"Pressure-volume" relations in isolated cat trabecula.

We studied isolated cat trabecula under conditions closely resembling those present for muscle fibers in the left ventricular wall. The purpose of the study was to see if muscle contraction under those circumstances could be described by a time-varying compliance as reported for intact canine left ventricle. We found the time of the end of systole to depend on the history of contraction. This time varied between 100 and 160 msec as measured from the onset of contraction. Similar dependency, although less percentage-wise, was found by reanalysis for intact feline left ventricles. We conclude that the behavior of the canine left ventricle as a time-varying compliance may be related to the complex organization of the cardiac muscle fibers in the wall of the heart rather than to muscle properties.