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...
Pressure within the microvascular bed of the frog mesentery has been recorded continuously with micropressure transducers which have tip diameters ranging between 0.5–5 µ. The mean values of pressure are in the range of those previously reported. The waveform of the pressure pulses in arterioles and metarterioles closely resembles that in the larger arteries. This observation signifies that the vascular walls are considerably stiffer than is generally believed. The stiffness is probably attributable to the constricted vascular smooth muscle.
The initial phase of ventricular systole has been termed the phase of isometric contraction because all the cardiac valves are closed while the pressure is rapidly elevated. Cyclic changes in the dimensions of the left ventricle, recorded by gauges applied directly to the ventricular walls have consistently exhibited an abrupt expansion of the internal diameter, external circumference and external length of the chamber at the onset of systole. Apparently the longitudinal axis of the chamber is abruptly shortened by early contraction of papillary muscles and trabeculae carnae. The lateral walls bulge outward so that the chamber assumes a more spherical configuration as the internal pressure rises. It is doubtful that any of the myocardial fibers actually contract without a change in length, and the term "isometric contraction" is not appropriate for this phase. The initial stage of ventricular systole is actually a period of asynchronous contraction or sphericalization.
The Doppler shift of ultrasound, scattered from moving elements within a stream of blood, is related to the velocity of blood flow. A flowmeter based on this principle has been constructed and was used to record blood flow through intact vessels in dogs.
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