Studies on Cardiac Dimensions in Intact, Unanesthetized Man

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Abstract
A method is described which permits measurement of relative changes in the external dimensions of individual cardiac chambers throughout the cardiac cycle in intact, unanesthetized man. It consists of suturing multiple radiopaque silver-tantalum clips to the surface of the heart at the time of cardiac operations. In the postoperative period, cine-radiograms are obtained and the distances between clips are measured on each individual frame. This technique has been found to be safe and has been employed in 68 patients without any complications. As a result of studies in eight patients utilizing biplane serial exposures, the effects of rotation of the heart in the sagittal plane during the cardiac and respiratory cycles were determined precisely. If clips were properly placed on the heart, the possible errors resulting from such rotation were found to be quite small. During inspiration right ventricular dimensions increased, while the opposite occurred during expiration and during the Valsalva maneuver. Left ventricular dimensions exhibited little change during normal respiration. During deep, slow inspiration, the changes in dimensions of the left ventricle lagged behind those of the right ventricle by one to five (generally two or three) cardiac cycles; the magnitude of the changes in the dimensions of the left ventricle was smaller than that which occurred in the right ventricle. The effects on ventricular dimensions of light muscular exercise performed in the supine position were studied in nine patients. The end-diastolic dimensions decreased by an average of 6.0% of control in the right ventricle, and by an average of 5.1% in the left ventricle. End-systolic dimensions decreased by an average of 5.6% of control in the right ventricle and by an average of 6.5% in the left ventricle. These decreases are considered to approximate one-half of the resting stroke volume. In the four patients in whom the rate of right ventricular pressure rise was determined continuously, exercise resulted in an elevation of dp/dt while ventricular end-diastolic dimensions decreased. These data are interpreted to indicate that an increase in myocardial contractility occurs during muscular exercise in man.