Circulatory volume in essential hypertension. Relationships with age, blood pressure, exchangeable sodium, renin, aldosterone and catecholamines.

The circulatory volume and exchangeable sodium were measured in 110 normal subjects and 120 patients with benign untreated essential hypertension. The two study groups did not differ in age, sodium and potassium metabolism, and plasma levels of renin, aldosterone and norepinephrine, while plasma epinephrine was slightly higher in essential hypertension. Total plasma and blood volume correlated with total exchangeable sodium (r = 0.64-0.75; p less than 0.001); these correlations were similar in normal and hypertensive subjects. Body surface area was found to be the most appropriate frame of reference for judging individual values of plasma and blood volume or exchangeable sodium; using this approach these body constituents were on average normal in the hypertensive population. Blood volume was unrelated to age or blood pressure in normal and hypertensive subjects. Exchangeable sodium tended to increase with age (r = 0.25; p less than 0.02) and correlated positively with blood pressure (r = 0.25; p less than 0.02) in essential hypertension but not in normal subjects. The latter body constituent was slightly but significantly decreased in hypertensive males aged less than 35 years as compared with appropriate normal controls (96.1 +/- 6.8% versus 99.6 +/- 6.7%; p less than 0.05). These findings confirm that blood volume and exchangeable sodium are on average normal in patients with benign essential hypertension. Body sodium may even be decreased in certain young hypertensive patients. These observations do not support the concept that hypervolemia may represent the initial event leading to high blood pressure in essential hypertension; in contrast, changes in blood volume appear to reflect variations in blood pressure.