Pulmonary hypertension with muscular exercise in the newborn calf

¹ Department of Medicine, University of Kentucky Medical Center, Lexington, Kentucky

Two types of pulmonary hypertension occur with muscular exercise (walking) in the calf on the day of birth: a) Pulmonary arterial pressure increased in all calves during exercise. The increase was greatest in the youngest calves. Pulmonary arterial pressures did not rise to systemic levels and arterial oxygen saturations remained normal. Pulmonary hypertension subsided in 2 min after stopping exercise. Pulmonary arterial pressure rose again when exercise was repeated. Both an increased pulmonary flow and pulmonary vasoconstriction may have contributed to the increased pulmonary arterial pressure during exercise. b) Pulmonary hypertension was observed in five calves for 30–50 min after exercise ceased. When pulmonary arterial pressure exceeded aortic pressure, arterial oxygen unsaturation occurred. This pulmonary hypertension which occurred only once per calf resembled "spontaneous" pulmonary vasoconstriction observed in resting calves on the day of birth. It is postulated that some substance remaining in the lung after fetal life, rather than the acutely reduced oxygenation of mixed venous blood, initiated this pressor response.

Submitted on May 11, 1964