The impact of intradialytic cycling on temporal changes in muscle sodium during hemodialysis

Abstract Background Sodium magnetic resonance imaging (23Na-MRI) studies indicate that patients undergoing maintenance hemodialysis (MHD) exhibit elevated muscle sodium concentrations that are associated with deleterious consequences. While muscle sodium concentrations have been shown to decline during a hemodialysis (HD) session, little is known about whether they subsequently rebound or how intradialytic muscle sodium dynamics might be modulated. We thus examined muscle sodium kinetics on HD and non-HD days and evaluated if an acute intradialytic exercise bout could enhance HD-associated changes in muscle sodium concentration. Methods Seven MHD patients participated in this pilot consisting of 2 studies. The ‘Time-Series’ study included 4 sequential 23Na-MRI scans between 2 HD treatments at: 1) pre-HD1 (T1); 2) post-HD1 (T2); 3) 24 hours post-HD1 (T3); and 4) pre-HD2 (T4). The ‘Na-Exercise’ study included two 23Na-MRI scans: 1) a pre-HD scan (T5); and 2) a post-HD (T6) scan on a day where participants cycled for 30 minutes during HD. Calf muscle sodium concentrations were quantified from 23Na-MRI images. Results After decreasing during HD (P < 0.001), calf muscle sodium concentration returned to the pre-HD1 level by 24 hours post-HD1 (P = 0.84) and was numerically, but not significantly, lower than baseline at pre-HD2 (P = 0.07). The intradialytic cycling bout did not significantly affect the decline in calf muscle sodium concentrations during HD (group × time interaction: P = 0.13). Conclusions Calf muscle sodium concentrations decrease during HD, return to baseline within 24 hours, and may show a smaller decline before the start of the next session. The effect of a single intradialytic cycling bout on the intradialytic reduction in muscle sodium concentration was not clearly detectable and remains inconclusive.