Hemodynamics of Prehypertension and Hypertension

Abstract

Blood pressure is a product of cardiac output and vascular resistance. In turn the cardiac output depends on the stroke volume and the heart rate. The vascular resistance, for all practical purposes, depends only on the diameter of the resistance vessels, whereas such factors as blood viscosity and length of the vascular system do not play a determinant role in human physiology. A simplified scheme of the very complex situation is given in Fig. 1. It can be seen that the output and resistance are influenced by numerous factors and that many of these fatcors are regulated by two main homeostatic systems; the kidneys and the autonomic nervous systems. These two systems are interrelated. Sympathetic innervation changes the renal blood flow and consequently the renal excretory function. The release of renin from kidneys is under strong sympathetic influence[1] and a specific blood flow independent β-receptor may be responsible for this [2] ? The renin-angiotensine system in turn controls the aldosterone secretion from adrenals so that both the kidneys and the autonomic nervous system relate to a hormone which is crucial for the sodium and water balance.