Excessive polycythaemia of high altitude. Pulmonary function studies including carbon monoxide diffusion capacity.

Pulmonary function studies were done in 21 soldiers (low landers) posted at high altitude (average height 4773 metres) for prolonged periods (average 77.09 months), who had developed excessive polycythaemia, mean haemoglobin concentration being 23.06 g/dl. Studies revealed significant reduction in diffusion capacity of lungs which gradually returned to normal on sojourn at low altitudes for 70 days. Both the degree of polycythaemia and reduction in lung diffusion capacity were much more pronounced in smokers than in non-smokers. Vital capacity did not show any difference in these subjects while forced expiratory volume in 1 sec and ratio of forced expiratory volume to vital capacity (FEV1/VC) revealed only obstructive features in smokers.