Effect of haemodialysis on the control of the circulation in patients with chronic renal failure.

The mechanisms of hypotension during haemodialysis were investigated by studying cardiovascular reflexes, body fluid volumes, and osmolality in 11 patients with renal failure before and after haemodialysis and in 17 normal subjects before and after furosemide diuresis. Blood pressure and heart rate responses to tests of autonomic nervous function were unaffected in either group except that in the patients, head-up tilt after haemodialysis caused a fall in blood pressure. This was associated with a greater fall in cardiac output than before haemodialysis but with a similar rise in peripheral vascular resistance. Resting plasma noradrenaline levels were higher than normal, and the rise in plasma noradrenaline levels in response to tilt was unaffected by haemodialysis. Plasma renin activity rose in response to head-up tilt in normal subjects, but not in patients either before or after haemodialysis. Our studies indicate that changes in plasma potassium and osmolality or the possible peripheral circulatory effects of acetate do not impair the regulation of the circulation in response to haemodialysis. Haemodialysis does not reduce plasma noradrenaline levels. Impaired myocardial function in response to fluid depletion or unresponsiveness of the renin-angiotensin system may contribute to haemodialysis hypotension.