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?

Background
Rationale:
Intradialytic hypotension (IDH) is a frequent and serious complication that may
occur during hemodialysis treatment. We 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 (Vasopressinestudie, ABR-nr
29707 + NDT ref DOI#) we 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 intra-dialytic
hemodynamic stability during HD 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.
In this study, we also want to investigate whether vasopressin is removed with
hemodialysis.

Objectives
1. To investigate whether the improved hemodynamic stability with Hemocontrol
dialysis is based on higher plasma levels of vasopressin or on enhanced
activity of the sympathetic nervous system and/or inhibition of nitric oxide
production.
2. To investigate whether vasopressin is removed by hemodialysis

Study design
In a randomized cross-over design, 30 hemodialysis patients who are on a thrice
weekly hemodialysis schedule, shall be treated once with standard hemodialysis
and once with Hemocontrol hemodialysis.
Non-invasive measurements performed are:
- Before, after 30, 60, 120 and 180 minutes and after dialysis blood is
withdrawn from the dialysis line to determine plasma levels of vasopressin,
sodium, noradrenalin, nitric oxide metabolites and plasma osmolality.
In addition, blood will also be drawn from all patients on Hemocontrol
hemodialysis when it has passed the artificial kidney at 30 minutes on dialysis.
In total, 168 ml of blood (84 ml per dialysis session) will be drawn.
- Measurement of blood pressure, heart rate, peripheral vascular resistance,
heart rate variability, baroreflex sensitivity and cardiac output with the
Finapress. This is a non-invasive measurement using a fingercuff.
- Relative blood volume changes are measured with an incorporated non-invasive
continuous hemotocrit meter.

Nature and extent of the burden and risks associated with participation,
benefit and group relatedness:
Patients who are normally treated with standard hemodialysis shall undergo one
hemodialysis with Hemocontrol and patients who are normally treated with
Hemocontrol hemodialysis shall undergo one standard hemodialysis. Both
treatments are routinely and qualitatively comparable treatments. A total of
168 ml of blood (84 ml per dialysis treatment) shall be withdrawn from the
dialysis line, so patients do not have to undergo extra venipunctures.
Patients will be asked to wear the vingercuff of the Finapress for ten minutes
every half hour. Patients will also be asked not to smoke or to consume
caffeine containing products like coffee, tea and chocolate from 10 o*clock pm
the night prior to the dialysis.
It is possible that patients undergo hemodialysis at a different point of time
than usual.
There are no risks associated with participating in this study. We believe that
the limited burden of this study is justifiable since we expect that the study
shall provide relevant knowledge about the pathofysiology of intradialytic
hypotension and might contribute to new options in the treatment of this
frequent complication occurring during hemodialysis.