Partie d'ouvrage collectif
| Résumé : | Altitude is a cause of hypobaric hypoxia. Hypoxia causes pulmonary vasoconstriction. Chronic hypoxia induces pulmonary hypertension in proportion to initial vasoconstriction. Hypoxic pulmonary hypertension in humans is usually mild to moderate, but pulmonary vascular pressure-flow relationships are steep. This corresponds to a substantial afterload on the right ventricle during exercise. Hypoxia has been reported to decrease myocardial fiber contractility in vitro. However, the acutely hypoxic right ventricle remains able to preserve the coupling of its contractility to increased afterload in intact animals. Echocardiographic studies of the right ventricle in healthy hypoxic human subjects show altered diastolic function, but systolic function that may be preserved or slightly depressed. These findings may be more pronounced in patients with chronic mountain sickness. However, exercise in high-altitude dwellers is associated with a normally increased right ventricular systolic function to preserve its coupling to the pulmonary circulation. Occasional severe hypoxic pulmonary hypertension may be associated with right-heart failure. This condition is poorly documented because of on-site scarcity of catheterization and imaging resources. |
