The occurrence of periodic apnea (apnea during periodic breathing) was studied in 27 normal, full-term infants during the first five weeks of life. The rate and mean length of apnea were analyzed both with respect to sleep state and with respect to respiratory pattern, ie, periodic vs nonperiodic breathing. The rate of apnea was found to vary according to sleep state and the pattern of breathing. The highest apnea rates were non-periodic apneas in active sleep. Periodic apnea rates were relatively low in both active and quiet sleep; however, this type of apnea was consistently observed from weeks 2 through 5. The proportion of apneas that are periodic is much higher in quiet sleep than in active sleep. Rates of periodic and nonperiodic apnea were more consistently correlated in active sleep than in quiet sleep. The mean length of periodic apnea was found to be significantly greater than the mean length of nonperiodic apnea in both sleep states, a difference that reflected a greater positive skew in the distribution of the nonperiodic apnea lengths. This variation in length between periodic and nonperiodic apnea explains, in part, the increased mean length in quiet sleep compared with active sleep. There were significant individual differences over weeks in both forms of apnea in active sleep and in quiet sleep. Female infants were observed to have higher rates of nonperiodic apnea than male infants in active sleep, although no significant differences in the distribution of lengths were obtained.

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