Orthostatic Disorders of Blood Pressure Control: Pathogenesis

Abstract

During a change from the lying to the standing position, gravitational forces would cause rapid accumulation of blood in the dependent parts of the body were it not for the constriction of arterioles and capacitance vessels that normally takes place almost instantaneously. Arteriolar constriction is essential for orthostatic maintenance of the diastolic blood pressure, whereas venous and venular constriction is required for the uninterrupted return of blood from the lower parts of the body to the heart, so that stroke volume continues to be adequate to maintain the systolic blood pressure at normal levels. Since increased activity of the sympathetic nervous system is the prime stimulus for constriction of the peripheral vessels, it follows that deficient catecholamine action at these vascular sites is the most important potential mechanism of orthostatic diastolic hypotension.