Reduced lung volume during behavioral active sleep in the newborn.

In a previous study of newborn infants we observed overall rib cage collapse during active sleep and postulated that the lungs also could be deflated, leading to reduced oxygen stores and circumstances favoring the rapid development of hypoxemia during apnea. In this study, thoracic gas volume (TGV) has been measured directly by occlusion plethysmography in six normal babies during behavioral quiet and active sleep and related to the different movements of the rib cage and abdomen-diaphragm that occur during each sleep state. TGV was significantly reduced in each baby during active sleep and was associated with rib cage deflation and increased abdomen-diaphragm excursions. The average reduction of TGV was 31% when compared with the volume in quiet sleep and did not depend on the order in which the sleep states were tested. The reduced lung volume in active sleep could have implications for the regulation of breathing in that state. A reduction of lung oxygen stores in active sleep suggests an age-related vulnerability of the young infant to hypoxemia.