Alveolar-arterial oxygen tension gradient due to diffusion

¹ Cardiovascular Research Institute and Department of Physiology, University of California Medical Center, San Francisco, California

This is a theoretical paper in which the absolute time course of O₂ uptake by the red blood cells during their passage through the pulmonary capillaries is calculated from recently obtained values of O₂ (the rate of O₂ uptake by human red cells per milliliter of blood as a function of O₂Hb saturation), the components of diffusion resistance (alveolar-capillary membrane and instantaneous pulmonary capillary blood volume), and the pulmonary blood flow. One result of these calculations is the alveolar-arterial Po₂ difference due to diffusion. Five situations of varying degrees of diffusion stress are examined. The diffusion gradient for O₂ is generally smaller than that computed by older techniques. Most of the diffusion resistance lies in the blood in normal subjects at rest breathing air. If the membrane and blood components of the diffusion resistance are unevenly distributed in the lung, the diffusion gradient will be greater than the ideal values. Regional variations in capillary transit time for any reason are more serious than membrane variation because of higher diffusion resistance of the blood normally.

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