Coronary vascular reserve and regional myocardial contractile force with special reference to myocardial metabolism.

Abstract

The relations among coronary vascular reserve, regional myocardial contractile force and myocardial metabolism were investigated in anesthetized dogs under open-chest condition. The reactive hyperemia response was examined during stepwise occlusion of circumflex artery. A change in percent repayment was used as an index of the coronary vascular reserve. Contractile force was measured with strain gauge arches sutured to ischemic and nonischemic areas of the left ventricle. The nonischemic muscle contractile force (NIMCF) increased or showed no significant change with the reduction of repayment by stepwise constriction of circumflex artery. The ischemic muscle contractile force (IMCF) began to decrease markedly following reduction of repayment below 50%. NIMCF was found to be slightly decreased by the severe reduction of coronary blood flow (CBF) in ischemic region. Thus there was a low (r = 0.39) correlation between NIMCF and CBF in ischemic region. However, the correlation between IMCF and CBF in ischemic region was relatively high (r = 0.68). The arterial and coronary sinus blood samples were obtained for the determination of oxygen content, lactate and potassium concentrations. In the range of constriction without reduction of CBF, IMCF decreased significantly following reduction of repayment below 50%, but O2, lactate and potassium extraction ratios were not significantly different. Application of further constriction revealed significant reductions of CBF, stroke volume, aortic pressure, IMCF and lactate extraction ratios, and it also revealed significant elevation of O2 extraction ratio. The above observation suggests that a reduction of coronary vascular reserve might affect regional contractile force without change in CBF, and reduction of CBF could decrease regional and global left ventricular performance with changes in myocardial metabolism.