Central nervous system integration of sensorimotor signals in oral and pharyngeal structures: oropharyngeal kinematics response to recurrent laryngeal nerve lesion

VIDEOFLUOROSCOPIC EVALUATION OF THE IMPACT OF CAPSULE SIZE AND SUBJECT'S AGE AND GENDER ON CAPSULE SWALLOWING

BACKGROUND

People recurrently have difficulties swallowing solid medications, which can be associated with the size of the medication and the age and gender of individuals.

OBJECTIVE

To evaluate the impact of capsule size and adults' age and gender on oral and pharyngeal capsule transit during capsule swallows.

METHODS

Videofluoroscopy was used to measure capsule oral and pharyngeal transit during swallows in 49 healthy individuals (17 men and 32 women), with a mean age of 46 years (ranging from 23 to 88 years). Smaller capsules were filled with 0.50 mL of barium sulfate, and larger capsules were filled with 0.95 mL of barium sulfate; the volume of liquid ingested with the capsules was also quantified in each ingestion. The measurements included the oral preparation time, oral transit time, swallowing reaction time, time to laryngeal vestibule closure, laryngeal vestibule closure duration, pharyngeal transit time, and upper esophageal sphincter opening duration.

RESULTS

The capsule size did not influence either the oral or pharyngeal transit time. Increased liquid volume was ingested with larger capsules and by people older than 40 years. The oral transit time was shorter in older adults (60-88 years), and the time to laryngeal vestibule closure was longer in women.

CONCLUSION

The size of large capsules did not make a difference in oral or pharyngeal transit when compared with smaller capsules. The capsule size and the participant's age influenced the volume of liquid ingested - larger capsules and older individuals required a larger volume. The capsule oral transit was faster in individuals older than 60 years.

BACKGROUND

•Swallowing is influenced by the characteristics of what is being swallowed.

BACKGROUND

•There was no difference in swallowing capsules containing 0.50 mL or 0.95 mL.

BACKGROUND

•Larger capsules need more liquid ingestion to make swallowing easier.

BACKGROUND

•Individuals older than 40 years need a greater volume of liquid to swallow capsules than younger adults.

The effect of stiffness and hole size on nipple compression in infant suckling

During infant feeding, the nipple is an important source of sensory information that affects motor outputs, including ones dealing with compression of the nipple, suction, milk bolus movement, and swallowing. Despite known differences in behavior across commercially available nipples, little is known about the in vivo effects of nipple property variation. Here we quantify the effect of differences in nipple stiffness and hole size on an easily measured metric representing infant feeding behavior: nipple compression. We bottle-fed 7-day old infant pigs (n = 6) on four custom fabricated silicone nipples. We recorded live X-ray fluoroscopic imaging data of feeding on nipples of two levels of hardness/stiffness and two hole sizes. We tested for differences in nipple compression at the nipple's maximum compression across different nipple types using a mixed model analysis of variance. Stiffer nipples and those with smaller holes were compressed less than compliant nipples and nipples with larger holes (p < 0.001). We also estimated the force applied on the nipple during feeding and found that more force was applied to the compliant nipple with disproportionately larger strains. Our results suggest that infant pigs' nipple compression depends on material type and hole size, which is likely detected by the infant pigs' initial assessment of compressibility and flow. By isolating nipple properties, we demonstrated a relationship between properties and suckling behavior. Our results suggest that sensory information affects feeding behaviors and may also inform clinical treatment of poor feeding performance.

Oropharyngeal Capsaicin Exposure Improves Infant Feeding Performance in an Animal Model of Superior Laryngeal Nerve Damage

Sensorimotor feedback is critical to safe and effective swallowing. Because of this, sensory interventions have the potential to treat dysphagia. One such treatment may be found in capsaicin, which activates the internal branch of the superior laryngeal nerve (iSLN). The iSLN initiates the pharyngeal swallow, and a more sensitive iSLN should more readily elicit swallowing and improve swallow safety. We explored the neurophysiological mechanism by which capsaicin improves swallow performance using an infant pig model with a unilateral iSLN lesion. Using high-speed videofluoroscopy, we collected oropharyngeal kinematic data while pigs suckled on bottles, before and after applying capsaicin to the posterior tongue and valleculae. We found that capsaicin application decreased maximal bolus sizes, which improved swallow safety. Furthermore, capsaicin improved performance when infant pigs swallowed more moderately sized boluses. However, capsaicin did not change swallow frequency, the number of sucks prior to each swallow, nor total pharyngeal transit time (TPT). Similarly, excursions of the hyoid, thyroid, and posterior tongue were unchanged. TPT and hyoid and thyroid excursions maintained relationships with bolus size post-capsaicin, suggesting that these variables are less sensitive to sensory intervention. The timing and extent of posterior tongue movement were only correlated with bolus size pre-capsaicin, which could imply that capsaicin fundamentally changes in relationships between tongue movements and bolus size. Our results provide insight into the neural control of swallowing and capsaicin's mechanism of action, and suggest that capsaicin may be beneficial in treating acute infant dysphagia.

Acute effects of radiation treatment to submental muscles on burrowing and swallowing behaviors in a rat model

Swallowing impairments are a major complication of radiation treatment for oropharyngeal cancers, influencing oral intake and quality of life. The timing and functional consequences of radiation treatment on the swallowing process is not clearly understood. A rodent radiation injury model was used to investigate the onset of oral and pharyngeal dysfunctions in deglutition related to radiation treatment. This study tested the hypothesis that (Wall et al., 2013) alterations in normal biting, licking, and swallowing performance would be measurable following 64Gy of fractionated radiation to the submental muscles; and (Kotz et al., 2004) radiation will affect the animal’s general well-being as measured via burrowing activity. Seven rats received radiation using a clinical linear accelerator given in 8 fractions of 8Gy and another seven animals received sham anesthesia only treatment. Swallowing bolus transit/size was assessed via videofluoroscopy, tongue movement during drinking was measured via an electrical lick sensor, and biting was analyzed from acoustic recordings of a vermicelli pasta test. Burrowing activity was measured by the amount of gravel substrate displaced within a container. Measurements were taken at baseline, during treatment (1–4 weeks), and after completion of treatment (weeks 5 & 6). Decreases in licking frequency and increases in inter-lick interval were observed 5- and 6-weeks post-treatment. Significant decreases in burrowing performance, swallowing frequency, and inter-swallow interval were observed starting the last week of treatment and continuing up to 2-weeks after completion. Results suggest that tongue dysfunction is one of the first treatment related feeding problems to present immediately after the completion of radiation to the submental muscles.

Nasal respiratory support and tachypnea and oral feeding in full-term newborn lambs

Newborn infants with respiratory difficulties frequently require nasal respiratory support such as nasal continuous positive airway pressure (nCPAP) or high-flow nasal cannulae (HFNC). Oral feeding of these infants under nasal respiratory support remains controversial out of fear of aspiration and cardiorespiratory events. The main objective of this study was to evaluate the safety of oral feeding under different types of nasal respiratory support in newborn lambs without or with tachypnea. Eight lambs aged 4-5 days were instrumented to record sucking, swallowing, respiration, ECG, oxygen saturation, and arterial blood gases. Each lamb was given two bottles of 30 mL of milk with a pause of 30 s under videofluoroscopy in four conditions [no respiratory support, nCPAP 6 cmH₂O, HFNC 7 L/min, HFNC_CPAP (= HFNC 7 L/min + CPAP 6 cmH₂O)] administered in random order. The study was conducted in random order over 2 days, with or without standardized tachypnea induced by thoracic compression with a blood pressure cuff. Generalized linear mixed models were used to compare the four nasal respiratory supports in terms of safety (cardiorespiratory events and aspiration), sucking-swallowing-breathing coordination, and efficacy of oral feeding. Results reveal that no nasal respiratory support impaired the safety of oral feeding. Most of the few laryngeal penetrations we observed occurred with HFNC_CPAP. Nasal CPAP modified sucking-swallowing-breathing coordination, whereas the efficiency of oral feeding decreased under HFNC_CPAP. Results were similar with or without tachypnea. In conclusion, oral feeding under nasal respiratory support is generally safe in a term lamb, even with tachypnea.NEW & NOTEWORTHY The practice of orally feeding newborns suffering from respiratory problems while on nCPAP or HFNC remains controversial for fear of triggering cardiorespiratory events or aspiration pneumonia, or aggravating chronic lung disease. The present results show that bottle-feeding is generally safe in full-term lambs under nasal respiratory support, both without and with tachypnea.

Swallowing dysfunction following radiation to the rat mylohyoid muscle is associated with sensory neuron injury

Radiation-based treatments for oropharyngeal and hypopharyngeal cancers result in impairments in swallowing mobility, but the mechanisms behind the dysfunction are not clear. The purpose of this study was to determine if we could establish an animal model of radiation-induced dysphagia in which mechanisms could be examined. We hypothesized that 1) radiation focused at the depth of the mylohyoid muscle would alter normal bolus transport and bolus size and 2) radiation to the mylohyoid muscle will induce an injury/stress-like response in trigeminal sensory neurons whose input might modulate swallow. Rats were exposed to 48 or 64 Gy of radiation to the mylohyoid given 8 Gy in 6 or 8 fractions. Swallowing function was evaluated by videofluoroscopy 2 and 4 wk following treatment. Neuronal injury/stress was analyzed in trigeminal ganglion by assessing activating transcription factor (ATF)3 and GAP-43 mRNAs at 2, 4, and 8 wk post treatment. Irradiated rats exhibited decreases in bolus movement through the pharynx and alterations in bolus clearance. In addition, ATF3 and GAP-43 mRNAs were upregulated in trigeminal ganglion in irradiated rats, suggesting that radiation to mylohyoid muscle induced an injury/stress response in neurons with cell bodies that are remote from the irradiated tissue. These results suggest that radiation-induced dysphagia can be assessed in the rat and radiation induces injury/stress-like responses in sensory neurons.NEW & NOTEWORTHY Radiation-based treatments for head and neck cancer can cause significant impairments in swallowing mobility. This study provides new evidence supporting the possibility of a neural contribution to the mechanisms of swallowing dysfunction in postradiation dysphagia. Our data demonstrated that radiation to the mylohyoid muscle, which induces functional deficits in swallowing, also provokes an injury/stress-like response in the ganglion, innervating the irradiated muscle.

Does birth weight affect neonatal body weight, growth, and physiology in an animal model?

Infant birth weight affects neuromotor and biomechanical swallowing performance in infant pig models. Preterm infants are generally born low birth weight and suffer from delayed development and neuromotor deficits. These deficits include critical life skills such as swallowing and breathing. It is unclear whether these neuromotor and biomechanical deficits are a result of low birth weight or preterm birth. In this study we ask: are preterm infants simply low birth weight infants or do preterm infants differ from term infants in weight gain and swallowing behaviors independent of birth weight? We use a validated infant pig model to show that preterm and term infants gain weight differently and that birth weight is not a strong predictor of functional deficits in preterm infant swallowing. We found that preterm infants gained weight at a faster rate than term infants and with nearly three times the variation. Additionally, we found that the number of sucks per swallow, swallow duration, and the delay of the swallows relative to the suck cycles were not impacted by birth weight. These results suggest that any correlation of developmental or swallowing deficits with reduced birth weight are likely linked to underlying physiological immaturity of the preterm infant.

Effects of Superior Laryngeal Nerve Lesion on Kinematics of Swallowing and Airway Protection in an Infant Pig Model

The superior laryngeal nerve provides detailed sensory information from the mucosal surfaces of laryngeal structures superior to the vocal folds, including the valleculae. Injury to this nerve results in airway penetration and aspiration. Furthermore, such injuries might have an impact on the function of multiple structures involved in intraoral transport and swallowing due to connections within the brainstem. We sought to determine the effects of a surgical lesion of the superior laryngeal nerve on kinematics of the tongue, hyoid, and epiglottis during swallowing. We implanted radio-opaque markers into five infant pigs under anesthesia. Then we fed milk mixed with contrast agent to the pigs while they were recorded via video fluoroscopy, before and after a surgery to transect the superior laryngeal nerve. We digitized and rated airway protection in 177 swallows. We found that in most animals, swallow duration was shorter after nerve lesion. The hyoid also traveled a shorter distance after lesion. Frequently, individuals reacted differently to the same nerve lesion. We suggest that these differences are due to individual differences in neurological connections. When comparing hyoid kinematics between swallows with successful or failed airway protection, we found more consistency among individuals. This indicates that protecting the airway requires specific sets of kinematic events to occur, regardless of the neurological differences among individuals.

Muscle activity and kinematics show different responses to recurrent laryngeal nerve lesion in mammal swallowing

Understanding the interactions between neural and musculoskeletal systems is key to identifying mechanisms of functional failure. Mammalian swallowing is a complex, poorly understood motor process. Lesion of the recurrent laryngeal nerve, a sensory and motor nerve of the upper airway, results in airway protection failure (liquid entry into the airway) during swallowing through an unknown mechanism. We examined how muscle and kinematic changes after recurrent laryngeal nerve lesion relate to airway protection in eight infant pigs. We tested two hypotheses: 1) kinematics and muscle function will both change in response to lesion in swallows with and without airway protection failure, and 2) differences in both kinematics and muscle function will predict whether airway protection failure occurs in lesion and intact pigs. We recorded swallowing with high-speed videofluoroscopy and simultaneous electromyography of oropharyngeal muscles pre- and postrecurrent laryngeal nerve lesion. Lesion changed the relationship between airway protection and timing of tongue and hyoid movements. Changes in onset and duration of hyolaryngeal muscles postlesion were less associated with airway protection outcomes. The tongue and hyoid kinematics all predicted airway protection outcomes differently pre- and postlesion. Onset and duration of activity in only one infrahyoid and one suprahyoid muscle showed a change in predictive relationship pre- and postlesion. Kinematics of the tongue and hyoid more directly reflect changes in airway protections pre- and postlesion than muscle activation patterns. Identifying mechanisms of airway protection failure requires specific functional hypotheses that link neural motor outputs to muscle activation to specific movements.NEW & NOTEWORTHY Kinematic and muscle activity patterns of oropharyngeal structures used in swallowing show different patterns of response to lesion of the recurrent laryngeal nerve. Understanding how muscles act on structures to produce behavior is necessary to understand neural control.

Preterm Birth Impacts the Timing and Excursion of Oropharyngeal Structures during Infant Feeding

Swallowing in mammals requires the precise coordination of multiple oropharyngeal structures, including the palatopharyngeal arch. During a typical swallow, the activity of the palatopharyngeus muscle produces pharyngeal shortening to assist in producing pressure required to swallow and may initiate epiglottal flipping to protect the airway. Most research on the role of the palatopharyngeal arch in swallowing has used pharyngeal manometry, which measures the relative pressures in the oropharynx, but does not quantify the movements of the structures involved in swallowing. In this study, we assessed palatopharyngeal arch and soft palate function by comparing their movements in a healthy population to a pathophysiological population longitudinally through infancy (term versus preterm pigs). In doing so, we test the impact of birth status, postnatal maturation, and their interaction on swallowing. We tracked the three-dimensional (3D) movements of radiopaque beads implanted into relevant anatomical structures and recorded feeding via biplanar high-speed videofluoroscopy. We then calculated the total 3D excursion of the arch and soft palate, the orientation of arch movement, and the timing of maximal arch constriction during each swallow. Soft palate excursion was greater in term infants at both 7 and 17 days postnatal, whereas arch excursion was largely unaffected by birth status. Maximal arch constriction occurred much earlier in preterm pigs relative to term pigs, a result that was consistent across age. There was no effect of postnatal age on arch or soft palate excursion. Preterm and term infants differed in their orientation of arch movement, which most likely reflects both differences in anatomy and differences in feeding posture. Our results suggest that the timing and coordination of oropharyngeal movements may be more important to feeding performance than the movements of isolated structures, and that differences in the neural control of swallowing and its maturation in preterm and term infants may explain preterm swallowing deficits.

Effect of Chin-down-plus-larynx-tightening maneuver on swallowing function after minimally invasive esophagectomy: A randomized controlled trail

Background

The incidence of swallowing abnormality was high after minimally invasive esophagectomy (MIE) for esophageal cancer (EC). Few reports, however, focused on interventions for dysphagia after esophagectomy.

Aim

The purpose of this research was to estimate the effect of Chin‐down‐plus‐larynx‐tightening maneuver on swallowing function for patients receiving esophagectomy.

Method

This was a 2‐arm, parallel‐group, single‐blind randomized clinical trial, performed in patients suffered from EC from November 2018 to January 2020. Patients were randomly assigned to the intervention group (IG) or the control group (CG). The participants in CG received routine care, and the IG received Chin‐down‐plus‐larynx‐tightening maneuver during feeding. The incidence of choking cough, swallowing function, and dietary outcomes were evaluated before and after intervention for 7 days.

Results

A total of 237 EC cases were enrolled and randomized to the IG (n = 118) or CG (n = 119). There was no significant difference between the two groups in terms of demographic and clinical characteristics. Postoperative choking cough occurred in 5 of 118 cases (4.24%) in IG and 18 of 119 cases (19.4%) in CG, the differences showed statistically significant (P < .001). The analysis showed that the participants in the IG compared with the CG have more total caloric intake of 24 hours and higher K/R (the ratio of calories oral achieved to total calories required of body) significantly from D1 to D7 of intervention (P < .05).

Conclusion

The findings suggest that the Chin‐down‐plus‐larynx‐tightening maneuver can improve swallowing function recovery and oral total food intake and calories in EC patients undergoing MIE.

Swallow Safety is Determined by Bolus Volume During Infant Feeding in an Animal Model

Feeding difficulties are especially prevalent in preterm infants, although the mechanisms driving these difficulties are poorly understood due to a lack of data on healthy infants. One potential mechanism of dysphagia in adults is correlated with bolus volume. Yet, whether and how bolus volume impacts swallow safety in infant feeding is unknown. A further complication for safe infant swallowing is recurrent laryngeal nerve (RLN) injury due to patent ductus arteriosus surgery, which exacerbates the issues that preterm infants face and can increase the risk of dysphagia. Here, we used a validated animal model feeding freely to test the effect of preterm birth, postnatal maturation and RLN lesion and their interactions on swallow safety. We also tested whether bolus size differed with lesion or birth status, and the relationship between bolus size and swallow safety. We found very little effect of lesion on swallow safety, and preterm infants did not experience more penetration or aspiration than term infants. However, term infants swallowed larger boluses than preterm infants, even after correcting for body size. Bolus size was the primary predictor of penetration or aspiration, with larger boluses being more likely to result in greater degrees of dysphagia irrespective of age or lesion status. These results highlight that penetration and aspiration are likely normal occurrences in infant feeding. Further, when comorbidities, such as RLN lesion or preterm birth are present, limiting bolus size may be an effective means to reduce incidences of penetration and aspiration.

The effect of preterm birth, recurrent laryngeal nerve lesion, and postnatal maturation on hyoid and thyroid movements, and their coordination in infant feeding

Movements of the hyoid and thyroid are critical for feeding. These structures are often assumed to move in synchrony, despite evidence that neurologically compromised populations exhibit altered kinematics. Preterm infants are widely considered to be a neurologically compromised population and often experience feeding difficulties, yet measuring performance, and how performance matures in pediatric populations is challenging. Feeding problems are often compounded by complications arising from surgical procedures performed to ensure the survival of preterm infants, such as damage to the recurrent laryngeal nerve (RLN) during patent ductus arteriosus correction surgery. Here, we used a validated infant pig model for infant feeding to test how preterm birth, postnatal maturation, and RLN lesion interact to impact hyoid and thyroid excursion and their coordination. We filmed infant pigs when feeding using videofluorscopy at seven days old (1-2 months human equivalent) and 17 days old (6-9 months human equivalent) and tracked movements of the hyoid and thyroid on both days. We found that preterm birth impacted the coordination between hyoid and thyroid movements, but not their actual excursion. In contrast, excursion of the two structures increased with postnatal age in term and preterm pigs. RLN lesion decreased thyroid excursion, and primarily impacted hyoid movements by increasing variation in hyoid excursion. This work demonstrates that RLN lesion and preterm birth have distinct, but pervasive effects on feeding performance in infants, and suggest that interventions targeted towards reducing dysphagia should be prescribed based off the etiology driving dysphagia, rather than the prognosis of dysphagia.

Swallow Safety in Infant Pigs With and Without Recurrent Laryngeal Nerve Lesion

Aerodigestive coordination is critical for safe feeding in mammals, and failure to do so can result in aspiration. Using an infant pig model, we analyzed the impact of recurrent laryngeal nerve (RLN) lesion on aerodigestive coordination and swallow safety at two time points prior to weaning. We used high-speed videofluoroscopy to record 23 infant pigs longitudinally at two ages (7 days, 17 days) feeding on barium milk. We measured respiration with a plethysmograph and used the Infant Mammalian Penetration-Aspiration Scale (IMPAS) to identify unsafe swallows. We tested for changes in swallow safety longitudinally in control and lesion pigs, and whether there was any interaction between the four different groups. On postnatal day 7, lesioned pigs exhibited differences in the frequency distribution of IMPAS scores relative to control pigs on day 7, and 17 day old lesion and control pigs. There were longitudinal changes in performance following RLN lesion through time, suggesting that the impact of RLN lesion decreases with time, as older lesioned pigs performed similarly to older control pigs. We found minimal differences in the impact of aerodigestive coordination on swallow safety, with shorter delays of inspiration onset reflecting higher rates of penetration in young lesioned pigs. Healthy pigs aspirated at a similar rate to those with an RLN lesion indicating that the occasional occurrence of dysphagia in infants may be a normal behavior.

Specific Vagus Nerve Lesion Have Distinctive Physiologic Mechanisms of Dysphagia

Swallowing is complex at anatomical, functional, and neurological levels. The connections among these levels are poorly understood, yet they underpin mechanisms of swallowing pathology. The complexity of swallowing physiology means that multiple failure points may exist that lead to the same clinical diagnosis (e.g., aspiration). The superior laryngeal nerve (SLN) and the recurrent laryngeal nerve (RLN) are branches of the vagus that innervate different structures involved in swallowing. Although they have distinct sensory fields, lesion of either nerve is associated clinically with increased aspiration. We tested the hypothesis that despite increased aspiration in both case, oropharyngeal kinematic changes and their relationship to aspiration would be different in RLN and SLN lesioned infant pigs. We compared movements of the tongue and epiglottis in swallows before and after either RLN or SLN lesion. We rated swallows for airway protection. Posterior tongue ratio of safe swallows changed in RLN (p = 0.01) but not SLN lesioned animals. Unsafe swallows post lesion had different posterior tongue ratios in RLN and SLN lesioned animals. Duration of epiglottal inversion shortened after lesion in SLN animals (p = 0.02) but remained unchanged in RLN animals. Thus, although SLN and RLN lesion lead to the same clinical outcome (increased aspiration), the mechanisms of failure of airway protection are different, which suggests that effective therapies may be different with each injury. Understanding the specific pathophysiology of swallowing associated with specific neural insults will help develop targeted, disease appropriate treatments.

Recurrent laryngeal nerve transection in mice results in translational upper airway dysfunction

The recurrent laryngeal nerve (RLN) is responsible for normal vocal-fold (VF) movement, and is at risk for iatrogenic injury during anterior neck surgical procedures in human patients. Injury, resulting in VF paralysis, may contribute to subsequent swallowing, voice, and respiratory dysfunction. Unfortunately, treatment for RLN injury does little to restore physiologic function of the VFs. Thus, we sought to create a mouse model with translational functional outcomes to further investigate RLN regeneration and potential therapeutic interventions. To do so, we performed ventral neck surgery in 21 C57BL/6J male mice, divided into two groups: Unilateral RLN Transection (n = 11) and Sham Injury (n = 10). Mice underwent behavioral assays to determine upper airway function at multiple time points prior to and following surgery. Transoral endoscopy, videofluoroscopy, ultrasonic vocalizations, and whole-body plethysmography were used to assess VF motion, swallow function, vocal function, and respiratory function, respectively. Affected outcome metrics, such as VF motion correlation, intervocalization interval, and peak inspiratory flow were identified to increase the translational potential of this model. Additionally, immunohistochemistry was used to investigate neuronal cell death in the nucleus ambiguus. Results revealed that RLN transection created ipsilateral VF paralysis that did not recover by 13 weeks postsurgery. Furthermore, there was evidence of significant vocal and respiratory dysfunction in the RLN transection group, but not the sham injury group. No significant differences in swallow function or neuronal cell death were found between the two groups. In conclusion, our mouse model of RLN injury provides several novel functional outcome measures to increase the translational potential of findings in preclinical animal studies. We will use this model and behavioral assays to assess various treatment options in future studies.

Chin-down-plus-larynx-tightening maneuver improves choking cough after esophageal cancer surgery

Background

Esophageal cancer patients can benefit from dissection of the recurrent laryngeal nerve (RLN) lymph node (LN); however, this procedure increases the risk of RLN injury. After nerve injury, many complications can occur, including choking cough, which can affect patients' quality of life. This study examined the effectiveness of the chin-down-plus-larynx-tightening maneuver for improving choking cough after radical thoracic esophageal cancer surgery.

Methods

Sixty-two patients with resectable thoracic esophageal cancer presented with choking cough, hoarseness or vocal cord paralysis after radical operations. Twenty-two patients who choked on water were guided to swallow 1 mL of warm water using a chin-down-plus-larynx-tightening maneuver. Choking cough relief results and their relationships with clinical factors were analyzed.

Results

No correlation was found between the occurrence of post-operative choking cough and gender, age, surgical method, hoarseness, vocal cord fixation type, vocal cord fixation, or glottal closure. Multivariate regression analysis revealed no independent risk factors associated with choking cough. Choking cough was completely relieved in 17 of 22 (77.3%) patients. Fifteen of 19 (78.9%) patients with choking cough and hoarseness, and 2 of 3 patients with only choking cough reported complete relief when they tried the new maneuver. The chin-down-plus-larynx-tightening maneuver was more effective for males than for females.

Conclusions

The chin-down-plus-larynx-tightening maneuver significantly relieved choking cough; thus, this maneuver can aid in managing choking cough after radical thoracic esophageal cancer surgery.

Reduced Coordination of Hyolaryngeal Elevation and Bolus Movement in a Pig Model of Preterm Infant Swallowing

Preterm infants often have dysphagia. Because reducing lifetime cumulative exposure to radiation in the context of diagnosis and treatment is a continuing goal of all medical fields which use X-ray imaging, efforts exist to reduce reliance on the gold standard diagnostic tool for dysphagia, VFSS. Alternatives, such as video of external hyolaryngeal movement using video recordings of the anterior surface of the neck, must be evaluated and validated against videofluoroscopy, a task for which non-human animal models are appropriate. In this study, we tested the hypotheses that (1) swallows could be identified equally well from video of external hyolaryngeal movement and bolus movement in videofluoroscopy, and that (2) the two measures would be tightly temporally linked in both term and preterm infant pigs. We recorded 222 swallows in simultaneous and precisely synchronized high-speed videofluoroscopy and high-speed camera films of 4 preterm and 3 term infant pigs drinking milk from a bottle. In term pigs, the two measures consistently identified the same swallows in each image stream. However, in preterm pigs there was a high rate of false positives (~ 10% per feeding sequence) and false negatives (~ 27% per feeding sequence). The timing of hyolaryngeal elevation (external video) and bolus movement (videofluoroscopy) was correlated and consistent in terms pigs, but not in preterm pigs. Magnitude of hyolaryngeal elevation was less in preterm pig swallows than term pig swallows. Absence of epiglottal inversion in preterm pigs was not linked to variation in the timing of the two swallow events. Video of external hyolaryngeal movement, though a reliable swallow indicator in term infant pigs, was unreliable in preterm infant pigs. The coordination of swallowing events differs in preterm and term infant pigs. More research is needed into the distinctive biomechanics of preterm infant pigs.

Respiratory-Swallow Pattern Following Total Laryngectomy

The goal of this study was to further characterize respiratory patterns in total laryngectomees with attention to respiratory-swallow pattern as it relates to presence/absence of tracheoesophageal puncture (TEP) and bolus consistency. It was hypothesized that participants with TEP would exhibit respiratory-swallow patterns that were significantly different than those without TEP and that bolus consistency (thin or solid) would modulate respiratory-swallow pattern. Data were collected from 12 adults (8 male), aged 46-67 years (mean 57) status post total laryngectomy (1-30 years; average 6 years). Those actively receiving chemoradiation, with history of esophageal cancer, with neurologic disease, with history of lung cancer, with known or suspected recurrence of head and neck cancer (HNC), or with severe cognitive deficits were excluded. Laryngectomy participants were asked to swallow three sips of water and three bites of graham cracker. Submental surface EMG activity was used to detect swallows and a custom stoma mask in line with a pneumotachograph measured airflow during the swallows. Non-parametric Mann-Whitney test for differences was used to detect significance for our dependent variables, TEP or bolus consistency and independent variables, respiratory-swallow pattern. Laryngectomee's showed preference for swallow during inspiration which is inconsistent with the expiratory pattern preference found in healthy adults with intact larynges by McFarland et al. (Respir Physiol Neurobiol 234:89-96, 2016) but consistent with the pattern preference for inspiration (or non-dominant respiratory-swallow phase pattern) found in the HNC population at-large by Brodsky et al. (J Appl Physiol 112(10):1698-1705, 2012). No significant difference was found in swallow pattern with regards to presence/absence of TEP or bolus consistency.

Preterm birth disrupts the development of feeding and breathing coordination

All mammals must breathe and breathe continuously from birth. Similarly, all mammals, including infants, have high functional demands for feeding. However, the pathway that food takes through the pharynx interrupts respiration. The coordination between swallowing and breathing is therefore critical for all infant mammals. Clinically, this coordination differs between term and preterm infants. However, the neurological mechanisms underlying this coordination and how it matures as infants grow are poorly understood. Here, we integrate high-resolution data from multiple physiologic processes across a longitudinal time frame to study suck-swallow-breathe dynamics in a preterm animal model, the infant pig. In doing so, we test the hypothesis that preterm birth will have an impact on some, but not all, behaviors associated with suck-swallow-breath performance. We hypothesize that coordination will be disrupted, reflecting incomplete connections in the brainstem. We found that preterm pigs became rhythmic and mature in sucking and swallowing behaviors, suggesting substantial postnatal maturation in the coordination of these behaviors. However, their ability to coordinate swallowing and breathing never developed. These results have implications for the nature of clinical care of human infants, as well as for how feeding processes develop in mammals. Clinically, they provide a foundation for developing interventions for preterm infants. Additionally, these results suggest that the lack of coordination between swallowing and breathing may be a significant factor in determining the minimum gestation time across mammals. NEW & NOTEWORTHY Preterm infants face a variety of challenges associated with safe feeding, but obtaining high-resolution longitudinal data to understand these challenges in humans is challenging. We used a pig model to acquire high-speed videofluoroscopic and respiratory inductance plethysmograph data throughout the nursing period to show that preterm birth does not have substantial impacts on the ability of infants to perform isolated behaviors. However, it does decrease the ability of preterm infants to coordinate among behaviors during feeding.

Impact of recurrent laryngeal nerve lesion on oropharyngeal muscle activity and sensorimotor integration in an infant pig model

The successful performance of a swallow requires dynamic integration between a wide range of sensory inputs and muscle activities to produce the coordinated kinematics of oropharyngeal structures. Damage to the recurrent laryngeal nerve (RLN) produces dysphagia in infants, with food or liquid entering the airway despite this nerve having minimal direct sensory or motor connections to the act of swallowing, apart from vocal fold closure. Previous results have demonstrated that a complete RLN lesion disrupts both performance and kinematics before initiation of the pharyngeal swallow in infants. We tested the hypothesis that a RLN lesion produces changes in the normal activity of oral floor, tongue, and infrahyoid muscles during a swallow. We recorded swallowing in our validated infant pig model, with synchronous high-speed imaging and fine-wire, chronic electromyography. We found changes in the timing, duration, and amplitude of the motor pattern in an array of muscles that are supplied by several different cranial and cervical nerves. Some of these changes in muscle activity are associated with the preparatory aspects of bolus aggregation or movement and so occur before the pharyngeal swallow. Taken with previous biomechanical results, these patterns suggest an intricate brain stem sensorimotor integration that occurs as part of a swallow. In particular, the execution of oral motor function is changed as a result of this simple lesion. NEW & NOTEWORTHY Damage to the recurrent laryngeal nerve compromises swallowing despite an absent or minimal contribution to either the motor or sensory aspects of this function. This study documents EMG changes, following RLN lesion, to non-RLN innervated muscles that are active during swallowing in an infant model. Some of these muscles fire before the pharyngeal swallow and are associated with the preparatory aspects of bolus aggregation and movement, suggesting important sensorimotor integration at a brain stem level.

Evidence of Oropharyngeal Dysfunction in Feeding in the Rat Rotenone Model of Parkinson's Disease

Swallowing disorders in Parkinson's disease are not responsive to dopamine depletion therapy and contribute to morbidity. They are poorly understood owing to a lack of adequate models. We present the first evidence of oropharyngeal changes in a rotenone toxicity model of Parkinson's disease. Rats were recorded while feeding before and after daily rotenone injections at two different doses (2.75 mg/kg and 3 mg/kg). The higher dose had a much more severe parkinsonian phenotype than the low dose. Timing and amplitude of chewing changed, as did the coordination of chewing and swallowing. Dose-dependent effects were evident. These preliminary results indicate that future research in toxicological models of Parkinson's disease should incorporate the study of oropharyngeal dysfunction. A better understanding of nongenetic models of Parkinson's disease in feeding may open new avenues for research into the neurological and behavioral bases for swallowing dysfunction in Parkinson's disease.

Maturation of the Coordination Between Respiration and Deglutition with and Without Recurrent Laryngeal Nerve Lesion in an Animal Model

The timing of the occurrence of a swallow in a respiratory cycle is critical for safe swallowing, and changes with infant development. Infants with damage to the recurrent laryngeal nerve, which receives sensory information from the larynx and supplies the intrinsic muscles of the larynx, experience a significant incidence of dysphagia. Using our validated infant pig model, we determined the interaction between this nerve damage and the coordination between respiration and swallowing during postnatal development. We recorded 23 infant pigs at two ages (neonatal and older, pre-weaning) feeding on milk with barium using simultaneous high-speed videofluoroscopy and measurements of thoracic movement. With a complete linear model, we tested for changes with maturation, and whether these changes are the same in control and lesioned individuals. We found (1) the timing of swallowing and respiration coordination changes with maturation; (2) no overall effect of RLN lesion on the timing of coordination, but (3) a greater magnitude of maturational change occurs with RLN injury. We also determined that animals with no surgical intervention did not differ from animals that had surgery for marker placement and a sham procedure for nerve lesion. The coordination between respiration and swallowing changes in normal, intact individuals to provide increased airway protection prior to weaning. Further, in animals with an RLN lesion, the maturation process has a larger effect. Finally, these results suggest a high level of brainstem sensorimotor interactions with respect to these two functions.

Involvement of hypoglossal and recurrent laryngeal nerves on swallowing pressure

Swallowing pressure generation is important to ensure safe transport of an ingested bolus without aspiration or leaving residue in the pharynx. To clarify the mechanism, we measured swallowing pressure at the oropharynx (OP), upper esophageal sphincter (UES), and cervical esophagus (CE) using a specially designed manometric catheter in anesthetized rats. A swallow, evoked by punctate mechanical stimulation to the larynx, was identified by recording activation of the suprahyoid and thyrohyoid muscles using electromyography (EMG). Areas under the curve of the swallowing pressure at the OP, UES, and CE from two trials indicated high intrasubject reproducibility. Effects of transecting the hypoglossal nerve (12N) and recurrent laryngeal nerve (RLN) on swallowing were investigated. Following bilateral hypoglossal nerve transection (Bi-12Nx), OP pressure was significantly decreased, and time intervals between peaks of thyrohyoid EMG bursts and OP pressure were significantly shorter. Decreased OP pressure and shortened times between peaks of thyrohyoid EMG bursts and OP pressure following Bi-12Nx were significantly increased and longer, respectively, after covering the hard and soft palates with acrylic material. UES pressure was significantly decreased after bilateral RLN transection compared with that before transection. These results suggest that the 12N and RLN play crucial roles in OP and UES pressure during swallowing, respectively. We speculate that covering the palates with a palatal augmentation prosthesis may reverse the reduced swallowing pressure in patients with 12N or tongue damage by the changes of the sensory information and of the contact between the tongue and a palates. NEW & NOTEWORTHY Hypoglossal nerve transection reduced swallowing pressure at the oropharynx. Covering the hard and soft palates with acrylic material may reverse the reduced swallowing function caused by hypoglossal nerve damage. Recurrent laryngeal nerve transection reduced upper esophageal sphincter negative pressure during swallowing.

LVC Timing in Infant Pig Swallowing and the Effect of Safe Swallowing

Recurrent laryngeal nerve (RLN) injury in neonates, a complication of head and neck surgeries, leads to increased aspiration risk and swallowing dysfunction. The severity of resulting sequelae range from morbidity, such as aspiration pneumonia, to mortality from infection and failure to thrive. The timing of airway protective events including laryngeal vestibule closure (LVC) is implicated in aspiration. We unilaterally transected the RLN in an infant pig model to observe changes in the timing of swallowing kinematics with lesion and aspiration. We recorded swallows using high-speed video-fluoroscopic swallow studies (VFSS) and scored them using the Infant Mammalian Penetration and Aspiration Scale (IMPAS). We hypothesized that changes would occur in swallowing kinematics (1) between RLN lesion and control animals, and (2) among safe swallows (IMPAS 1), penetration swallows (IMPAS 3), and aspiration swallows (IMPAS 7). We observed numerous changes in timing following RLN lesion in safe and unsafe swallows, suggesting pervasive changes in the coordination of oropharyngeal function. The timing of LVC, posterior tongue, and hyoid movements differed between pre- and post-lesion in safe swallows. Posterior tongue kinematics differed for post-lesion swallows with penetration. The timing and duration of LVC and posterior tongue movement differed between aspiration swallows pre- and post-lesion. After lesion, safe swallows and swallows with aspiration differed in timing of LVC, laryngeal vestibule opening, and posterior tongue and hyoid movements. The timing of thyrohyoid muscle activity varied with IMPAS, but not lesion. Further study into the pathophysiology of RLN lesion-induced swallowing dysfunction is important to developing novel therapies.

Pre-pharyngeal Swallow Effects of Recurrent Laryngeal Nerve Lesion on Bolus Shape and Airway Protection in an Infant Pig Model

Recurrent laryngeal nerve (RLN) damage in infants leads to increased dysphagia and aspiration pneumonia. Recent work has shown that intraoral transport and swallow kinematics change following RLN lesion, suggesting potential changes in bolus formation prior to the swallow. In this study, we used geometric morphometrics to understand the effect of bolus shape on penetration and aspiration in infants with and without RLN lesion. We hypothesized (1) that geometric bolus properties are related to airway protection outcomes and (2) that in infants with RLN lesion, the relationship between geometric bolus properties and dysphagia is changed. In five infant pigs, dysphagia in 188 swallows was assessed using the Infant Mammalian Penetration-Aspiration Scale (IMPAS). Using images from high-speed VFSS, bolus shape, bolus area, and tongue outline were quantified digitally. Bolus shape was analyzed using elliptical Fourier analysis, and tongue outline using polynomial curve fitting. Despite large inter-individual differences, significant within individual effects of bolus shape and bolus area on airway protection exist. The relationship between penetration-aspiration score and both bolus area and shape changed post lesion. Tongue shape differed between pre- and post-lesion swallows, and between swallows with different IMPAS scores. Bolus shape and area affect airway protection outcomes. RLN lesion changes that relationship, indicating that proper bolus formation and control by the tongue require intact laryngeal sensation. The impact of RLN lesion on dysphagia is pervasive.