1. A haemodynamic study which included estimation of cardiopulmonary blood volume (CPBV), total blood volume (TBV) and vascular reactivity to noradrenaline was performed in seventeen borderline and sixteen permanent hypertensive patients.
2. Borderline hypertensive patients had higher values of cardiac index, stroke index and heart rate when compared with the permanent hypertensive patients, and lower values of blood pressure and total peripheral resistance.
3. The CPBV/TBV ratio was significantly higher in borderline hypertensive patients. In that group, this ratio was directly correlated with cardiac index, stroke index and the pressor dose of noradrenaline (P < 0.01).
4. In permanent hypertensive patients, none of these correlations was observed. Only the total blood volume was correlated directly with cardiac index and inversely with total peripheral resistance.
5. The study suggests that a redistribution of intravascular volume from peripheral veins to the cardiopulmonary capacitance bed occurs in borderline hypertension when compared with permanent hypertension and that hypertension is related to a neural mechanism in the borderline state and to a volume mechanism in the permanent state.