PLASMA NOREPINEPHRINE IS A MAJOR DETERMINANT OF HEMODYNAMIC-ALTERATIONS WITH SODIUM LOADING

Objective: To assess hemodynamic responses to 3 weeks of sodium loading and to evaluate factors which contribute to hemodynamic alterations. Design: Analysis of patients' central hemodynamic and laboratory variables before and after sodium loading. Setting: A referral centre. Patients: Thirty-one elderly hypertensives. Interventions: Doppler flowmetry and laboratory examinations were performed during different sodium intake; 120 mmol/ day for 8 weeks and 344 mmol/'day for 3 weeks. Results: Patients were divided into three groups; those in whom sodium loading increased total peripheral resistance (SST); those in whom salt repletion increased cardiac index (SCC); a non-salt-sensitive group (NSS). The overwhelming reaction to salt loading is that, with time, the NSS and SSC groups became part of the SST group. When the SSC patients became SST with sodium loading, serum sodium and plasma arginine vasopressin decreased and haematocrit increased, suggesting that the excretion of sodium and water accompanied with a decrease in circulating plasma volume may be responsible for the hemodynamic alteration from SSC to SST. In those who remained in the SSC group throughout the 3 weeks of salt repletion, plasma norepinephrine decreased on all of days 7,14 and 21 of the high-sodium diet compared with the regular-sodium regimen, whilst in patients in the SST group on day 21 of the high-sodium diet plasma norepinephrine remained unchanged throughout the 3 weeks of salt loading. Conclusions: We confirmed a changing patten of initially high cardiac index giving way to a persistantly elevated total peripheral resistance with sodium loading. Plasma norepinephrine proved to be the best predictor of which subjects were or became SST.