Models for Cutaneous Gas Exchange and Transport

SYNOPSIS. Models suited for quantitative analysis of cutaneousgas exchange and transport with particular emphasis on diffusionlimitation are discussed. I. The diffusive transfer of gasesbetween body and environment can be compared to diffusion acrossa homogeneous flat tissue sheet characterized by a diffusionconductance or diffusing capacity (D). II. A flat barrier separatingthe medium from blood flow is a widely useful model. The characteristic parameter is theratio , where rß is the effective solubility of the gas in blood. A high value means predominant perfusionlimitation; low signifies diffusion limitation. III. In some conditions, as in still wateror at body-soil contact, a considerable diffusion resistancein the medium may become important. IV. Unequal distributionof D to may strongly reduce gas exchange efficiency. V. Diffusive arteriovenous shuntingof gases may lead to additional reduction of gas exchange efficiency.VI. The parallel arrangement of skin circulation with respectto tissue circulation (in contrast to the arrangement in seriespresent in fish gills and in tetrapod lungs) leads to mixingof arterialized with venous blood and reduced efficiency ofblood flow in gas transport.