No change in automatic function tests during uncomplicated haemodialysis.

Uraemic autonomic dysfunction is reckoned to participate in dialysis hypotension, but a clear relationship has not been established. However, autonomic function is usually tested at rest, and possibly autonomic dysfunction arises or worsens during dialysis. We therefore performed easily repeatable tests of efferent sympathetic function, that is static exercise test and parasympathetic function, that is heart rate variability during Valsalva manoeuvre and deep breathing, at successive stages of a standard haemodialysis session; before dialysis, 20 min after dialysis without ultrafiltration, after 3 h of dialysis combined with ultrafiltration, and 20 min after dialysis. Studies were performed in 22 patients on chronic haemodialysis on a cuprophane dialyser. The mean ultrafiltration volume was 2.2 +/- 0.61. We found that blood pressure elevation upon static exercise, and heart rate variability during Valsalva or deep breathing test remained unaltered at the various stages of dialysis. On past performance the patients were divided into hypotension prone (n = 6) or resistant (n = 16). Hypotension prone patients showed a greater blood pressure drop during dialysis, but also showed an appropriately enhanced heart rate acceleration. The occurrence of autonomic dysfunction was not elevated in this group, nor did such dysfunction develop along dialysis. Predialysis parasympathetic function tests were abnormal in 10 patients. These patients also showed an augmented intradialytic blood pressure decrease, but no enhanced acceleration in heart rate. Their parasympathetic dysfunction did not worsen during dialysis. Based upon the predialysis exercise test, low responding patients (blood pressure increase 5 +/- 2 mmHg, n = 11) were distinguished. These subjects were not characterized by a greater blood pressure decrease or different heart rate acceleration. Generally, the responses upon exercise, whether low or high, remained unaltered during dialysis. we conclude that haemodialysis has no systematic effect on autonomic function. Hypotension-prone patients are not distinguished by a disturbed predialytic or intradialytic autonomic blood pressure control.