Page 163 - Functional impairment and cues for rehabilitation of head and neck cancer patients -

DISCUSSION
The aim of this explorative biomechanical study was to identify the muscles activated during swallowing muscle strength exercises with the SEA (CTAR+, JOAR+ and ES+ exercise) and conventional swallowing exercises without an exercise tool providing external load (cES, Masako and Shaker exercise), by means of mfMRI T2-mapping using 12 echo-times, resulting in precise estimation of the true T2-values. The three SEA exercises caused a significant increase of the T2-value, indicating activation of three relevant muscle groups (i.e., lateral pterygoid, suprahyoid and infrahyoid muscles) plus the sternocleidomastoid muscles. After the conventional exercises, two relevant muscle groups (i.e., suprahyoid and infrahyoid muscles) plus the sternocleidomastoid muscles showed a significant increase of the T2-value. Mouth opening muscles (masseter and medial pterygoid muscles), tongue muscles and superior pharyngeal constrictor muscle did not show a significant increase of the T2-value in this experiment.
Swallowing is a complex function which is facilitated by over thirty muscles of the head and neck area (1, 2). After head and neck cancer treatment, jaw opening, tongue strength, pharyngeal constriction as well as laryngeal elevation might be impaired. Muscles involved in these functions are firstly the lateral pterygoid muscle which enables mouth opening by depressing the mandible. Tongue strength comprises of the strength of the intrinsic and extrinsic tongue musculature which contribute to the oral transport phase of the swallow. The superior, middle and pharyngeal constrictors cause pharyngeal constriction and the stylopharyngeus, salpingopharyngeus, and palatopharyngeus muscles elevate the pharynx. Laryngeal elevation is facilitated by the suprahyoid muscles, including the geniohyoid, mylohyoid, stylohyoid and digastric muscles. These muscles also contribute to depression of the mandible and stabilizing the hyoid. The infrahyoid muscles mainly depress the larynx, but also play a role in the elevation, mainly the thyrohyoid muscle.
The SEA exercises were designed to target jaw opening, tongue strength, pharyngeal constriction as well as laryngeal elevation. Specifically, we hypothesized that the SEA exercises would target the suprahyoid muscles (CTAR+, JOAR+, and ES+), pharyngeal musculature (ES+), jaw opening musculature (JOAR+ , ES+), and tongue muscles (ES+). The present study indicates that during the SEA exercises suprahyoid and jaw opening musculature are indeed activated, but tongue musculature and the superior pharyngeal constrictor muscle do not show significant activation.
The absence of a measurable effect in the superior pharyngeal constrictor muscle, both after the cES and after the ES+, might be due to insufficient activation of the pharyngeal constrictors, even not when additional load is provided by the SEA. Another issue might be the small size of the superior pharyngeal constrictor muscle, making the selection of a substantial region of interest harder, resulting in higher uncertainty of the measured T2-value. This is also reflected in the relatively low inter-rater reliability of the measurements of the superior pharyngeal constrictor muscle (ICC = 0.68 (95%-CI 0.49-0.80)).
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Muscle activation during swallowing exercises
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