Biological and behavioral correlates of quiet sleep respiration rates in infants.

The sleep and respiration of 88 infants were recorded for 24-h periods on the first 2 postnatal days and again at 6 months. The recordings were made with the Motility Monitoring System, which does not require instrumentation of the infants. Quiet sleep respiration rates (QSRR) increased over the first 2 days (mean = 42.2, SD = 1.0 and mean = 44.5, SD = 1.1, respectively), then decreased by 6 months (mean = 25.3, SD = 0.5); females showed lower QSRR on the first 2 days, infants delivered vaginally showed lower QSRR at 6 months; by 6 months QSRR was significantly higher during the day than at night; and significant individual differences across age and from day to nighttime were found at each age. Delivery mode, maternal age and education, and mental scores at 6 and 12 months were negatively related to QSRR at 6 months. Taken together, these data suggest a developmental advantage of slower QSRR and evidence for the role of the higher central nervous centers in the regulation of QSRR.