Serum electrolyte concentrations and skeletal muscle excitability in vivo

Abstract

ObjectiveMulti-fibre muscle velocity recovery cycle (MVRC) assessment is a well-tolerated method of evaluating sarcolemmal excitability in vivo that shows promise as a research tool and biomarker. MVRC parameters correlate with venous electrolyte concentrations in myopathies. We sought to determine the nature of any such relationships in individuals without muscle disease. MethodsTibialis anterior MVRCs were recorded and electrolyte concentrations measured from two groups of healthy volunteers. After studying a single measure cohort (n = 65, one recording/person), we studied a repeated measures cohort (n = 4, eight recordings/person) to better study intra-individual relationships using repeated measures correlation (rmcorr). ResultsIn the single measure cohort, no significant correlations were present between MVRC parameters and electrolyte levels after accounting for age. In the repeated measures cohort, the relative refractory period (P < 0.01) and stimulus frequency measures (P < 0.01) correlated positively with potassium levels. Multiple late supernormality group measures correlated negatively with bicarbonate levels (P < 0.01). ConclusionsMVRC measures that vary with the resting muscle membrane potential correlate with venous potassium concentrations, as in myopathies. Late supernormality measures correlate with bicarbonate levels. SignificanceDetermination of serum electrolyte levels may inform the interpretation of MVRC study results if variation in concentrations is anticipated to be significant.