Haemodynamic characteristics of systemic arterial blood supply to the lungs.

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, but fell 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