Non-invasive Real-time Detection of Potassium Level Changes in Skeletal Muscles During Exercise by Magnetic Resonance Spectroscopy

Introduction: Potassium is essential in cellular functions, with specific importance in muscle activity and cardiovascular health. It is the main intracellular cation in the human body with 70% located in muscle. Traditional methods to measure potassium levels are invasive and lack specificity for intracellular concentrations. Recently, non-invasive in vivo investigation of K+ ion homeostasis has become feasible by using 39K Magnetic Resonance Imaging (MRI) and MR spectroscopy (MRS) at ultrahigh magnetic fields. However, studies demonstrating the sensitivity of 39K MRI or MRS to detect potassium alterations in disease or upon intervention are sparse. This study utilizes 39K MRS to non-invasively track real-time intramuscular potassium changes during exercise, providing an assessment of potassium dynamics and explores the potential for technical artifacts in the measurements. Methods: Five healthy subjects (three males, two females) were recruited to perform standardized dynamic knee extensions inside a 7T MR scanner. Potassium levels were measured using a 39K MRS protocol that included periods of rest, moderate, and heavy exercise followed by recovery. Additionally, possible measurement artifacts due to muscle movement or changes in coil position relative to the thigh were evaluated using 39K MRS and 1H MRI monitoring in separate sessions. Results: The study revealed a consistent decrease in potassium levels during both moderate and heavy exercise, with an average decrease of 5-6%. These changes were rapidly detectable and were reversed upon cessation of exercise, indicating effective in vivo monitoring capability. Possible experimental artifacts were investigated, and the results suggested not to be responsible for the detected potassium changes during exercise. The results of the non-localized 39K MRS measurements during exercise correlated well with expected physiological changes based on previous literature. Discussion: The application of 39K MRS provides a valuable non-invasive tool for studying potassium dynamics in human skeletal muscle. This technique could enhance our understanding of muscle physiology and metabolic disorders. The ability to measure these changes in real time and non-invasively highlights the potential for clinical applications, including monitoring of diseases affecting muscle and cellular metabolism. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This study was funded by the sitem-insel Support Funds (SISF) from the Swiss lnstitute for Translational and Entrepreneurial Medicine (SISF) ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Cantonal Ethics Committee, Bern, Gesundheits-, Sozial- und Integrationsdirektion des Kantons Bern (GSI), gave ethical approval for this work. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors