Interaction of Ventilation and Perfusion with Diffusion in Cutaneous Gas Exchange

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The proposed research will continue an ongoing analysis of cutaneous gas exchange in vertebrates and the means by which it may be regulated. One critical question concerns how effective changes in blood flow can be in regulating cutaneous gas exchange; resolution of this question requires a precise distinction among the ways in which changes in bulk blood flow to the skin might be manifested at the microcirculatory level. Variation in cutaneous microcirculation, (2) tube hematocrit, (3), capillary recruitment, (4) the spacing of recruited capillaries, and/or (5) spatial and temporal heterogeneity in 1- 4. These five variables will first be quantified while oxygen uptake is measured in an isolated perfused skin preparation; this preparation will yield information on how experimental variation in these five variables is related to the magnitude of cutaneous gas exchange. A complementary study will characterize the five variables in vivo to determine how they actually vary in an intact animal. Another critical question concerns the resistance of diffusion boundary layers about skin in water: Is their resistance large, negligible, or somewhere in between? A second series of experiments will directly examine the extent to which oxygen diffusion boundary layers may limit cutaneous gas exchange with animals of different flow regimes. In an experimental preparation, the absolute and relative resistances of the skin and the oxygen diffusion boundary layer will be quantified. These issues are important ones because, although skin is one of the primary gas exchangers of vertebrates, our knowledge of cutaneous gas exchange is as yet too sketchy to achieve a general and comprehensive understanding of vertebrate gas exchange.