Quantitative significance of hypoxic vasoconstriction in the ferret lung

Stimulus-response curves for the pulmonary vascular bed to alveolar hypoxia have been measured in ferrets under conditions of perfusion either at constant pressure or a constant flow in vivo or in isolated lungs. In all circumstances the relationship between alveolar oxygen tension and the fall in blood flow or rise in pulmonary artery pressure was sigmoid although there were important differences between the in vivo and in vitro preparations. The significance of these observations in constant pressure and constant flow preparations in relation to pulmonary hypertension and ventilation/perfusion regulation is discussed.