The rate and depth of breathing in new-born infants in different sleep states.

1. Ventilation was recorded on ten male and ten female healthy full-term infants during the first week after delivery, using a trunk plethysmograph. Tidal volume (V(T)), respiration rate (f) and pulmonary ventilation (V) for each respiratory cycle were measured during periods of rapid eye movement sleep (REM) and during quiet sleep when eye movements were absent (NREM).2. It was found that mean instantaneous V and f were significantly higher in all infants during REM than during NREM sleep, while mean V(T) was either unchanged or showed a decrease. In addition, there was significantly greater variation in instantaneous V, V(T) and f during REM as compared with NREM sleep.3. Positive correlations were found in most infants in both sleep states between individual values of V(T) and the duration of the respiratory cycle (T).4. Periodic changes in T were found in all infants during both sleep states; these periodicities may reflect the behaviour of respiratory control mechanisms operating over a longer time span than the individual respiratory cycle.