Renal filtration fraction, effective vascular compliance, and partition of fluid volumes in sustained essential hypertension.

Extracellular fluid volume, hemodynamic parameters, total effective compliance, and renal indices were measured in 58 patients with sustained essential hypertensive in comparison with 56 normotensive subjects of the same age and sex. All subjects had a balanced sodium intake and urinary output with inulin clearance and extracellular fluid volume within normal ranges. In patients with hypertension, the ratio between plasma volume (PV) and interstitial fluid volume (IFV) was decreased (P less than 0.01) and was negatively correlated with the filtration fraction (FF) (r = -0.43; P less than 0.001). Total effective compliance was significantly reduced (P less than 0.001) and was positively correlated with the PV/IFV ratio (r = 0.73; P less than 0.001) and negatively correlated with FF (r = -0.56; P less than 0.001. The study provides evidence that the relationships between PV/IFV, FF, and vascular compliance reflect an alteration of the postcapillary segment of the circulation in hypertension.