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

Objective To assess the influence of different breathing patterns on autono mic cardiovascular modulation during acute exposure to altitude-induced hyp oxia. Design We measured relative changes in minute ventilation (VE), oxygen satu ration (%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 hypoba ric chamber). Methods We studied 19 human subjects: nine controls and 10 Western yoga tra inees of similar age, while breathing spontaneously, at 15 breaths/min (con trolled breathing) and during 'complete yogic breathing' (slow diaphragmati c + thoracic breathing, similar to5 breaths/min) in yoga trainees, or simpl e 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 trainee s; %SaO(2) decreased in all subjects (P < 0.0001), but more in controls tha n 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 (f rom 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 systo lic 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 stimulat ion of carotid baroreceptors in both groups. Conclusions Well-performed slow yogic breathing maintains better blood oxyg enation without increasing VE (i.e. seems to be a more efficient breathing) and reduces sympathetic activation during altitude-induced hypoxia. J Hype rtens 19:947-958 (C) 2001 Lippincott Williams & Wilkins.