Pulmonary veins in high-altitude residents: a morphometric study.

The thickness of the media of pulmonary veins and arteries was morphometrically assessed in 12 normal adults resident at altitudes over 3000 m and 12 resident at sea level. The pulmonary veins in the latter group were very thin walled. The average thickness of the pulmonary venous media in the group of highlanders was significantly thicker but this appeared to be due to prominent medial hypertrophy in seven individuals, five others having normal or near-normal pulmonary veins. In six of the 12 highlanders bundles of longitudinal smooth muscle cells occurred in the venous intima. There was close correlation between the thickness of the venous and that of the arterial media, suggesting an individual reactivity with a simultaneous response of all pulmonary vascular smooth muscle to high-altitude hypoxia. Hypertrophy of the media of pulmonary veins is likely to be an expression of venoconstriction and narrowing of the venous lumen may be enhanced by the development of longitudinal smooth muscle cells in the intima. Possibly venoconstriction is one of the factors responsible for high-altitude pulmonary oedema.