Tsakiris, Anastasios G.

Multiple measurements of left ventricular volumes, ejection fractions, and circulatory pressures were made under conditions of varied outflow resistance in five intact anesthetized dogs by using a biplane videoangiographic recording system which displays simultaneously two roentgen images on the same television screen, records the images on video tape, and requires low radiation levels and small amounts of contrast medium. Aortic pressure was controlled by intra-aortic infusion of angiotensin or acetylcholine. With spontaneous sinus rhythm and normal aortic pressure, end-diastolic volume averaged 35 ml (2.3 ml/kg), and ejection fraction averaged 47% of end-diastolic volume. When aortic pressure was increased, average end-diastolic volumes increased to 53 ml and ejection fractions decreased to 29%. Conversely, when aortic pressure was decreased, average ejection fraction increased to 73%, although changes in stroke volume were usually not large under these conditions. Concomitant large changes in the shape of the left ventricular cavity were also observed. Similar changes were observed when heart rate was maintained constant by electrical pacing of the atria and ventricles with a constant atrial-ventricular stimulus interval. The variability in left ventricular volume and ejection fraction observed in the same animal during different circulatory states may account in part for the differences in values for these variables reported by different investigators.

Intrapericardial pressures were recorded via a saline-filled Teflon catheter (o. d., 1.3 mm) in 11 anesthetized dogs studied without thoracotomy. Seven animals were studied before, during, and after 1-min exposures to transverse accelerations that ranged from 1G (normal gravitational environment) to 7G when in the supine (+G j ), prone (-G x ), left decubitus (+G v ), and right decubitus (-G y ) positions. Four additional animals were studied at 1G only, while in these same body positions. Pressures also were recorded from both atria, right ventricle, aorta, esophagus, and the potential pleural space. Mean end-expiratory intrapericardial pressure varied directly with the vertical height of the recording site in the thorax during all conditions studied, as would be expected in a hydrostatic system. Transpericardial pressures were not significantly different from zero at all levels of acceleration studied. Transmural left and right atrial pressures were independent of the height of the recording site in the thorax and were unchanged during exposures to transverse accelerations that ranged from plus to minus 7G x .

The effect of the mitral Starr-Edwards ball-valve prosthesis on cardiac function was investigated in the dog. Fifteen dogs were studied for the first 48 hours after replacement of the mitral valve (the chordae tendineae [see Figure in the PDF file] had been totally resected, partially resected, or preserved). The cardiac output and left atrial pressure were similar in these three groups of animals and in two animals subjected to sham operation. Ten dogs (five with intact chordae and five with excised chordae) were studied two months after the insertion of a Starr-Edwards prosthesis. In these animals normal hemodynamic values were obtained at rest and during infusion of acetylcholine, except for a marked (liastolic gradient across the prosthesis, which developed at high cardiac output and heart rate. Six dogs were able to complete a standard test of substantial, unrestrained, graded exercise and gave a normal heart rate response. Heart rate increased and was maintained during maximal efforts, to levels of about 300 beats/min, demonstrating that heart rate need not be a limit of cardiac performance. No evidence of left ventricular dysfunction or of a decrement in cardiac performance could be demonstrated in dogs early or late after replacement of the mitral valve with a Starr-Edwards prosthesis. The presence or absence of chordae tendineae was irrelevant to cardiac performance.