Measuring sensory loss in the throat as a component of swallowing dysfunction
In 1859 “On the Origin of Species” was published, a work by Charles Darwin. Even back 154 years ago, they were writing about swallowing. In this work, Darwin stated “every particle of food and drink which we swallow has to pass over the orifice of the trachea, with some risk of falling into the lungs”. The word that I take from this quote is “risk”. As a medical speech-language pathologist for 15 years, I am asked many times a day from families, physicians, and nurses about the aspiration “risk” for a patient. A physician may ask how “risky” is it to feed a patient who might have signs and symptoms of aspiration. Through the years, speech language pathologists and physicians have led the research in terms of developing methods to assess aspiration “risk”.
One of the components of the swallow that has gained ongoing interest in assessing this “risk” is laryngopharyngeal sensory awareness. Laryngopharyngeal sensation in the throat is controlled by the internal branch of the superior laryngeal nerve (ISLN), which is a branch of Cranial Nerve X the Vagus Nerve. In the throat, the mucosal areas considered to receive the most abundant innervations of the ISLN are the laryngeal surface of the epiglottis, vocal cords, and arytenoid cartilage bilaterally. Darwin speaks of “risk” in his quote above. What is the risk of a bolus entering the trachea, if the sensory clearing mechanisms in the laryngopharynx are not functional?
Conventional wisdom would suggest that if food, liquid, mucus were in the larynx and the patient was not sensing it in the larynx, then there might be a greater “risk” for substance to enter the trachea. For my Doctoral dissertation, the goal was to assess the sensory function of the ISLN to determine if there was a positive correlation between severity of sensory loss in the throat and severity of tracheal aspiration of food. Patients in the study were tested with Flexible Endoscopic Evaluation of Swallowing with Sensory Testing (FEESST). Patients received air pulse testing in the throat through an endoscope to the ISLN. The goal was to determine if stimulating the ISLN with the air pulses would trigger a Laryngeal Adductor Reflex (LAR), which is a brief, reflexive true vocal cord adduction. Air pulses had different levels of intensity. This research showed that patients who had more severe sensory loss in the throat (not feeling the air pulses) had higher “risk” for more severe aspiration (silent, without sensory clearing response in the trachea). Research suggested that there is high value in knowing the sensory function of the throat for its potential predictive ability in determining severity of aspiration “risk”.
I would have never thought that such a quote from Charles Darwin, 154 years ago, would have relevance to my Doctoral dissertation, and my job. Through my research and clinical experience, I developed a continuing education website as a resource for clinicians to enhance their knowledge in medical speech-language pathology.
CEUALLIEDHEALTH.COM has courses for all experience levels of speech-language pathology. As an ASHA approved CE provider, clinicians can take courses from the comfort of their own home, in an on-line format. One of the more popular courses has been “Internal Branch Superior Laryngeal Nerve: Sensory/Swallow Functions”.
Much of the coursework is based on my experiences as a Doctoral Level, Board Recognized Swallowing Disorders Specialist. I welcome you to take a look at the CE website, which is for clinicians, designed by a practicing clinician. We always welcome any feedback, which can help enhance our product delivery to our consumer, the speech-language pathologist.
