Models for cutaneous gas exchange and transport

Abstract

SYNOPSIS. Models suited for quantitative analysis of cutaneous gas exchange and transport with particular emphasis on diffusion limitation are discussed. I. The diffusive transfer of gases between body and environment can be compared to diffusion across a homogeneous flat tissue sheet characterized by a diffusion conductance or diffusing capacity (D). II. A flat barrier separating the medium from blood flow (. Q.) is a widely useful model. The characteristic parameter is the ratio D/(. Q.rβ), where rβ is the effective solubility of the gas in blood. A high D/(. Q.rβ) value means predominant perfusion limitation; low D/(. Q.rβ}) signifies diffusion limitation. III. In some conditions, as in still water or at body-soil contact, a considerable diffusion resistance in the medium may become important. IV. Unequal distribution of D to . Q. may strongly reduce gas exchange efficiency. V. Diffusive arteriovenous shunting of gases may lead to additional reduction of gas exchange efficiency. VI. The parallel arrangement of skin circulation with respect to tissue circulation (in contrast to the arrangement in series present in fish gills and in tetrapod lungs) leads to mixing of arterialized with venous blood and reduced efficiency of blood flow in gas transport. © 1988 by the American Society of Zoologists.