Classical Krogh model does not apply well to coronary oxygen exchange

By fitting of simulations with an oxygen exchange model to measured responses of the arteriovenous oxygen content difference after a flow step, coronary volumes can be estimated. In this study the dependence of the volume estimates on the choice of the oxygen exchange model for the coronary circulation was investigated. A model consisting of a single well-mixed compartment results in smaller volume estimates than a series array of mixed compartments in which Po₂ declines gradually (Krogh-like model). Use of the former model for data analysis resulted in realistic volume estimates. Thus, these results indicate that the oxygen exchange vessels are better represented by a single mixed compartment than by a cylinder having Krogh characteristics. This conclusion agrees with capillary Po₂ being equal to or smaller than venous Po₂ which cannot be explained by a Krogh model. From these arguments we conclude that though both models are rough representations of the coronary circulation, the coronary O₂ exchange vessels of the beating heart can be represented better by a single mixed compartment than by a series array of mixed compartments which has Krogh characteristics.