Orthostatic hypotension is characterized chiefly by a sharp decrease in blood pressure when a patient afflicted with it stands. The blood pressure is ordinarily normal when the patient lies. If the blood pressure decreases to a low level, weakness and syncope result. Other relevant signs or symptoms are deficient sweating, either localized or generalized, secretion of larger amounts of urine when the patient is recumbent than when he is erect and in some cases a failure of the pulse rate to increase markedly when the patient assumes the erect posture. Orthostatic hypotension should be suspected whenever a patient has exhaustion in the morning which lessens during the day, whenever weakness, dimness of vision or syncope occurs on assumption of the erect posture and disappears on lying down, whenever episodes of syncope are inadequately explained and whenever there is diminished sweating. This condition has been considered by some to be the result of failure of adequate constriction of arterioles when patients stand.1 The failure of the arterioles in turn has been assumed to result from a defect in the auto¬ nomie nervous system. This concept has been based on logical interpretations of clinical data: 1. Exten¬ sive sympathectomy in cases of essential hypertension results in a diminution of arteriolar tone which has seemed to explain the orthostatic hypotension which ordinarily results from extensive sympathectomy. 2. Drugs which increase arteriolar tone dramatically relieve the orthostatic symptoms and markedly improve the blood pressure in the erect posture.2 The natural assumption followed that it is deficiency in arteriolar resistance which results in the low blood pressure when the patient stands. 3. The disturbances in sweating frequently found in cases of orthostatic hypotension have appeared to demonstrate a primary disturbance in the autonomie nervous system.1 Hypofunction of this cholinergic part of the autonomie nervous system seemed an index of a similar disturbance in the adrenergic portion of the autonomie nervous system which resulted in a loss of arteriolar tone.Recent studies, which we are not presenting in detail in this paper, suggest that the defect in postural adap¬ tation is not a defect in arteriolar vasoconstriction but rather one in the maintenance of adequate return of venous blood to the heart. The evidence in brief may be summarized as follows : 1. Weiss and his associates have shown that circulatory collapse may be induced by the erect posture when normal subjects are given appropriate amounts of sodium nitrite.3 Syncope produced by this artificial method appears to be the result of the loss of venous tone and the pooling of blood in the dependent portions of the body and closely resembles the syncope observed in cases of orthostatic hypotension. 2. We have been able to demonstrate a deficient "potential" in the venous return to the heart in all cases of orthostatic hypoten¬ sion which we have studied by the Flack test, which consists in having the patient blow against the column of mer...

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