Extracellular fluid volume determined by a single injection of inulin in men with untreated essential hypertension

The extracellular volume (ECV) and plasma volume (PV) were determined simultaneously in nine men with untreated essential hypertension and in nine healthy matched control subjects, using a single injection of inulin and of 131I-labelled human serum albumin, respectively. The average mean arterial blood pressure in the hypertensive group was 178/118 mmHg. ECV was nearly the same in the two groups, viz. 151 ml/kg body weight (SD 17) in the hypertensive group compared to 147 ml/kg (SD 16) in the control group. The corresponding figures for PV were 38.2 ml/kg body weight (SD 4.7) and 43.7 ml/kg (SD 7.9) respectively (P less than 0.1). The calculated interstitial fluid volume (IV) was 113 ml/kg (SD 16) and 103 ml/kg (SD 10) (P less than 0.2). The PV/IV ratio was significantly lower (P less than 0.02) in the hypertensive group (0.34, SD 0.06) than in the normal group (0.42, SD 0.06). The difference might suggest increased transcapillary water filtration in hypertension.