Effects of modality change and transplant on peak oxygen uptake in patients with kidney failure

Background: Exercise capacity as measured by peak oxygen uptake (Vo _2peak) is low in hemodialysis patients. The present study assesses determinants of VO_2peak in patients with chronic kidney failure who either changed kidney replacement modality to frequent hemodialysis therapy or received a kidney transplant. Study Design Cohort study with assessment at baseline and 6 months after modality change. Setting & Participants Participants included nondiabetic individuals receiving conventional hemodialysis who: (1) remained on conventional hemodialysis therapy (n = 13), (2) changed to short daily hemodialysis therapy (n = 10), or (3) received a transplant (n = 5) and (4) individuals who underwent a pre-emptive transplant (n = 15). Additionally, 34 healthy controls were assessed at baseline only. Predictor Modality change. Measurement & Outcomes Exercise capacity, assessed using the physiologic components of the Fick equation (Vo₂ = cardiac output × a-vo_2dif, where a-vo_2dif is arterial to venous oxygen difference) was determined using measurement of Vo_2peak and cardiac output during symptom-limited exercise testing. Analysis of covariance was used to compare differences in changes in Vo _2peak, cardiac output, heart rate, stroke volume, and a-vo _2dif at peak exercise between participants who remained on hemodialysis therapy and those who underwent transplant. Results Transplant was the only modality change associated with a significant change in Vo _2peak, occurring as a result of increased peak cardiac output and reflecting increased heart rate without a change in peak a-vo_2dif despite increased hemoglobin levels. There were no differences in participants who changed to daily hemodialysis therapy compared with those who remained on conventional hemodialysis therapy. Limitations Small nonrandomized study. Conclusions Vo_2peak increases significantly after kidney transplant, but not with daily hemodialysis; this improvement reflects increased peak cardiac output through increased peak heart rate. Despite statistical significance, the increase in Vo_2peak was not clinically significant, suggesting the need for interventions such as exercise training to increase Vo_2peak in all patients regardless of treatment modality.