Intra-dialytic training accelerates oxygen uptake kinetics in hemodialysis patients

End-stage renal disease is associated with several hemodynamic and peripheral muscle abnormalities that could slow the rate of change in oxygen uptake ($\stackrel{·}{\text{V}}$O₂) at the onset and at the end of exercise. This study was performed to determine whether an intra-dialytic aerobic training program would speed $\stackrel{·}{\text{V}}$O₂ kinetics at the transition to and from moderate and high-intensity exercise.

This study was a randomized controlled trial.

Twenty-four patients with end-stage renal disease (14 females; 47.0 ± 11.9 years) were randomly assigned to either 12-week cycle ergometer-based training at moderate exertion or a similar control period. At initial and final evaluations, patients underwent 6 min moderate and high-intensity tests to exercise intolerance (Tlim).

Training improved Tlim by ∼90% (median (inter-quartile range) = 232 (59) s to 445 (451) s, p < 0.05); in contrast, Tlim decreased by ∼30% in controls (291 (134) s to 202 (131) s). $\stackrel{·}{\text{V}}$O₂ kinetics at the onset of moderate-intensity exercise were significantly accelerated with training leading to lower oxygen (O₂) deficit (mean ± standard deviation (SD) = 3.2 ± 1.3 l vs 2.3 ± 1.2 l). Similar positive effects were found at the high-intensity test either at the onset of, or recovery from, exercise (p < 0.05). “Excess” $\stackrel{·}{\text{V}}$O₂ at the high-intensity test was also lessened with training. Changes in Tlim correlated with faster $\stackrel{·}{\text{V}}$O₂ kinetics and lower “excess” $\stackrel{·}{\text{V}}$O₂ (Spearman's ρ = –0.56 and –0.75, respectively; p < 0.01).

A symptom-targeted intra-dialytic training program improved sub-maximal aerobic metabolism and endurance exercise capacity. $\stackrel{·}{\text{V}}$O₂ kinetics are valuable in providing relatively effort-independent information on the efficacy of exercise interventions in this patient population.