MECHANOENERGETICS OF NEGATIVE INOTROPISM OF VENTRICULAR WALL VIBRATION IN DOG HEART

Mechanical vibration depresses cardiac contractility. We studied the m echanoenergetic effects of this negative inotropism in the left ventri cle (LV) of an isolated, cross-circulated dog heart preparation. We to ok. full advantage of the mechanoenergetic relationship among the LV e nd-systolic elastance (E(max), contractility index), systolic pressure -volume area (PVA), and myocardial oxygen consumption (Vet). PVA is a measure of the total mechanical energy that cardiac contraction genera tes. PVA correlates closely with Vet. The Vo(2) intercept of the Vo(2) -PVA relation reflects the Vo(2) component for excitation-contraction (E-C) coupling plus basal metabolism (PVA-independent Vo(2)). Vo(2) ab ove the PVA-independent Vo(2) reflects the Vo(2) component for mechani cal contraction (PVA-dependent Vo(2)). When we applied 70-Hz vibration of 2-mm amplitude to a LV wall region, it instantly decreased E(max) and PVA by 20%, followed by a 10% decrease in Vo(2) at a fixed volume. However, the vibration neither lowered the Vo(2)-PVA relation obtaine d at different LV volumes, unlike ordinary negative inotropism, nor ch anged its slope (1.88 +/- 0.23 vs. 1.86 +/- 0.23 x 10(-5) ml O-2 . mmH g(-1). ml(-1)). The virtually zero Delta PVA-independent Vo(2)/Delta E (max) with vibration indicates a much smaller O-2 cost Of E(max) than that seen with calcium and propranolol inotropism. These mechanoenerge tics support the hypothesis that mechanical vibration primarily suppre sses cardiac contractility without suppressing E-C coupling.