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.