Changes in dimensions of the ventricular chambers and the displacement of specific points on the wulls of the heart have been studied by the cinefluorographic technic. The contributions of the various myocardial layers to ventricular ejection have been considered in terms of the anatomic architecture of the heart. The mechanical effectiveness of myocardial contraction is closely related to the degree of diastolic distension and the magnitude of the stroke volume. During contraction, the various layers must exert tension on the connections between them. Energy expended in this manner does not contribute to ventricular ejection but could theoretically promote rapid filling (luring the early diastolic period. P REVIOUS investigations1 " 4 have indicated that the two ventricles have different functional and anatomic characteristics. Ventricular contraction cannot be visualized as though the two ventricles were a single unit. The mechanical effectiveness of the various layers of myocardial fibers depends in part upon their anatomic location and orientation within the ventricular walls.2 Information of this sort cannot be obtained from cardiometer records which indicate the combined effects of the musculature of the two ventricles. Further, ITaycraft 5 has clearly shown that movements of the ventricular walls must be studied with the thorax intact.This report deals with an analysis of the factors which influence the mechanical effectiveness of myocardial contraction in terms of the anatomic architecture of the heart. METHODSWhile cinefluorographic angiocardiography has proved valuable in studying absolute and relative changes in the dimensions of hearts during the cardiac cycle, 2 it had serious limitations for the_ proposed investigation. For example, the movements of specific points on the ventricular wall could not be observed. The rapid injection of radio-opaque From the Department of Physiology and Biophysics, University of Washington, School of Medicine, Seattle, Wash.This investigation was supported, in part, by a research grant from the National Heart Institute of the National Institutes of Health, Public Health Service.Received for publication Oct. 27, 1952. substances produced abnormal conditions within the circulation. The cardiac chambers could be observed only for very brief intervals during which they were outlined by the contrast media. Reliable measurements of the right ventricular cavity were rarely obtained because the septal border of the chamber was rarely visible. 1 ' 2 Another method of measuring changes in size and position of the heart has therefore been developed. 4 Stainless steel wire (3 mm. in diameter) was cut into segments approximately 0.5 to 1.0 cm. long. A shallow groove was filed around the midpoint of each pin. Pairs of these pins were connected by short lengths of very fine rubber fibers covered by windings of linen thread. The metal markers were lined up within the lumen of a stainless steel tube fitted with a stylus by which the pins could be individually ejected from the tube...
Cinefluorographic angiocardiography has been used to record the sequential changes in the size and shape of the right and left ventricular chambers and the external cardiac silhouette in dogs. Evidence is presented which indicates that (1) the left ventricle is usually filled more rapidly than it is emptied, (2) the diastolic size appears to remain remarkably constant during a major portion of the diastolic period and (3) residual blood remains within the ventricle at the end of systole.C YCLIC changes in the size of the ventricles, the essential feature of cardiac function, have been widely studied by a variety of methods: (1) direct volumetric measurements by the plethysmographic technic, (2) analysis of arterial pulse waves, (3) roentgenkymography, (4) electrokymography and (5) indirect information concerning changes in stroke volume, gained from cardiac output determination by the Fick principle or ballistocardiography. The length of this list emphasizes the importance of information concerning the mechanism of ventricular contraction, and each method has certain advantages. Motion pictures of fluoroscopic images during angiocardiography present a combination of advantages not available in other methods. The size and the shape of the heart and of the individual chambers can be observed and measured during multiple cardiac cycles in the intact experimental animal. The presence of residual blood is readily detected in the ventricle. The sequence of events in the great vessels and heart can be related. Two disadvantages of this method are recognized: (1) the recorded images represent a two dimensional projection of the cavities, (2) rapid injection of radiopaque materials imposes an unusual load on the heart and circulation.
Changes in length and circumference of the left ventricle were recorded simultaneously by variable resistance gages on its external surface in intact dogs. The absolute changes in circumference were considerably greater than the changes in length, but the relative changes in these dimensions were similar (averaging around 2 to 3 per cent). Under most circumstances, the length and circumference vary in the same direction but occasionally inexplicable differences in response were observed.
Left ventricular dimensions have been directly measured for extended periods of time in intact unanesthetized dogs under various conditions. The diameter of the left ventricle during diastole is very large in relation to the change in diameter during each cycle. Thus, considerable quantities of blood remain within the chamber at the end of systolic ejection. The stroke output can be increased by either more complete systolic ejection during exercise or by greater diastolic filling during a startle reaction. Accelerated heart rate occurs in both cases. Changes in left ventricular diameter occur very rapidly, often being manifest within the duration of a single cardiac cycle. Mechanisms by which changes in ventricular size can be directly affected by neural and hormonal influences are briefly considered.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.