The swallowing process involves a series of complex, highly coordinated, and fixed muscle movement behaviors. The passageways of the mouth, pharynx, and esophagus contract and open, in turn, resulting in a pressure gradient that pushes food from the mouth to the esophagus. Safe and effective swallowing depends on the accuracy and timing of the integration between sensory and motor systems. Pharyngography is a common diagnostic tool for evaluating swallowing function in patients. Clinically, the location can be determined and symptoms of dysphagia can be observed by angiography during swallowing, although much of the information recorded during VFSS cannot be fully utilized because of the inability to quantify the symptoms of aspiration, dysphagia, and retention. Previous studies [15–18] have confirmed that dynamic contrast quantitative analysis technology can effectively clarify the relationship between the movements of the organs involved in swallowing as a food bolus passes. Applying VFSS to the analysis of muscle relaxation and contraction of the upper sphincter of the esophagus and pharynx can provide more detailed information than can be determined by assessments based on contrast alone. Determining the relationship between quantitative and descriptive findings could be useful in clinical practice, although it was previously unknown whether such outcomes would consistently match up. Therefore, the VFSS qualitative and quantitative results were compared and analyzed in this study.
The quantitative values of the kinematic parameters differed based on the qualitative grades of the VFSS. First, weakening of the movement of the hyoid–laryngeal complex resulted in lower HSM and HAM values, confirming the weaker the movement of the hyoid laryngeal bone complex, the greater the degree of swallowing dysfunction. This finding is consistent with the results of other studies that have investigated swallowing physiology and pathology [19, 20]. Movement of the hyoid–laryngeal complex is a crucial component of swallowing function, as it helps ensure the closure of the throat, the return of the epiglottis, the opening of the cricopharyngeal muscle, and the smooth and safe completion of swallowing activities. Measuring the displacement of the hyoid bone is often used to quantify the movement ability of the hyoid–laryngeal complex. During swallowing, the vertical movement of the hyoid bone drives the closure of the epiglottis, which is beneficial for the protection of the airway, whereas the forward movement of the hyoid is beneficial for the opening of the UES [21]. Theoretically, upward and forward displacement of the hyoid bone plays a positive role in swallowing. The results of this study also confirmed that the measuring the displacement of the hyoid bone can help to objectively evaluate the motion amplitude of the hyoid-laryngeal complex and can compensate for the lack of information provided in clinical evaluations based solely on observation of tongue extension or swallowing angiography to describe the motion of the hyoid-laryngeal complex.
An increase in the cricopharyngeal muscle opening duration, however, did not significantly alter the opening diameter of the UES. Similarly, the opening duration of the UES did not change significantly with the different qualitative total value categories. Physiologically, the coordination of activities involved in swallowing mainly the coordination of UES relaxation and pharyngeal muscle contraction, as well as the sequential movement of upper and lower pharyngeal muscle contractions. The evaluation of swallowing coordination via VFSS is mainly based on the observation and description of the opening of the cricopharyngeal muscle; however, such observations may be subjective, and no unified diagnostic criteria have been established. In contrast, quantitative analysis allows for the assessment of the opening range of the UES, which is an important quantitative index that reflects the coordination of the swallowing process [22]. The quantitative analysis of the VFSS data facilitated the measurement of the opening range of the UES, although no obvious difference with qualitative total value; one possible explanation for this could be related to the primary disease associated with the dysphagia among the patients included in this study. Previous studies [23–24] have reported that coordination of movements involved in swallowing is regulated by the swallowing pattern generator within the brainstem. The development of a brainstem lesion usually manifests as weakening of the pharynx’s ability to push and/or an abnormal UES relaxation function, which can easily lead to serious consequences that include leakage or aspiration. However, the present study did not include patients with such brainstem diseases; therefore, the value of the UES opening diameter does not reliably reflect the relaxation of the cricopharyngeal muscle.
Finally, there was no significant difference in the pharyngeal area at rest between the different qualitative grades of vallecular and pyriform fossa residues. The pharyngeal area at rest can be used as another objective index for evaluating the coordination of the pharyngeal phase of swallowing. The pharyngeal cavity contraction rate reflects the degree of contraction during swallowing in the pharyngeal phase [25–26]. In this stage, the hyoid bone on the larynx moves upward, the arytenoepiglottis and thyrohyoid muscles contract, and the base of the tongue inclines backward to ensure the epiglottis forms a proper cover; while the epiglottis valley on both sides is oriented close to the midline, the muscle group in the larynx contracts, the vocal cord and the ventricular band retracts, the glottis closes, and the pharyngeal constrictor retracts. During this time, the laryngopharynx and pyriform fossa are open, and the food mass is squeezed across the epiglottis, reaching the esophageal entrance; the opening of the upper esophageal sphincter is coordinated to ensure smooth passage of food through the pharyngeal cavity for entry into the esophagus. Thus, the main function of the pharyngeal cavity and the related muscle contraction is to clear the pharyngeal mass and squeeze the food bolus downward into the esophagus during swallowing. When swallowing disorders are caused by various organic and neuromuscular abnormalities, the ability of the pharyngeal cavity to clear food decreases, the corresponding size of the food mass remaining in the pharyngeal cavity increases, and the corresponding pharyngeal cavity contraction rate decreases. Aspiration can easily occur when the glottis reopens. Previous studies [27] have shown that in the treatment of dysphagia, improving pharyngeal contraction can effectively reduce the residue remaining after swallowing. However, the pharyngeal cavity contraction rate in this study did not significantly correlate with the grading of epiglottic valley and pyriform fossa residues. Considering the limited inclusion of primary diseases in this study, measurements of the pharyngeal cavity area and contraction rate may have had little correlation with the presence of such residues. In addition, the results of this study revealed that 96.58% of the patients had vallecular residues, 83.76% had pyriform fossa residues, and the average contraction rate of the pharyngeal cavity was 40–55%. Therefore, it is also possible that the 5 mL volume of food paste administered in this study was too small, which could have resulted in weak sensory and motor stimulation of the pharynx, thereby affecting the contraction of the pharyngeal constrictor muscle and resulting in insufficient peristalsis.
In this study, most of the quantitative and time parameter values showed statistically significant differences according to the different qualitative grades assigned during the VFSS, including the oral transit time, swallowing reaction time in the pharyngeal phase, soft palate lift duration, hyoid movement duration, pharyngeal cavity transit time, and LVC duration. However, the UES opening duration poorly reflected the degree of cricopharyngeal muscle opening, which is consistent with the UES opening diameter results.
All quantitative values were measured or calculated built-in software tools and formulas, reflecting a portion of the time sequence and interval during the swallowing process. A factor analysis for dimensionality reduction of the 12 quantitative variables was conducted, and the results suggested that the quantitative items were relatively independent. The five principal components selected barely represented all of the quantitative values; that is, the measurements of the 12 quantitative variables could still adequately describe the entire swallowing process. The results of this study also show that there is a certain positive correlation between the quantitative total value and the qualitative total value, which means quantitative results can reveale that the highest correlation and a high sensitivity with qualitative results. However, since the types and definitions of the parameters used by various institutions are not yet unified, this study suggests that in the future selection of quantitative parameters of VFSS, studies should continue to optimize the existing parameters and attempt to screen out and standardize effective and comprehensive parameters to fully describe the swallowing process. This could help promote their use in clinical settings to better evaluate the effects on patients before and after treatment or the differences between patients.
This study has the following limitations: 1) the types of patients with dysphagia selected in the study was relatively limited, the patients with PD were in phase 1–2, and the existing dysphagia was relatively mild, and the representativeness of the sample was relatively weak, so further research must be conducted in the future with an improved design; 2) the type of food balls selected was relatively fixed, which could have had a certain impact on the results; 3) the sample size needs to be further expanded; 4) during video acquisition, due to the patients’ conditions, the body position, head control, and degree of cooperation could have been impacted, among other factors, which could have affected the clarity of imaging of various anatomical components, resulting in difficulties and errors in the qualitative analysis; 5) when obtaining various quantitative results, semi-automatic methodologies may lead to some measurement errors due to deviations of the measurer's understanding of the measurement technique, and the workload of the data acquisition process is large with many steps, so fatigue could have led to some measurement errors; 6) considering the imaging factors, the radiation amplification effect could give the impression that the distance between two points on the image is larger than the actual value, and the radial distortion of the ray could stretch the length of the structure around the image. Radiation amplification and radial distortion of the rays may have affected the accuracy of the analysis.
The extraction of the most effective and valuable information from dysphagia angiography and the objective comparison of the levels of functionality within-patients before and after treatment, as well as between patients, can fully meet the comprehensive needs of scientific research, stimulate more innovative research, and generate ideas and references for the evaluation and follow-up treatment of dysphagia. The quantitative results based on pathological samples collected from a wide range of individuals with multiple diseases should be used for evaluation, and future studies should assess other valuable parameters and improve those with poor reliability, validity, and matching. In the future, with progress in science and technology and further deepening of research in this field, fully automated quantitative analysis of VFSS data could become possible, improving the effectiveness of swallowing assessments and reducing the burden on clinical workers.