Postural (orthostatic) hypotension is a symptom or sign, not a disease. A slight fall in systolic and diastolic blood pressure occurs in some people when they stand up from the recumbent position.1 The common symptoms of postural hypotension are faintness, dizziness and generalised weakness. In the ill, the elderly and those who have been confined to bed or have cardiovascular disease the symptoms may progress to a blackout of vision and loss of consciousness. In the normal person a fall in blood pressure on standing is prevented by a reflex increase in arterial resistance and in venous tone which prevents pooling of blood. Postural hypotension ensues if these compensatory responses are prevented. In patients with loss of sympathetic tone the horizontal posture causes a marked sodium diuresis because the pressure-sensitive site in the kidney which regulates sodium excretion is left unprotected when the afferent arteriole loses its sympathetic control.2 If a patient has been lying in bed for some time, postural hypotension will occur when he gets up.
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