Sleep respiratory instability in term neonates under hyperthermic conditions: age, sex, type of feeding, and rapid eye movements.

The purpose of this study was to examine the influence of neonatal age, sex, type of feeding, and rapid eye movements on the occurrence of apneic pauses during sleep in a hyperthermic environment. One hundred and twenty fullterm infants (equally divided by sex and type of feeding) were observed during a complete nap within the first and approximately fourth wk of life. Each sleep session was characterized by twenty-one measures including the longest apneic pause, mean apnea duration, relative frequency of apnea, apnea periodicity, respiratory rate, and relative frequency of REM epochs. The relative frequency of REM epochs decreased with age and was greater in formula-fed (versus breast-fed) infants. The longest apneic pauses were greater in the first wk of life and in breast-fed infants. In addition, the average Longest Duration:REM was greater than the average Longest Duration:NREM. Of potential importance was the demonstration that this latter effect was greater in the first wk than in the fourth wk of life. Breast-fed infants and females had larger apnea Mean Duration scores. The relative frequency of apneic pauses (greater than or equal to 2 sec in duration), periodicity, and the relative amount of apnea were greater in the fourth-wk study and in breast-fed infants. The relative frequency of apneic pauses greater than or equal to 6 sec in duration (Apnea6%) and the A6/D% measure were greater in breast-fed infants. Numerous interactions were observed between age, sex, and type of feeding. Respiratory rate decreased with age and was greater during NREM epochs and in formula-fed infants.