Figure 1.

Changes in cardiac output and renal function in hypertension. (A) Relationship between cardiac output (liters/min) and age (yr) in 110 male individuals diagnosed with essential hypertension. Measurements were taken while subjects were at rest in a seated position, from Fagard and Staessen (1991). (B) Guytonian pressure–natriuresis curve relationship. Normotensive individuals undergo a brisk diuresis, excretion of sodium and water, in response to elevations in blood volume and blood pressure, allowing for maintenance of a normal mean arterial pressure. In order for sustainment of hypertension, this curve must be shifted. The shifting of the curve results from changes that occur within the kidney that decrease its capacity to excrete sodium and water. Thus, the mean arterial pressure over which sodium and water are excreted increases to compensate for these deficits in kidney function.