Haemodynamic characteristics of systemic arterial blood supply to the lungs.

The haemodynamic characteristics of the systemic arterial blood supply to the lungs were investigated in 9 out of IO patients with absence of the sixth aortic arch, by means of selective catheterization of the major aortopulmonary collateral arteries. Three patients were infants. Total pulmonary resistance was severely raised, and exceeded 9 .5 units m2 in all patients while breathing room air, butfell significantly upon breathing IOO per cent oxygen. The younger patients had a significantly lower pulmonary resistance than the older patients. Important stenoses were shown in the aortopulmonary collateral arteries of all but one patient, either by angiocardiography, pressure measurements, or at necropsy. These stenoses, since they lay distal to any suitable site for surgical anastomosis to a right ventricular conduit, were an important factor contributing to the high total pulmonary resistance. They appear to be present from birth, and probably give rise to the continuous murmurs heard in all these patients.