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High Density Laryngeal Surface Electromyography: A Visualization Method of Laryngeal Muscle Activity of the Anterior Neck

Dr. David Bracken

Dr. Bracken is a PGY-3 Head and Neck surgery resident; Dr. Philip Weissbrod is the Director of the UCSD Center for Voice and Swallowing and an Assistant Professor in the Department of Surgery, Dr. Todd Coleman is an Associate Professor in the Department of Bioengineering and the Director of the UCSD Neural Interaction Lab. Ms. Gladys Ornelas is a Graduate Student Researcher with the UCSD Neural Interaction Lab.

The neck is a complex and anatomically dense region in the body. Complex tasks of the neck—such as phonation and swallowing—are typically evaluated using invasive needle electrodes and/or two- or three-point surface electrodes. The former are painful, require expertise in placement, and have limited duration of inquiry. The latter are noninvasive and can monitor the neck for longer periods, but are limited in their ability to clearly capture and differentiate the electrical activity of neck muscles. Surface evaluation is often inconsistent and results are undermined by the influence of surrounding or interposed muscles. Can the neck be evaluated non-invasively without sacrificing spatial selectivity?

To capture and demonstrate the activity of the neck with greater detail, Dr. David Bracken, NIH Research Fellow, in collaboration with Dr. Philip Weissbrod, Assistant Professor Surgery in the Division of Otolaryngology/Head and Neck Surgery, and bioengineering colleagues, Dr. Todd Coleman and Gladys Ornelas, fabricated a high-density array and developed signal processing techniques to analyze the acquired data from a set of 20 electrodes applied to the anterior neck. Among their goals were to maintain a noninvasive modality that could be applied by non-expert operators; allow for high fidelity electrical data capture; and display this data in a meaningful and intuitive way. Energy maps were explored as a technique that assigns myoelectric energy values of varying magnitude to a color spectrum of red to blue. This means of visual output affords a dynamic view of laryngeal muscle activity in the same plane as the array itself during rest, low pitch voicing, and high pitch voicing.  Researchers wanted to demonstrate a sensitivity for symmetry and an ability to identify specific muscles within the neck (cricothyroid) with high anatomical concordance.

Among their findings, researchers showed an ability to identify statistically significant variance in electrical energy among 10 healthy adult volunteers through different regions of the high-density array during rest and voice use. These areas were consistent with where the expected laryngeal muscles would be located based on known anatomical relationships to palpable surface landmarks for which the array was oriented. The area activated during high pitch voicing specifically was consistent to where the cricothyroid muscle would lay. Reviewing the energy maps provided a dynamic and intuitive means of recognizing muscle activity.

This technology has exciting potential for application as a wearable electronic to the anterior neck for diagnosis of muscle activity disorders. It may also serve as a tool to provide patient biofeedback during therapy—allowing patients to see the electrical activity in their own necks when rehabilitating or demonstrating physiologic tasks.  Future research is already underway to understand the effect of increased electrode density, and to explore microfabrication techniques and applications to swallowing function.

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