Respiratory-swallow coordination in a rat model of chemoradiation

Effects of chemoradiation and tongue exercise on swallow biomechanics and bolus kinematics

BACKGROUND

Common treatments for head and neck cancer (radiation and chemotherapy) can lead to dysphagia; tongue exercise is a common intervention. This study aimed to assess swallow biomechanics and bolus kinematics using a well-established rat model of radiation or chemoradiation treatment to the tongue base, with or without tongue exercise intervention.

METHODS

Pre- and post-treatment videofluoroscopy was conducted on 32 male Sprague-Dawley rats treated with radiation/chemoradiation and exercise/no exercise. Rats in the exercise groups completed a progressive resistance tongue training paradigm. Swallow biomechanics, bolus kinematics, jaw opening, and post-swallow respiration were assessed.

RESULTS

Both treatments impacted outcome measures; the addition of exercise intervention showed benefit for some measures, particularly in rats treated with radiation, vs. chemoradiation.

CONCLUSIONS

Radiation and chemoradiation can significantly affect aspects of deglutition; combined treatment may result in worse outcomes. Tongue exercise intervention can mitigate deficits; more intensive intervention may be warranted in proportion to combined treatment.

Breathing-Swallowing discoordination after definitive chemoradiotherapy for head and neck cancers is associated with aspiration pneumonia

PURPOSE

Swallowing dysfunction and the risk of aspiration pneumonia are frequent clinical problems in the treatment of head and neck squamous cell carcinomas (HNSCCs). Breathing-swallowing coordination is an important factor in evaluating the risk of aspiration pneumonia. To investigate breathing-swallowing discoordination after chemoradiotherapy (CRT), we monitored respiration and swallowing activity before and after CRT in patients with HNSCCs.

METHODS

Non-invasive swallowing monitoring was prospectively performed in 25 patients with HNSCCs treated with CRT and grade 1 or lower radiation-induced dermatitis. Videoendoscopy, videofluoroscopy, Food Intake LEVEL Scale, and patient-reported swallowing difficulties were assessed.

RESULTS

Of the 25 patients selected for this study, four dropped out due to radiation-induced dermatitis. The remaining 21 patients were analyzed using a monitoring system before and after CRT. For each of the 21 patients, 405 swallows were analyzed. Swallowing latency and pause duration after the CRT were significantly extended compared to those before the CRT. In the analysis of each swallowing pattern, swallowing immediately followed by inspiration (SW-I pattern), reflecting breathing-swallowing discoordination, was observed more frequently after CRT (p = 0.0001). In 11 patients, the SW-I pattern was observed more frequently compared to that before the CRT (p = 0.00139). One patient developed aspiration pneumonia at 12 and 23 months after the CRT.

CONCLUSION

The results of this preliminary study indicate that breathing-swallowing discoordination tends to increase after CRT and could be involved in aspiration pneumonia. This non-invasive method may be useful for screening swallowing dysfunction and its potential risks.

Chemoradiation to the submental muscles alters hyoid movement during swallowing in a rat model

Hyolaryngeal dysfunction is a commonly reported swallowing problem after chemoradiation treatment for head and neck cancer. The displacement of the hyolaryngeal complex during swallowing protects the airway and assists in opening the upper esophageal sphincter. Activation of the submental muscles, specifically the mylohyoid and geniohyoid muscles, is thought to facilitate movement of the hyoid. The purpose of this study was to determine if targeted radiation to the submental muscles given concurrently with chemotherapy alters hyolaryngeal displacement 1 mo after treatment. We hypothesized that chemoradiation treatment would result in abnormal patterns of hyoid movement compared with controls. Furthermore, we propose that these changes are associated with alterations in bolus size and discoordination of the jaw during drinking. Eighteen rats underwent either chemoradiation, radiation, or no treatment. Radiation treatment was targeted to submental muscles using a clinical linear accelerator given in 12 fractions of 4 Gy (3 days per week). Cycles of 1 mg/kg of cisplatin were administered concurrently each week of radiation. One month posttreatment, videofluoroscopy swallow studies (VFSS) were performed in self-drinking rats using a fluoroscope customized with a high-speed camera. The hyoid, jaw, and hard palate were tracked during swallowing from VFSS. Hyoid kinematics were analyzed from the start to the end of hyoid movement, and parameters were compared with bolus size and jaw movement. Significant differences in hyoid retraction parameters were found postchemoradiation. Alterations in the trajectory of hyoid motion during swallowing were observed. The findings demonstrate early changes in hyoid motion during swallowing associated with chemoradiation treatment.NEW & NOTEWORTHY Chemoradiation treatment for head and neck cancer can cause functional impairments in swallowing, which can adversely affect quality of life. This study provides new evidence that chemoradiation targeted to the submental muscles provokes early adaptations in hyoid movement during swallowing, which correlate with changes in bolus size. We also demonstrate a method for tracking the hyoid during swallowing in a rat model of chemoradiation injury.

Swallowing-related muscle inflammation and fibrosis induced by a single dose of radiation exposure in mice

BACKGROUND

Although radiotherapy is commonly used to treat head and neck cancer, it may lead to radiation-associated dysphagia (RAD). There are various causes of RAD, however, the mechanism has not yet been fully identified. Currently, the only effective treatment for RAD is rehabilitation. Additionally, there are few available animal models of RAD, necessitating the development of new models to establish and evaluate RAD treatments. We hypothesize that radiation-induced neck muscle fibrosis could be one of the causes of RAD due to impairment of laryngeal elevation. Therefore, in this study, we focused on the changes in inflammation and fibrosis of the strap muscles (Sternohyoid, Sternothyroid, and Thyrohyoid muscles) after a single-dose irradiation. This research aims to provide a reference animal model for future studies on RAD.

RESULTS

Compared to control mice, those treated with 72-Gy, but not 24-Gy, irradiation had significantly increased tumor necrosis factor-α (TNF-α) (p < 0.01) and α-smooth muscle actin (αSMA) (p < 0.05) expression at 10 days and significantly increased expression levels of motif chemokine ligand-2 (CCL2), α-SMA, tumor growth factor-β1 (TGF-β1), type1 collagen, and interleukin-1β (IL-1β) (p < 0.05) in the muscles at 1 month by real-time PCR analysis. The results of immunohistochemistry showed that the deposition of type 1 collagen gradually increased in extracellular space after radiation exposure, and the positive area was significantly increased at 3 months compared to non-irradiated control.

CONCLUSIONS

A single dose of 72-Gy irradiation induced significant inflammation and fibrosis in the strap muscles of mice at 1 month, with immunohistochemical changes becoming evident at 3 months. This cervical irradiation-induced fibrosis model holds potential for establishing an animal model for RAD in future studies.

LEVEL OF EVIDENCE

N/A.

Pink1-/- Rats Demonstrate Swallowing and Gastrointestinal Dysfunction in a Model of Prodromal Parkinson Disease

Early motor and non-motor signs of Parkinson disease (PD) include dysphagia, gastrointestinal dysmotility, and constipation. However, because these often manifest prior to formal diagnosis, the study of PD-related swallow and GI dysfunction in early stages is difficult. To overcome this limitation, we used the Pink1-/- rat, a well-established early-onset genetic rat model of PD to assay swallowing and GI motility deficits. Thirty male rats were tested at 4 months (Pink1-/- = 15, wildtype (WT) control = 15) and 6 months (Pink1-/- = 7, WT = 6) of age; analogous to early-stage PD in humans. Videofluoroscopy of rats ingesting a peanut-butter-barium mixture was used to measure mastication rate and oropharyngeal and pharyngoesophageal bolus speeds. Abnormal swallowing behaviors were also quantified. A second experiment tracked barium contents through the stomach, small intestine, caecum, and colon at hours 0-6 post-barium gavage. Number and weight of fecal emissions over 24 h were also collected. Compared to WTs, Pink1-/- rats showed slower mastication rates, slower pharyngoesophageal bolus speeds, and more abnormal swallowing behaviors. Pink1-/- rats demonstrated significantly delayed motility through the caecum and colon. Pink1-/- rats also had significantly lower fecal pellet count and higher fecal pellet weight after 24 h at 6 months of age. Results demonstrate that swallowing dysfunction occurs early in Pink1-/- rats. Delayed transit to the colon and constipation-like signs are also evident in this model. The presence of these early swallowing and GI deficits in Pink1-/- rats are analogous to those observed in human PD.

Longitudinal Effects of Base of Tongue Concurrent Chemoradiation Therapy in a Pre-Clinical Model

BACKGROUND/OBJECTIVES

Base of tongue (BOT) dysfunction is common following oropharyngeal concurrent chemoradiation therapy (CCRT). We present a clinically relevant animal model quantifying the effects of CCRT on tongue strength and elasticity over time.

METHODS

Fifty-three male and 53 female Sprague-Dawley rats were randomized to control or experimental groups. Experimental animals received cisplatin, 5-fluorouracil, and 5 fractions of 7 Gy directed to the BOT. Controls received no intervention. At 2 weeks, 5 months, or 10 months after CCRT, animals underwent non-survival surgery to measure twitch and tetanic tongue strength, which were analyzed using multivariate linear mixed effects models. Tongue displacement, a surrogate for tongue elasticity, was also determined via stress-strain testing and analyzed via a multivariate linear mixed effects model.

RESULTS

Reporting the combined results of both sexes, the estimated experimental group mean peak twitch forces became more divergent over time compared to controls, being 8.3% lower than controls at 2 weeks post-CCRT, 15.7% lower at 5 months, and 31.6% lower at 10 months. Estimated experimental group mean peak tetanic forces followed a similar course and were 2.9% lower than controls at 2 weeks post CCRT, 20.7% lower at 5 months, and 27.0% lower at 10 months. Stress-strain testing did not find CCRT to have a significant effect on tongue displacement across experimental timepoints.

CONCLUSIONS

This study demonstrates an increasing difference in tongue strength over time between controls and animals exposed to CCRT. Tongue elasticity was not significantly affected by CCRT, suggesting that changes in strength may not be caused by fibrosis.

LEVEL OF EVIDENCE

NA Laryngoscope, 133:1455-1461, 2023.