The primary findings of this study showed significant between-group differences among the normal, aspiration, and stasis groups, considering parameters including anterior hyoid displacement, maximal hyoid displacement, and velocity of hyoid movement in detecting aspiration. The ROC analyses and the corresponding AUC calculated from anterior hyoid displacement, velocity of anterior hyoid displacement, and average velocity of maximal hyoid displacement showed acceptable discrimination ability. Our findings add to the growing body of evidence suggesting that the kinematic analysis of hyoid bone movement could aid in detecting aspiration . Nonetheless, one of the huge drawbacks of VFSS is the limited patient accessibility, which favors patients with good cognition and mobility . To expand the utility, further research is needed to investigate the diagnostic power of other tools such as ultrasound examination based on the results of the kinematic analysis obtained with VFSS studies.
Abnormal swallowing kinematic parameters including anterior or superior hyoid displacement, timing of hyoid bone excursion, and velocity of hyoid bone movement during swallowing have been postulated as possible contributing factors for aspiration [11–20]. Nonetheless, there is no consensus thus far. Several studies suggested that anterior hyoid displacement is related to pharyngeal processes during swallowing, including opening of the upper esophageal sphincter, whereas vertical displacement of the hyoid bone was highly variable because of the different resting positions in anatomical variations and its relation to oral processes only . In this study, pairwise comparison between aspiration and normal groups showed a significantly lower value of anterior hyoid displacement and velocity of anterior hyoid displacement, superior hyoid displacement, and maximal hyoid displacement in the aspiration group. Nevertheless, whether there is a single convincing parameter of swallowing kinematics that leads to aspiration still requires further evidence.
Pyriform sinus stasis is a crucial factor that might be correlated with the severity of aspiration . Reduced anterior movement of the hyoid bone might lead to insufficient opening of the cricopharyngeal muscle, causing stasis in the pyriform sinuses and after swallowing aspiration [24, 25]. Likewise, kinematic analysis of the hyoid bone displacement between the stasis group and the normal group in this article revealed significantly reduced anterior and maximal movement of the hyoid. To the best of our knowledge, the current study is the first to attempt to use kinematic parameters to predict the presence of pyriform sinus stasis. Nonetheless, our data showed suboptimal predictability. One important explanation is that not only anterior and superior hyoid movement but also neuronal inhibition of the tonic cricopharyngeal muscle and sufficient intrabolus pressure are crucial in the adequate opening of the cricopharyngeal muscle . VFSS could provide detailed information for structural and timely kinematic analyses . However, other tools including manometry or electromyography for the cricopharyngeal muscle might be needed to delineate the underlying process of inadequate cricopharyngeal muscle opening leading to pyriform sinus stasis .
Only a few previously published studies have postulated that some parameters might be helpful in detecting aspiration [11, 17, 20]. Seo et al analyzed multiple VFSS swallowing kinematic parameters among populations with poststroke dysphagia and found that the maximal tilt angle of the epiglottis had predictive value for the detection of aspiration . According to the results of the study by Steele et al, the sensitivity of anterior hyoid displacement as a diagnostic parameter for detecting aspiration was as high as 90% . In addition, only maximum anterior hyoid displacement might predict the risk of penetration and aspiration according based on the research from Zhang et al, but the predicted and observed probability did not always match. In this article, acceptable predictability was attained while using anterior hyoid displacement and average velocity of maximal hyoid displacement to conduct ROC analyses, which was similar to the result from Steele et al . In addition, the results of our study showed that the sensitivity was close to 90% using 33.0 mm/s as the cutoff value for the average velocity of maximal hyoid displacement. Therefore, we assumed that the average velocity of maximal hyoid displacement might be used as a screening parameter for the detection of populations with aspiration.
This study has several limitations. First, the analysis was not conducted in accordance with stratification of different food consistencies. Available evidence has shown that different bolus textures have a possible influence on hyoid movement [27, 28]. Therefore, the predictability of kinematic analysis of the hyoid bone in aspiration or pyriform sinus stasis with regard to specific food consistency requires further research. Second, the populations studied in this research included various kinds of disease entities. Our research result provided a general scope of using swallowing kinematic analysis to detect aspiration, but disease-specific analysis is needed in clinical scenarios such as possible aspiration in patients with stroke, Parkinson’s disease, and head and neck cancer as well as in elderly individuals [11, 29–31]. Third, our study focused on the analysis of hyoid movement, and the result showed that the distance and velocity of anterior hyoid displacement and the average velocity of maximal hyoid displacement were acceptable predictors of aspiration. Nonetheless, other clinical parameters including epiglottic movement, larynx movement, and maximum pharyngeal constriction might also be contributing factors of aspiration and pyriform sinus stasis [11, 13, 32]. Further studies are required to investigate other potential parameters in detecting aspiration.