Hypoxia and pulmonary arterial pressure in the rabbit.

1. The effect of hypoxia on pulmonary arterial pressure was studied in young and adult rabbits.2. In isolated perfused lungs, hypoxia caused no rise in pulmonary arterial pressure in rabbits on the day of birth. The size of the hypoxic response increased progressively until 9-11 days of age, when the adult response of a 20% rise of pulmonary arterial pressure at constant flow was attained.3. The intact adult rabbit responded to hypoxia with a 14-30% rise in pulmonary arterial pressure, attributed to vasoconstriction and independent of frequency or tidal volume during positive pressure ventilation.