Plasma Volume in Men with Essential Hypertension

Plasma volume (RISA) was measured in 37 men with essential hypertension uncomplicated by cardiac or renal failure, and results compared with values obtained in 20 normal male subjects. Body height was found to be a better reference index than weight for expressing results, but conclusions were identical whatever the frame of reference used. Plasma volume was diminished in hypertensive men. This decrease was greater the higher the diastolic pressure (r equal to -0.434; p less than 0.01), so that it was only evident in the patients with diastolic blood pressures over 105 mm of mercury. Plasma volume measured 19.4 ml per centimeter in normotensive, and 19.6 ml per centimeter in hypertensive men with diastolic pressure less than 105 mm of mercury, and 16.9 ml per centimeter in those with higher blood pressure (p less than 0.02). These findings contrast with reports of expanded plasma volume in primary aldosteronism and renoprival hypertension, and emphasize the importance of diagnostic grouping in studies of hypertension.