Effect of coronary perfusion on the basal performance, volume loading and oxygen consumption in the isolated resistance-headed heart of the troutOncorhynchus mykiss

Abstract

SUMMARYBasal performance, volume loading response and oxygen consumption were determined in a resistance-headed preparation of the isolated trout heart. Two groups of hearts were used: the +CF group, in which the coronary vascular tree was perfused with a flow directly related to the pressure generated by the heart, and the -CF group, in which the coronary flow was set to zero. As a criterion for setting basal performance, the atrial input pressure was set in order to induce the ventricle to produce a cardiac output of 15 ml min-1 kg-1. Once basal conditions were obtained, the preparation was perfused for 30 min, and atrial and aortic pressure, cardiac output, heart rate, coronary pressure and coronary flow were determined at 5 min intervals. At the onset of perfusion, there was no difference in the basal performance between the two groups: the same preload was necessary to get the same cardiac output in both perfusion groups. None of the other performance parameters determined were different. However, after only 5 min of perfusion,the -CF hearts displayed significant adjustments, with increased atrial preload and ventricular preload (mean atrial pressure), and a significant decrease in cardiac output. At the end of the 30 min basal perfusion period,hearts were challenged with a stepwise increase in preload in order to obtain maximal stroke work (volume loading). The effect of coronary perfusion on the heart's response to volume loading was highly significant: the stroke work-preload relationship was significantly shifted towards higher preload values in the -CF group. Also, the maximal work produced by the heart under the experimental conditions used was lower in the -CF group. Rate of oxygen consumption of the heart increased significantly with volume loading, from a basal value of approximately 20 μl O2 min-1g-1 to approx. 40 μl O2 min-1g-1, but was not significantly affected by the absence of coronary perfusion. Mechanical efficiency under basal conditions was approximately 17%,but was not affected by either volume loading or coronary perfusion. Taken as a whole, these data represent direct evidence of the effect of coronary perfusion on the mechanical performance of the trout heart, but also show that these effects are limited by significant self-adjustments that occur in the heart.