The pulmonary circulation and the heart in chronic lung disease.

Most studies devoted to the investigation of pulmonary haemodynamics and right ventricular function in chronic lung diseases have concerned patients with chronic obstructive pulmonary disease (COPD). In COPD, pulmonary hypertension is closely linked to the presence of chronic alveolar hypoxia. Pulmonary hypertension is most often mild to moderate (mean pulmonary artery pressure (PAP) in the range 20-35 mmHg) but it may worsen markedly during acute exacerbations of the disease, sleep and exercise. Long-term oxygen therapy is the logical treatment for hypoxic pulmonary hypertension. In time, pulmonary hypertension leads to right ventricular enlargement, which includes right ventricular hypertrophy and dilatation. This is a beneficial adaptation, allowing the right ventricle to cope with an increased afterload and to maintain a normal cardiac output. The right ventricular function, and in particular the right ventricular contractility, are generally preserved in patients with advanced COPD. "True" right ventricular failure can be observed during acute exacerbations of the disease, when worsening of hypoxaemia induces a marked increase in afterload (PAP and pulmonary vascular resistance).