Alveolar dimensions in the lungs of animals raised at high altitude.

Abstract

In mammals the diffusing surface area per unit of lung volume correlates interspecifically with rate of resting O2 consumption. The ratio of O2 flow-to-pulmonary surface area is a constant over a wide range of body size. Chronic environmental hypoxic stress introduces a diffusion handicap for the lung, and the question arises whether natural selection would lead, intraspecifically, to a change of alveolar dimensions and surface-volume relations of the lungs that would increase pulmonary diffusing capacity over usual sea-level values. The lungs of a high-altitude population of guinea pigs and of domestic sheep have been compared with lungs from equivalent populations raised at sea level. The lungs of one llama have been compared with lungs of sea-level mammals of comparable body size. No significant morphologic differences between the high-altitude and sea-level groups were demonstrable. Apparently, endogenous metabolic need is not comparable to exogenous O2 want on the growth factors which determine alveolar dimensions and by inference, on maximal pulmonary diffusing surface area.