Noninvasive determination of total respiratory system compliance in infants by the weighted-spirometer method.

The weighted-spirometer method for noninvasive determination of static total respiratory system compliance (Crs) was adapted for use in infants. Ten normal newborns and 5 infants with bronchopulmonary dysplasia (BPD) were studied. The newborns had a mean Crs of 3.8 ml/cm H2O. Their mean specific Crs was 1.13 ml/cm H2O/kg body weight and 0.075 ml/cm H2O/cm body length. These Crs values were similar to those reported by other investigators who used the Hering-Breuer airway occlusion technique. The infants with BPD, who were of the same weight, height, and postconception age as the normal newborns, had significantly (p less than 0.05) lower mean specific Crs (0.60 ml/cm H2O/kg body weight and 0.047 ml/cm H2O/cm body length) relative to the normal newborns. These data suggest that intrinsic changes in lung elastic characteristics may contribute to the reduced lung compliance of infants with BPD. The weighted-spirometer method for measuring Crs is a potential tool for the noninvasive study of the elastic properties of the respiratory system during infancy in health and disease.