Is the Lower Incidence of Intradialytic Hypotension During Hemocontrol Dialysis in Comparison With Standard Hemodialysis Attributable to Enhanced to Higher Plasma Vasopressin Levels or to Enhanced Sympathetic Activity and/or to Less Nitric Oxide Production

Intradialytic hypotension (IDH) is a frequent and serious complication that may occur during hemodialysis treatment. The investigators and others have shown that the Hemocontrol biofeedback system is associated with improved hemodynamic stability. Hemocontrol is a technique that guides the patients' blood volume along a pre-set trajectory by continuously adjusting the ultrafiltration rate and dialysate conductivity. In a recent pilotstudy, the investigators found significantly higher plasma vasopressin levels during the first hour of dialysis with Hemocontrol in comparison with standard hemodialysis. Increased vasopressin levels may contribute to intradialytic hemodynamic stability during hemodialysis by enhanced vasoconstriction. These results, however, did not prove directly that the improved hemodynamic stability with Hemocontrol is indeed caused by higher initial plasma vasopressin levels. Alternative explanations might be that 1) the higher initial plasma sodium levels with Hemocontrol dialysis enhance activity of the sympathetic nervous system directly, causing vasoconstriction and thereby improved hemodynamic stability and/or 2) that the higher initial plasma levels of sodium in Hemocontrol inhibit the release of nitric oxide by the vascular endothelium. Another goal of this study is to investigate whether vasopressin is removed with hemodialysis.