Blood Pressure during Supine Exercise in Idiopathic Orthostatic Hypotension

The arterial blood pressure was measured during exercise in six patients with idiopathic orthostatic hypotension. In five there was a pronounced fall of arterial pressure while the subjects exercised in the supine position on a horizontal table. The systolic and diastolic pressures fell by an average of 50 and 32 mm. of mercury, respectively. During comparable exercise with the table tilted 15 degrees head downward, the pressures fell to a similar degree. Thus, an abnormal response of blood pressure occurred under conditions in which venous pooling was unlikely to be present. It is suggested that the fall in blood pressure during exercise in the supine position was the result of failure of compensatory constriction of other vascular beds and not of failure of the cardiac output to increase. Thus, the net peripheral resistance in such patients is less than that in normal persons performing comparable exercise.