Infradian Rhythmicity in Sleep/Wake Ratio in Developing Infants

L. DIAMBRA; L. MENNA-BARRETO

CHRONOBIOLOGY INTERNATIONAL

Dekker

Lugar: EUA; Año: 2004 vol. 21 p. 217 - 227

0742-0528

Although there are several reports on ultradian and circadian rhythms innewborns, we found only one report in which infradian periodicities are describedfor heart-rate measurements in the early stages of human development. Here, wereport infradian rhythms in the monthly range in the sleep/wake cycle of fourinfants studied along 24 consecutive weeks. Our procedure was applied to sleepdiary records from four healthy newborns. The data were arranged in binarytime series representing sleep (
1) or wake (1) states. These time series wereintegrated in order to obtain the cumulative sleep/wake time. A measure ofthe sleep/wake ratio (SWR) was obtained by computing the average slope of thecumulative sleep/wake time. To extract periodicities we applied the Fourierperiodogram to the temporal course of the SWR. We found a notoriousdifference in the SWR pattern among infants. In two infants the SWR showed amarked linear decay, spending more time asleep than awake, while in the twoother infants oscillated near zero. We found robust oscillations in all children. Inall cases the Fourier periodogram results present significant power in the infradian range. From these results, we suggest that sleep and wake durations areprobably modulated by some internal stimuli.