Influence of the velocity of changes in end-diastolic volume on the starling mechanism of isolated left ventricles

Abstract

1. In this study the relationships between active developed systolic pressure, end-diastolic pressure and different diastolic volumes are studied in Tyrode perfused isolated rabbit left ventricles. Contractions were isovolumic. 2. Rapid diastolic volume changes were imposed on top of different preset basic diastolic volumes. These volume changes are shown to produce systolic and diastolic pressure values that cannot be explained by assuming a single pressure-volume relation during systole and diastole. The changes in pressure are in the same direction but higher than is expected on the basis of the increase or decrease of the ventricular end-diastolic volume alone. 3. The variation of the diastolic pressure-volume relation cannot be explained by assuming variations of the heart's passive elasticity or viscous effects within its wall. During diastole the effect is completely reversible without concomitant systolic effects. No velocity dependent effect of the quick volume change could be observed if the time duration was varied between 10 and 65 ms. The results are in keeping with the hypothesis that active force generating mechanisms may be present during the diastolic pause. 4. The effects observed during systole suggest the possibility of length dependent activation of the myocardial cells. This results in different inotropic conditions of the heart at identical volumes, depending on how these volumes were installed. These volumes may be considered to affect intrinsic properties of the muscle cells on a beat to beat basis.

The effect of controlled changes in volume on the active state of the rabbit isolated left ventricle

“…The heart was filled at the same pressures as used for the EDP values of protocol I. The ventricular volume at each pressure value was measured by sucking out the fluid from the ventricle (2,16,18). The passive diastolic volumes so obtained were used in the analysis of the results of protocol I.…”

“…The procedure is described elsewhere (16,18). Rabbits of about 2.5 kg were anesthetized with sodium pentobarbital, injected intravenously (30 mg/kg).…”

“…Length changes alter the contractile activation of cardiac muscle (1,3,8,9,14,20,30) so that ventricular volume changes produced in systole as well as in diastole affect the pressure generation during the remainder of the cardiac cycle (16,17,18,25). Therefore, differences in isovolumic pressure generation throughout the activation pcriod should be quantified in order to study these activation changes fully.…”

The step response of left ventricular pressure to ejection flow: A system oriented approach

“…In contrast, after increasing afterload, the opposite occurred (8,31,84). These findings were confusing since, for instance, preload, either to heart muscle (38,44), or to the intact ventricle (61,84), as well as afterload (84), were found to enhance the contractile state. The results of the present study suggest how at least parts of this seeming contradiction can be resolved.…”

“…The first term 61 "O" H~(t) = e--- where * denotes convolution over the time interval from t I to t. H2 is unequal to zero only when 6 2 ~ e 1 . As will be shown in results, this is the case for ~2 ( t~l" Equa- 2 are at the same pressure value, which is lower than isovolumic pressure.…”