1. Blood pressure and heart rate responses to head-up tilt, standing, the Valsalva manoeuvre, sustained handgrip and cutaneous cold were measured in 27 haemodialysis patients (10 of whom had episodes of haemodialysis-induced hypotension) and 15 control subjects to assess autonomic nervous function. Plasma noradrenaline levels were measured at rest and during head-up tilt. 2. Mean resting supine blood pressure, heart rate and plasma noradrenaline levels were higher in haemodialysis patients than in the control subjects. There was no fall in blood pressure during head-up tilt or standing. The ratio of the R--R intervals of the thirtieth and the fifteenth heart beat after standing (30:15) was lower in the patients; this may be related to their higher resting heart rate. Head-up tilt raised plasma noradrenaline levels in both groups. Heart rate responses to the Valsalva manoeuvre were similar in the patients and control subjects. 3. Systolic blood pressure and heart rate responses to sustained handgrip were similar in both groups. Diastolic and mean blood pressure changes, however, were lower in the patients. The blood pressure and heart rate responses to cutaneous cold were similar in the patients and control subjects. 4. We conclude that generalized autonomic nervous dysfunction does not appear to cause haemodialysis-induced hypotension in patients with chronic renal failure on maintenance haemodialysis.

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