SUMMARY1. Ventilation was recorded in thirty term infants during the first week after delivery using the trunk plethysmograph, during periods of rapid eye movement sleep (r.e.m.) and quiet sleep (n.r.e.m.).2. Continuous histograms of tidal volume (VT) and instantaneous respiration rate (f) were sampled at 0-5 see intervals, passed through a digital filter to remove longterm trends in the data, and then subjected to frequency analysis.3. In all the infants oscillations in VT and f were detected, with mean periods varying from 6-7 to 12-5 sec. The amplitude of these oscillations was higher during r.e.m. than n.r.e.m. sleep in all the infants.4. The oscillations in Vr tended to be out of phase with those for f, particularly during n.r.e.m. sleep; this contrasted with in-phase oscillations in VT and f found during periodic breathing in an additional six premature infants studied.

4. The jugular veins in the baby's neck are occluded by finger pressure and there follows an increase in skull volume, which is rapid at first, but which decreases exponentially as venous drainage diverts to non-occluded channels such as the vertebral venous plexus. At the instant of jugular occlusion the rate of skull volume increase is representative of the rate of flow in the jugular vessels prior to occlusion, and so provides an index of the relative magnitude of the intracranial blood flow. The method thus allows changes in intracranial blood flow to be followed. When occlusion is released cranial volume decreases, initially rapidly, but slowing exponentially as resting volume is regained.5. A theoretical model of the events occurring during the inflow and outflow phases has been developed, and a formula derived which allows an estimation to be made of the flow of blood through uncompressed channels. The measured value of jugular blood flow can then be augmented to an estimate of total intracranial flow.6. The mean cerebral blood flow of sixteen normal babies was estimated to be 40 ml. 100 g-1. min-' (S.D. = + 11t63).

SUMMARY1. 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 (VT), respiration rate (f) and pulmonary ventilation (r) 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 J andf were significantly higher in all infants during REM than during NREM sleep, while mean VT was either unchanged or showed a decrease. In addition, there was significantly greater variation in instantaneous J7, VT 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 VT 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.

1. Ventilation was measured in eleven healthy term infants during both quiet and active sleep, using the trunk plethysmograph, and instantaneous heart rate was derived from the electrocardiogram. Variations in individual respiratory and cardiac cycles were compared in each sleep state, and cross-correlations between ventilation and heart rate were used in the analysis of the data. 2. It was found that heart rate and respiratory rate were higher and more variable during active than during quiet sleep, with a small reduction in tidal volume. 3. Cross-correlations showed that respiratory sinus arrhythmia was present in both sleep states, but was more marked during quiet sleep. 4. Running cross-correlations using a 5 s window showed that phase relationships between ventilation and heart rate, were, on the whole, stable during quiet sleep, but markedly unstable during active sleep. 5. It is concluded that in the investigation of respiratory sinus arrhythmia in the new-born, it is important to take account of sleep state, the methods of measuring ventilation and heart rate, and to use analytical techniques suited to the specific purpose of the study. 6. Respiratory sinus arrhythmia is considered to be due to an interaction between systems controlling breathing and those controlling the cardiovascular system, and that this interaction is affected by sleep state.