Evaluation of sternocleidomastoid muscle activity by electromyography recorded with concentric ring electrodes

The use of non-invasive methods for the study of respiratory muscle signals can provide clinical information for the evaluation of the respiratory muscle function. The aim of this study was to evaluate the electrical activity of the sternocleidomastoid muscle recorded superficially by means of a concentric ring electrode (CRE) in bipolar configuration. This sensor enhances the spatial resolution of the signal recorded, attenuates interferences, as the cardiac activity, and also simplifies the orientation problem associated to the electrode location on the muscle under study. Five healthy subjects underwent a respiratory load test in which an inspiratory load was imposed during the inspiratory phase. During the test, the electromyographic signal of the sternocleidomastoid muscle (EMGsc) and the inspiratory mouth pressure (Pmouth) were acquired. The EMGsc signal was processed using the fixed sample entropy (fSampEn), a technique for the amplitude estimation of signals that is robust in presence of impulsive noise as cardiac activity. The agreement between the Pmouth and the fSampEn over the EMGsc signal showed a moderate Pearson’s correlation value at the lowest inspiratory load (0.46 ± 0.11) and a very strong value at the highest inspiratory load (0.84 ± 0.08). In conclusion, the surface recordings of the EMGsc signal using a CRE and the estimation of its amplitude using the fSampEn technique can be used for the study of muscle respiratory activity.