THE RÔLE PLAYED BY THE VENTRICULAR RELAXATION PROCESS IN FILLING THE VENTRICLE

Abstract

Experiments were made on the isolated turtle ventricle connected to a reservoir, which tended to keep the pressure of the system constant, in order to see what role ventricular relaxation played in filling the heart chamber. It was found that during relaxation the pressure within the ventricle dropped below the zero level of the system. The amount of this drop was a direct function of the initial length of the muscle in the range studied. The drop in pressure was not due to an overawing, for when filling was prevented at the onset of relaxation by making relaxation isometric, the pressure drop below the zero level of the system was magnified. Other considerations are discussed which also disprove that it is an artefact. The minimum elastic state of the ventricle can be expressed by a smooth curve, along which the pressure/volume ratios of the relaxed heart fall, regardless of whether the diastolic volume or the diastolic pressure is set. The drop of pressure during relaxation below that set by the reservoir is taken as evidence that the ventricle is drawing in fluid. These experiments are not contradicted by those on skeletal muscle suspended on Hg. The sources of energy for the sucking action are mainly potential stores, created by the contraction process, such as energy of position and of elastic state. The distinction is made between the source of energy for the sucking action and for the flow of fluid. The distinction is shown to be the same as in an aspirating pump. The conclusion is drawn that relaxation is of similar nature to contraction. Both are dependent on some reversible physico-chemical process which alters the elastic state of the muscle between 2 limits, the minimum for the relaxed and the maximum for the contracted heart. Evidence is given to show that the ventricle not only can but does exert a sucking action in the intact mammal.