Alteration of Swallowing and Ventilation Coordination in Respiratory Diseases in Small Mammals

Physiological analyses of swallowing changes due to chronic obstructive pulmonary disease in anesthetized male rats

Chronic obstructive pulmonary disease (COPD) was previously known as chronic bronchitis and emphysema. It has various main symptoms, such as dyspnea, chronic cough, and sputum, and is often accompanied by dysphagia. Although many published clinical reports have described COPD-related dysphagia, the physiological mechanisms underlying swallowing changes due to COPD remain unclear. Therefore, we analyzed how COPD affects the swallowing reflex using COPD model rats. We performed an electrophysiological study of respiration and swallowing using COPD model induced by intratracheal administration of porcine pancreatic elastase and lipopolysaccharide in Sprague-Dawley male rats. To identify the respiration and swallowing responses, electromyographic activity was recorded from the diaphragm, digastric (Dig), and thyrohyoid (TH) muscles. We confirmed COPD using micro-computed tomography analysis and hematoxylin and eosin staining of the lungs. The duty cycle was defined as the ratio of the inspiration duration to the total respiratory duration. In COPD model rats, the duty cycle was significantly higher than that in control rats. The frequency of the swallowing reflex evoked by electrical stimulation of the superior laryngeal nerve during the inspiration phase was higher in COPD model rats than in control rats. Furthermore, long-term COPD altered Dig and TH muscle activity without pathological muscle change. Our results suggest that COPD increases the frequency of swallowing initiation during the inspiration phase. Furthermore, long-term COPD affects swallowing-related muscle activity without pathological muscle changes. These physiological changes may increase the risk of developing dysphagia. Further studies are necessary to clarify the mechanisms contributing to the functional changes in respiration and swallowing in COPD.

Respiratory-swallow coordination in a rat model of chemoradiation

BACKGROUND

Chemoradiation treatment (CRT) for head and neck cancer (HNC) is associated with postswallow inhale events that elevate the risk of penetration/aspiration. The purpose of this study was to assess the validity of a rat model for investigating the effect of CRT on respiratory-swallow coordination.

METHODS

Videofluoroscopic swallow study was performed on 10 Sprague-Dawley rats 3 months post-CRT (3 mg/kg Cisplatin, 10 fractions of 4.5 Gy/day radiotherapy to tongue base), and 10 naïve controls. We examined the effect of CRT on swallow apnea duration, diaphragm movement, and bolus kinematics.

RESULTS

CRT rats had a significant increase in postswallow inhale (p = 0.008), which was associated with significantly longer swallow apnea durations, lower diaphragm displacement at swallow onset, and faster pharyngoesophageal bolus speed.

CONCLUSION

The rat CRT model is valid for the study of respiratory-swallow coordination due to the consistency of findings in this study with those reported in clinical CRT studies in HNC.

A Systematic Review of Oropharyngeal Dysphagia Models in Rodents

Oropharyngeal dysphagia is a condition characterized by swallowing difficulty in the mouth and pharynx, which can be due to various factors. Animal models of oropharyngeal dysphagia are essential to confirm the cause-specific symptoms, pathological findings, and the effect of treatment. Recently, various animal models of dysphagia have been reported. The purpose of this review is to organize the rodent models of oropharyngeal dysphagia reported to date. The articles were obtained from Medline, Embase, and the Cochrane library, and selected following the PRISMA guideline. The animal models in which oropharyngeal dysphagia was induced in rats or mice were selected and classified based on the diseases causing oropharyngeal dysphagia. The animal used, method of inducing dysphagia, and screening methods and results were collected from the selected 37 articles. Various rodent models of oropharyngeal dysphagia provide distinctive information on atypical swallowing. Applying and analyzing the treatment in rodent models of dysphagia induced from various causes is an essential process to develop symptom-specific treatments. Therefore, the results of this study provide fundamental and important data for selecting appropriate animal models to study dysphagia.