Lung Mechanics in Normal Infants and Infants with Congenital Heart Disease

The results of a study of pulmonary mechanics in 24 normal infants and 28 infants with congenital heart disease aged 1 to 32 weeks are presented. The two groups were matched for length and weight. The diagnosis of the infants with congenital heart disease varied from simple stenoses to complex septal defects and transpositions. 6 infants were studied before and after operation designed to improve their haemodynamic situation. Pulmonary compliance and mean pulmonary resistance were measured using a pneumotachygraph, integrator, and oesophageal balloon; thoracic gas volume was measured by the plethysmographic method. Results were found to be reproducible both in the individual and within the normal group. Thoracic gas volume in relation to weight and pulmonary resistance were normal in the infants with congenital heart disease, but the pulmonary compliance was often abnormal even when related to lung volume. The change in compliance was not simply related to pulmonary blood flow or pressure but was related to the radiological assessment of pulmonary plethora or oligaemia—the more plethoric the lower the compliance. Surgery altered both the radiological grading and the compliance appropriately. It is postulated that changes in the elastic properties of the lungs are related to changes in the pulmonary capillary blood volume.