RELATION OF BLOOD-VOLUME AND BLOOD-PRESSURE IN ORTHOSTATIC INTOLERANCE

A complex but crucial relationship exists between blood volume and blo od pressure in human subjects; it has been recognized that in essentia l hypertension, renovascular hypertension, and pheochromocytoma, the r elationship between plasma volume and diastolic blood pressure is an i nverse one, This phenomenon has not been studied in individuals with l ow normal and reduced blood pressures. Orthostatic intolerance is a co mmonly encountered abnormality in blood pressure regulation often asso ciated with tachycardia in the standing position. Most of these patien ts have varying degrees of reduced blood volume, We tested the hypothe sis that the relationship previously found between plasma volume and d iastolic blood pressure in presser states would also hold in orthostat ic intolerance, We studied 16 patients with a history of symptomatic o rthostatic intolerance associated with an elevation in plasma norepine phrine in the upright posture and hypovolemia in 9 patients and normov olemia in 7 patients. Our studies demonstrate an inverse relationship between plasma volume and diastolic blood pressure in patients with or thostatic intolerance. This finding also holds for the change in diast olic blood pressure in response to upright posture, In this relationsh ip, patients with orthostatic intolerance with high plasma norepinephr ine resemble those with essential hypertension, renovascular hypertens ion, and pheochromocytoma. We conclude that in a variety of conditions at both ends of the blood pressure spectrum, the seemingly paradoxica l association of hypovolemia and diastolic blood pressure is preserved .