The Heart as a Generator of Pressure

Abstract

While traversing the heart loop, the flow of blood undergoes a complete reversal in direction and encounters significant resistance as it passes through the spongy endomyocardial trabeculations. Additionally, the blood flow is subject to rhythmical interruption by the contracting heart, giving rise to upsurge and dissipation of pressure. Taken together, the morphologic and hemodynamic phenomena suggest that the heart, rather than being the source of flow, is an organ of flow restraint. It rhythmically interrupts flow and generates pressure in the arterial limb of the circuit. Of the total power produced by the ventricle, about 75% is expended on maintaining of pressure, and the balance is used for pulsatile filling of the arterial bed. This ratio appears to be tightly controlled and is preserved during perturbations of flow and volume. Partial ligation of the conotruncus (aortic inlet) in chick embryo causes a marked increase in systolic pressures, results in hyperplasia of the cardiomyocytes, and promotes spiral trabeculation of the myocardium. There is no change in the cardiac output. Occlusion of the vitelline artery results in decrease in stroke volume and aortic flow but not in change of pressure.