Essex, Hiram E.

Curves that relate the amplitude of the first heart sound to the P-Q interval have been obtained in 13 dogs with complete atrioventricular (AV) heart block. The amplitude was highest at a P-Q interval of approximately 0.05 second, became lowest at a P-Q interval of 0.13 second and continued low for intervals up to 0.25 second or longer and then increased again to some extent with further prolongation of the P-Q interval. Cardiac failure or infusions into peripheral or pulmonary veins caused an earlier and higher rise of the amplitude with very long P-Q intervals, whereas exsanguination had the opposite effect. These factors probably alter reopening of the AV valves during atrial diastole and thereby change the intensity of the first heart sound.

Measurements of the left atrial and ventricular pressure pulse in dogs with complete atrioventricular (AV) heart block revealed positive and negative differences in pressure across the mitral valve which were associated with high and low amplitudes of the first heart sound, respectively. Congestive heart failure, infusions and bleeding altered the duration of the negative difference in pressure and the amplitude of the first heart sound during atrial diastole. High and low amplitudes of the first heart sound are coincident with the opened and closed AV valves, respectively. The position of the valve leaflets at the onset of ventricular excitation seems to affect the rise of the ventricular pressure.

Circulation through the heart of the turtle ( Chelydra serpentina) was studied by means of simultaneous recordings of oxygen saturation, blood-saturation dye curves and pressure measurements in the cardiac chambers and arteries leaving the heart. The saturation levels of the blood leaving the heart via the right and left aortas are the same while pulmonary artery blood is distinctly more venous. Resection of the septal mechanism resulted in oxygen saturations of similar value in all vessels leaving the heart. The dye curves showed that less than 10% of the blood of the turtle may pass from right to left but a much larger volume of blood passes from left to right. The findings in the turtle heart resemble those found in human patients with congenital ventricular septal defects. Blood pressure patterns in the carotid, subclavian arteries and the two aortas are very similar. Systolic pressures in the aortas and pulmonary artery are the same, but diastolic pressure in the pulmonary artery is distinctly lower than in the aortas.