Development of CO2 sensitivity: effects of gestational age, postnatal age, and sleep state.

To determine the independent effects of sleep state, gestational age, and postnatal age on eucapnic ventilation and steady-state CO2 sensitivity, nine premature (146 +/- 3 days) and eight full-term (168 +/- 2 days) monkeys, Macaca nemestrina, from accurately timed conceptions were studied serially over the first 3 wk of life. Minute volume (VE)/kg,tidal volume (VT)/kg, and respiratory frequency were quantitated during rapid-eye-movement sleep (REM) and nonrapid-eye-movement sleep (NREM)in room air and when animals were breathing varied concentrations of cO2 in 21% O2. Eucapnic VE/kg and CO2 sensitivity [(deltaVE/kg)/delta PaCO2] increased progressively with advancing postnatal age during NREM sleep in grouped term and premature animals. CO2 sensitivity was not significantly different between REM and NREM sleep except in full-term animals at the highest postconceptual age studied (189 +/- 2 days) when [(delta VE/kg)/delta PaCO2] was lower in REM sleep than in NREM sleep (209 +/- 54 vs. 301 +/- 71 ml.min-1.kg-1.Torr-1; P less than 0.05, paired-t test). Gestational age had no measurable effect on eucapnic ventilation or CO2 sensitivity. These results support the hypothesis that REM sleep-induced depression of CO2 sensitivity develops in the neonatal monkey with advancing postconceptual age.