Work of the Left Ventricle in Normal,Hypertension and Arteriosclerosis.

Abstract

It is very probable that increased work of any chamber of the heart is followed after some time by hypertrophy and dilation of that chamber. It is of interest to know the exact increase in work for the left ventricle of the heart in hypertension and in generalized arteriosclerosis.

The work of the left ventricle per beat is represented by the equation:

where P is the pressure of the blood in the aorta, P₁ the diastolic and P₂ the systolic pressures, respectively; V the volume of the arterial system, corresponding to the pressure P, and dV an infinitesimal change in the volume when a small amount of blood is ejected from the left ventricle and the pressure increased by the amount dP. S is the stroke volume, v the velocity of the blood in the aorta and g the constant of gravity. The second term may be neglected in our problem because it makes up only 1 or 2 per cent of the work of the left ventricle and is constant for equal stroke volumes and velocities in the aorta.

If we can find the relation between P and V we can integrate the first term of the work equation and can thus find the work of the left ventricle per beat. Bramwell, Downing and Hill 1 have determined the relation between the volume and pressure in the “mean normal” artery of man. The curve, Fig. 1, is a reproduction of their curve of this relation. If we assume that in the “normal” person the diastolic Mood pressure is 80 and the systolic 120, then, according to this curve, the corresponding change in volume when the pressure rises from the diastolic to the systolic is 80 cc.