EARLY EFFECTS OF ORAL SALT ON PLASMA-VOLUME, ORTHOSTATIC TOLERANCE, AND BARORECEPTOR SENSITIVITY IN PATIENTS WITH SYNCOPE

Salt loading of patients with orthostatic-related syncope has been sho wn to increase plasma volume and orthostatic tolerance and to decrease baroreceptor sensitivity. This study aims to define the time course o f these changes and reveal indications as to the likely mechanisms inv olved. We measured plasma volume by Evans blue dilution, orthostatic t olerance by time to presyncope in a test of combined head-up tilt and lower body suction, and baroreceptor sensitivity as the cardiac interv al prolongation to neck suction. Tests were carried out in patients wi th poor orthostatic tolerance and low initial urinary salt excretion, before and after 7 or 3 days of salt loading (120 mmol/d). In both gro ups after salt loading plasma volume and orthostatic tolerance increas ed and baroreceptor sensitivity decreased. These results confirm the b eneficial effects of salt in some patients and show that all these cha nges occur within 3 days.