Effects of high salt intake on hemodynamic responses to isometric exercise in normotensive subjects and in patients with essential hypertension.

Hemodynamic responses to isometric exercise were compared between 9 normotensive subjects (NT) and 16 patients with essential hypertension (EH) before and during high salt intake. The subjects were hospitalized and placed on a diet containing 6g of salt per day. Baseline hemodynamic studies were carried out on supine subjects before and 3 min after isometric exercise (30% of the maximal voluntary handgrip). Plasma concentration of norepinephrine (PNE) was also measured. Brachial arterial pressure was directly recorded and cardiac output (CO) was measured by the dye-dilution technique using a cuvette. The hemodynamic studies were repeated on the 5th day of a high salt diet (16g of salt per day). Retention of sodium was calculated on a daily basis by measuring the actual intake of sodium and 24-hour urinary excretion of sodium. Pressor responses to isometric exercise were significantly greater in the EH than in the NT group. Patterns of hemodynamic responses were different in the 2 groups, i.e., the elevation of arterial pressure was maintained by an increase in CO in the NTs, while it was maintained by increases in CO and total peripheral vascular resistance (TPR) in the EHs. The increase in CO was significantly greater in the NT than in the EH group [15 +/- 3 (mean +/- SE) vs 7 +/- 1%, p less than 0.05]. Although the salt loading reduced heart rate similarly in both groups (-9.0 +/- 2.1, p less than 0.01, in the NTs and -11.9 +/- 2.9%, p less than 0.01, in the EHs), the high salt diet did not significantly alter mean arterial pressure (MAP), CO or TPR in either group.(ABSTRACT TRUNCATED AT 250 WORDS)