orthostaticorthostatic(posturai)hyotension: The gravitational stress of sudden standing normally causes pooling of blood in the venous capacitance vessels of the legs and trunk the subsequent transient decrease in venous return and cardiac output results in reduced BP and can cause the individual to faint. Baroreceptors in the aortic arch and carotid bodies sense the change in BP and activate autonomic reflexes the rapidly nomailze BP by causing a transient tachycahycardia and vasoconstrition in the lower limbs Agents that interfere with this reflex response can cause orthostatic (postural) hypotension ie.alpha-blockers ganglinic blockers and guanethidine