The progressive response of the newborn infant to added respiratory loads

The responses of 10 normal full-term infants to 10-sec airway occlusions at functional residual capacity were studied. The responses were quantified by measuring the pressure generated on successive inspiratory efforts following occlusions in room air and 100% oxygen. The response after oxygen breathing was 30-40% less than after air breathing, indicating that hypoxia accounted for part of the response. There was an increase in the response in air from the first to the fourth day of life. Endtidal carbon dioxide tension was shown to increase during the occlusion, but the response remaining after hypoxia was eliminated may not have been due entirely to hypercapnea. We conclude that the compensatory response of the infant to added respiratory loads is in part due to hypoxia, and that the hypoxic response increases over the first week of life.