Hypoxia and the pulmonary circulation.

The first description of the effects of hypoxia on the pulmonary circulation was made by Bradford and Dean in the UK exactly 100 years ago.' However, scientific interest in this field only began with the discovery of hypoxic pulmonary vasoconstriction in the cat by von Euler and Liljestrand2 in 1946, and in man a year later in Andre Coumand's laboratory.3 Despite extensive research in this field for nearly half a century, we still do not fully understand the mechanism of hypoxic vasoconstriction or why the response of the pulmonary vasculature to hypoxia is diametrically opposite to that of the systemic circulation. Teleologically, hypoxic pulmonary vasoconstriction serves a useful purpose. It acts as a local homeostatic mechanism and, by diverting blood away from the unventilated or poorly ventilated lung, helps to maintain ventilationperfusion homogeneity and thus arterial oxygenation. It is not surprising, therefore, to find that a similar response exists in most animal species."