Serum electrolyte concentrations and skeletal muscle excitability in vivo

Abstract

Objective: Multi-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.

Methods: Tibialis 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).

Results: In 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).

Conclusions: MVRC measures that vary with the resting muscle membrane potential correlate with venous potassium concentrations, as in myopathies. Late supernormality measures correlate with bicarbonate levels.

Significance: Determination of serum electrolyte levels may inform the interpretation of MVRC study results if variation in concentrations is anticipated to be significant.

Keywords: Bicarbonate; Electrolytes; Muscle velocity recovery cycles; Potassium; Skeletal muscle.