Effect of position of body on the length of systole and diastole and rate of pulse in man

There is need of a practical method of determining the condition of the heart muscle in man. The contraction period of other muscles is lengthened if they are fatigued or degenerated, and this may be true of heart muscle. An accurate determination of the length of systole might be of use, provided its normal relationship to the heart rate and the ordinary variations were known. At the Minneapolis meeting of the American Physiological Society December 28, 1917, the writers reported that they had studied the length of systole and diastole in man, by recording the carotid pulse and measuring the systole from the beginning of the upstroke to the dicrotic notch. The subjects were 20 normal men, and 1,600 cycles were measured. A curve in which the average duration of systole and of diastole were plotted in relation to pulse gave a striking picture of the shortening of systole and diastole by increasing heart rate. The great variation in the length of systole and diastole which may occur within a single minute was emphasized. Both are affected by respiration, and diastole, at least, by vaso-motor influences. It can now be definitely stated that the changes in the length of the systole and the diastole observed in succeeding cycles have no constant relation to each other, and therefore are probably brought about in different ways. The special object of this communication is to attract attention to the great difference in the average length of systoles and diastoles caused by a change in the position of the human body. It has been found that, in sitting the systoles average by pulse rates from 50-95.9 per cent. longer than in standing, and in lying down 17 per cent. longer than in standing.