Ventilatory responses to carbon dioxide in infants at risk for sudden infant death syndrome.

We examined the ventilatory response to inhaled CO2 in 77 infants at postconceptional ages ranging from 31 to 50 wk, 43 of whom were also evaluated with a 12-h pneumocardiogram (PCG). Infants were tested after sedation with chloral hydrate, and monitored with ECG and transcutaneous oxygen and CO2 monitors. Sleep state was evaluated by visual inspection of the infant's behavior. Among the 43 infants examined with the PCG, 22 had abnormal PCGs. Of these, 27% had significantly (p less than .05) abnormal CO2 response slopes, compared to 9% of those with normal PCGs. Breathing frequency did not change after CO2 inhalation in 82% of the abnormal PCG and in 33% of the normal PCG groups.