This study was undertaken to assess the importance of an elevated cardiac output in the generation of the hypertension associated with chronic renal failure. Forty stable uremic patients on a program of maintenance hemodialysis underwent hemodynamic studies. Cardiac index measured by dye dilution was found to be significantly elevated. Calculated peripheral vascular resistance was normal despite elevated blood pressure. Six patients underwent serial hemodynamic studies over a period of 6 to 12 weeks while being transfused with packed red blood cells to a normal hematocrit. Blood volume and body weight were constant during the study period. Cardiac index decreased during transfusion, reaching a normal level at a hematocrit of 30%. Diastolic blood pressure progressively rose, averaging an increase of 20 mm Hg at a hematocrit of 40%. Peripheral vascular resistance increased by 80% at a hematocrit of 40%. We concluded that the elevation of cardiac index in uremic patients is secondary to anemia and is reversible when the hematocrit is raised over 30%. The high cardiac index is not responsible for hypertension because restoration of cardiac index to normal by transfusion raises blood pressure rather than lowers it.

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