Some factors affecting oxygen uptake by red blood cells in the pulmonary capillaries

In this study we investigate the equations governing the transport of oxyge n in pulmonary capillaries. We use a mathematical model consisting of a red blood cell completely surrounded by plasma within a cylindrical pulmonary capillary. This model takes account of convection and diffusion of oxygen t hrough plasma, diffusion of oxygen through the red blood cell, and the reac tion between oxygen and haemoglobin molecules. The velocity field within th e plasma is calculated by solving the slow flow equations. We investigate t he effect on the solution of the governing equations of: (i) mixed-venous b lood oxygen partial pressure (the initial conditions); (ii) alveolar gas ox ygen partial pressure (the boundary conditions); (iii) neglecting the conve ction term; and (iv) assuming an instantaneous reaction between the oxygen and haemoglobin molecules. It is found that: (a) equilibrium is reached muc h more rapidly for high values of mixed-venous blood and alveolar gas oxyge n partial pressure: (b) the convection term has a negligible effect on the time taken to reach a prescribed degree of equilibrium; and (c) an instanta neous reaction may be assumed. Explanations are given for each of these res ults. (C) 2001 Elsevier Science Inc. All rights reserved.