Baroreceptor, not left ventricular, dysfunction is the cause of hemodialysis hypotension

Many patients with chronic renal failure experience profound hypotension during hemodialysis. This has been attributed both to autonomic and ventricular dysfunction. In an attempt to distinguish which, if either, is important in this role, we assessed both autonomic and left ventricular function in 10 such patients. Cardioactive medication was stopped 24 hours prior to the investigations. Autonomic function was assessed from day/night blood pressure and heart rate variation and from the hemodynamic response to tilting and the Valsalva maneuver using an intra-arterial ambulatory monitoring technique. Left ventricular function was assessed scintigraphically both before and during hemodialysis. Day/night variation was significantly reduced in the patients with chronic renal failure (BP 13/7 +/- 8/6 mmHg, HR 5 +/- 4) compared with a control population (BP 36/28 +/- 10/5 mmHg, HR 19 +/- 6). Nine patients had a "square wave" response to the Valsalva maneuver. Both of these abnormalities are usually seen in patients with heart failure and are attributed to volume overload and a consequent failure of baroreceptor response. Blood pressure fell during hemodialysis (mean fall 40/22 +/- 20/10 mmHg) in all patients, but heart rate did not change (-2 +/- 16) despite the hypotension. All patients had a normal or high resting ejection fraction (mean 66%, range 55-79%), and there was no change during dialysis. This indicates that the hypotension was not due to left ventricular dysfunction in this group of patients, but to a failure of the baroreceptor response to volume depletion during hemodialysis.