Polygraphic studies on normal infants during the first six months of life. II. Respiratory rate and variability as a function of state.

Abstract

Summary: This study examined spontaneous respiratory rate and variability as a function of age and sleep state in eight normal full-term infants. Each infant was admitted at 5:00 PM to the sleep laboratory for 12-hr monitoring sessions during the first week of life and at 1, 2, 3, 4, and 6 months of age. Both sleep and cardiopulmonary variables were recorded. A Beckman pCO2 monitor sampled expired gas through a miniature cannula taped under the infant's nostrils. Peaks and troughs of breaths were measured by a computer peak sensing program. Median respiratory rates and interquartile ranges of breath intervals for each minute were determined. Each minute was coded as quiet sleep (QS), active sleep (AS), waking (AW), and indeterminate state (IN). Respiratory rates and variability were highest during the first week of life. They declined during the next 2 months and began to level out at 3 months of age (Table 3).The state-relationship was not homogeneous at all ages. Respiratory rates and variability during wakefulness were always higher than those during sleep states. The strongest relation between respiration and sleep states was found between birth and 3 months of age. QS values were uniformly low, and those of AS and IN minutes were intermediate between AW and QS.Speculation: Respiration rates and variability decreased linearly between birth and three months of age. The differences between the developmental course of respiratory rates and variability between 1 and 3 months reported here and cardiac rates and variability previously reported in the same infants suggest a difference in the central nervous system modulation of these systems.