Chronic mountain sickness in Tibet.

A clinical syndrome identical to the chronic mountain sickness of the Andes occurs commonly in Lhasa, Tibet. It affects, almost exclusively, the immigrant Han population and develops after an average of 15 years' residence at high altitude. The early symptoms are attributable to polycythaemia--headache, dizziness, loss of memory and fatigue being prominent. In the later stages of the disease, dyspnoea and peripheral oedema develop. Haemodynamic investigations show pulmonary hypertension with a normal cardiac output and dilatation of the right ventricle in the long-established case. Respiratory gas studies provide evidence of alveolar underventilation and ventilation: perfusion inhomogeneity. Both clinical and investigatory data suggest that the earlier stages of the disease are dominated by polycythaemia, while cardiopulmonary involvement increases with the duration of the disease. The disease is rare in women and uncommon in Tibetans. Cigarette smoking appears to be a contributory factor.