Quantification of ischemic stress during repeated coronary artery occlusion in the dog. A method for validation of therapeutic effects. I. Estimation of O2-debt and O2-repayment.

In 9 open-chest mongrel dogs 4-6 intermittent 3-min occlusions of the LAD artery were performed with time intervals of about 45 min. Using a mu-computer, the following variables were calculated online: energy demand according to the Bretschneider equation (Et) from digitized hemodynamic data; myocardial oxygen consumption (MVO2) from fiberoptically measured coronary sinus oxygen saturation and coronary sinus blood flow. Coronary occlusion led to a decrease in MVO2 in comparison to Et. The integral of the difference between MVO2 and Et over the entire occlusion time yielded a total O2-deficiency (DO2) of 76 (+/- 12%) microliter O2/g ischemic tissue and a correlation coefficient with the weights of the intravitally stained ischemic areas of r = 0.96. Additional O2-uptake in relation to Et during the early perfusion period yielded a correlation to the size of the ischemic area of r = 0.95 and an average O2-repayment (RO2) of 32 (+/- 14%) microliter O2/g ischemic tissue. The determination of total myocardial O2-deficiency during ischemic stress as well as determination of O2-repayment during the early reperfusion period could be used to estimate the extent of ischemic stressed myocardium. Subsequently, the evaluation of pharmacological effects on myocardial ischemia should be possible.