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 VO2 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 micromol/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.