[Hypoxia and pulmonary circulation. The importance of hypoxia in pulmonary arterial hypertension of chronic obstructive bronchopneumopathies].

In chronic airflow obstruction (CAO), there are grounds for distinguishing between the effects of acute alveolar hypoxia and those of chronic hypoxia. Acute hypoxia leads, in healthy subjects, to pulmonary vasoconstriction. In patients with CAO, there is however a great variability in the pulmonary vascular response to hypoxia. Chronic hypoxia leads in the long term to structural modifications in the pulmonary vessels (arteriolar muscularization, hypertrophy of the small arterial muscles, and intimal fibrosis), which are similar enough to those seen in residents at high altitude and which lead to an elevation of the pulmonary vascular resistance. These structural changes are potentially reversible but one does not know up to which point they are. This potential reversibility represents one of the justifications of long term oxygen therapy in these patients. The pulmonary arterial hypertension of CAO is generally moderated; it evolves slowly over years and years in the majority of cases; it certainly doesn't merit to be treated at any cost. Up to the present, pulmonary vasodilators have given rather disappointing results. Prolonged oxygen therapy (for greater than 16 hours in 24), which improves in other respects the expectation of life in patients is currently the most logical treatment for pulmonary hypertension in CAO.