Effect of progressive hypoxia on breathing during sleep.

We examined the effects of progressive hypoxia on breathing during wakefulness and quiet (NREM) sleep in 17 healthy young adults (11 males and 6 females). Ventilation was determined from quantitative measurements of abdominal and rib cage excursions using magnetometers or inductive plethysmography. Hypoxia was induced by blending N2 into the inspiratory line of a loose-fitting mask while O2 saturation was monitored with an ear oximeter. No attempt was made to maintain isocapnia. Ventilatory responses to hypoxia were depressed in 2 male subjects by sleep, but were unchanged or increased in the others. Thus on the average, sleep produced no change in ventilatory responses to hypoxia. There was no consistent difference in the frequencies or tidal volumes attained at a given level of ventilation during hypoxia awake and asleep. During sleep there was relatively more rib cage than abdominal movement. Relief of hypoxia was followed by periodic breathing during sleep in 12 subjects but in only 2 subjects when awake. In two thirds of the trials, hypoxia failed to produce arousal even though arterial O2 saturation was allowed to fall below 75%. The results suggest that (1) sleep potentiates apnea producing effects of O2 changes but has inconsistent effects on ventilatory responses to hypoxia, and (2) hypocapnic hypoxia is not an invariably potent stimulus for arousal.