Objective To assess the impact of acute hypoxia-induced periodic breathing on respiratory efficiency in young healthy males. Methods 20 healthy male (median (IQR) age: 24 (22 to 25) years; body mass index: 22.5 (20.9 to 24.9) kg/m 2 )—no sleep-disordered breathing in normoxia—underwent polysomnography in normobaric hypoxia simulating 3500 m altitude. Measurements included oesophageal pressure-time curve, airflow and exhaled fraction of carbon dioxide (CO 2 ). Inspiratory pressure-time product (iPTP, index of respiratory muscle effort) was calculated from oesophageal pressure. Physiological dead-space volume, ventilation ( V ˙ D est ) and alveolar ventilation ( V ˙ A est ) were calculated from exhaled fractions of CO 2 (Bohr equation). Within-subject comparisons of periodic (PB) and regular breathing (RB) periods were made using the Wilcoxon signed-rank test. Results In hypoxia, 17 participants had sufficient (>3 min) breathing periods of both periodic and non-periodic breathing for analysis. The median (IQR) Apnoea-Hypopnoea Index was 76.9 (62.8 to 122.7)/hour and participants spent 40.8% (27.3% to 64.6%) of sleep in periodic breathing (n=17). Tidal volume was greater in periodic breathing (n=17, median (IQR), PB vs RB; 0.815 (0.636 to 0.928) L vs 0.633 (0.517 to 0.673) L, p V ˙ D est was lower in periodic breathing (n=17; PB vs RB; 1.9 (1.7 to 2.2) L/min vs 3.0 (2.6 to 3.4) L/min, p V ˙ A est remained similar (n=17, PB vs RB; 6.9 (6.3 to 7.4) L/min vs 7.3 (6.8 to 7.7) L/min, p=0.102). iPTP/min was lower in PB (n=14, PB vs RB; 185.4 (154.3 to 203.8) cm H 2O×s/min vs 221.5 (189.2 to 291.9) cm H 2O×s/min, p=0.002). Conclusions Periodic breathing in acute normobaric hypoxia reduces inspiratory effort without impairing alveolar ventilation, suggesting an adaptive mechanism to optimise respiratory efficiency in young healthy males.
Heiniger et al. (Tue,) studied this question.