Hypoxia and the pulmonary circulation.

It is a singularly interesting fact that sustained hypoxia exerts diametrically opposite effects on the systemic and pulmonary circulations. In general, hypoxia has a relaxing effect on smooth muscle and it brings about vasodilatation in the systemic circulation. Native highlanders and sojourners at high altitude for many years exhibit a fall in systemic blood pressure (Heath and Williams, 1977). In sharp contrast to this, hypoxia is the most powerful pulmonary vasoconstrictor known, giving rise to increased pulmonary vascular resistance and hence to pulmonary arterial hypertension. Since the original demonstration of this in the cat by von Euler and Liljestrand (1946) there has been an impressive accumulation of supporting experimental evidence from a variety of animal species and from man and recently we have extensively reviewed these data (Harris and Heath, 1977).