EFFECT OF RESIDUAL-STRESS ON TRANSMURAL SARCOMERE-LENGTH DISTRIBUTIONS IN RAT LEFT-VENTRICLE

It has been previously shown that the myocardium in the walls of the u nloaded passive left ventricle (LV) is not stress free. To assess the functional significance of residual stress in the ventricular wall, we compared the transmural distributions of sarcomere length (SL) in spe cimens of rat LV myocardium fixed in the unloaded (residually stressed ) and stress-free states. When a cross-sectional ring cut from the equ atorial region of the freshly arrested rat hearts was cut radially to relieve residual stress, it sprang open into an arc with a mean openin g angle of 45 +/- 15-degrees (SD) (n = 8). During immersion fixation i n glutaraldehyde, the opening angle increased 9.3 +/- 7.1-degrees (SD) overall. SLs were measured at 16 equally spaced transmural locations from the free wall in the stress-free tissue sections and were compare d with control measurements from adjacent cross-sectional rings in whi ch residual stress had not been relieved. Average SL for the stress-fr ee tissue (n = 11) was 1.84 +/- 0.05 (SD) mum and for the unloaded tis sue was 1.83 +/- 0.06 (SD) mum. However, analysis of covariance on the pooled data showed that the transmural distributions were significant ly different (P < 0.0001). Whereas SL was uniform across the wall in t he stress-free state with a mean gradient of -0.014 +/- 0.044 (SD) mum /total wall thickness, there was a significant decrease (P = 0.001) in SL from epicardium to endocardium in the intact unloaded tissue [slop e = -0.114 +/- 0.054 (SD) mum/total wall thickness]. This gradient may offset the opposite gradient in sarcomere extension during filling th us leading to a more uniform transmural distribution of SL at end dias tole and hence more uniform development of systolic force.