Relationships between body movements and phase of respiratory cycle in newborns

To determine the relationships between body movements and phase of the respiratory cycle, we performed polygraphic recordings during daytime sleep in 12 normal newborns: 6 premature infants of 31 to 36 weeks conceptional age and 6 full-term infants of 39-41 weeks conceptional age. Chin and eye movements, movements detected during sighs and body movements not related to sighs were analysed separately. We analysed 1838 chin and body movements with a clearly defined beginning. Data obtained were similar in both premature and full-term infants, without statistically significant differences when active and quiet sleep states were compared. We found that: (a) The 96 movements concomitant with sighs all started during inspiratory diaphragmatic bursts. (b) The 1270 body movements unrelated to sighs started predominantly (78.6% in premature infants, 81.3% in full-term infants) during expiration, after the end of diaphragmatic contraction (P less than 0.002). (c) The 472 chin movements and eye movements occurred randomly with respect to phases of respiration. In conclusion, our data show that central motor command level determines relationships between movement initiation and respiratory phase. They suggest inhibition of trunk and limb movements (under pyramidal control) during diaphragmatic contraction as early as 31 weeks CA. This inhibition is absent during sighs, which involve the inspiratory augmenting reflex, and does not apply to chin and eye movements, which are mediated by cranial nerves.