Correlation between the linearized Frank-starling relationship and myocardial energetics in the ejecting heart: effect of unprotected and protected global ischemia

Previous studies noted augmented postischemic myocardial oxygen consumption as a subtle indicator of ischemic injury in the isovolumically contracting left ventricle. The present study was done to determine if the linear relationship between oxygen utilization and stroke work present in the ejecting heart would facilitate compartmentalization of this increased oxygen consumption into resting and working metabolic demands. Therefore, 18 canine hearts instructed for computerized acquisition of instantaneous pressure-volume data and quantitation of myocardial oxygen consumption were studied during incremental volume infusion while undergoing right heart bypass. Data acquisition before and after either 20 minutes of 37 degrees C global ischemia or 2 hours of 20 degrees C cardioplegic arrest allowed construction of stroke work versus end-diastolic volume and myocardial oxygen consumption versus stroke work relationships by least squares regression analysis. Although contractility was depressed 48% (p less than 0.01) after unprotected ischemia and was unchanged after cardioplegic arrest, neither group demonstrated a change in the efficiency of converting consumed oxygen to external mechanical work. In contrast, in both groups the oxygen utilization for unloaded contraction was comparably augmented by 21% and 16% (p less than 0.05), despite the varying ischemic conditions and disparate preservation of contractile function. These data suggest a highly linear correlation between oxygen consumption and external mechanical work that persists after ischemia and discriminates the components of postischemic energetic derangements. This model may be useful in the development and assessment of specific myoprotective strategies.