The effect of oedema upon the diffusion of oxygen from capillary blood into the surrounding metabolizing tissue is considered in calculations based on the Krogh-Erlang model. While diffusion distances are increased in oedema, the oxygen consumption per unit volume of tissue is correspondingly reduced and the increments of capillary Po2 necessary to meet the tissue oxygen requirements are small. Pericapillary cuffs of oedema fluid would appear to have minimal effects on oxygen diffusion. It appears unlikely that pericapillary cuffs containing fibrin act as diffusion barriers to oxygen unless the fibrin molecules occupy more than half the volume of the cuff.
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