An isolated increase in preload does not influence the time course of isovolumetric relaxation when systolic pressure is held constant.
Does an isolated increase in preload affect the time course of isovolumetric relaxation in cardiac muscle?
This preclinical study demonstrates that an isolated increase in preload does not alter the intrinsic time course of myocardial isovolumetric relaxation provided the total load remains constant.
p-value: p=NS
We studied the effect of an isolated increase in preload on isovolumetric relaxation in the intact dog heart and isometric relaxation in isolated cardiac muscle (dog and rat) preparations. In eight anesthetized dogs, 8 to 12 ml of blood was infused into the left ventricle during a single diastole. The exponential time constant (T) of isovolumetric relaxation was measured in single-beat experiments in which the left ventricular systolic pressure increased (112 +/- 2 to 128 +/- 3 mm Hg; p less than .05, n = 62). In a second series of experiments, left ventricular systolic pressure was held constant (109 +/- 2 to 107 +/- 2 mm Hg; p = NS, n = 23) by simultaneous ventricular infusion and aortic unloading. In the first protocol, T increased from 28.0 +/- 0.4 to 30.7 +/- 0.4 msec (p less than .05), whereas in the second protocol (constant systolic pressure) there was no change in T. The time course of isometric relaxation was also studied in six rat left ventricular papillary muscles and four dog right ventricular trabecular muscles. Preload was varied from 30% to 100% of the peak of the isometric length-tension curve in each muscle. Over this wide range of preload, the isometric force decline recordings were superimposable as long as the comparisons were made at equal levels of total load. Thus an isolated increase in preload does not influence the time course of isovolumetric relaxation.
Gaasch et al. (Thu,) conducted a other in Normal cardiac physiology (n=18). Isolated increase in preload vs. Baseline / constant systolic pressure was evaluated on Exponential time constant (T) of isovolumetric relaxation (p=NS). An isolated increase in preload does not influence the time course of isovolumetric relaxation when systolic pressure is held constant.