RELAXATION WITHIN THE LEFT-VENTRICULAR MYOCARDIAL WALL

To evaluate relaxation mechanics in the wall of the left ventricle nee dle mounted miniature pressure transducers were inserted at the subend ocardial (ENDO) and subepicardial (EPI) level of the anterior wall of the left ventricle during acute open-chest experiments in 10 mongrel d ogs. Pressures were recorded during control, volume load and after ver apamil administration. The relaxation time constant (tau) was determin ed by fitting a monoexponential with offset to the isovolumic relaxati on period of the ENDO, EPI and left ventricular pressure (LVP) tracing s: p = p(0)e(-t/tau) + p(1). Mean tau-values for LVP, ENDO and EPI dur ing control were (mean +/- 1 SD, ms): 38 +/- 5, 60 +/- 12, 83 +/- 5; d uring volume overload: 55 +/- 10, 72 +/- 20, 85 +/- 31 and after verap amil administration: 58 +/- 13, 60 +/- 17 and 73 +/- 15, respectively. Relaxation time constants of ENDO and EPI were significantly longer t han those of LVP during control and volume loading but not after verap amil when only EPI was significantly different from LVP. These results demonstrate that relaxation indices obtained from LVP may not always reflect intramyocardial mechanics.