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

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Abstract
To determine the independent effects of sleep state, gestational age and postnatal age on eucapnic ventilation and steady-state CO2 sensitivity 9 premature (146 .+-. 3 days) and 8 full-term (168 .+-. 2 days) monkeys, Macaca nemestrina, from accurately timed conceptions were studied serially over the first 3 wk of life. Minute volume (.ovrhdot.VE)/kg, tidal volume (VT)/kg and respiratory frequency were quantitated during rapid-eye-movement sleep (REM) and non-rapid-eye-movement sleep (NREM) in room air and when animals were breathing varied concentrations of CO2 in 21% O2. Eucapnic .ovrhdot.VE/kg and CO2 sensitivity [(.DELTA..ovrhdot.VE/kg) per .DELTA.Pa[arterial partial pressure]CO2] increased progressively with advancing postnatal age during NREM sleep in group 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..ovrhdot.VE/kg) per .DELTA.PaCO2] was lower in REM sleep than in NREM sleep (209 .+-. 54 vs. 301 .+-. 71 ml/min per kg per Torr; P < 0.05, paired-t test). Gestational age had no measurable effect on eucapnic ventilation or CO2 sensitivity. REM sleep-induced depression of CO2 sensitivity apparently develops in the neonatal monkey with advancing postconceptual age.