Effects of exercise training during hemodialysis on cardiac baroreflex sensitivity.
Arterial baroreflex sensitivity (BRS) evaluation has been increasingly used as an index of cardiac autonomic control. Cardiac autonomic dysfunction leading to depressed BRS has been associated with an increased risk of ventricular arrhythmias and sudden death in patients with chronic kidney disease (CKD) on hemodialysis (HD). The purpose of this study was to investigate the effects of an exercise training program during hemodialysis on BRS in CKD patients. 43 HD patients participated in the study. They were randomly assigned into either a 7-month exercise training program during HD (Group A: n=22 patients) or a sedentary control group (Group B: n=21 patients). Additionally, 20 sex- and age-matched sedentary individuals comprised a healthy control group (Group C). All patients at the beginning and the end of the study underwent a tilt test for evaluation of BRS and an exercise testing with spiroergometric study for cardiorespiratory capacity estimation. The level of Hb, medications and the HD procedure remained stable during the study. At baseline BRS was found to be reduced by 51.5% (p<0.05) and baroreflex effectiveness index (BEI) by 36.4% (p<0.05) in Group A compared with Group C. Initially, all HD patients had also significantly lower exercise time and VO2 peak than the healthy subjects. After training, Group A showed a significant improvement in BRS by 23.0% (p<0.05), in BEI by 27.0% (p<0.05), in event and ramp count by 35.0% (p<0.05) and 29.0% (p<0.05), respectively as well as in VO2 peak by 22.4% (p<0.05) and in exercise time by 40.9% (p<0.05). Significant correlations were found between BRS and METs (r=0.476, p<0.05), BRS and VO2 peak (r=0.443, p<0.05), BEI and METs (r = 0.492, p<0.05), BEI and VO2 peak (r=0.467, p<0.05), event count and VO2 peak (r=0.715, p<0.01), event count and exercise time (r=0.799, p<0.01), in Group A at the end of the study. Our results indicate that HD patients had considerably reduced cardiorespiratory capacity and impaired cardiac BRS compared to healthy sedentary individuals. Importantly, exercise training during HD yielded a marked increase of the indices representing baroreflex activity in association to the improvement of their functional capacity.