Salt supplementation improves orthostatic cerebral and peripheral vascular control in patients with syncope

Salt supplementation improves orthostatic tolerance in many patients with posturally related syncope (PRS). This study aimed to examine whether in those patients who responded to salt loading there was also evidence of improved cerebral autoregulation and more powerful peripheral vasoconstriction during orthostasis. Eleven PRS patients were studied before and after ingestion of 100 mmol/d slow sodium for 2 months. Subjects underwent an orthostatic stress test of combined head-up tilting and lower body suction. We continuously monitored heart rate (ECG), blood pressure (Finapres), forearm and cerebral blood flow velocities (Doppler ultrasound), and end-tidal carbon dioxide (CO2). Forearm vascular resistance was calculated from pressure divided by velocity. Cerebral autoregulation was assessed from the correlation coefficient of the relationship between cerebral blood pressure and velocity. Salt loading had no effect on resting heart rate or blood pressure. Symptoms and orthostatic tolerance significantly improved in 10 of the patients. This was associated with a significant increase in the maximal forearm vasoconstriction from 64.4%+/-13.7% (SEM) to 135.2%+/-23.9% (P<0.005). The relationship between cerebral velocity and pressure was less strong (before salt: r=0.74+/-0.8; after salt: r=0.41+/-0.1; P<0.02), indicating improved autoregulation. End-tidal CO2 levels were not different between the 2 tests. Salt loading in PRS patients increases orthostatic tolerance and improves cerebrovascular and peripheral vascular control without affecting blood pressures. These changes are likely to contribute to the beneficial effects of salt loading in these patients.