Abstract
Variations in the sympathetic tone are known to induce changes in plasma volume. Infusion of catecholamines decreases the plasma volume (1, 2). Some patients with pheochromocytoma show subnormal values of plasma volume (3). Increased sympathetic activity after hypoxia is associated with a reduction of plasma volume (4).
During the course of an investigation on plasma volume in borderline hypertension (5) we encountered data related to the role of the sympathetic nervous system in the regulation of plasma volume. Plasma volume was measured before and after beta-adrenergic blockade with propranolol. In order to better understand observed changes in plasma volume an attempt is made to separate the effect of beta blockade on cardiac output, peripheral resistance and central venous pressure from its other hemodynamic effects.
Materials and Methods. Twenty-seven males from 18 to 26 years of age were studied. Fourteen subjects had borderline hypertension, i.e., at least one diastolic above and one below 90 out of a minimum of three readings taken in the last year. A full description of these patients can be found elsewhere (5).
A set of resting recumbent measurements of intraarterial blood pressure, cardiac output, hematocrit, and plasma volume were taken 10 min after all the catheters were introduced. After an additional 20 min at rest, 0.2 mg/kg of body weight of propranolol was injected intravenously. Seven minutes later, cardiac output and plasma volume were determined. This was followed in 2 min by an intravenous injection of 0.04 mg/kg of atropine with repeat measurements 7 min after this injection.
Cardiac output was determined by dye dilution with indocyanine green. Details of the procedure are described in a previous paper (6).
The plasma volume was determined by the dye T-1824 (Evans blue, Warner Chilcot) reading optical density of 10, 15, 20 min samples in a Coleman junior spectrophotomer and extrapolating the slope to zero time.
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