STANDARDIZED ELECTROMYOGRAPHIC ANALYSIS OF SWALLOWING AND CLINICAL APPLICATIONS.

BACKGROUND AND AIMS. Swallowing is a complex function which needs coordination between all the structures involved. To date a non-invasive method for the instrumental evaluation of oro-pharyngeal phase of swallowing is lacking. The aims of this study were: phase 1) to develop an electromyographical (EMG) protocol for the assessment of submental muscles (SM), to demonstrate its repeatability and to apply it to maximal voluntary clench (MVC), to quantify the relative contribution of SM; phase 2) to electromyographically analyse the oropharyngeal phase of swallowing finding a standardized and repeatable protocol, to find the physiological muscular pattern involved and to draw the standard model. MATERIALS AND METHODS. In 20 healthy subjects, aged 19-35 years, surface electromyography of SM, masseter (MM) and anterior temporalis (TA) muscles was performed; for phase 1, during maximal voluntary clenching (MVC) with and without cotton rolls and the pushing of the tongue against the palate, while for phase 2 during swallowing. Clenching on cotton rolls and pushing the tongue against the palate were used to standardise respectively MM and TA, and SM muscular potentials. Both phases were repeated in two appointments (T1-T2); submental muscles standardisation (during phase 1) and swallowing (during phase 2) were also repeated twice (A-B) in each session to assess repeatability. RESULTS. Phase 1: symmetry and activity were calculated for each couple of muscles. A two-way analysis of variance was computed for SM: no Factor 1 (T1 vs T2) or Factor 2 (A vs B) or F1 X F2 significant effects were found. SM recruitment was 31% of the maximal activity, with symmetry values larger than 80%. Phase 2: symmetry, activity and duration of activation for each couple of muscles were detected. In addition the duration of the whole exercise and the time of the maximal spike of activation for each muscle were evaluated. A two-way analysis of variance similar to the one of phase 1 was computed : no Factor 1 (T1 vs T2) or Factor 2 (A vs B) or F1 X F2 significant effects were found. Symmetry values were close to 80% for all the muscles, recruitment values were between 22 and 28% of the maximal activity for all the muscles with differences between all the muscles (the MM were the less recruited, while the TA were the most activated). Also the duration of activation of each couple of muscles resulted to be different between all the couples, the MM showed the shortest activation (an average value of approximately 1 s), while the submental muscles the longest one (an average value of more than 1.5 s). The duration of the whole swallowing was found to be between 1.5 and 2 s. Finally, the results showed that all the couples of muscles had their spike of activation between 35.87 and 42.65% of their total duration of activation. The sEMG graphic assessment of the position of the spike was reliable (two-way analysis of variance). CONCLUSIONS. The protocol demonstrated a high repeatability of the EMG indexes both intra and inter-appointment for MVC. Regarding swallowing it is reported that the protocol was repeatable for all the analysed indexes, although an high inter-individual variability. These results are probably due to the existence of different physiological models of swallowing among healthy population.