Alveolo‐Arterial Gas Exchange at Rest and During Work at Different O₂, Tensions

Abstract

Abstract The mean alveolar and the arterial gas tensions in healthy young male subjects have been determined at rest and during muscular exercise of varying intensities up to maximal work. Determinations were made while the subjects were breathing air containing 33 to 50 per cent, 21 per cent and 12 per cent oxygen. From the experimental data the alveolo‐arterial oxygen tension differences and the arterial oxygen deficits ( i. e. the difference between the oxygen content of blood in full equilibrium with the mean alveolar air and the actual oxygen content of peripheral arterial blood) were calculated. Under the assumption that the B ohr integration procedure can be used for determining the mean pulmonary capillary P O2 in the human lung it can be concluded that the arterial oxygen deficit when breathing normal air both at rest and during maximal work is caused by true venous admixture (anatomical shunts) and the effect of uneven distribution in the lungs, and it is found that about 80 per cent is due to the distribution effect and the remaining 20 per cent to the true venous admixture. Further, the effect of the distribution factor at low oxygen pressures increases manifold as compared with the effect at normal O 2 pressure. The large arterial O 2 deficit found in the low O 2 experiments (in ml per min equal to 62 and 36 per cent of the total O 2 uptake at rest, respectively during maximal work) can, therefore, be explained by the true venous admixture and the greatly increased effect of the distribution factor. According to this view it is not possible to determine the lung diffusion capacity for O 2 on the basis of the alveolo‐end pulmonary capillary O 2 gradient by the procedure of R iley and C ournand (which assumes a constant effect of the distribution factor at high and low oxygen tension) or by the procedure of B artels et al. (which does not take the distribution factor into account).