Thoracico-abdominal respiratory correlations in infants: constancy and variability in different sleep states

28 polygraphic recordings were made in normal infants: 20 in full-term newborns and 8 in 2- to 10-wk-old babies. Data were analysed by 20-sec epochs. Relationships between thoracic (3rd-4th rib level) and abdominal respiratory movements were studied according to their maximum out-of-phase occurring (180 degrees maximum) in every 20-sec period. The thoracico-abdominal phase relationships according to sleep states do not change during the first trimester of life. In quiet sleep, while in-pase thoracico-abdominal respiration was the most frequent pattern, the out-of-phase one was also a possible pattern. In active sleep, out-of-phase respiration is characteristic, in-phase relation being a rare exception. In transitional sleep, respiratory relationships could be those appropriate for the preceding or the following sleep state. Nasal air flow always occurred in the phase with abdominal movements. Total flatteninf of thoracicorespiratory movements only were found in all sleep states; these thoracic flattenings must be differentiated from apnea. Transient fluctuations in the degree of phase relations are possible. There exists both interand intraindividual variability in normal infants. Variability of fusimotor system tonus is probably the neurological mechanism underling these phenomena.