ON THE DURATION OF THE ISOVOLUMETRIC RELAXATION PERIOD (IVRP) IN DOG AND MAN.

Abstract The isovolumetric relaxation period (IVRP) was studied in 13 normal, anesthetized dogs and in 30 human subjects without hemodynamically significant abnormalities. In dogs, this period was measured for the left heart from the aortic component of the second sound to the crossing of left atrial and ventricular pressure curves. A correlation between this period and the heart rate was made. In human subjects, this period was measured on catheterization of the right side of the heart in 14 cases, on catheterization of the left side of the heart in 5 cases, and on catheterization of both the right and left sides in 9 cases. Measurements were made from the incisura of the pulmonary artery or aorta, respectively, and crossing of atrial and ventricular pressures of the respective side. In dogs, the IVRP increased when passing from severe tachycardia to normal rate. On the contrary, a trend toward decrease was noted in bradycardia. The averages varied from 37 to 74.3 msec. In human subjects the IVRP of the left heart was longer than that of the right heart in 7 cases, and shorter in 2 cases. No difference was found in the various age groups, and no correlation with heart rate, possibly because the rates varied within a limited range. In human subjects the average duration of the IVRP of the left heart was 81.6 msec., with a maximum of 120 and a minimum of 55. For the right heart, the average was 49.2, the maximum, 11.5, and the minimum, 35. Even though the IVRP of the right heart is shorter than that of the left, pulmonary incisura follows aortic incisura. Thus, the openings of the tricuspid and mitral valves may be simultaneous.