The effects of hypoxia on load compensation during sustained incremental resistive loading in patients with obstructive sleep apnea

Abstract

Inspiratory load compensation is impaired in patients with obstructive sleep apnea (OSA), a condition characterized by hypoxia during sleep. We sought to compare the effects of sustained hypoxia on ventilation during inspiratory resistive loading in OSA patients and matched controls. Ten OSA patients and 10 controls received 30 min of isocapnic hypoxia (arterial oxygen saturation 80%) and normoxia in random order. Following the gas period, subjects were administered six incremental 2-min inspiratory resistive loads while breathing room air. Ventilation was measured throughout the loading period. In both patients and controls, there was a significant increase in inspiratory time with increasing load (P = 0.006 and 0.003, respectively), accompanied by a significant fall in peak inspiratory flow (P = 0.006 and P < 0.001, respectively). The result was a significant fall in minute ventilation in both groups with increasing load (P = 0.003 and P < 0.001, respectively). There was no difference between the two groups for these parameters. The only difference between the two groups was a transient increase in tidal volume in controls (P = 0.02) but not in OSA patients (P = 0.57) during loading. Following hypoxia, there was a significant increase in minute ventilation during loading in both groups (P < 0.001). These results suggest that ventilation during incremental resistive loading is preserved in OSA patients and that it appears relatively impervious to the effects of hypoxia.