Regional differences in gas exchange in the lung of erect man

Abstract

Measurements of regional ventilation and blood flow using radioactive CO 2 show that both increase from apex to base of the lung; the results are used to build an integrated picture of gas exchange. Ventilation-perfusion ratios at nine levels of the lung have been calculated and differences in local gas exchange deduced. In the resulting model, alveolar O 2 tension changes by more than 40 mm Hg from apex to base while CO 2 and N 2 tensions change by about 14 and 29 mm Hg, respectively. Maximal differences in O 2 saturation of end-capillary blood are 4% but differences in CO 2 contents of 7 vol % and pH variations of 0.12 units occur. The O2 uptake per unit lung volume increases eightfold down the lung while corresponding variations in CO 2 output are less than threefold. N 2 passes out of the blood in upper parts of the lung but into the blood in basal regions (net exchange is zero). Over-all O 2 uptake and CO 2 outputs are reduced by only 2–3% by the ventilation-perfusion ratio inequality, causing alveolar-arterial differences of 4, 1, and 3 mm Hg for O 2, CO 2, and N 2, respectively. Submitted on April 6, 1962