Physical performance and associated electrolyte changes after haemoglobin normalization: a comparative study in haemodialysis patients

Background, To determine the effects of different haemoglobin (Hb) levels on exercise performance and associated electrolyte changes, a prospective, randomized, double-blinded crossover study was completed in 14 haemodialysis patients. Methods. Performance and changes in arterial [K+] and lactate were compared at rest and during a maximal incremental cycling exercise at a Hb concentration ([Hb]) of 10 g/dl ([Hb](10)) and 14 g/dl([Hb](14)) following an initial baseline test (Hb: 8.3 +/- 0.2 g/dl, mean +/- SEM). Ages ranged from 23 to 65 years and patients were divided into younger (age 23-45 years, n = 9) and older (aged 55-65 years, n = 5) groups. Results. Peak work rate and V-02 peak were higher at [Hb](14) than at [Hb](10). 145 +/- 9 vs 134 +/- 9 W, mu +/- SEM, P < 0.01, and 1.90 +/- 0.11 vs 1.61 +/- 0.11 l/min, P < 0.01, respectively. Improvements were demonstrated in both younger and older groups at the higher target [Hb], with an improved aerobic performance evident particularly in younger patients. However, performance remained below that predicted for comparable sedentary controls. Resting plasma [K+] was raised at both [Hb](10) and [Hb](14) compared with baseline (P < 0.01) although the change in [K+] from rest to peak exercise (Delta[K+]) was similar at each level. The Delta[K+] per unit work performed (used as a marker of K+ regulation) was, however, inversely related to the [Hb] (baseline: 80 +/- 12 mu mol/l/kJ vs [Hb](10.) 61 +/- 8, P < 0.01, vs [Hb](14.) 49 +/- 7, P < 0.05). Exercise induced a significant but similar rise in lactate concentration at both target [Hb] (P < 0.001), which remained markedly elevated for at least 10 min after exercise in both younger and older groups. Conclusions. These data demonstrate that a physiological [Hb] improves, but does not normalize, exercise performance in end-stage renal failure. Both younger and older patients appear to benefit similarly from the enhanced oxygen transport. Impaired K+ regulation is apparently related to [Hb] and could well contribute to the observed limitations in performance.