A look into the Laryngeal Electromyography world! Re: Influence of Superior Laryngeal Nerve Injury on Glottal Function

Summary

In a study by Dr. Armando De Virgilio from the September 2014 issue of “Otolaryngology - Head and Neck Surgery”[1], he enters the world of laryngeal electromyography (LEMG) in order to evaluate certain laryngeal functions to help enhance standard neurolaryngeal methodologies. He explains that Recurrent laryngeal nerve (RLN) injuries may induce unilateral vocal fold paralysis (UVFP). During thyroidectomy, the most common cause of UVFP, the superior laryngeal nerve (SLN), is also at risk of injury. In the literature, the influence of SLN injury on glottal configuration and function in patients with UVFP remains controversial. His study investigates SLN injury influence on glottal configuration and function in patients with UVFP after thyroidectomy.

The SLN and RLN function of 34 patients with UVFP after thyroidectomy was determined by laryngeal electromyography. The subjects were dichotomized into the isolated RLN injury group (n = 26) or the concurrent SLN/RLN injury group (n = 8). He evaluated glottal angle and paralyzed vocal fold shape during inspiration, normalized glottal gap area, and glottal shape during phonation. The glottal function measurements included voice acoustic and aerodynamic analyses and the Voice Handicap Index. The aforementioned parameters of the RLN and concurrent SLN/RLN injury groups were compared.

There were no statistical differences in glottal configuration such as glottal angle, paralyzed vocal fold shape, normalized glottal gap area, and glottal shape between the RLN and concurrent SLN/RLN injury groups. He explained that there were also no significant differences in other glottal function analyses including fundamental frequency, mean airflow rate, phonation quotient, maximal phonation time, and Voice Handicap Index. In the present study, Dr. De Virgilio did not find any evidence that SLN injury could significantly influence the glottal configuration and function in patients with UVFP.

Reflection

This study by Dr. Armando De Virgilio is fascinating and discovers underlying topics in glottal configuration aside from unilateral vocal fold paralysis patients. These results can help singers and speakers discover a thing or two. As the field of Neurolaryngology evolves, I find that literature is starting to understand the neurological role of intrinsic laryngeal muscles, which help us understand the overall function. In this study, laryngeal electromyography (LEMG) is used to report the integrity of the neuromuscular system in the larynx by recording action potentials generated in the laryngeal muscles during voluntary and involuntary contraction. LEMG is particularly useful for helping to differentiate between disorders involving upper motor neurons, lower motor neurons, peripheral nerves, the neuromuscular junction, muscle fibers, and the laryngeal cartilages and joints.

As I read this article, I cannot help but be happy that studies like Dr. De Virgilio exist so we can understand the exact mechanism of the problem and why it is important in helping the physician, speech language pathologist and singing teacher comprehend how to rehabilitate the voice by using neurological data. He strictly states that a study with a larger scale remains necessary to further clarify this specific topic. What about evaluating the breathing mechanism simultaneously with his LEMG data? What is lacking in Dr. De Virgilio’s study is muscle activity that can be recorded by an ambulatory monitoring system with surface EMG using silver/silver chloride bipolar electrodes. Laryngeal muscles (especially the phonatory/glottal process) cannot function without the breathing mechanism. This occurs when air is expelled from the lungs through the glottis, creating neurological connections to the brain and a pressure drop across the larynx. When this drop becomes sufficiently large, the vocal folds start to oscillate. If the breath is not sufficient, there will be a lacking result in neurological connectivity and pressure drop across the larynx.

If Dr. De Virgilio added breathing muscle activity to his study, would these results in unilateral vocal fold paralysis patients cause an alternative discussion and help enhance standard methodology for evaluating superior laryngeal nerve function? In 2005, Dr. De Viggo Pettersen did a SLN/RLN study[2] using LEMG but also connecting breathing muscles and thorax movement. It concluded that Sternocleidomastoideus and Scaleus muscle activity in classical singing is of greater functional significance in balancing the subglottal pressure than the role of Upper trapezius as a pressure generator during glottal configuration. Dr. De Virgilio may be lacking data from unilateral vocal fold paralysis patients without recorded data from these three breathing muscle groups.

Far more research is needed to fully understand the complex relations between posture, muscle usage and breathing in any patient, unilateral vocal fold paralysis or not. I appreciate how Dr. De Virgilio approached this study because I personally think he is enhancing standard methodologies in LEMG.

---

[1] "Influence of Superior Laryngeal Nerve Injury on Glottal Configuration/Function of Thyroidectomy-Induced Unilateral Vocal Fold Paralysis." American Academy of Otolaryngology—Head and Neck Surgery September.2014 (2014). SAGE Publications. Web. <http://oto.sagepub.com/content/early/2014/09/11/0194599814549740.full.pdf>.

[2] Pettersen, Viggo. "From Muscles to Singing The Activity of Accessory Breathing Muscles and Thorax Movement in Classical Singing." University of Stavanger Department of Music and Dance. NTNU, 2005. Web. <http://www.diva-portal.org/smash/get/diva2:125600/FULLTEXT01.pdf>.