2011 Volume 15 Issue 2 Pages 149-155
The Repetitive Saliva Swallowing Test (RSST) is in widespread clinical use as a highly sensitive, low-risk method of dysphagia screening. However, conducting the RSST is challenging when laryngeal elevation cannot be confirmed due to thick cervical subcutaneous fat or high positioning of the thyroid cartilage. During evocation of the swallowing reflex, movement is observable in both the suprahyoid and infrahyoid muscles. Therefore, in the present study, we investigated whether it was possible to improve the accuracy of RSST by concurrent palpation of the thyroid cartilage and the inferior aspect of the mandible. This hypothesis was verified by videofluorographic (VF) assessment of swallowing in addition to simultaneous measurement of surface electromyography (SEMG) and swallowing sounds. Methods comprised simultaneous measurement of 1) VF, SEMG and palpation of the inferior aspect of the mandible in four healthy adults; and 2) SEMG, palpation of the thyroid cartilage, palpation of the inferior aspect of the mandible and swallowing sounds in 20 healthy adults. When reflex was detected by palpation, a corresponding mark was made by the investigator on the EMG. Muscle activity was calculated using integration after absolute value processing. SEMG was recorded from the suprahyoid and infrahyoid muscles. The following results were obtained. 1) Comparison of the swallowing reflex marks made for swallowing sounds and during palpation revealed that the swallowing reflex detection rate was significantly increased by palpation of the suprahyoid muscles (95%) compared with thyroid cartilage palpation alone (58%). Furthermore, suprahyoid muscle group activation was significantly greater during evocation than during failed attempts. These findings suggest that the accuracy of RSST can be improved by concurrent palpation of the inferior aspect of the mandible in patients in whom confirmation of the swallowing reflex is difficult using thyroid cartilage palpation alone. In addition 2) Up and down movements of the larynx thought to be swallowing hesitation (swallowing reflex failed attempt) were observed on VF in addition to laryngeal elevation and epiglottic inversion (swallowing reflex evocation).
