Screening of aspiration pneumonia using the modified Mallampati classification tool in older adults.

Pneumonia is a major cause of morbidity and mortality in older adults. In the aging society, screening methods for predicting aspiration pneumonia are crucial for its prevention. Changes in the oropharyngeal morphology and hyoid bone position may increase the risk of aspiration pneumonia. This multicenter study aimed to investigate a simple and effective screening method for predicting dysphagia and aspiration pneumonia. Overall, 191 older adults (aged 65 years or older) were randomly sampled using the simple random sampling technique. Oropharyngeal morphology was assessed using the modified Mallampati classification, which reflects the size of the tongue in the oropharyngeal cavity. The hyoid position was measured as the distance between the menton and laryngeal prominence to evaluate aging-related changes in the muscles of the laryngopharynx. Dysphagia was assessed using the repetitive saliva swallowing test (RSST), which measures the number of swallowing movements in 30 seconds; dysphasia is defined as less than 3 swallowing movements in 30 seconds. The aspiration signs were assessed based on history of choking or coughing reflex during eating or drinking and medical history of pneumonia. The study findings revealed that the modified Mallampati classification was significantly correlated with a medical history of pneumonia. A higher incidence of pneumonia was evident in the lower Mallampati classification, which shows the smaller size of the tongue base in the oropharyngeal cavity. The results of this study suggest that the modified Mallampati classification may be a possible screening method to predict the occurrence of pneumonia.

Assessment of swallowability and acceptability of scored darunavir/cobicistat/emtricitabine/tenofovir alafenamide (D/C/F/TAF) fixed-dose combination (FDC) tablets in HIV-1-infected children aged ≥6 to <12 years, using matching placebo tablets: A randomized study.

BACKGROUND: Darunavir/cobicistat/emtricitabine/tenofovir alafenamide (D/C/F/TAF) fixed-dose combination (FDC) was developed as a once-daily, complete antiretroviral (ARV) regimen therapy to address the need for simplified protease inhibitor-based ARV regimens. This study assessed the swallowability and acceptability for long-term use of scored placebo tablets matching the D/C/F/TAF FDC tablets in children living with HIV-1. METHODS: This study (NCT04006704) was a Phase 1, open-label, randomized, single-dose, 2-period, 2-sequence crossover study in children living with HIV-1, aged ≥6 to <12 years and weighing ≥25 to <40 kg, on a stable ARV regimen for ≥3 months. Participants were asked to swallow whole (size, 21 × 11 × 7 mm) and split matching placebo D/C/F/TAF tablets. Swallowability of the matching placebo D/C/F/TAF tablets (primary endpoint) was assessed by observers. Acceptability of taking matching placebo D/C/F/TAF tablets and current ARVs was evaluated by participants using a 3-point questionnaire. Participants rated the acceptability for long-term daily use of the placebo D/C/F/TAF tablets, and observers assessed how easily caregivers could split a scored tablet by hand, using 3-point questionnaires. RESULTS: Among the 24 participants who enrolled and completed the study, 95.8% (23/24) were able to swallow the whole and split matching placebo D/C/F/TAF tablets after 1 or 2 attempts. Most participants (>70%) rated the acceptability of tablets for long-term daily use as acceptable or good to take. Breaking the tablets was considered easy or OK by 79.2% (19/24) of caregivers. CONCLUSION: Scored D/C/F/TAF FDC tablets are swallowable - with whole favoured over split - and considered at least acceptable for long-term daily intake in children living with HIV-1 aged ≥6 to <12 years. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT04006704.

A comparison of swallowing related quality of life in patients undergoing transoral endoscopic versus open thyroid surgery.

INTRODUCTION: It is important for the endoscopic thyroid surgeon to understand the pros and cons of trans-oral endoscopic thyroidectomy-vestibular approach (TOETVA) vis-à-vis, open conventional thyroidectomy (OTx) so he/she can help patients in making informed choices regarding the type of procedure to opt for. Swallowing related quality of life (SWAL-QoL) has not been compared between the two approaches. Using a rigorous qualitative methodology and validated reliable tool, this study set out to compare the swallowing related quality of life in patients undergoing TOETVA versus OTx. METHODS: Prospective study at 3 time points in patients planned for hemithyroidectomy (Preoperative, 1 week and 12 weeks). Data were collected on patients at a tertiary teaching institute in India. Participants ranged from age 18-60 years with a diagnosis of benign euthyroid nodule undergoing hemithyroidectomy. Exclusion criteria were-(1) pre-existing vocal cord abnormalities, (2) undergoing surgery for recurrent nodules, and (3) any neuro-muscular disease affecting swallowing ability. Main outcome measure was comparison of swallowing related quality of life domain scores between patients undergoing hemithyroidectomy via either endoscopic trans-oral or open approach. RESULTS: Of the 82 included patients, 40 underwent TOETVA and 42 OTx. Both the groups were comparable in terms of demographic and clinicopathological profile. The mean preoperative SWAL-QOL scores were comparable in all domains. Mean SWAL-QoL scores for all domains on postoperative day 7 were significantly better in TOETVA group with domains burden, eating desire, mental health and communication having medium effect sizes. Physical symptom domain was better in the OTx group but had a small effect size. The difference in SWAL-QoL domains between the two groups persisted for 3 months also. CONCLUSION: Swallowing related quality of life after trans-oral endoscopic thyroidectomy compared to conventional open surgery has not been reported in the literature. Our findings suggest that trans-oral endoscopic thyroidectomy results in significant superior swallowing related quality of life in the majority of domains.

Feasibility of Oral Function Evaluation According to Dementia Severity in Older Adults with Alzheimer's Disease.

Oral function evaluation in older adults with dementia is important for determining appropriate and practical dietary support plans; however, it can be challenging due to their difficulties in comprehending instructions and cooperating during assessments. The feasibility of oral function evaluation has not been well studied. This cross-sectional study aimed to determine the feasibility of oral function evaluation in older adults with Alzheimer's disease (AD) according to Functional Assessment Staging of Alzheimer's Disease (FAST) stages. In total, 428 older adults with AD (45 men and 383 women; mean age: 87.2 ± 6.2 years) were included. Multilevel logistic regression models were used to examine the prevalence of participants who were unable to perform oral function evaluations, including oral diadochokinesis (ODK), repeated saliva swallow test (RSST), and modified water swallow test (MWST). In comparison to the reference category (combined FAST stage 1-3), FAST stage 7 was associated with the infeasibility of ODK (adjusted odds ratio, 95% confidence interval = 26.7, 4.2-168.6), RSST (5.9, 2.2-16.1), and MWST (8.7, 1.6-48.5, respectively). Oral function evaluation is difficult in older adults with severe AD. Simpler and more practical swallowing function assessments and indicators that can be routinely observed are required.

The effect of behavioral therapy on dysphagia of acute ischemic stroke patients feeding with a nasogastric tube.

This prospective observational study aimed to assess the impact of behavioral therapy on dysphagia in patients with acute ischemic stroke undergoing nasogastric tube feeding. The study was conducted between June 2020 and May 2022 at the Neurological Center of Bach Mai Hospital, Vietnam, with a sample size of 230 patients divided into two groups: a normal and a behavioral therapy group. The normal therapy group received routine care and treatment based on standard protocols, while the behavioral therapy group underwent daily swallowing exercises for approximately 60 minutes. The Gugging Swallowing Screen (GUSS) was utilized to screen individuals with dysphagia, and the difference-in-differences (DID) method was adopted to estimate the effect of behavioral therapy on dysphagia patients. The study concluded that behavioral therapy improved dysphagia in patients with acute ischemic stroke undergoing nasogastric tube feeding. This study highlights the potential of behavioral therapy as an effective intervention for dysphagia rehabilitation in stroke patients.

Neuroendocrine cells initiate protective upper airway reflexes.

Airway neuroendocrine (NE) cells have been proposed to serve as specialized sensory epithelial cells that modulate respiratory behavior by communicating with nearby nerve endings. However, their functional properties and physiological roles in the healthy lung, trachea, and larynx remain largely unknown. In this work, we show that murine NE cells in these compartments have distinct biophysical properties but share sensitivity to two commonly aspirated noxious stimuli, water and acid. Moreover, we found that tracheal and laryngeal NE cells protect the airways by releasing adenosine 5'-triphosphate (ATP) to activate purinoreceptive sensory neurons that initiate swallowing and expiratory reflexes. Our work uncovers the broad molecular and biophysical diversity of NE cells across the airways and reveals mechanisms by which these specialized excitable cells serve as sentinels for activating protective responses.

Relationship between endoscopic gastroesophageal valve grading and mean nocturnal baseline impedance and postreflux swallow-induced peristaltic wave index in patients with gastroesophageal reflux disease.

This study aimed to investigate the relationship between endoscopic gastroesophageal valve grading and mean nocturnal baseline impedance (MNBI) and postreflux swallow-induced peristaltic wave index (PSPWI) in patients with gastroesophageal reflux disease (GERD). A total of 120 patients diagnosed with GERD disease were included in the study. According to the classification of endoscopic gastroesophageal valves, the patients were divided into 5 groups, group 1 as baseline group, and Group 2-4 as Hill grade I-IV. Basic information about the patients was collected, including age and gender. The mean nocturnal baseline impedance and creep wave index induced by swallowing after rumination were measured by high resolution creep measurement technique. Through statistical analysis, the relationship between valve classification and observation index was discussed. In terms of MNBI, impedance values gradually decreased with increasing valve classification. The average impedance of the Grade 1 group was 23.5 mm Hg/cm2, while the average impedance of the Grade 5 group was 15.2 mm Hg/cm2. This reduction showed a significant decreasing trend (P < .001). In addition, in terms of the peristaltic wave index caused by swallowing after regurgitation, the peristaltic wave index gradually increased with the increase of valve classification. The mean index in the Grade 1 group was 1.8 beats/min, while the mean index in the Grade 5 group was 3.6 beats/min. This increase showed a significant positive relationship (P < .001). Endoscopic gastroesophageal valve grading was significantly correlated with MNBI and PSPWI in patients with GERD. These observations can serve as useful tools for assessing the severity of GERD and monitoring disease progression.

Efficacy of natural enzymes mouthwash: a randomised controlled trial.

OBJECTIVES: Natural enzymes mouthwash has been proposed as salivary substitutes to treat xerostomia. This study aims to evaluate the efficacy of the mouthwash to treat xerostomia. MATERIALS AND METHODS: A double-blind, parallel group randomised control clinical trial involving N = 49 adult participants with xerostomia was carried out. Intervention group received natural enzymes moisturising mouthwash (with active ingredients lactoferrin, lysozyme, lactoperoxidase and glucose oxidase); while control group received benzydamine mouthwash. Mouthwashes were repacked, labelled with specific code, and were given to participants by third-party. Subjects were instructed to rinse with the mouthwash 4 times per day at a specific period, for 2 weeks. Symptoms of xerostomia were assessed using Xerostomia Inventory at day 0 and 14; together with the assessment of Clinical Oral Dryness Score (CODS), and measurement of resting and stimulated salivary flow rate. RESULTS: 48 participants completed the clinical follow-up, and n = 1 had lost of follow-up. From the 48 participants, n = 23 received natural enzymes mouthwash, while n = 25 received benzydamine mouthwash. Intervention group achieved reduction in symptoms of xerostomia from baseline. Intervention group also showed significantly better improvements in the cognitive perception of dry mouth and oromotor function such as chewing, swallowing and speech of the participants; and reduction in waking up at night to drink water (p < 0.05). The CODS and resting salivary flow rate were also significantly improved in intervention group (p < 0.05). CONCLUSION: Use of natural enzymes mouthwash improved signs and symptoms of xerostomia. CLINICAL RELEVANCE: Natural enzymes mouthwash is potentially effective to treat xerostomia, well-tolerated and safe to be used by xerostomia patients. CLINICAL TRIAL REGISTRATION NUMBER: This study was retrospectively registered in ClinicalTrials.gov ID NCT05640362 on 7 December 2022.

Swallowing and feeding of young children on high-flow oxygen therapy.

BACKGROUND:  Oral feeding practices of young patients on high-flow oxygen (HFO2) have been controversial. Limited literature exists on this topic, but new studies suggest introducing oral feeds. OBJECTIVE:  This study aims to describe the changes in swallowing and feeding of a group of young children on HFO2. METHOD:  Twelve participants (mean age 34.17 months [s.d. = 3.97]) on HFO2 were assessed clinically at the bedside using the Schedule of Oral Motor Assessment. Assessments were conducted twice to determine the change in characteristics: upon approval from the managing doctor when respiratory stability on HFO2 was achieved and for a second time on the last day of receiving HFO2 (mean 2.6 days apart). Patients received standard in-patient care and speech therapy intervention. RESULTS:  Most participants displayed typical oral motor function at initial and final assessments for liquid, puree and semi-solid consistencies. Purees and soft solid consistencies were introduced to most participants (n = 11, 91.7%). Solids and chewables were challenging for all participants during both assessments. Half of the participants displayed gagging and a wet vocal quality with thin liquids at the initial assessment only. CONCLUSION:  This small-scale study found that HFO2 should not preclude oral diets, but in this sample, small amounts of oral feeding could be introduced with caution, in an individualised manner, and with a collaborative multidisciplinary approach. Further research is essential.Contribution: Partial oral feeding of specific consistencies was possible during the assessment of young paediatric in-patients on HFO2. Monitoring of individual patient characteristics and risk factors by a specialist feeding team is essential.

Predominantly unilateral laryngomalacia in infants with unilateral vocal fold paralysis.

BACKGROUND: Neonatal unilateral vocal fold paralysis may arise iatrogenically, idiopathically, or in the context of an underlying neurologic disorder. Management is often supportive, focusing on diet modification to allow for safe oral feeding. We describe the clinical course of six infants with unilateral vocal fold paralysis who developed predominantly unilateral laryngomalacia ipsilateral to the affected vocal fold with associated severe respiratory symptoms and feeding difficulty. METHODS: Retrospective review of six infants with unilateral vocal fold paralysis and predominantly unilateral laryngomalacia. Charts were reviewed for etiology of vocal fold paralysis, presenting symptoms, operative details, postoperative course, and outcomes for breathing and swallowing. RESULTS: Etiology of vocal fold paralysis included cardiac surgery in four patients, intubation-related in one, and idiopathic in one. Presenting symptoms included increased work of breathing, stridor, feeding difficulty, respiratory failure requiring noninvasive respiratory support, and weak cry. All infants were on nasogastric tube feedings. Direct microlaryngoscopy with unilateral or predominantly unilateral (conservative contralateral aryepiglottic fold division) supraglottoplasty was performed. Stridor and work of breathing improved in all six patients within 1 week postoperatively. Oral feeding improved in three patients within 2 weeks. Three patients had persistent feeding impairment with improvement within one year. CONCLUSIONS: Predominantly unilateral laryngomalacia may arise in the context of unilateral vocal fold paralysis. Addressing the ipsilateral cuneiform collapse can improve breathing and feeding. This may be an under-described phenomenon and represents an additional reason to include the otolaryngologist early in the care of infants with suspected possible new unilateral vocal fold paralysis. Breathing and swallow can improve post-operatively, but feeding may remain limited by the vocal fold paralysis and any medical comorbidities. Ongoing follow-up and collaboration with speech-language pathology to optimize feeding are important.

Sparing Swallowing-Related Structures Reduces Post-Radiotherapy Dysphagia in Oropharyngeal Cancer.

OBJECTIVE: To identify swallowing-related structures (SRSs) predicting post-radiotherapy dysphagia in oropharyngeal carcinoma patients. MATERIAL AND METHODS: Between September 2020 and October 2022, oropharyngeal cancer patients who had completed radiotherapy at least one year before without recurrence or residuals were selected. They underwent flexible endoscopic evaluation of swallowing (FEES) assessments and dysphagia grading. The mean radiation doses delivered to their SRSs were recalculated. The correlation between radiation doses to each SRS and FEES scores was analysed. RESULTS: Twenty-nine participants, aged 51-73 years, were enrolled. Six patients had received two-dimensional radiotherapy, eight had undergone three-dimensional conformal radiotherapy, and fifteen had received intensity-modulated radiation therapy. Radiation doses to the inferior pharyngeal constrictor, cricopharyngeus and glottic larynx significantly predicted dysphagia for both semisolids (p = 0.023, 0.030 and 0.001) and liquid diets (p = 0.021, 0.013 and 0.002). The esophageal inlet significantly predicted swallowing outcomes for only the liquid diet (p = 0.007). CONCLUSIONS: This study supports that SRS-sparing during radiotherapy for oropharyngeal cancers improves swallowing outcomes.

Factors Associated With Time to Decannulation in Patients With Tracheostomy Following Severe Traumatic Brain Injury.

BACKGROUND: Prolonged tracheal tube placement following severe traumatic brain injury (TBI) can cause serious complications. Safe removal requires sufficient ability for independent breathing and airway protection. Thus, identifying important factors for time to removal of the tracheal tube (decannulation) is essential for safe and efficient weaning. This study aimed to identify significant factors for time to decannulation in a Danish population of subjects with tracheostomy after TBI. METHODS: This was a retrospective register-based cohort study. Subjects with moderate and severe TBI and a tracheal tube were selected from the Danish Head Trauma Database between 2011-2021. Time to decannulation was calculated as time from injury to decannulation. Associations between selected explanatory variables representing demographic and clinical characteristics and time to decannulation were analyzed using linear regression models. RESULTS: A total 324 subjects were included with a median of 44 d to decannulation. Primary analysis found that an improvement in swallowing ability during the initial 4 weeks of rehabilitation was associated with an 8.2 d reduction in time to decannulation (95% CI -12.3 to -4.2, P < .001). Change in overall sensorimotor ability reduced time to decannulation by 0.94 (95% CI -0.78 to -0.10, P = .03) d. Change in cognitive abilities from rehab admission to 4-week follow-up did not significantly affect the number of days to decannulation (P = .66). Secondary analysis showed pneumonia was associated with the largest estimated increase of 24.4 (95% CI 15.9-32.9, P < .001) d and that increased cognitive functioning at rehabilitation admission was associated with a significant reduction in time to decannulation. CONCLUSIONS: This study found that a change in swallowing ability is a potentially significant factor for reducing time to decannulation. Identifying factors that could explain differences in time to decannulation is essential for patient outcomes, especially if these factors are modifiable and could be targeted in rehabilitation and treatment.

In-depth analysis of pre- and postoperative functional outcome parameters in patients receiving laryngotracheal surgery.

OBJECTIVES: Surgical treatment for airway stenosis necessitates personalized techniques based on the stenosis location and length, leading to favourable surgical outcomes. However, there is limited literature on functional outcomes following laryngotracheal surgery with an adequate number of patients. METHODS: We conducted a retrospective analysis of patients who underwent laryngotracheal surgery at the Department of Thoracic Surgery, Medical University of Vienna, from January 2017 to June 2021. The study included standardized functional assessments before and after surgery, encompassing spirometry, voice measurements, swallowing evaluation and subjective patient perception. RESULTS: The study comprised 45 patients with an average age of 51.9 ± 15.9 years, of whom 89% were female, with idiopathic being the most common aetiology (67%). Procedures included standard cricotracheal resection in 11%, cricotracheal resection with dorsal mucosal flap in 49%, cricotracheal resection with dorsal mucosal flap and lateral cricoplasty in 24% and single-stage laryngotracheal reconstruction in 16%. There were no in-hospital mortalities or restenosis cases during the mean follow-up period of 20.8 ± 13.2 months. Swallowing function remained intact in all patients. Voice evaluations showed a decrease in fundamental vocal pitch [203 (81-290) Hz vs 150 (73-364) Hz, P < 0.001] and dynamic voice range (23.5 ± 5.8 semitones vs 17.8 ± 6.7 semitones, P < 0.001). However, no differences in voice volume were observed (60.0 ± 4.1 dB vs 60.2 ± 4.8 dB, P = 0.788). The overall predicted voice profile changed from R0B0H0 to R1B0H1. CONCLUSIONS: Laryngotracheal surgery proves effective in fully restoring breathing capacity while preserving vocal function. Even in cases of high-grade and complex airway stenosis necessitating laryngotracheal reconstruction, favourable functional outcomes can be achieved.

Factor Analysis of Patients Who Find Tablets or Capsules Difficult to Swallow Due to Their Large Size: Using the Personal Health Record Infrastructure of Electronic Medication Notebooks.

BACKGROUND: Understanding patient preference regarding taking tablet or capsule formulations plays a pivotal role in treatment efficacy and adherence. Therefore, these preferences should be taken into account when designing formulations and prescriptions. OBJECTIVE: This study investigates the factors affecting patient preference in patients who have difficulties swallowing large tablets or capsules and aims to identify appropriate sizes for tablets and capsules. METHODS: A robust data set was developed based on a questionnaire survey conducted from December 1, 2022, to December 7, 2022, using the harmo smartphone app operated by harmo Co, Ltd. The data set included patient input regarding their tablet and capsule preferences, personal health records (including dispensing history), and drug formulation information (available from package inserts). Based on the medication formulation information, 6 indices were set for each of the tablets or capsules that were considered difficult to swallow owing to their large size and concomitant tablets or capsules (used as controls). Receiver operating characteristic (ROC) analysis was used to evaluate the performance of each index. The index demonstrating the highest area under the curve of the ROC was selected as the best index to determine the tablet or capsule size that leads to swallowing difficulties. From the generated ROCs, the point with the highest discriminative performance that maximized the Youden index was identified, and the optimal threshold for each index was calculated. Multivariate logistic regression analysis was performed to identify the risk factors contributing to difficulty in swallowing oversized tablets or capsules. Additionally, decision tree analysis was performed to estimate the combined risk from several factors, using risk factors that were significant in the multivariate logistic regression analysis. RESULTS: This study analyzed 147 large tablets or capsules and 624 control tablets or capsules. The "long diameter + short diameter + thickness" index (with a 21.5 mm threshold) was identified as the best indicator for causing swallowing difficulties in patients. The multivariate logistic regression analysis (including 132 patients with swallowing difficulties and 1283 patients without) results identified the following contributory risk factors: aged <50 years (odds ratio [OR] 1.59, 95% CI 1.03-2.44), female (OR 2.54, 95% CI 1.70-3.78), dysphagia (OR 3.54, 95% CI 2.22-5.65), and taking large tablets or capsules (OR 9.74, 95% CI 5.19-18.29). The decision tree analysis results suggested an elevated risk of swallowing difficulties for patients with taking large tablets or capsules. CONCLUSIONS: This study identified the most appropriate index and threshold for indicating that a given tablet or capsule size will cause swallowing difficulties, as well as the contributory risk factors. Although some sampling biases (eg, only including smartphone users) may exist, our results can guide the design of patient-friendly formulations and prescriptions, promoting better medication adherence.

Extrinsic Laryngeal Muscle Activity With Different Diameters and Water Depths in a Semi-Occluded Vocal Tract Exercise.

PURPOSE: Surface electromyography (sEMG) has been used to evaluate extrinsic laryngeal muscle activity during swallowing and phonation. In the current study, sEMG amplitudes were measured from the infrahyoid and suprahyoid muscles during phonation through a tube submerged in water. METHOD: The sEMG amplitude values measured from the extrinsic laryngeal muscles and the electroglottographic contact quotient (CQ) were obtained simultaneously from 62 healthy participants (31 men, 31 women) during phonation through a tube at six different depths (2, 4, 7, 10, 15, and 20 cm) while using two tubes with different diameters (1 and 0.5 cm). RESULTS: With increasing depth, the sEMG amplitude for the suprahyoid muscles increased in men and women. However, sEMG amplitudes for the infrahyoid muscles increased significantly only in men. Tube diameter had a significant effect on the suprahyoid sEMG amplitudes only for men, with higher sEMG amplitudes when phonating with a 1.0-cm tube. CQ values increased with submerged depth for both men and women. Tube diameter affected results such than CQ values were higher for men when using the wider tube and for women with the narrower tube. CONCLUSIONS: Vocal fold vibratory patterns changed with the depth of tube submersion in water for both men and women, but the patterns of muscle activation differed between the sexes. This suggests that men and women use different strategies when confronted with increased intraoral pressure during semi-occluded vocal tract exercises. In this study, sEMG provided insight into the mechanism for differences between vocally normal individuals and could help detect compensatory muscle activation during tube phonation in water for people with voice disorders.

Chronic intermittent hypoxia reveals role of the Postinspiratory Complex in the mediation of normal swallow production.

Obstructive sleep apnea (OSA) is a prevalent sleep-related breathing disorder that results in multiple bouts of intermittent hypoxia. OSA has many neurological and systemic comorbidities, including dysphagia, or disordered swallow, and discoordination with breathing. However, the mechanism in which chronic intermittent hypoxia (CIH) causes dysphagia is unknown. Recently, we showed the postinspiratory complex (PiCo) acts as an interface between the swallow pattern generator (SPG) and the inspiratory rhythm generator, the preBötzinger complex, to regulate proper swallow-breathing coordination (Huff et al., 2023). PiCo is characterized by interneurons co-expressing transporters for glutamate (Vglut2) and acetylcholine (ChAT). Here we show that optogenetic stimulation of ChATcre:Ai32, Vglut2cre:Ai32, and ChATcre:Vglut2FlpO:ChR2 mice exposed to CIH does not alter swallow-breathing coordination, but unexpectedly disrupts swallow behavior via triggering variable swallow motor patterns. This suggests that glutamatergic-cholinergic neurons in PiCo are not only critical for the regulation of swallow-breathing coordination, but also play an important role in the modulation of swallow motor patterning. Our study also suggests that swallow disruption, as seen in OSA, involves central nervous mechanisms interfering with swallow motor patterning and laryngeal activation. These findings are crucial for understanding the mechanisms underlying dysphagia, both in OSA and other breathing and neurological disorders.

Scaling of buccal mass growth and muscle activation determine the duration of feeding behaviours in the marine mollusc Aplysia californica.

The mechanical forces experienced during movement and the time constants of muscle activation are important determinants of the durations of behaviours, which may both be affected by size-dependent scaling. The mechanics of slow movements in small animals are dominated by elastic forces and are thus quasistatic (i.e. always near mechanical equilibrium). Muscular forces producing movement and elastic forces resisting movement should scale identically (proportional to mass2/3), leaving the scaling of the time constant of muscle activation to play a critical role in determining behavioural duration. We tested this hypothesis by measuring the duration of feeding behaviours in the marine mollusc Aplysia californica whose body sizes spanned three orders of magnitude. The duration of muscle activation was determined by measuring the time it took for muscles to produce maximum force as A. californica attempted to feed on tethered inedible seaweed, which provided an in vivo approximation of an isometric contraction. The timing of muscle activation scaled with mass0.3. The total duration of biting behaviours scaled identically, with mass0.3, indicating a lack of additional mechanical effects. The duration of swallowing behaviour, however, exhibited a shallower scaling of mass0.17. We suggest that this was due to the allometric growth of the anterior retractor muscle during development, as measured by micro-computed tomography (micro-CT) scans of buccal masses. Consequently, larger A. californica did not need to activate their muscles as fully to produce equivalent forces. These results indicate that muscle activation may be an important determinant of the scaling of behavioural durations in quasistatic systems.