EFFECTS OF ARTERIAL DISTENSIBILITY ON LEFT-VENTRICULAR EJECTION IN THE DEPRESSED CONTRACTILE STATE

Objective: The aim was to evaluate the effects of arterial distensibility on ventricular ejection in various ventricular contractile states: (1) control: (2) a regionally depressed contractile state due to left circumflex coronary artery occlusion (ligation); (3) a globally depressed contractile state induced by lignocaine (lignocaine); and (4) a globally augmented contractile state due to dobutamine infusion (dobutamine). Methods: Arterial compliance was decreased from 2.3 X 10(4) dyne-1.cm5 (C2.3) to 0.4 X 10(-4) dyne-1.cm5 (C0.4), maintaining other afterload components and left ventricular end diastolic pressure constant. Nine excised perfused and paced canine hearts, supported from donor dogs, were used. Results: In control, ligation. lignocaine, and dobutamine groups, the difference in cardiac output between the compliance values of C0.4 and C2.3 was 124(SEM 32), 204(36), 163(33), and 130(24) ml, respectively. Thus cardiac output at CO.4, as a percentage of that at C2.3, was 88(2.8)% (control), 75(2.9)% (ligation), 82(2.9)% (lignocaine), and 88(2.4)% (dobutamine), respectively: control v ligation, and lignocaine v ligation, p<0.001; control v lignocaine, and dobutamine v ligation, p<0.01. Stroke work at C0.4 decreased in the ligation group (63%, p<0.001) and in the lignocaine group (70%, p<0.001). Conclusions: When cardiac dysfunction is already present, decreased arterial distensibility has a further deleterious effect on cardiac output. This may be due to the fact that the pressure at the end of ejection is higher and as a result the change in dimension during ejection is considerably reduced, especially in cases with depressed cardiac function caused by afterload dependency.