Urea rebound results as urea re-equilibrates between intracellular and intravascular compartments post haemodialysis. The mechanism of the rebound is thought to be due to either a reduced diffusion rate or blood flow. It is hypothesized that low blood flow in the skeletal muscles might be responsible. We tested this by studying the effect of exercise during dialysis on the removal of urea, creatinine and potassium. Eleven patients (aged 32-78 years) on haemodialysis (4-58 months) were studied on paired dialysis sessions; one with exercise and the other as a control. Patients pedalled on a cycle for 5-20 min at submaximal workload followed by 10 min rest to achieve a total of 60 min exercise. Plasma concentrations of urea, creatinine and potassium were measured pre-, post- and 30-min post dialysis. The post-dialysis rebound (% rebound) and reduction ratios (RR) of the solutes and equilibrated (two-pool) urea Kt/V were calculated for comparison. The rebound of all three solutes was reduced significantly following exercise. The rebound of urea decreased from 12.4 to 10.9% (median, P<0.01 Wilcoxon signed rank test), creatinine from 21.2 to 17.2% (P<0.001) and potassium from 62 to 44% (P<0.05). Kt/V and RR increased significantly as a result: Kt/V urea from 1.00 to 1.15 (P=0.001), RR urea from 0.63 to 0.68 (P<0.001); Kt/V creatinine from 0.71 to 0.84 (P<0.01); and RR creatinine from 0.51 to 0.57 (P<0.05). Exercise increased the efficiency of dialysis by reducing the rebound of solutes due to increased perfusion of the skeletal muscles.
