Abstract

Pulmonary and systemic blood flow and pulmonary vascular resistance were measured in 21 children with congenital heart disease. Blood flow was calculated by the direct Fick method, using measurements of metabolic gas exchange obtained by remote respiratory mass spectrometry. The observations showed that the administration of oxygen caused an appreciable fall in pulmonary vascular resistance in 16 of the 21 children studied and that this fall would not have been appreciated from a study of pulmonary arterial pressure alone as it was masked by a corresponding rise in blood flow. In 10 of 14 children, in whom superior vena caval blood was also sampled, the rise in flow was largely due to an increase in intracardiac left to right shunt. It was accompanied by widening of the alveolar-arterial oxygen gradient, perhaps due to imperfect gas equilibration within the lung.