Ventilatory response to 100% and 15% O2 during wakefulness and sleep in preterm infants.

To examine the ventilatory response to 100% and 15% O2 during wakefulness and sleep, we studied eleven preterm infants birthweight 1770 +/- 102 g; gestational age 32 +/- 1 weeks; postnatal age 31 +/- 5 days) on two occasions each. Wakefulness (W) was present around feeding time and was defined by open eyes for more than 2 min plus presence of purposeful movements. Rapid eye movement (REM) and non-rapid eye movement (N-REM) sleep were defined using electroencephalogram (EEG), electrooculogram (EOG), electrocardiogram (ECG), and body movements. During 100% O2 breathing, immediate (30 s) decreases of 28, 39 and 37% followed by late (5 min) increases in ventilation (Ve) of 42, 49 and 27% were observed during W, REM and N-REM sleep (P greater than 0.05 between states). PaCO2 decreased significantly towards the end of 5 min of breathing 100% O2 in W, REM and N-REM sleep (P greater than 0.05). Average duration of apnea following sudden administration of 100% O2 was 8.5, 11.1 and 8.8 s during W, REM and N-REM sleep (P greater than 0.05 between states). During inhalation of 15% O2, there was a late decrease in ventilation of 19 and 23% during wakefulness and REM sleep, and a sustained increase in Ve of 17% during N-REM sleep (P less than 0.05). PaCO2 at the end of hypoxia (5 min) was significantly decreased in N-REM sleep only (P less than 0.05). We suggest that (i) peripheral chemoreceptor activity is qualitatively intact during W and sleep, as reflected by (a) the immediate changes in Ve during inhalation of high and low O2, and (b) apnea following administration of 100% O2. (ii) The late decrease in ventilation with hypoxia is absent in N-REM sleep.