UREMIC MYOPATHY LIMITS AEROBIC CAPACITY IN HEMODIALYSIS-PATIENTS

Eleven end-stage renal disease patients trained by stationary cycling during their hemodialysis treatments. After a 6-week control period, 12 weeks of training began and was increased to 30 to 60 minutes at ≥70% of peak heart rate. Baseline, pretraining and, posttraining exercise tests were performed. Workload (WL), oxygen uptake ( V˙O 2peak), cardiac output ( Q˙), heart rate (HR), and arterial oxygen content (CaO2) were measured. Stroke volume (SV), arteriovenous oxygen difference ((a-v)O2), and mixed-venous oxygen content (CvO2) were calculated. Rectus femoris biopsies were obtained pretraining and posttraining. At peak exercise, WL increased from 60 ± 4 to 70 ± 6 W (P < 0.05), V˙O 2peak showed an upward trend from 14.8 ± 0.9 to 16.8 ± 1.3 mL/kg/min (P < 0.1), and Q˙, HR, SV, CaO2, CvO2, and (a-v)O2 were unchanged. Ten of the 11 patients increased WL, but only six increased V˙O 2peak (five of 11 patients decreased V˙O 2peak). The difference between groups (P < 0.02) was attributable to (a-v)O2, which increased in those who increased V˙O 2peak (P < 0.02). There was an upward trend for succinate dehydrogenase activity (P < 0.06), and phosphofructokinase activity increased (P < 0.05). However, the rectus femoris capillary to fiber ratio, type I and II fiber areas, and fiber area variability were unchanged, and neither histomorphologic nor enzymatic activity changes were related to change in V˙O 2peak. We conclude that not all dialysis patients increase V˙O 2peak after training, but most can improve exercise capacity. Patients who improved V˙O 2peak widened their (a-v)O2 difference, increasing oxygen extraction and showing that oxygen delivery is not always the limiting factor. Thus, the limitation of V˙O 2peak in dialysis patients is a complex interaction of central and peripheral factors. Muscle therapies, such as exercise training, are needed in addition to increased oxygen delivery in rehabilitation of dialysis patients. © 1993, National Kidney Foundation, Inc.. All rights reserved.