GRADED MYOCARDIAL-ISCHEMIA IS ASSOCIATED WITH A DECREASE IN DIASTOLICDISTENSIBILITY OF THE REMOTE NONISCHEMIC MYOCARDIUM IN THE ANESTHETIZED DOG

Objectives. This study was designed to investigate the changes in regi onal distensibility of the ischemic segment and of a remote nonischemi c segment brought about by graded myocardial ischemia. Background. Ven tricular distensibility is a major determinant of left ventricular end -diastolic pressure. The effects of graded myocardial ischemia on the regional distensibility of the ischemic area have not been studied. Mo reover, there are few data on the effects of myocardial ischemia on th e regional distensibility of the nonischemic myocardium. Methods. Nine anesthetized open chest mongrel dogs were fitted with instruments to measure left ventricular pressure and circumferential length (sonomicr ometry) in the ischemic segment and in a nonischemic segment. The pres sure-length relation was modified by stepwise infusion and withdrawal of 200 ml of each dog's own blood over 30 min in five consecutive stag es of regional ischemia. Unstressed dimensions were obtained by repeat ed inferior vena cava occlusions. In both segments, regional distensib ility was assessed at end-diastole by means of the constants of the pr essure-length (chamber stiffness), the pressure-strain and the force-s train (myocardial stiffness) relations. Results. In the ischemic segme nt, partial and complete coronary occlusions were associated with a tw ofold increase in the chamber stiffness constant, the pressure-strain constant and the myocardial stiffness constant, whereas in the nonisch emic segment the chamber stiffness constant, the pressure-strain const ant and the myocardial stiffness constant increased by 50%. Conclusion s. Regional myocardial ischemia is associated with a decrease in diste nsibility of both the ischemic and the remote nonischemic myocardium.