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.
Effect of Acetylcholine on Pulmonary Vascular Resistance in a Patient with Idiopathic Pulmonary Hypertension
Necropsy studies in cases of pulmonary hypertension of unknown cause show structural changes in the pulmonary vessels that are called irreversible. Acetylcholine chloride was infused at a rate of 2 mg. per minute into the outflow tract of the right ventricle of a 48-year-old woman who had pulmonary hypertension. The mean pulmonary artery pressure decreased from 56 to 25 mm. Hg and the pulmonary flow increased slightly. These findings are consistent with the theory that so-called idiopathic pulmonary hypertension may at some stage be maintained by vasoconstriction.