The treatment of any disorder relies on the ability to recognize when an impairment exists. This can be problematic when it comes to swallowing as the understanding of “normal” continues to evolve. This article will discuss some often outdated notions concerning the swallow.
Molfenter examined the literature concerning hyoid and laryngeal kinematics. The article revealed that healthy normals exhibit great variability in these areas. Anterior hyoid displacement ranges from 7.6 mm to 18.0 mm. Superior hyoid movement was found to range from 5.8 mm to 25 mm. Anterior laryngeal displacement ranges from 3.4 mm to 8.2 mm and superior movement was found to be between 21.1 mm to 33.9 mm. In addition to variation in each individual’s anatomy, these differences are influenced by bolus properties. Due to the highly variable nature of movement, it is not possible to “eyeball” a deficit in hyoid or laryngeal excursion during imaging and it is certainly not quantifiable with palpation.1
In another paper Molfenter examined temporal measures of swallowing. Using the ramus of the mandible as a marker, she found the pharyngeal swallow to be initiated (first evidence of hyoid burst) between -0.22 to +0.54 seconds. That is to say, some normals trigger a swallow before the head of the bolus reaches the ramus of the mandible and some significantly after.2 Harris-Martin reports 83% of the participants, during one trial, initiated a swallow after the head of the bolus passed the ramus of the mandible.3 This information would lead to the conclusion that normal swallows cannot be defined by a trigger at the ramus of the mandible.
Laryngeal penetration is often considered a pathology. Daggett examined a group of healthy normals and found that penetration was a common occurrence in the swallow. Starting at age 50 she found penetration to occur in 16.8% of swallows.4 Harris-Martin (2007) found 100% of her participants penetrated with a Penetration Aspiration Scale (PAS) of 1-3 on one clinical trial.3 In addition, because the internal branch of the superior laryngeal nerve provides innervation to the hypopharynx and it is not responsible for a cough response, there should be no anticipated response to penetration.5, 6 Consequently the phrase “silent penetration” is quite misleading.
Finally, a more recent study sheds doubt on aspiration being a pathology of the swallow. Butler analyzed swallowing in a large cohort between the ages of 20 and 90. She found that 18% of the participants aspirated without regard to bolus presentation (cup verses straw) and 75% of the aspiration events were “silent.” This led the author to conclude: “Many clinicians and researchers have held the presupposition that aspiration is pathologic and use this observation as one of the components to diagnose a swallowing disorder. However, the findings from this large cohort... refute this presupposition and introduce a new paradigm of understanding as to what constitutes normal swallowing.”7
Finally, a yet unpublished study by Alicia Vose indicates that this lack of understanding of normal physiology may be detrimental to patients. She found dysphagia to be grossly over-diagnosed. When presented with a video of a patient with a simple, one component swallow impairment, 75% of clinicians over-diagnosed the issue. When presented with a complex case, the number escalated to 93%. This means an added burden to the patient, the healthcare system, and does not create confidence in our profession.8
Normal swallowing is a very complex, highly variable physiologic process. One size does not fit all as there is no “perfect” swallow. Based on the current literature, we still have much to learn. Even more important is our quest to keep up with the latest information to ensure we are providing our patients with the best possible care.
References:
1. Molfenter SM, Steele CM: Physiological variability in the deglutition literature: hyoid and laryngeal kinematics. Dysphagia. 26(1):67-74, 2011.
2. Molfenter SM, Steele CM: (2012). Temporal variability in the deglutition literature. Dysphagia. 27(2):162-177, 2012.
3. Harris, Bonnie & Brodsky, Martin & Michel, Yvonne & Lee, Fu-Shing & Walters, Bobby: Delayed Initiation of the Pharyngeal Swallow: Normal Variability in Adult Swallows. JSLHR. 50:585-94, 2007.
4. Daggett A, Logemann J, Rademaker A, Pauloski B: Laryngeal penetration during deglutition in normal subjects of various ages. Dysphagia. 21(4): 270-274, 2006.
5. Ludlow, Christy: Laryngeal Reflexes: Physiology, Technique, and Clinical Use. Journal of Clinical Neurophysiology: official publication of the American Electroencephalographic Society. 32:284-293, 2015.
6. Polverino M, Polverino F, Fasolino M, Andò F, Alfieri A, De Blasio F: Anatomy and neuro-pathophysiology of the cough reflex arc. Multidisciplinary Respiratory Medicine. 7(1):5, 2012.
7. Butler S, Stuart A, Markley L, Feng X, Kritchevsky S: Aspiration as a function of age, sex, liquid type, bolus volume, and bolus delivery across the healthy adult lifespan.
Ann Otol Rhinol Laryngol. 127(1):21-32, 2018.
8. Vose A, Kesneck S, Sunday K, Plowman, EK, Humbert IA: A survey of clinician decision making when identifying swallowing impairments and determining treatment. 2017 (in review).
