Lack of smooth muscle in the small pulmonary arteries of the native Ladakhi. Is the Himalayan highlander adapted?

Chronic hypobaric hypoxia induces a mild degree of pulmonary arterial hypertension with structural alterations in the peripheral portions of the pulmonary arterial tree of the native Andean highlanders. On the other hand, animals indigenous to high altitude do not show these changes and are adapted to hypobaric hypoxia. The small pulmonary arteries of seven native Himalayan highlanders were examined at autopsy and found to be thin-walled with no medial hypertrophy of the muscular pulmonary arteries or muscularization of the arterioles. These findings suggest that the Himalayan highlanders may be adapted to hypobaric hypoxia.

Echocardiography shows persistent thickness of the wall of the right ventricle in infants at high altitude.

We have applied M-mode and two-dimensional echocardiography to infants living at high altitude in La Paz, Bolivia (3800m) and infants living at low altitude in Santa Cruz, Bolivia (400m). At low altitude, the thickness of the anterior wall of the right ventricle decreases during the first month of extrauterine life to a dimension which remains constant for the rest of infancy. At high altitude, the thickness of the anterior wall of the right ventricle at birth is similar to that found at low altitude but does not decrease in the succeeding twelve months. The ratio of the diameter of the aorta to that of the pulmonary artery was higher at low altitude in all age-groups. The observations are consistent with the persistence of a high pulmonary arterial pressure during infancy at high altitude.