Transport during Exercise in Patients with Chronic Renal Failure

Erythropoietin (rHuEPO) has proven to be effective in the treatment of anemia of chronic renal failure (CRF). Despite improving the quality of life, peak oxygen uptake after rHuEPO therapy is not improved as much as the increase in hemoglobin concentration ([Hb]) would predict. We hypothesized that this discrepancy is due to failure of O 2 transport rates to rise in a manner proportional to [Hb]. To test this, eight patients with CRF undergoing regular hemodialysis were studied preand post-rHuEPO ([Hb] 5 7.5 6 1.0 vs. 12.5 6 1.0 g · dl 2 1 ) using a standard incremental cycle exercise protocol. A group of 12 healthy sedentary subjects of similar age and anthropometric characteristics served as controls. Arterial and femoral venous blood gas data were obtained and coupled with simultaneous measurements of femoral venous blood flow ( leg) by thermodilution to obtain O 2 delivery and oxygen uptake ( O 2 ). Despite a 69% increase in [Hb], peak O 2 increased by only 33%. This could be explained largely by reduced peak leg blood flow, limiting the gain in O 2 delivery to 37%. At peak O 2 , after rHuEPO, O 2 supply limitation of maximal O 2 was found to occur, permitting the calculation of a value for muscle O 2 conductance from capillary to mitochondria (DO 2 ). While DO 2 was slightly improved after rHuEPO, it was only 67% of that of sedentary control subjects. This kept maximal oxygen extraction at only 70%. Two important conclusions can be reached from this study. First, the increase in [Hb] produced by rHuEPO is accompanied by a significant reduction in peak blood flow to exercising muscle, which limits the gain in oxygen transport. Second, even after restoration of [Hb], O 2 conductance from the muscle capillary to the mitochondria remains considerably below normal. ( J. Clin. Invest. 1996. 97:2092–2100.).