Interindividual Differences Concerning the Oxygen Diffusion-Transport Function in the Lung

The oxygen diffusion/transport function is accomplished at the level of the air blood-barrier. Diffusion occurs through the surface of the air-blood barrier (ABB) and of the red blood cells (RBC). Diffusion is therefore directly proportional to the overall extension of the alveolar surface and to the external surface of the RBC; conversely, lung diffusion is inversely proportional to the thickness of the ABB and of the RBC cellular membrane. The transport function occurs through the RBC flow through lung capillaries carrying oxygen bound to hemoglobin. The oxygen diffusion/transport function can be profitably discussed based on individual measurements of total lung diffusion properties and cardiac output (CO). Lung diffusion is defined by the overall diffusion (DLCO) and its subcomponents, namely: Dm (representing surface membrane diffusivity), and Vc (volume of blood present in the lung capillary allowing oxygen-Hb binding. Subjects differ substantially in terms of DLCO, Dm and Vc. Interestingly, subjects also substantially differ when considering an important ratio, namely DLCO/CO. This ratio defines indeed the kinetics of equilibration of oxygen partial pressure between alveoli and capillaries. We will explore how this kinetics differs among subjects due to individual changes in diffusion properties and cardiac output, in response to the need to increase the oxygen-diffusion-transport on hypoxia exposure that implies a decrease in partial pressure gradient for oxygen.