Vascular reactivity to norepinephrine and hemodynamic parameters in borderline hypertension.

Pressor response to norepinephrine, cardiopulmonary blood volume, and hemodynamic parameters were studied in 41 borderline hypertensive patients in comparison with 42 permanent essential hypertensive patients and 28 normal subjects. Borderline hypertensive subjects had high cardiac index (p less than 0.0001), normal total peripheral resistance, and low total blood volume (p less than 0.005). The ratio between cardiopulmonary blood volume (CPBV) and total blood volume (TBV) was significantly higher in comparison with normal subjects (p less than 0.01) and permanent hypertensive subjects subjects (p less than 0.0001). The pressor dose of norepinephrine was elevated (p less than 0.0001) and was directly correlated with the basal values of the cardiac output (p less than 0.005), the cardiopulmonary blood volume (p less than 0.001), and the CPBV/TBV ratio (p less than 0.01). None of these results was observed in permanent hypertensive subjects: the only significant result was a negative correlation between the pressor dose of norepinephrine and the basal diastolic arterial pressure (p less than 0.0001). This study provides evidence that the cardiac output elevation in borderline hypertensive subjects was related to increased venous return and enhanced sympathetic venous tone.