Chronic hypotension. In the shadow of hypertension

Understanding the causes and treatment of chronic hypotension is of benefit to affected patients and may also shed light on the physiology and genetics of mechanisms of blood pressure control. Symptomatic hypotension (almost always with a blood pressure fall greater than or equal to 20/10 mm Hg) may reflect unrecognized medication effects or a variety of other causes. Autonomic neuropathies include those secondary to diabetes, peripheral autonomic impairment (the Bradbury-Eggleston syndrome), central autonomic impairment (the Shy-Drager syndrome), or newly described gene defects such as dopamine-beta-hydroxylase deficiency (which causes the absence of norepinephrine with an accumulation of dopamine). Baroreceptor dysfunction causes wide swings in blood pressure that are unrelated to posture, whereas a variety of stimuli (cough, micturition, or carotid sinus pressure) may precipitate paroxysmal parasympathetic activation, and sympathetic orthostatic hypotension associated with hypovolemia may occur with mitral valve prolapse or as an idiopathic condition. The differentiation of these and other causes of symptomatic hypotension may in many cases lead to beneficial therapy.