Effects of surface electrical stimulation both at rest and during swallowing in chronic pharyngeal Dysphagia

Abstract

We tested two hypotheses using surface electrical stimulation in chronic pharyngeal dysphagia: that stimulation (1) lowered the hyoid bone and/or larynx when applied at rest, and (2) increased aspiration, penetration, or pharyngeal pooling during swallowing. Bipolar surface electrodes were placed on the skin overlying the submandibular and laryngeal regions. Maximum tolerated levels of stimulation were applied while patients held their mouth closed at rest. Videofluoroscopic recordings were used to measure hyoid movements in the superior-inferior and anterior-posterior dimensions and the subglottic air column position while stimulation was on or off. Patients swallowed 5 ml liquid when stimulation was off, at low sensory stimulation levels, and at maximum tolerated levels (motor). Speech pathologists, blinded to condition, tallied the frequency of aspiration, penetration, pooling, and esophageal entry from videofluorographic recordings of swallows. Only significant (p = 0.0175) hyoid depression occurred during stimulation at rest. Aspiration and pooling were significantly reduced only with low sensory threshold levels of stimulation (p = 0.025) and not during maximum levels of surface electrical stimulation. Those patients who had reduced aspiration and penetration during swallowing with stimulation had greater hyoid depression during stimulation at rest (p = 0.006). Stimulation may have acted to resist patients' hyoid elevation during swallowing.

Figures

Figure 1

A schematic drawing of the placement of the surface electrodes over the submental region and the laryngeal region relative to palpation of the hyoid bone and the thyroid cartilage in the neck.

Figure 2

Line graphs showing the mean values for each participant during the off and on stimulation conditions for (A) the hyoid position on the y axis. In (B) the traces of hyoid position during stimulation “on”, stimulation “off” followed by stimulation “on” are shown for each of the participants in the study. Line graphs also show the mean values for each participant during the “off” and “on” stimulation conditions for (C) the hyoid position on the x axis and (D) the larynx position on the y axis.

Figure 3

Line graphs showing individual participants rating during the stimulated and non-stimulated swallows at sensory levels of stimulation on the NIH Swallowing Safety Scale (A) and the Penetration-Aspiration scale (B).

Figure 4

Line graphs showing individual participants rating during the stimulated and non-stimulated swallows at motor levels of stimulation on the NIH Swallowing Safety Scale (A) and the Penetration-Aspiration scale (B). These graphs are autoscaled to the range of the data in the two conditions, therefore the (A) is on a larger scale than (B).

Figure 5

Scatterplots with linear trend showing the relationship between improvements on the swallowing and the extent of hyoid depression during stimulation at rest for the NIH Swallowing Safety Scale (A) and the Penetration-Aspiration scale (B).