Laryngeal activity during swallow, phonation, and the Valsalva maneuver: an electromyographic analysis

A Scoping Review on the Intersection Between Voice and Swallowing Measures in Healthy and Disordered Populations

PURPOSE

Voice and swallowing are distinct functions that share anatomical and physiological properties; however, research investigating their intersection is limited. The purpose of this scoping review was to explore the literature surrounding the relationship between voice and swallowing measures in healthy adults and those with non-degenerative disorders. Specifically, we aimed to elucidate whether objective voice measures could be used as correlates of swallowing function.

METHOD

We systematically searched four databases (Embase, PubMed, CINAHL, and Web of Science) for relevant literature using a combination of key words and controlled vocabulary generated from the Yale Mesh Analyzer. The inclusion criteria consisted of peer-reviewed studies in the English language that reported on healthy adults and/or patients with non-degenerative neurological disorders and pulmonary diseases and contained instrumental and/or objective voice and swallowing measures. Two raters completed the abstract screening process followed by independent full-text reviews. Case studies, review studies, gray literature, or abstract-only studies were excluded.

RESULTS

Among 5,485 screened studies, 182 were fully reviewed, with only 11 studies meeting the inclusion criteria. Eight studies found an association between voice and swallowing objective measures, whereas the other three did not. Significant voice measures that were related to swallowing safety and/or physiology included maximum fundamental frequency (F0), F0 range, maximum phonation time, biomechanics of effortful pitch glides, and voice onset time.

CONCLUSIONS

Although there was heterogeneity in the measures used, specific objective voice measures showed promise in clinical practice as a screening tool for dysphagia. Further investigations are needed to validate the clinical utility of these measures across diverse patient populations.

Neuromotor control of spontaneous quiet breathing in awake rats evaluated by assessments of diaphragm EMG stationarity

The neuromotor control of the diaphragm muscle (DIAm) is dynamic. The activity of the DIAm can be recorded via electromyography (EMG), which represents the temporal summation of motor unit action potentials. Our goal in the present study was to investigate DIAm neuromotor control during quiet spontaneous breathing (eupnea) in awake rats by evaluating DIAm EMG at specific temporal locations defined by motor unit recruitment and derecruitment. We evaluated the nonstationarity of DIAm EMG activity to identify DIAm motor unit recruitment and derecruitment durations. Combined with assessments of root mean square (RMS) and sum of squares (SS) EMG, the durations of these phases provide physiological information about the temporal aspects of motor control. During eupnea in awake rats (n = 10), the duration of motor unit recruitment comprised 61 ± 19 ms of the onset-to-peak duration (214 ± 62 ms) of the DIAm RMS EMG. The peak-to-offset duration of DIAm EMG activity was 453 ± 96 ms, with a terminating period of derecruitment of 161 ± 44 ms. The burst duration was 673 ± 128 ms. Both the RMS EMG amplitude and the SS EMG were higher at the completion of motor unit recruitment than at the start of motor unit derecruitment, suggesting that offset discharge rates were lower than onset discharge rates. Our analyses provide novel insights into the time domain aspects of DIAm neuromotor control and allow indirect estimates of the contribution of recruitment and frequency to RMS EMG amplitude during eupnea in awake rats.NEW & NOTEWORTHY We characterized three phases of neuromotor control-motor unit recruitment, sustained activity, and derecruitment-based on statistical assessments of stationarity of the diaphragm muscle (DIAm) EMG activity in awake rats. Our findings may allow indirect estimates of the contribution of motor unit recruitment and frequency coding toward generating force and provide novel insights about the temporal aspects of DIAm neuromotor control and descending respiratory drive in unanesthetized animals.

Vocal fold vibration mode changes due to cricothyroid and thyroarytenoid muscle interaction in a three-dimensional model of the canine larynx

Using a continuum model based on magnetic resonance imaging of a canine larynx, parametric simulations of the vocal fold vibration during phonation were conducted with the cricothyroid muscle (CT) and the thyroarytenoid muscle (TA) independently activated from zero to full activation. The fundamental frequency (f₀) first increased and then experienced a downward jump as TA activity gradually increased under moderate to high CT activation. Proper orthogonal decomposition analysis revealed that the vocal fold vibrations were dominated by two modes representing a lateral motion and rotational motion, respectively, and the f₀ drop was associated with a switch on the order of the two modes. In another parametric set where only the vocalis was active, f₀ increased monotonically with both TA and CT activity and the mode switch did not occur. The results suggested that the active stress in the TA, which causes large stress differences between the body and cover, is essential for the occurrence of the rotational mode and mode switch. Relatively greater TA activity tends to promote the rotational mode, while relatively greater CT activity tends to promote the lateral mode. The results also suggested that the vibration modes affected f₀ by affecting the contribution of the TA stress to the effective stiffness. The switch in the dominant mode caused the non-monotonic change of f₀.

Social isolation alters ultrasonic vocalizations but not thyroarytenoid neuromuscular junctions in old rats

OBJECTIVE

Age-related muscle atrophy of the laryngeal muscles contributes to presbyphonia. Remodeling of the neuromuscular junction is one aspect underlying age-related muscle atrophy. Although muscle disuse has been shown to exacerbate age-related neuromuscular changes in the limb muscles, it is unknown if reduced vocal use has a similar effect in the laryngeal muscles. The objective of this study was to examine the use of social isolation as a novel method to reduce vocal use in old rats-and the impact of that reduced vocal use on ultrasonic vocalization acoustics and neuromuscular junction morphology in the thyroarytenoid muscle.

STUDY DESIGN

Animal group comparison.

METHODS

Old F344/BN rats (31 months of age) were socially isolated (n = 8) or communally housed (n = 8) for 8 weeks. Effect of housing condition on ultrasonic vocalization acoustics was assessed by calculating the changes in vocalization fundamental frequency and amplitude from baseline to 8 weeks. Neuromuscular junction morphology was measured in the lateral and medial portions of the thyroarytenoid muscle at the conclusion of the experiment.

RESULTS

Vocalization amplitude decreased by a mean of -4.4 dB (standard deviation [SD], 4.49) after social isolation, whereas amplitude increased by a mean of 5.7 dB (SD, 5.07) in the communally housed rats (P = 0.002). There was no significant difference in the change in fundamental frequency between groups. Furthermore, there were no group differences in any measure of neuromuscular junction morphology.

CONCLUSION

These results suggest that neuromuscular junctions in the thyroarytenoid muscle of old rats are unaffected by 8 weeks of social isolation, despite functional changes in vocalizations.

LEVEL OF EVIDENCE

NA Laryngoscope, 129:E9-E14, 2019.

Tumor Size and Pretreatment Speech and Swallowing in Patients with Resectable Tumors

The pretreatment relationship of tumor burden to speech and swallowing function in 230 patients with oral or oropharyngeal cancer before surgery was assessed. Reduced articulation, reduced conversational understandability, or self-reported dysphagia were present in at least 34% of patients before treatment. Videofluoroscopy showed at least 9% of patients had reduced swallowing efficiency on liquid, paste, or cookie boluses. By use of regression techniques, the percentages of the oral tongue and of the anterior floor of mouth affected by neoplasm were found to be significantly related to reduced articulation; T stage and the percentage of the oral tongue affected with tumor were mildly related to reduced understandability; tumor volume and having soft palate affected by neoplasm were significantly related to self-reported dysphagia; and percentages of affected oral tongue and of affected tongue base were significantly related to reduced swallowing efficiency. Tumor burden may contribute to functional deficits at diagnosis in patients who have resectable tumors.

Laryngeal Electromyographic, Cardiovascular, and Respiratory Effects of Neuropeptide Injections into the Nucleus Tractus Solitarius of Rats

Identifying central neurotransmitters that mediate laryngeal adductor activity may aid in managing pathological laryngeal adduction as occurs in laryngospasm or apparent life-threatening events in infants. We studied the effect on cricothyroid (CT) and thyroarytenoid (TA) electromyography (EMG) and on cardiovascular parameters of neurotransmitter injections into the rat nucleus tractus solitarius (NTS), the primary sensory relay center of the larynx. Twenty nanoliters of vasoactive intestinal peptide (VIP; 2.5 pmol), neurokinin B (NKB, 16 pmol), calcitonin gene-related peptide (3.0 pmol), neurokinin A (NKA; 35 pmol), or artificial cerebrospinal fluid (control solution) was stereotactically injected into the region of the NTS and the control nucleus gracilis in 119 studies performed in 24 mature, anesthetized Sprague-Dawley rats. Changes in diaphragm, CT, and TA EMG activity and blood pressure (BP) were compared. Injection sites were verified histologically. Injections of both VIP and NKB into the region of the NTS, but not the nucleus gracilis, induced life-threatening changes, including apnea, a marked decline in BP (p < .05), and increases in EMG activity of the CT and TA adductor muscles ranging from sustained contraction to mild phasic increases during inspiration. Calcitonin gene-related peptide injection also decreased BP (p < .05), but caused only mild increases in CT and TA EMG activity. NKA and control injections into the NTS did not alter respiration, BP, or CT or TA EMG activity. VIP and NKB may play important roles in modulating EMG activity of the CT and TA muscles. This information may prove useful in evaluating pharmacological targets of central reflex activity to manage life-threatening laryngeal adduction.

Treatment for dysphagia (swallowing difficulties) in hereditary ataxia

BACKGROUND

Hereditary ataxias are a heterogeneous group of disorders resulting in progressive inco-ordination. Swallowing impairment, also known as dysphagia, is a common and potentially life threatening sequel of disease progression. The incidence and nature of dysphagia in these conditions is largely unknown. The loss of an effective and safe swallow can dramatically affect the health and well-being of an individual. Remediation of difficulties of eating and drinking is an important goal in the clinical care of people with hereditary ataxia.

OBJECTIVES

To assess the effects of interventions for swallowing impairment (dysphagia) in people with hereditary ataxias.

SEARCH METHODS

We searched the Cochrane Neuromuscular Disease Group Specialized Register, the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, CINAHL Plus, PsycINFO, and the Education Resources Information Center (ERIC) on 14 September 2015. We also searched Linguistics and Language Behavior Abstracts (LLBA), Dissertation Abstracts, and Trials Registries on 24 September 2015.

SELECTION CRITERIA

We considered all randomised controlled trials (RCTs) and quasi-RCTs that compared treatments for hereditary ataxia with placebo or no treatment. We only included studies measuring dysphagia.

DATA COLLECTION AND ANALYSIS

Three review authors (ES, KJ, MK) independently screened all titles and abstracts. In the event of any disagreement or uncertainty over the inclusion of a particular paper, the review authors planned to meet and reach consensus.

MAIN RESULTS

We identified no RCTs from the 519 titles and abstracts screened. We excluded papers primarily for not including participants with a hereditary ataxia (that is, being focused on other neurological conditions), being theoretical reviews rather than intervention studies, or being neither randomised nor quasi-randomised trials.We identified five papers of various design that described treatment for dysphagia, or improvement to swallow as a by-product of treatment, in people with hereditary ataxia. None of these studies were RCTs or quasi-RCTs.

AUTHORS' CONCLUSIONS

There is an absence of any significant evidence supporting the use of any dysphagia intervention in hereditary ataxia. The lack of evidence highlights the critical need for well-controlled treatment trials in the field.

Cross-activation and detraining effects of tongue exercise in aged rats

Voice and swallowing deficits can occur with aging. Tongue exercise paired with a swallow may be used to treat swallowing disorders, but may also benefit vocal function due to cross-system activation effects. It is unknown how exercise-based neuroplasticity contributes to behavior and maintenance following treatment. Eighty rats were used to examine behavioral parameters and changes in neurotrophins after tongue exercise paired with a swallow. Tongue forces and ultrasonic vocalizations were recorded before and after training/detraining in young and old rats. Tissue was analyzed for neurotrophin content. Results showed tongue exercise paired with a swallow was associated with increased tongue forces at all ages. Gains diminished after detraining in old rats. Age-related changes in vocalizations, neurotrophin 4 (NT4), and brain derived neurotrophic factor (BDNF) were found. Minimal cross-system activation effects were observed. Neuroplastic benefits were demonstrated with exercise in old rats through behavioral improvements and up-regulation of BDNF in the hypoglossal nucleus. Tongue exercise paired with a swallow should be developed, studied, and optimized in human clinical research to treat swallowing and voice disorders in elderly people.

The effects of treadmill running on aging laryngeal muscle structure

OBJECTIVES/HYPOTHESIS

Age-related changes in laryngeal muscle structure and function may contribute to deficits in voice and swallowing observed in elderly people. We hypothesized that treadmill running, an exercise that increases respiratory drive to upper airway muscles, would induce changes in thyroarytenoid muscle myosin heavy chain (MHC) isoforms that are consistent with a fast-to-slow transformation in muscle fiber type.

STUDY DESIGN

Randomized parallel group controlled trial.

METHODS

Fifteen young adult and 14 old Fischer 344/Brown Norway rats received either treadmill running or no exercise (5 days/week/8 weeks). Myosin heavy chain isoform composition in the thyroarytenoid muscle was examined at the end of 8 weeks.

RESULTS

Significant age and treatment effects were found. The young adult group had the greatest proportion of superfast-contracting MHCIIL isoform. The treadmill running group had the lowest proportion of MHCIIL and the greatest proportion of MHCIIx isoforms.

CONCLUSION

Thyroarytenoid muscle structure was affected both by age and treadmill running in a fast-to-slow transition that is characteristic of exercise manipulations in other skeletal muscles.

LEVEL OF EVIDENCE

NA. Laryngoscope, 126:672-677, 2016.

Electrophysiological evaluation of oropharyngeal Dysphagia in Parkinson's disease

Parkinson’s disease (PD) is a chronic, neurodegenerative movement disorder that typically affects elderly patients. Swallowing disorders are highly prevalent in PD and can have grave consequences, including pneumonia, malnutrition, dehydration and mortality. Neurogenic dysphagia in PD can manifest with both overt clinical symptoms or silent dysphagia. Regardless, early diagnosis and objective follow-up of dysphagia in PD is crucial for timely and appropriate care for these patients. In this review, we provide a comprehensive summary of the electrophysiological methods that can be used to objectively evaluate dysphagia in PD. We discuss the electrophysiological abnormalities that can be observed in PD, their clinical correlates and the pathophysiology underlying these findings.

Altered pharyngeal muscles in Parkinson disease

Dysphagia (impaired swallowing) is common in patients with Parkinson disease (PD) and is related to aspiration pneumonia, the primary cause of death in PD. Therapies that ameliorate the limb motor symptoms of PD are ineffective for dysphagia. This suggests that the pathophysiology of PD dysphagia may differ from that affecting limb muscles, but little is known about potential neuromuscular abnormalities in the swallowing muscles in PD. This study examined the fiber histochemistry of pharyngeal constrictor and cricopharyngeal sphincter muscles in postmortem specimens from 8 subjects with PD and 4 age-matched control subjects. Pharyngeal muscles in subjects with PD exhibited many atrophic fibers, fiber type grouping, and fast-to-slow myosin heavy chain transformation. These alterations indicate that the pharyngeal muscles experienced neural degeneration and regeneration over the course of PD. Notably, subjects with PD with dysphagia had a higher percentage of atrophic myofibers versus with those without dysphagia and controls. The fast-to-slow fiber-type transition is consistent with abnormalities in swallowing, slow movement of food, and increased tone in the cricopharyngeal sphincter in subjects with PD. The alterations in the pharyngeal muscles may play a pathogenic role in the development of dysphagia in subjects with PD.

Otolaryngology head and neck surgery: an integrative view of the larynx

The glottis is composed of muscular, cartilaginous, and other viscoelastic tissues which perform some of our most important, complex, coordinated, and life-sustaining functions. Dominated by the thyroarytenoid muscles and associated glottic closure muscles, the larynx is involved in respiration, swallowing, voicing, coughing, valsalva, vomiting, laughing, and crying. With respiration continuing in the background, all other "secondary" laryngeal events seamlessly occur. When the delicate balance of coordinating these events is disrupted by disease or disorder, many of these tasks are compromised. Due to the complex innervation of these volitional and reflexive tasks with brainstem central pattern generators, primary sensorimotor areas and importantly, limbic areas, failure can occur due to disease, anatomic compromise, and even emotional state. Understanding the level of sensorimotor control and interaction among systems that share these laryngeal neuromuscular substrates will improve the diagnostic and therapeutic skill of the clinician when treating compromise of laryngeal function.

Targeted exercise therapy for voice and swallow in persons with Parkinson's disease

Sensorimotor deficits affecting voice and swallowing ability can have a devastating impact on the quality of life of people with Parkinson disease (PD). Recent scientific findings in animal models of PD pinpoint targeted exercise therapy as a potential treatment to reduce neurochemical loss and decrease parkinsonian symptoms. Although there may be beneficial effects, targeted exercise therapy is not a standard component of therapy for the cranial sensiromotor deficits seen in PD. In this paper, we review the scientific evidence for targeted training for voice and swallowing deficits. The literature search revealed 19 publications that included targeted training for voice and only one publication that included targeted training for swallowing. We summarize 3 main findings: (1) targeted training may be associated with lasting changes in voice behavior; (2) targeted training of sensorimotor actions with anatomical or functional overlap with voice and swallowing may improve voice and swallowing to some degree, but it is unknown whether these effects endure over time; and (3) evidence regarding cranial sensorimotor interventions for Parkinson disease is sparse. We concluded that targeted training for voice and swallow is a promising but understudied intervention for cranial sensorimotor deficits associated with PD and posit that animal models can be useful in designing empirically based studies that further the science on targeted training.

Identification of distinct swallowing patterns for different bolus volumes

OBJECTIVE

To investigate the time interval between glottic closure and the opening of upper esophageal sphincter during swallowing, by means of the coupling of electromyographical (EMG) recordings on the thyroarytenoid (TA) and the cricopharyngeus (CP) muscles.

METHODS

TA-EMG and CP-EMG pause were recorded by concentric needle electrodes using time-locked delay-line circuitry of the EMG apparatus. EMG data obtained from a total of 273 swallows of saliva, 3, 5, 10 and 15 ml volumes of water, were compared.

RESULTS

The relation between the onsets of TA-EMG activity and the CP-EMG pause demonstrated three different patterns of swallows. Pattern A was the delay of the onset of TA-EMG between 50-500 ms, and pattern B was the overlap of its activity with the CP-EMG pause. Pattern C was the earlier occurrence of the TA-EMG 50-550 ms before the CP-EMG pause. Pattern A was the most frequent type of swallows whereas the pattern C appeared during swallowing of larger volumes.

CONCLUSIONS

Physiologically, there is a delay of the TA activation after the onset of CP-EMG pause during swallowing of small amounts in healthy subjects.

SIGNIFICANCE

This physiological phenomenon could be a potential risk of aspiration in patients with neurogenic dysphagia.

Multiple forebrain systems converge on motor neurons innervating the thyroarytenoid muscle

The present study investigated the central connections of motor neurons innervating the thyroarytenoid laryngeal muscle that is active in swallowing, respiration and vocalization. In both intact and sympathectomized rats, the pseudorabies virus (PRV) was inoculated into the muscle. After initial infection of laryngomotor neurons in the ipsilateral loose division of the nucleus ambiguus (NA) by 3 days post-inoculation, PRV spread to the ipsilateral compact portion of the NA, the central and intermediate divisions of the nucleus tractus solitarii, the Botzinger complex, and the parvicellular reticular formation by 4 days. Infection was subsequently expanded to include the ipsilateral granular and dysgranular parietal insular cortex, the ipsilateral medial division of the central nucleus of the amygdala, the lateral, paraventricular, ventrolateral and medial preoptic nuclei of the hypothalamus (generally bilaterally), the lateral periaqueductal gray, the A7 and oral and caudal pontine nuclei. At the latest time points sampled post-inoculation (5 days), infected neurons were identified in the ipsilateral agranular insular cortex, the caudal parietal insular cortex, the anterior cingulate cortex, and the contralateral motor cortex. In the amygdala, infection had spread to the lateral central nucleus and the parvicellular portion of the basolateral nucleus. Hypothalamic infection was largely characterized by an increase in the number of infected cells in earlier infected regions though the posterior, dorsomedial, tuberomammillary and mammillary nuclei contained infected cells. Comparison with previous connectional data suggests PRV followed three interconnected systems originating in the forebrain; a bilateral system including the ventral anterior cingulate cortex, periaqueductal gray and ventral respiratory group; an ipsilateral system involving the parietal insular cortex, central nucleus of the amygdala and parvicellular reticular formation, and a minor contralateral system originating in motor cortex. Hypothalamic innervation involved several functionally specific nuclei. Overall, the data imply complex CNS control over the multi-functional thyroarytenoid muscle.

Surgical treatment of dysphagia

The role of surgery in the management of dysphagia is clear in some areas and controversial in others. Evaluation for the causes of dysphagia can elucidate conditions in which surgery can improve safety, quality of life, or both. Surgical therapy, when indicated, is safe and effective for many causes of dysphagia. This article includes a general overview of the causes of dysphagia that can be addressed successfully with surgery as well as a discussion of why surgery may be less appropriate for other conditions associated with dysphagia.

Cricopharyngeal electromyography: patterns of injury based on etiology

OBJECTIVE

Although cricopharyngeal electromyography (CP-EMG) is recognized as a diagnostic tool for dysphagia assessment, few reports in the literature characterize CP-EMG abnormalities in relation to clinical presentation. The aim of this study was to review a large series of CP-EMG studies, and compare the CP-EMG results with the patients' diagnoses.

METHODS

A retrospective review of all CP-EMG performed at our institution over a 10-year period was executed. CP-EMG findings were then compared with the patients' clinical history, focusing on potential etiologies of neurogenic injury.

RESULTS

Seventy CP-EMGs were reviewed, with 47 (67%) demonstrating neural injury. Of those cases with neural injury on EMG, 29 (60%) had known vagal injuries, 13 (28%) had idiopathic nerve palsies, and 5 (11%) had central etiologies, such as stroke. Each of these three neurogenic subgroups revealed a distinct pattern of EMG abnormalities.

CONCLUSION

This study suggests there is an association between patterns of CP-EMG abnormalities and underlying etiology based on clinical history.

Proteomic profiling of rat thyroarytenoid muscle

PURPOSE

Proteomic methodologies offer promise in elucidating the systemwide cellular and molecular processes that characterize normal and diseased thyroarytenoid (TA) muscle. This study examined methodological issues central to the application of 2-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis (2D SDS-PAGE) to the study of the TA muscle proteome using a rat model.

METHOD

2D SDS-PAGE was performed using 4 chemically skinned rat TA muscle samples. Gel images were analyzed and compared. Protein spot detection and matching were performed using computational image analysis algorithms only and computational image analysis followed by visual inspection and manual error correction. A synthetic master gel, constructed to control for uninteresting biological variation and technical artifact due to differences in protein loading and staining, was evaluated against its constituent gels.

RESULTS

Manual error correction resulted in a consistent increase in the number of protein spots detected (between 5.8% and 40.9%) and matched (from 25.8% to 70.8%) across all gels. Sensitivity and specificity of the automatic (computational) spot detection procedure, evaluated against the manual correction procedure, were 74.1% and 97.9%, respectively. Evaluation of protein quantitation parameter values revealed statistically significant differences (p < .0001) in optical density, area, and volume for matched protein spots across gels. The synthetic master gel successfully compensated for these intergel differences.

CONCLUSIONS

Valid and reliable proteomic data are dependant on well-controlled manageable variability and well-defined unmanageable variability. Manual correction of spot detection and matching errors and the use of a synthetic master gel appear to be useful strategies in addressing these issues. With these issues accounted for, 2D SDS-PAGE may be applied to quantitative experimental comparisons of normal and disease conditions affecting voice, speech, and swallowing function.

Biomechanical correlates of surface electromyography signals obtained during swallowing by healthy adults

PURPOSE

The purpose of this study was to describe biomechanical correlates of the surface electromyographic signal obtained during swallowing by healthy adult volunteers.

METHOD

Seventeen healthy adults were evaluated with simultaneous videofluoroscopy and surface electromyography (sEMG) while swallowing 5 mL of liquid barium sulfate. Three biomechanical swallowing events were analyzed: hyoid elevation, pharyngeal constriction, and opening-closing of the pharyngoesophageal segment. For each biomechanical event and from the sEMG signal, the authors identified onset, peak, and offset time points. From these points, duration measures were calculated. Means and 95% confidence intervals were calculated for each measure. Subsequently, correlations were evaluated between timing aspects of the sEMG traces and each biomechanical event.

RESULTS

Swallow onset in the sEMG signal preceded the onset of all biomechanical events. All biomechanical events demonstrated a strong correspondence to the sEMG signal. The strongest relationship was between hyoid elevation-anterior displacement and the sEMG signal.

CONCLUSIONS

These results suggest that the sEMG signal is a useful indicator of major biomechanical events in the swallow. Future studies should address the impact of age and disease processes, as well as bolus characteristics, on the biomechanical correlates of sEMG signals obtained during swallowing.

Timing of glottic closure during swallowing: a combined electromyographic and endoscopic analysis

OBJECTIVES

We performed a case series to enhance our understanding of the coupling between neuromuscular events and glottic closure.

METHODS

We performed combined flexible video laryngoscopy and electromyography in 4 healthy human subjects. Hooked-wire electrodes were placed in the superior pharyngeal constrictor, longitudinal pharyngeal, cricopharyngeus, thyroarytenoid, genioglossus, suprahyoid, and posterior cricoarytenoid muscles. A flexible endoscope tip was positioned in the oropharyngeal-hypopharyngeal region. The subjects performed multiple trials each of 10-mL normal and super-supraglottic liquid swallows.

RESULTS

Arytenoid movement consistently preceded full glottic closure and was associated with cessation of activity of the posterior cricoarytenoid muscle. In 89% of normal swallows, the glottis was partially open in the video frame before bolus passage. The maximum amount of thyroarytenoid electromyographic activity occurred during endoscopic whiteout. When subjects executed a super-supraglottic swallow, early thyroarytenoid activity coincided with arytenoid contact.

CONCLUSIONS

The initial medialization of the arytenoids is due to a decrease in motor tone of the posterior cricoarytenoid muscle. Full glottic closure typically occurs late in the process of swallowing, with activation of the thyroarytenoid muscle. Shifting of arytenoid medialization and glottic closure earlier in the super-supraglottic swallow indicates that glottic closure is under significant voluntary control.

Neurophysiology of swallowing

Swallowing is a complex motor event that is difficult to investigate in man by neurophysiological experiments. For this reason, the characteristics of the brain stem pathways have been studied in experimental animals. However, the sequential and orderly activation of the swallowing muscles with the monitoring of the laryngeal excursion can be recorded during deglutition. Although influenced by the sensory and cortical inputs, the sequential muscle activation does not alter from the perioral muscles caudally to the cricopharyngeal sphincter muscle. This is one evidence for the existence of the central pattern generator for human swallowing. The brain stem swallowing network includes the nucleus tractus solitarius and nucleus ambiguus with the reticular formation linking synaptically to cranial motoneuron pools bilaterally. Under normal function, the brain stem swallowing network receives descending inputs from the cerebral cortex. The cortex may trigger deglutition and modulate the brain stem sequential activity. The voluntarily initiated pharyngeal swallow involves several cortical and subcortical pathways. The interactions of regions above the brain stem and the brain stem swallowing network is, at present, not fully understood, particularly in humans. Functional neuroimaging methods were recently introduced into the human swallowing research. It has been shown that volitional swallowing is represented in the multiple cortical regions bilaterally but asymmetrically. Cortical organisation of swallowing can be continuously changed by the continual modulatory ascending sensory input with descending motor output.

SIGNIFICANCE

Dysphagia is a severe symptom complex that can be life threatening in a considerable number of patients. Three-fourths of oropharyngeal dysphagia is caused by neurological diseases. Thus, the responsibility of the clinical neurologist and neurophysiologist in the care for the dysphagic patients is twofold. First, we should be more acquainted with the physiology of swallowing and its disorders, in order to care for the dysphagic patients successfully. Second, we need to evaluate the dysphagic problems objectively using practical electromyography methods for the patients' management. Cortical and subcortical functional imaging studies are also important to accumulate more data in order to get more information and in turn to develop new and effective treatment strategies for dysphagic patients.

Effect of substance P injection into the nucleus tractus solitarius of rats on cricothyroid and thyroarytenoid motor activity and cardiovascular and respiratory systems

Identification of central neurotransmitters that mediate laryngeal adductor and/or tensor activity may prove useful in managing pathological laryngeal adduction as occurs in laryngospasm or apparent life-threatening events. The putative transmitter substance P (SP) is found in the nucleus tractus solitarius (NTS), in which laryngeal afferents terminate. Therefore, we studied the laryngeal, cardiovascular, and respiratory effects of SP injected into the NTS of rats. We completed bilateral stereotactic injections of 20 nL of SP (15 micromol) or control solution into the region of the NTS, the dorsal motor nucleus (DMN), or the nucleus gracilis (GR) in 30 anesthetized rats. Changes in diaphragm, cricothyroid (CT), and thyroarytenoid (TA) electromyography (EMG), as well as blood pressure (BP), were compared. The injection sites were verified histologically. Injection of SP into the NTS altered CT and/or TA EMG activity in all animals. The change ranged from complete inhibition, to a phasic increase, to a tonic increase. No change in laryngeal adductor EMG activity was seen in 8 of 9 animals after SP injections into the DMN (4/5) or GR (4/4), but 1 animal demonstrated brief inhibition of CT and TA EMG activity after SP injection into the DMN. Injection of SP into the NTS induced central apnea and a significant decrease in BP in all animals. The duration of apnea tended to be longer after NTS injections than after DMN or GR injections (p < .10 and p < .05, respectively). We conclude that stereotactic injections of putative neurotransmitters in rats may be accomplished to identify effects on laryngeal motor activity. Direct application of SP into the NTS consistently elicits a change in CT and/or TA EMG activity, ranging from inhibition to excitation. This model may prove useful in evaluating pharmacological targets of central reflex activity to manage life-threatening laryngeal reflex activity.

Neuromuscular junction changes in aged rat thyroarytenoid muscle

Dynamic remodeling of neuromuscular junction (NMJ) structure is postulated as a cause of age-related muscular atrophy. Direct study of NMJ morphology in laryngeal muscles is important to our understanding of age-related decrements in voice and swallowing. The morphology of NMJs was studied in a rat model to compare young and old specimens of thyroarytenoid muscle--a muscle critical to airway protection and phonation. Fluorescent, triple-label immunohistochemical analysis and confocal microscopic visualization were used to analyze the structure of NMJs. We found that laryngeal NMJs underwent significant changes that were similar to those observed after denervation. Specifically, the axon terminal area was significantly reduced, there were a number of postsynaptic acetylcholine receptor areas unoccupied by nerve terminals, and there was increased variability in end plate architecture in the old muscles. The results of this study increase our understanding of the age-related morphological changes in the larynx, and may serve as a baseline to test the effectiveness of future interventions.

Electronic analysis of intrinsic laryngeal muscles in canine sound production

This study explores the relationship between voice production and intrinsic laryngeal muscle (ILM) activities as expressed by orderly recruitment of their specific motor units. In 5 dogs, both the recurrent laryngeal nerve (RLN) and the vagus nerve (cranial nerve X) were stimulated via tripolar electrodes with stimulating frequencies (Fs) of 10 to 60 Hz and 0 to 7 mA during application of symmetric 600 Hz, 7 to 0 mA blocking currents. The fundamental frequency (Fo) and the intensity (I) of sounds generated by tracheal insufflation of humidified air were recorded while electromyograms of the cricothyroideus (CT), thyroarytenoideus (TA), and posterior cricoarytenoideus (PCA) were obtained via surface electrodes. Contractions of the CT were concurrently induced by stimulating the superior laryngeal nerve (SLN). The recruitment rates were highly specific and were affected by which nerve was stimulated. For the RLN, PCA ramping was lowest for Fs of < or =50 Hz. For Fs of 10 to 30 Hz, the recruitment rate of the TA was significantly steeper than that for the other ILMs, and the CT had the highest rate for Fs of 40 to 50 Hz. Conversely, for the vagus nerve, PCA recruitment was highest for Fs of > or =30 Hz. The average Fo was significantly higher with the RLN than with the vagus nerve. When the TA recruited faster than the CT (ie, via the RLN, but not the vagus nerve), the Fo was higher. While only CT ramping was significantly related to changes in sound intensity, there was a trend toward a decrease when PCA ramping was higher than CT ramping, as occurred when only the vagus nerve was stimulated. Stimulation of the SLN always increased Fo and loudness. We conclude that changes in Fo occur mainly through RLN-mediated CT and TA contraction. Loudness is controlled by the CT. The PCA exerts reciprocal coupling on both functions via the vagus nerve, and they are boosted across the board by the SLN. These findings may allow artificial manipulation of voice.

Tumor size and pretreatment speech and swallowing in patients with resectable tumors

The pretreatment relationship of tumor burden to speech and swallowing function in 230 patients with oral or oropharyngeal cancer before surgery was assessed. Reduced articulation, reduced conversational understandability, or self-reported dysphagia were present in at least 34% of patients before treatment. Videofluoroscopy showed at least 9% of patients had reduced swallowing efficiency on liquid, paste, or cookie boluses. By use of regression techniques, the percentages of the oral tongue and of the anterior floor of mouth affected by neoplasm were found to be significantly related to reduced articulation; T stage and the percentage of the oral tongue affected with tumor were mildly related to reduced understandability; tumor volume and having soft palate affected by neoplasm were significantly related to self-reported dysphagia; and percentages of affected oral tongue and of affected tongue base were significantly related to reduced swallowing efficiency. Tumor burden may contribute to functional deficits at diagnosis in patients who have resectable tumors.

The electromyographic behavior of the thyroarytenoid muscle during swallowing

The electromyographic (EMG) behavior of the laryngeal adductors (e.g., the thyroarytenoid [TA] muscle) during swallowing has been scarcely studied. However, the detailed analysis of TA muscle is important to understand the physiology of swallowing. We investigated 14 healthy adult subjects. Activation of the TA laryngeal adductor muscle was compared with the mechanically measured laryngeal up-down movement and with the onset of excitation of laryngeal elevators, such as submental (SM) muscles, during swallowing. The laryngeal adductor of TA and laryngeal elevators of SM muscles were electromyographically (integrated/rectified) recorded. The vertical laryngeal movements during swallowing were recorded using a piezoelectric sensor. The EMG behavior of the TA muscle revealed three different activities during swallowing. The basic activity was stable; it almost started with the upward movement of larynx and after the SM-EMG onset. A fore-burst was recorded just before the upward movement of the larynx and a late-burst appeared just after the downward movement. The fore-burst was proposed to be related with oral-laryngeal reflexes, and the late-burst could be a rebound activity after a short expiration of swallowing, while the basic activity is accepted to be a part of activity of central-pattern generator of swallowing program.

Electromyographic activity from human laryngeal, pharyngeal, and submental muscles during swallowing

The durations and temporal relationships of electromyographic activity from the submental complex, superior pharyngeal constrictor, cricopharyngeus, thyroarytenoid, and interarytenoid muscles were examined during swallowing of saliva and of 5- and 10-ml water boluses. Bipolar, hooked-wire electrodes were inserted into all muscles except for the submental complex, which was studied with bipolar surface electrodes. Eight healthy, normal, subjects produced five swallows of each of three bolus volumes for a total of 120 swallows. The total duration of electromyographic activity during the pharyngeal stage of the swallow did not alter with bolus condition; however, specific muscles did show a volume-dependent change in electromyograph duration and time of firing. Submental muscle activity was longest for saliva swallows. The interarytenoid muscle showed a significant difference in duration between the saliva and 10-ml water bolus. Finally, the interval between the onset of laryngeal muscle activity (thyroarytenoid, interarytenoid) and of pharyngeal muscle firing patterns (superior pharyngeal constrictor onset, cricopharyngeus offset) decreased as bolus volume increased. The pattern of muscle activity associated with the swallow showed a high level of intrasubject agreement; the presence of somewhat different patterns among subjects indicated a degree of population variance.