RESPIRATORY ADAPTATION TO ANOXEMIA

Abstract

Observations on the pulmonary ventilation, the composition of the alveolar and expired air, the CO2 content and O saturation of the arterial blood, and the total pulmonary capacity and its subdivisions, made on 3 healthy [male] subjects at a simulated altitude of 16,400 ft. in a low pressure chamber, supplemented and correlated with anatomic studies of the lungs of guinea pigs under the same experimental conditions, showed an increase in red cell count, Hb and viscosity in the arterial blood, with a moderate decrease in CO2 and marked diminution in O content and saturation. The ventilation per min. increased slightly in 2 subjects and decreased in the other 1. A marked reduction in CO2 occurred, and also in O tension of the alveolar air, though not as great as the O tension in the inspired air would lead one to expect. Structural changes in the lungs, apparently compensatory responses to anoxemia (chiefly a widening in capillaries and a dilatation of alveoli), accompanied by a moderate increase in residual air and a corresponding decrease in vital capacity with little or no change in the total pulmonary capacity, tend to produce an increase in the surface for diffusion between the circulating blood and alveolar air, a condition favorable for a more efficient exchange of the respiratory gases. The volume of the respiratory dead space was not significantly altered at low barometric pressure.