Pulse Pressure, Its Probable Relationship to Stroke Volume.

Abstract

Numerous investigators have shown that in hyperthyroidism the tachycardia varies in degree directly with the metabolic rate. It seems reasonable to suppose that this increased heart rate is an adaptation for increasing the cardiac minute volume, since the minute volume is known to be increased in this condition. Previously I have pointed out that the pulse pressure also varies directly with metabolism. In Table I are shown the values obtained in 1000 observations of the pulse rate, blood pressure and metabolic rate made simultaneously under basal conditions. It will be observed that the rise in pulse pressure with increasing b.m.r. is due to rise in systolic pressure, since the diastolic pressure remains practically constant. The pulse rate and pulse pressure both increase in a parallel manner with elevation of the basal metabolic rate. When gathering these data it was observed that some subjects showed a disproportionate increase in either pulse rate or pulse pressure, with little or no change in the other. This suggested that some subjects might increase the minute volume by increasing the rate of output per minute, while others accomplished the same increase in total blood flow by increasing the volume ejected into the aorta at each systole. Pulse pressure might then be a rough measure of stroke volume. Recently there came under observation two individuals with complete heart block, as shown by electrocardiogram, neither of whom stiffered limitation of activity imposed by circulatory insufficiency. One was a woman, 47 years old whose slow pulse had excited interest since girlhood. P. R. 36-44, blood pressure, systolic 180, diastolic 80. The other was a man, 70 years old. P. R. 28-38. Systolic pressure, 200-210; diastolic, 70-100. Neither had aortic insufficiency.