Tissue sodium in hemodialysis patients and healthy humans assessed by sodium magnetic resonance imaging

Fang, Hsin-Yu

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https://hdl.handle.net/2142/121243 Copy

Description

Title

Tissue sodium in hemodialysis patients and healthy humans assessed by sodium magnetic resonance imaging

Author(s)

Fang, Hsin-Yu

Issue Date

2023-07-11

Director of Research (if dissertation) or Advisor (if thesis)

Wilund, Kenneth

Doctoral Committee Chair(s)

Wilund, Kenneth

Committee Member(s)

• Burd, Nicholas
• Sutton, Brad
• Ikizler, Alp

Department of Study

Kinesiology & Community Health

Discipline

Kinesiology

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Hemodialysis
• Sodium magnetic resonance imaging

Abstract

Sodium magnetic resonance imaging (23Na-MRI) is an emerging technology allowing non-invasive quantification of tissue sodium stores in humans. Recent research based on 23Na-MRI reveals elevated skeletal muscle and skin sodium concentrations in patients with kidney failure on hemodialysis (HD) treatment compared to healthy counterparts. Higher sodium concentrations in the skeletal muscle and skin are associated with clinical complications in HD patients, but it remains unknown if tissue sodium can be reduced to improve the patients’ health. The primary purpose of this dissertation was to expand current knowledge on tissue sodium mobilization and its clinical impacts in HD patients using 23Na-MRI. Previous studies have demonstrated significant muscle and skin sodium reductions immediately after a HD session compared to baseline. In Study 1, we showed that the reduction in muscle sodium caused by a HD session no longer existed at 24 hours post-HD, and that muscle sodium remained at baseline levels thereafter until the next HD session. We additionally showed that the magnitude of HD-enforced muscle sodium removal was not influenced by a 30 minute-bout of intradialytic cycling exercise. In Study 2, we developed a new 23Na-MRI technique enabling the division of total tissue sodium signal into 2 parts, which were respectively contributed by the fast- and slow-T2-relaxing sodium components. By using this technique, we found that 3 minutes of ankle plantar flexion exercise induced the greatest muscle sodium increase in the peroneal muscles in healthy individuals. In the peroneal muscles, the sodium signals contributed by the fast- and slow-T2-relaxing sodium components were increased and decreased, respectively, at 0 – 20 minutes post-exercise relative to pre-exercise. The post-exercise responses of the signals from the fast- and slow-T2-relaxing sodium components were similar to those reported in the exercise literature for the intracellular and extracellular muscle sodium concentrations, respectively. Such similarities suggest that the signals from the fast- and slow-T2-relaxing sodium components may be proxies for the intracellular- and extracellular-weighted muscle sodium signals, respectively. In Study 4, we employed the 23Na-MRI technique developed in Study 3 to examine the effect of a 2-month low-sodium meal intervention on tissue sodium in HD patients. We found no significant pre- to post-intervention changes (Δ) in muscle and skin sodium and in other outcomes, such as the composition and function of muscles, and the indices of fluid overload. However, the change in muscle sodium concentration was positively correlated with the change in muscle fat content in the medial gastrocnemius. Furthermore, the change in sodium concentration in most of the muscle beds studied was inversely related to the change in patient’s physical function, as assessed by a sit-to-stand test. Overall, the studies presented in this dissertation suggest that in HD patients: (1) muscle sodium accumulation is related to impairments in muscle structure and function; (2) neither HD treatment alone or low-sodium meal provision are effective strategies for reducing muscle sodium accumulation, and (3) an acute bout of intradialytic exercise may not influence HD-enforced muscle sodium removal. These findings may serve as rationale for the development of new intervention strategies targeting tissue sodium to improve patient outcomes. Our results in healthy individuals also necessitates future work to validate if the signals from the fast- and slow-T2-relaxing tissue sodium components represent the intracellular- and extracellular-weighted tissue sodium signals, respectively. If validated, these proxy measures may open new research avenues to study the mechanisms of tissue sodium accumulations in HD patients and in other populations as well.

Graduation Semester

2023-08

Type of Resource

Thesis

Copyright and License Information

Copyright 2023 Hsin-Yu Fang

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