilation (VE), oxygen saturation (%SaO(2)), spectral analysis of RR interval and blood pressure, and response to stimulation of carotid baroreceptors (neck suction) at baseline and after acute (1 h) hypobaric hypoxia (equivalent to 5000 m, in a hypobaric chamber). Methods We studied 19 human subjects: nine controls and 10 Western yoga trainees of similar age, while breathing spontaneously, at 15 breaths/min (controlled breathing) and during 'complete yogic breathing' (slow diaphragmatic + thoracic breathing, similar to5 breaths/min) in yoga trainees, or simple slow breathing in controls. Results At baseline %SaO(2), VE and autonomic pattern were similar in both groups; simulated altitude increased VE in controls but not in yoga trainees; %SaO(2) decreased in all subjects (P < 0.0001), but more in controls than in yoga trainees (17 versus 12%, 14 versus 9%, 14 versus 8%, all P < 0.05 or better, during spontaneous breathing, controlled breathing and yogic or slow breathing, respectively). Simulated altitude decreased RR interval (from 879 +/- 45 to 770 +/- 39, P < 0.01) and increased indices deducted from spectral analysis of heart rate variability (low frequency/high frequency (LF/HF) ratio from 1.6 <plus/minus> 0.5 to 3.2 +/- 1.1, P < 0.05) and systolic blood pressure (low-frequency fluctuations from 2.30 <plus/minus> 0.31 to 3.07 +/- 0.24 ln-mmHg(2), P < 0.05) in controls, indicating sympathetic activation; these changes were blunted in yoga trainees, and in both groups during slow or yogic breathing, No effect of altitude was seen on stimulation of carotid baroreceptors in both groups. Conclusions Well-performed slow yogic breathing maintains better blood oxygenation without increasing VE (i.e. seems to be a more efficient breathing) and reduces sympathetic activation during altitude-induced hypoxia. J Hypertens 19:947-958 (C) 2001 Lippincott Williams & Wilkins.