COMPARISON OF DIFFERENT OXYGEN-EXCHANGE MODELS

A functional distribution of coronary volume can be estimated from the response of arterio-venous O-2 content difference (AVO(2)) to a flow step. However, the results depend on the assumed O-2 exchange model, T he previously used model consisted of a single mixed compartment with O-2 exchange in series with an unmixed compartment without O-2 exchang e (reference model). The purpose of this study is to provide an estima te of the errors made in the volume estimations by not taking into acc ount factors as flow heterogeneity, different mixing sites or Krogh-li ke O-2 exchange. The approach is indirect: the response of the AVO(2) to a flow step has been calculated with alternative O-2 exchange model s in which the factors mentioned are incorporated. These transients ar e fitted with the reference model. The resulting estimated volumes are different from the volumes assumed in the alternative models. Large d ifferences are obtained with some of the alternative models, e.g. the model with Krogh characteristics. However, these models seem unrealist ic because capillary pO(2) is higher than venous pO(2). Only small dif ferences in volume are obtained with the more realistic models, Theref ore, these results indicate that the coronary volumes are approximated well by the estimations obtained with the reference model, These volu me estimations were 9.9 and 3.8 mi 100 g(-1) for the O-2 exchange vess els and the distal venous volume, respectively.