Pulmonary vasoconstriction in asphyxia during cross-circulation between twin foetal lambs.

1. The effect of asphyxia on pulmonary vascular resistance was measured in anaesthetized foetal lambs whose left lung was supplied with arterial blood from a twin, both still being attached to their placentas by intact umbilical cords.2. In foetal lambs of 91-92 days gestation asphyxia of the recipient caused no pulmonary vasoconstriction so long as its left pulmonary artery was supplied with normal blood from a twin donor. Asphyxia of the donor caused pulmonary vasoconstriction in the unasphyxiated recipient; this was therefore wholly due to a local effect of the blood passing through the lung.3. In foetal lambs of 98-142 days gestation asphyxia of the recipient caused a small degree of pulmonary vasoconstriction, even though the left pulmonary artery was supplied with normal blood from the twin donor. This vasoconstriction was abolished by administration of hexamethonium or by cutting the sympathetic nerves to the left lung.4. In mature foetal lambs pulmonary arterial inflow and venous outflow were measured simultaneously. Broncho-pulmonary blood flow was less than 5% of total pulmonary flow. Pulmonary O(2) consumption was 0.75 +/- 0.11 ml./100 g.min, or about 5% of total foetal O(2) consumption.