Effect of lingual paralysis on swallowing and breathing coordination in rats

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.

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.

Experimental Injury Rodent Models for Oropharyngeal Dysphagia

Oropharyngeal dysphagia is a disorder that can make swallowing difficult and reduce the quality of life. Recently, the number of patients with swallowing difficulty has been increasing; however, no comprehensive treatment for such patients has been developed. Various experimental animal models that mimic oropharyngeal dysphagia have been developed to identify appropriate treatments. This review aims to summarize the experimentally induced oropharyngeal dysphagia rodent models that can be used to provide a pathological basis for dysphagia. The selected studies were classified into those reporting dysphagia rodent models showing lingual paralysis by hypoglossal nerve injury, facial muscle paralysis by facial nerve injury, laryngeal paralysis by laryngeal and vagus nerve injury, and tongue dysfunction by irradiation of the head and neck regions. The animals used in each injury model, the injury method that induced dysphagia, the screening method for dysphagia, and the results are summarized. The use of appropriate animal models of dysphagia may provide adequate answers to biological questions. This review can help in selecting a dysphagia animal system tailored for the purpose of providing a possible solution to overcome dysphagia.

Home-Based Orolingual Exercise Improves the Coordination of Swallowing and Respiration in Early Parkinson Disease: A Quasi-Experimental Before-and-After Exercise Program Study

Introduction: The coordination of swallowing and respiration is important for safety swallowing without aspiration. This coordination was affected in Parkinson disease (PD). A noninvasive assessment tool was used to investigate the effect of an easy-to-perform and device-free home-based orolingual exercise (OLE) program on swallowing and respiration coordination in patients with early-stage PD.

Materials and Methods: This study had a quasi-experimental before-and-after exercise program design. Twenty six patients with early-stage PD who were aged 62.12 ± 8.52 years completed a 12-week home-based OLE program. A noninvasive assessment tool was used to evaluate swallowing and respiration. For each patient, we recorded and analyzed 15 swallows (3 repeats of 5 water boluses: 1, 3, 5, 10, and 20 mL) before and after the home-based OLE program. Oropharyngeal swallowing and its coordination with respiration were the outcome measures. The frequency of piecemeal deglutition, pre- and post-swallowing respiratory phase patterns, and parameters of oropharyngeal swallowing and respiratory signals (swallowing respiratory pause [SRP], onset latency [OL], total excursion time [TET], excursion time [ET], second deflexion, amplitude, and duration of submental sEMG activity, and amplitude of laryngeal excursion) were examined.

Results: The rate of piecemeal deglutition decreased significantly when swallowing 10- and 20-mL water boluses after the program. In the 1-mL water bolus swallowing trial, the rate of protective pre- and post-swallowing respiratory phase patterns was significantly higher after the program. For the parameters of oropharyngeal swallowing and respiratory signals, only the amplitude of laryngeal excursion was significantly lower after the program. Moreover, the volume of the water bolus significantly affected the SRP and duration of submental sEMG when patients swallowed three small water bolus volumes (1, 3, and 5 mL).

Conclusion: The home-based OLE program improved swallowing and its coordination with respiration in patients with early-stage PD, as revealed using a noninvasive method. This OLE program can serve as a home-based program to improve swallowing and respiration coordination in patients with early-stage PD.

Effect of liquid properties on swallowing and ventilation coordination in rats

BACKGROUND

One aspect of rehabilitation in swallowing disorders is to change liquid properties. The objective of our study was to test how liquid properties could improve oropharyngeal dysphagia and swallowing and ventilation coordination in an animal model.

METHODS

Forty-two healthy male rats were distributed in six groups, including a control group. Rats were deprived of water for 24 h and then each group was administered liquid with different properties: tap water, sugar water, sparkling water, salt water, cold water, and acidic water. Rats were studied without and with oropharyngeal dysphagia achieved by unilateral section of the hypoglossal nerve. Swallowing and ventilation were analyzed by barometric plethysmograph.

KEY RESULTS

In healthy rats, swallowing occurred during expiratory time for all liquid properties. Most deglutitions were during expiratory time for all liquid properties (88±12%) and were not modified. There was an increase in VT/TI during swallowing with sparkling water and cold water (P<.05). In the operated groups, rats had significantly fewer swallows with tap water (P<.05) and significantly more swallows with sparkling water (P<.001), sugar water (P<.001) and cold water (P<.001) during expiratory time. The mean inspiratory volume (VT/TI) increased with sparkling water (P<.05).

CONCLUSION AND INFERENCES

Sparkling water seemed to improve swallowing and ventilation coordination in an animal model, to be confirmed in a study including patients with oropharyngeal dysphagia.

Minimally Invasive Approach to the Lingual and Hypoglossal Nerves in the Adult Rat

Surgical manipulation of the sensory and motor nerves of the rat tongue is often employed in studies evaluating the oral cavity functions of mastication and deglutition. A noninvasive, atraumatic approach that will then facilitate sufficient manipulation of these structures is required. In this study, we detail an approach that consistently allows identification of the hypoglossal (motor) and lingual (sensory) nerves of the rat. Six Wistar rats (250-500 g) were anesthetized and dissected either as fresh tissue (N = 3) or following transcardial perfusion with 4% paraformaldehyde (N = 3). Both fixed and non-fixed specimens of the rat head and neck were incised in the right submandibular region. The first animal in each group was used to gain a basic understanding of the regional muscular anatomy with reference to the hypoglossal and lingual nerves. Subsequent animals were used for the development of an efficient and minimally invasive approach to these nerves. The resultant approach begins as an incision through skin and platysma, followed by medial reflection of the digastric muscle. This allows visualization of the hypoglossal nerve in the region of the bifurcation of the common trunk into medial and lateral subdivisions. Next, the lingual nerve dissection is approached by reflection rostrally of the transversus mandibularis muscle and a caudal reflection of the mylohyoid muscle. This dissection reveals the geniohyoid muscle which when separated bluntly using forceps, exposes the lingual nerve. The anatomical approach described and illustrated herein will aid investigators in consistent identification of these two nerves as fundamental methods of their projects.

Inactivity-induced phrenic and hypoglossal motor facilitation are differentially expressed following intermittent vs. sustained neural apnea

Reduced respiratory neural activity elicits a rebound increase in phrenic and hypoglossal motor output known as inactivity-induced phrenic and hypoglossal motor facilitation (iPMF and iHMF, respectively). We hypothesized that, similar to other forms of respiratory plasticity, iPMF and iHMF are pattern sensitive. Central respiratory neural activity was reversibly reduced in ventilated rats by hyperventilating below the CO2 apneic threshold to create brief intermittent neural apneas (5, ∼1.5 min each, separated by 5 min), a single brief massed neural apnea (7.5 min), or a single prolonged neural apnea (30 min). Upon restoration of respiratory neural activity, long-lasting (>60 min) iPMF was apparent following brief intermittent and prolonged, but not brief massed, neural apnea. Further, brief intermittent and prolonged neural apnea elicited an increase in the maximum phrenic response to high CO2, suggesting that iPMF is associated with an increase in phrenic dynamic range. By contrast, only prolonged neural apnea elicited iHMF, which was transient in duration (<15 min). Intermittent, massed, and prolonged neural apnea all elicited a modest transient facilitation of respiratory frequency. These results indicate that iPMF, but not iHMF, is pattern sensitive, and that the response to respiratory neural inactivity is motor pool specific.