Adapting human videofluoroscopic swallow study methods to detect and characterize dysphagia in murine disease models.

This study adapted human videofluoroscopic swallowing study (VFSS) methods for use with murine disease models for the purpose of facilitating translational dysphagia research. Successful outcomes are dependent upon three critical components: test chambers that permit self-feeding while standing unrestrained in a confined space, recipes that mask the aversive taste/odor of commercially-available oral contrast agents, and a step-by-step test protocol that permits quantification of swallow physiology. Elimination of one or more of these components will have a detrimental impact on the study results. Moreover, the energy level capability of the fluoroscopy system will determine which swallow parameters can be investigated. Most research centers have high energy fluoroscopes designed for use with people and larger animals, which results in exceptionally poor image quality when testing mice and other small rodents. Despite this limitation, we have identified seven VFSS parameters that are consistently quantifiable in mice when using a high energy fluoroscope in combination with the new murine VFSS protocol. We recently obtained a low energy fluoroscopy system with exceptionally high imaging resolution and magnification capabilities that was designed for use with mice and other small rodents. Preliminary work using this new system, in combination with the new murine VFSS protocol, has identified 13 swallow parameters that are consistently quantifiable in mice, which is nearly double the number obtained using conventional (i.e., high energy) fluoroscopes. Identification of additional swallow parameters is expected as we optimize the capabilities of this new system. Results thus far demonstrate the utility of using a low energy fluoroscopy system to detect and quantify subtle changes in swallow physiology that may otherwise be overlooked when using high energy fluoroscopes to investigate murine disease models.

Improving the Utility of Laryngeal Adductor Reflex Testing: A Translational Tale of Mice and Men.

OBJECTIVES: Evaluation of the laryngeal adductor reflex (LAR) entails delivering air through an endoscope positioned 1 to 2 mm from the arytenoid mucosa to elicit bilateral vocal fold (VF) closure. This short working distance limits visualization to only the ipsilateral arytenoid and results in quantification of a single LAR metric: threshold pressure that evokes the LAR. Our goal was to evolve the LAR procedure to optimize its utility in clinical practice and translational research. STUDY DESIGN: Prospective translational experiment. SETTING: Academic institution. SUBJECTS: Young healthy human adults (n = 13) and 3 groups of mice: healthy, primary aging mice (n = 5), a transgenic mouse model of amyotrophic lateral sclerosis (ALS; n = 4), and young healthy controls (n = 10). METHODS: The VFs were visualized bilaterally during supramaximal air stimulation through an endoscope. Responses were analyzed to quantify 4 novel metrics: VF adduction phase duration, complete glottic closure duration, VF abduction phase duration, and total LAR duration. RESULTS: The 4 LAR metrics are remarkably similar between healthy young humans and mice. Compared to control mice, aging mice have shorter glottic closure durations, whereas ALS-affected mice have shorter VF abduction phase durations. CONCLUSIONS: We have established a new LAR protocol that permits quantification of novel LAR metrics that are translatable between mice and humans. Using this protocol, we showed that VF adduction is impaired in primary aging mice, whereas VF abduction is impaired in ALS-affected mice. These preliminary findings highlight the enhanced diagnostic potential of LAR testing.

Videofluoroscopic Validation of a Translational Murine Model of Presbyphagia.

Presbyphagia affects approximately 40% of otherwise healthy people over 60 years of age. Hence, it is a condition of primary aging rather than a consequence of primary disease. This distinction warrants systematic investigations to understand the causal mechanisms of aging versus disease specifically on the structure and function of the swallowing mechanism. Toward this goal, we have been studying healthy aging C57BL/6 mice (also called B6), the most popular laboratory rodent for biomedical research. The goal of this study was to validate this strain as a model of presbyphagia for translational research purposes. We tested two age groups of B6 mice: young (4-7 months; n = 16) and old (18-21 months; n = 11). Mice underwent a freely behaving videofluoroscopic swallow study (VFSS) protocol developed in our lab. VFSS videos (recorded at 30 frames per second) were analyzed frame-by-frame to quantify 15 swallow metrics. Six of the 15 swallow metrics were significantly different between young and old mice. Compared to young mice, old mice had significantly longer pharyngeal and esophageal transit times (p = 0.038 and p = 0.022, respectively), swallowed larger boluses (p = 0.032), and had a significantly higher percentage of ineffective primary esophageal swallows (p = 0.0405). In addition, lick rate was significantly slower for old mice, measured using tongue cycle rate (p = 0.0034) and jaw cycle rate (p = 0.0020). This study provides novel evidence that otherwise healthy aging B6 mice indeed develop age-related changes in swallow function resembling presbyphagia in humans. Specifically, aging B6 mice have a generally slow swallow that spans all stages of swallowing: oral, pharyngeal, and esophageal. The next step is to build upon this foundational work by exploring the responsible mechanisms of presbyphagia in B6 mice.

Semiautomatic marker tracking of tongue positions captured by videofluoroscopy during primate feeding.

Videofluoroscopy (VF) is one of the most commonly used tools to assess oropharyngeal dysphagia as well as to visualize musculoskeletal structures of humans and animals engaged in various behaviors, including feeding. Despite its importance in clinical and scientific use, processing VF data has historically been extremely tedious because it is performed using manual frame-by-frame methods. With recent technological advances, the frame rate for scientific use has been increasing along with the use of high speed data capture systems. In the current study, we used non-human primates as a model animal to study human feeding behaviors to capture tongue movement based on markers implanted into the tongue. Here, we introduce a semi-automatic marker tracking algorithm that yields high tracking accuracy (> 90%) and dramatic speed improvements (faster than real time labeling). Furthermore, we quantify the sources of tracking errors and the tracking performance as a function of marker speeds. Our results indicate that there is more room for methodological improvements both in detection and prediction of marker positions. Moreover, correspondingly faster frame rates will be required to capture faster kinematic behaviors such as those of mice, which are extensively used to study both control and pathological conditions.