READJUSTMENT IN DISTRIBUTION OF ALVEOLAR VENTILATION AND LUNG PERFUSION IN THE NEWBORN

An increased urinary-alveolar PN2 difference was demonstrated in normal, full-term infants during time first 6 days of life. This uADN2 results only from regions of the lungs with a low VA/Q and is not affected by true venous admixture, a diffusion barrier, or the presence of atelectasis. The mean aADN2 of 25 mm Hg on the first day of life was comparable to the N2 difference found in patients with severe emphysema. The mean PN2 difference decreased gradually and by time sixth day was approximately 10 mm. The histologic signs of amniotic detritus in the lungs of virtually all new-born infants dying of non-respiratory causes on the first day of life and the subsequent lower incidence of these materials in the lungs of infants dying during the first week suggests the possibility of partial obstruction and low VA/Q in some regions of the lung. The temporary increase in uADN2, which was found in some cases may indicate that atelectatic areas may open at different times.