Absence of effects of hypoxia on small airway function in humans.

We measured the effects of sustained isocapnic hypoxia (PAO2 = 40--50 Torr; PACO2 = 38--42 Torr) on tests sensitive to small airway function in healthy human subjects. Maximum expiratory flow-volume curves on air, nitrogen-hypoxic, helium-normoxic, and helium-hypoxic mixtures as well as closing volumes while subjects breathed air and a hypoxic mixture were obtained. We then measured total lung capacity (TLC), both plethysmographically and by inert gas dilution, and used the nonplethysmographic method to measure the effects of hypoxia on TLC. In none of these tests were there any statistically significant changes when values obtained during hypoxia were compared with those during normoxia. It is suggested that previous reports that indicated that TLC was increased by hypoxia might have arisen from a plethysmographic artifact.