Assessment of impaired coordination between respiration and deglutition in children and young adults with ataxia telangiectasia

AIM

This cross-sectional investigation aimed to assess the value of non-invasive measures of temporal respiratory-swallow coupling in individuals with ataxic swallowing.

METHOD

Twenty participants (11 males, 9 females; range 9-21y) with ataxia telangiectasia were presented with water and pudding boluses. Their 193 swallows were compared with 2200 swallows from 82 age-matched healthy controls. The two components of airway protection during swallowing that were analyzed were: direction of peri-deglutitive airflow and duration of deglutitive inhibition of respiratory airflow (DIORA).

RESULTS

Safe expiratory patterns of peri-deglutitive airflow occurred significantly less often in participants with ataxia telangiectasia than in age-matched control participants (younger p<0.015 and older p<0.001). The frequency of an expiratory pattern of peri-deglutitive airflow increased with age in participants in the comparison group (p=0.006), but not in those with ataxia telangiectasia (p=0.234). With age, mean duration of DIORA decreased in controls (p<0.001) but was unchanged in participants with ataxia telangiectasia (p=0.164).

INTERPRETATION

Non-invasive quantitative measures of respiratory-swallow coupling capture temporal relationships that plausibly contribute to airway compromise from dysphagia. Changes in respiratory-swallow coupling observed with advancing age in control participants were not seen in participants with ataxia telangiectasia. Measures of perturbations may herald swallowing problems prior to development of pulmonary and nutritional sequelae.

Neuroanatomy and Neurophysiology: Implications for Swallowing

Deglutition is a complicated neuromuscular process that requires a complex level of communication between the central and peripheral nervous systems, and which results in highly coordinated actions from the muscles of mouth, pharynx, larynx, and esophagus. The actions of the individual muscles involved in deglutition and their cranial nerve innervation for the oral and pharyngeal stages of the swallow are presented. This is followed by a discussion of the research relating to potential areas of breakdown, and the corresponding symptomology, associated with the oral and pharyngeal stages of swallowing following a stroke.

Teledynamic evaluation of oropharyngeal swallowing

PURPOSE

The objective of the present investigation was to test the feasibility and clinical utility of a real-time Internet-based protocol for remote, telefluoroscopic evaluation of oropharyngeal swallowing.

METHOD

In this prospective cohort study, the authors evaluated 32 patients with a primary diagnosis of stroke or head/neck cancer. All patients participated in 2 separate fluoroscopic swallowing evaluations--one traditional on site and one telefluoroscopic off site--through the use of a telemedicine system. Agreement between sites was tested for 3 categories of variables: (a) overall severity of swallowing difficulty, (b) presence and extent of laryngeal penetration and aspiration as rated by the 8-point Penetration-Aspiration scale, and (c) treatment recommendations.

RESULTS

Results showed overall good agreement in subjective severity ratings (κ = 0.636) and in Penetration-Aspiration scale ratings (mean absolute difference = 1.1 points) between the onsite and offsite clinicians. Agreement in treatment recommendations was moderate to high, ranging from 69.3% to 100%.

CONCLUSIONS

The present study supports the feasibility and clinical utility of a telemedicine system for evaluating oropharyngeal swallowing. Given the difficulty and expertise needed to complete such evaluations, this study offers promising clinical avenues for patients in rural, remote, and underserved communities and countries where expert swallowing specialists are not available.

Reduced somatosensory activations in swallowing with age

Understanding the neural functional organization of swallowing in healthy elders is essential in diagnosing and treating older adults with swallowing difficulties. The primary aims of this investigation were to identify the neural activation sites of different components of deglutition in healthy elders using functional Magnetic Resonance Imaging (fMRI) and to investigate age differences in the neural control of swallowing. Ten young (age range 19-25 years of age) and nine older (age range 66-77 years of age) right-handed healthy individuals were scanned in a 3-Tesla MRI scanner. Subjects were visually cued for both a "Swallow" task and for component/control tasks ("Prepare to swallow," "Tap your tongue," and "Clear your throat"). Behavioral interleaved gradient (BIG) methodology was used to address movement related artifacts. Between-group comparisons revealed statistically stronger activations in the primary somatosensory cortex of young adults during the motor tasks examined. Both groups showed activations in the major motor areas involved in the initiation and execution of movement; however, areas involved in sensory processing, sensorimotor integration and/or motor coordination and control, showed reduced or limited activity in the elderly. Potential implications of these findings for clinical practice are discussed.

Hyoid displacement in post-treatment cancer patients: preliminary findings

PURPOSE

Dysphagia after head and neck cancer treatment is a health care issue; in some cases, the cause of death is not cancer but, rather, the passage of food or liquid into the lungs. Hyoid displacement is known to be important to safe swallowing function. The purpose of this study was to evaluate hyoid displacement after cancer treatment.

METHOD

Hyoid displacement was measured in healthy persons with normal swallowing function, head and neck cancer patients postradiation only, and head and neck cancer patients postsurgery only. Three bolus conditions (5 ml and 10 ml liquid and 5 ml paste) were examined. The influence of 2 different measurement algorithms on the extent of hyoid movement was also explored.

RESULTS

Radiation-therapy patients in this study had greater hyoid displacement than did surgery patients. Bolus viscosity and measurement method significantly influenced displacement results, whereas bolus volume did not. However, more multiple swallows occurred with 10 ml liquid; this may account for the apparent insignificance of bolus volume.

CONCLUSIONS

These findings can be used to assist head and neck cancer treatment planning and counseling. Because hyoid measurement methods influence research conclusions, this aspect of design should be considered when interpreting research findings.

Neural activation of swallowing and swallowing-related tasks in healthy young adults: an attempt to separate the components of deglutition

Understanding the underlying neural pathways that govern the highly complex neuromuscular action of swallowing is considered crucial in the process of correctly identifying and treating swallowing disorders. The aim of the present investigation was to identify the neural activations of the different components of deglutition in healthy young adults using functional magnetic resonance imaging (fMRI). Ten right-handed young healthy individuals were scanned in a 3-Tesla Siemens Allegra MRI scanner. Participants were visually cued for both a "Swallow" task and for component/control tasks ("Prepare to swallow", "Tap your tongue", and "Clear your throat") in a randomized order (event-related design). Behavioral interleaved gradient (BIG) methodology was used to address movement-related artifacts. Areas activated during each of the three component tasks enabled a partial differentiation of the neural localization for various components of the swallow. Areas that were more activated during throat clearing than other components included the posterior insula and small portions of the post- and pre-central gyri bilaterally. Tongue tapping showed higher activation in portions of the primary sensorimotor and premotor cortices and the parietal lobules. Planning did not show any areas that were more activated than in the other component tasks. When swallowing was compared with all other tasks, there was significantly more activation in the cerebellum, thalamus, cingulate gyrus, and all areas of the primary sensorimotor cortex bilaterally.

A Dynamic 3D Model of Hyoid Muscle Groups

Problem

A 3D dynamic model of supra and infrahyoid muscle groups was developed to provide information relative to the extent of muscle contraction. This model can provide valuable information relative to the physiology and pathophysiology of speech production, swallowing, and effects of surgical reconstruction. The rotation of the 3D model permits the viewer to appreciate the internal anatomy from several vantage points. Transparency can be used to study underlying anatomy without change the surroundings. In this study, a 3D dynamic model of suprahyoid and infrahyoid muscle groups during swallowing was created based on still 3D and dynamic MRI. This model will be further developed to examine the effects of muscle forces on functional changes after head and neck surgery.

Methods

3D MRI of head and neck area were used to reconstruct 3D polygonal meshes of hyoid muscle groups, hyoid bone, mandible, and larynx. Measurement was performed using Amira 4.1. The polygonal meshes were imported in to Alias Maya 8.5. By mapping the dynamic MRI of the swallow, the muscle meshes were reshaped to generate a 3D movie of swallowing.

Results

Using MR images, an accurate and realistic computer reconstruction of supra and infra hyoid muscles, in situ, was constructed. A 3D movie was created to demonstrate the anatomy, larynx, and hyoid displacement in all directions.

Conclusion

MRI provides high quality soft tissue information. 3D modeling using MRI provide muscle information in situ. The dynamic movie created the opportunity for researchers and physicians to observe anatomical changes in all coordinate planes. These offer a promising future toward increased understanding of head and neck physiology and pathophysiology.

Significance

This is the first 3D model to provide dynamic information on the hyoid muscle groups. It will eventually include forces that will animate functional change after surgical reconstruction.

Support

NIH-NIDCD, Award No. PHS 1 R01 Dc005603-01A2.

Bolus location associated with videofluoroscopic and respirodeglutometric events

The purpose of the present investigation was to determine the relation between specific events observed with simultaneous videofluoroscopy and respirodeglutometry. The order of occurrence was determined for each of 31 events (18 videofluoroscopic, 13 respirodeglutometric). Using 1 video frame (33.3 ms) as the maximum distance allowed between the average times of 2 events in the same cluster, 8 potential clusters were identified, 3 of which were statistically confirmed based on 90% confidence intervals on the mean time distances between events. Confirmed clusters included the time of (a) complete velar descent and the onset of the small noninspiratory flow (SNIF), (b) full separation of the base of the tongue from the pharyngeal wall and SNIF nadir, complete upper esophageal sphincter closure, and SNIF nadir, and (c) onset of epiglottic return and apnea offset. The onset of respiratory flow occurred within 13 ms after the onset of epiglottic return. Additionally, the percentage of swallows during which the bolus head or tail was located at each of 6 locations was determined for 20 of these events (10 videofluoroscopic, 10 respirodeglutometric). The 6 locations of interest included the oral cavity, base of tongue, valleculae, pyriform sinuses, upper esophageal sphincter, and the esophagus. Lastly, of the 72 swallows performed by these healthy, young adults, 65 (90.3%) were preceded by expiration, and all (100%) were followed by expiration.

Real-time remote telefluoroscopic assessment of patients with dysphagia

Dysphagia is a serious health problem that affects persons of all ages, from the neonate to those of advanced age. Many smaller communities and areas with sparse populations do not have regular access to professionals with expertise in the area of oral/pharyngeal dysphagia. Telemedicine is one method by which people in these areas can receive quality of service. The intent of this work was to develop an Internet system that permits real-time, remote, interactive evaluation of oral/pharyngeal swallowing function. The system consists of two major components. The first is a PC that is located in the fluoroscopy suite of a hospital. The computer is connected to the fluoroscope output and is responsible for (1) capturing video signals, (2) converting the analog video data into digitized video formats of both full resolution and transmission-optimized resolution, (3) simultaneously transmitting the transmission-optimized video stream over the network while the examination is being performed, and (4) storing the full-resolution data as a file in local storage for later retrieval. The second component is the controller computer which is located at a site some distance from the hospital. That controller computer manages the video capture process at the remote hospital site, manages the transmission of the stored images, and is then used for video analysis. The delay between the image as it was captured at the remote hospital site and viewed on the controller computer in the Principal Investigator's (PI's) laboratory ranged from 3 to 5 s. Video transmission occurred over a standard T1 line.

Magnetic resonance imaging of the levator veli palatini muscle during speech

OBJECTIVE

To obtain detailed anatomic information on the levator veli palatini (LVP) muscle from magnetic resonance imaging (MRI). Quantitative measures of the configuration of the LVP muscle at rest and during speech activities were obtained.

DESIGN

Prospective study using MRI of adult subjects with normal velopharyngeal mechanisms to determine anatomic and physiologic parameters of the levator muscle. The levator veli palatini muscle was imaged at rest and during speech activities consisting of nasal and non-nasal sounds mixed with vowels, consonants, or both (e.g., /ansa, asna, amfa, afma/).

PARTICIPANTS

Ten normal healthy adults (five men, five women) between 21 and 53 years of age and free of oropharyngeal abnormalities.

MAIN OUTCOME MEASURES

Two-dimensional spin echo static images and dynamic fast gradient echo images of the levator muscle in both the sagittal and oblique/coronal planes.

RESULTS

On average across female (F) and male (M) subjects: distance between LVP muscle origin points, 52.6 mm (F), 54.6 mm (M); angle of levator muscle origin at rest, 64.5 degrees (F), 60.4 degrees (M); length of the levator muscle at rest, 44.1 mm (F), 46.4 mm (M); width of levator muscle at lateral margin of velum, 5.5 mm (F), 6.6 mm (M). Both the levator muscle angle of origin and length became progressively smaller from rest, nasal consonants, low vowels, high vowels, and fricatives for both female and male subjects. Across all subjects, there was a 19% reduction in length of the LVP muscle from rest position to fricative production.

CONCLUSIONS

MRI is an effective method of imaging and measuring the LVP muscle and related structures in living subjects. Understanding the normal tissue distribution and quantification of the LVP muscle provides important information for development of a functional biomechanical model of the velopharynx and for improved surgical treatment.

Respiratory and acoustic signals associated with bolus passage during swallowing

In order to advance our understanding of the relation between respiration and deglutition, simultaneous videofluoroscopy and respirodeglutometry was performed. Fifteen normal, healthy, young adults (20-29 years of age) were connected to a respirodeglutometer and positioned for simultaneous videofluoroscopic assessment in the lateral plane. Subjects performed three swallows each of a 5-ml and a 10-ml bolus of liquid barium and a 5-ml bolus of paste barium, for a total of nine swallows per subject. Location of the bolus head as identified with videofluoroscopy was associated with eight respirodeglutometric variables. In addition, temporal relations for seven respirodeglutometric variables were calculated as a function of bolus volume and viscosity. Significant temporal differences were found for five of the variables by volume. No significant temporal differences were noted by viscosity. Expiration occurred before 79% and after 96% of the swallows. The number of inspirations preceding a swallow suggested a possible effect resulting from the need to hold a bolus in the mouth before receiving instructions to swallow during videofluoroscopic assessment. This effect may be important during patient evaluation. For a significant number of swallows, respiratory flow ceased before the velum was fully elevated.

Temporal and durational patterns associating respiration and swallowing

This study obtained initial normative data on the temporal coordination of respiration and swallowing events in 12 young adults using a first-generation Respirodeglutometer. In addition, direction of airflow before and after deglutive apnea was obtained. Three swallows of two viscosities of bolus material were performed by each subject, yielding a total of 72 swallows. Qualitative and quanitative analyses were performed. Time of onset of submental surface electromyography and time of laryngeal movement were found to differ between males and females. Males began submental muscle contraction before females and laryngeal movement after females. Duration of deglutition apnea for all swallows was 0.75 +/- 0.14 sec. Expiration occurred before the deglutition apnea 93% of the time and after the deglutition apnea 100% of the time. A modal pattern of events obtained with the Respirodeglutometer was present in 42% of the swallows, and an additional 47% had only one event differ from that order.

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.

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

To better understand the mechanisms of airway protection during swallow, the authors of this study performed an electromyographic (EMG) analysis on the thyroarytenoid (TA) and interarytenoid (IA) muscles during a variety of tasks. The tasks included high, low, and comfortable pitch phonation, the Valsalva maneuver, saliva swallow, and 5- and 10-mL water swallows. Raw EMG signals were analyzed to obtain root mean square data, which correspond to a relative magnitude of muscle activation. The data show that both TA and IA muscles generate a similar level of relative activation, with the greatest electrical activity observed during swallow tasks followed by the Valsalva maneuver and phonation. The duration, onset, offset, and pattern of activity during the swallowing tasks also showed close synchronization between the two muscles. These data can be used in designing therapy for voice disorders and pharyngeal dysphagia.

Quantitative assessment of hyoid bone displacement from video images during swallowing

Given the relationship between hyoid displacement and aspiration, a simple, accurate, clinically useful method for identification of reduced hyoid displacement is needed. The purpose of this investigation was to validate a quantitative method for clinically assessing hyoid bone movement during swallowing. Videofluoroscopic evaluations of 20 male subjects--10 who had been subjectively assessed as demonstrating normal hyoid displacement during swallowing, and 10 who had been subjectively assessed as demonstrating reduced displacement during swallowing--were analyzed. A video measuring gauge was used, and a software spreadsheet was developed to perform trigonometric calculations for determination of anterior/superior hyoid trajectories. Statistically significant differences were found between groups in both the anterior and superior directions of hyoid movement. No significant differences were found between liquid and paste swallows within groups. This method is simple in that it is necessary to identify only three to five points on two video images. Those values are then input onto a preprogrammed spreadsheet that automatically performs the necessary calculations. Although the present investigation focused on the movements of the hyoid bone during swallowing, this method of tracking displacement can be used for virtually any task or structure whose movements can be captured on videotape.

Intrinsic fibre architecture and attachments of the human epiglottis and their contributions to the mechanism of deglutition

Two mechanisms have been proposed which address the downfolding of the epiglottis during swallowing. The passive mechanism (Fink et al. 1979) focuses on passive mechanical forces transmitted through the median hyoepiglottic ligament and pre-epiglottic adipose tissue to the epiglottis. The active mechanism (Ekberg & Sigurjonsson, 1982) expands the passive mechanism to include active contributions from the aryepiglotticus and thyroepiglotticus muscles. By means of laryngeal microdissection and whole mount orcein staining, distinct bands of fascial condensations were identified running from the lateral edge of the epiglottis just superior to the attachment of the median hyoepiglottic ligament to the hyoid bone near the ends of the greater horns. Neither the proposed active nor the passive mechanisms address the possible contribution of these paired lateral hyoepiglottic ligaments to epiglottic downfolding. Computer image analysis of videofluoroscopic examinations of swallowing was then used to assess the dynamic movements of the larynx during swallowing. It was observed that the downfolding of the epiglottis occurred in the same video frame as initiation of anterior displacement of the hyoid bone and thyrohyoid approximation. Based on the anatomical and dynamic relationship of the epiglottis to other laryngeal structures, we propose that as the larynx elevates and the hyoid bone moves anteriorly, these lateral ligaments exert traction preferentially on the upper third of the epiglottis to bring it to a position below the horizontal.

Laryngeal movement, oropharyngeal pressure, and submental muscle contraction during swallowing

This study examined temporal relationships of laryngeal movement, oropharyngeal pressure and submental muscle contraction during swallowing. Techniques used to obtain the temporal measures were electroglottography (EGG), oropharyngeal manometry, and submental surface electromyography. Liquid bolus swallows were performed by 40 normal subjects evenly divided by young and elderly, men and women. Results of this investigation suggest that the EGG waveform is reflective of the temporal aspects of laryngeal movement during swallowing and that the EGG has potential as a behavioral modification technique in swallowing therapy. A case study is presented to illustrate the use of the electroglottograph for biofeedback.

Videofluoroscopic predictors of aspiration in patients with oropharyngeal dysphagia

The purpose of this investigation was to determine the relationship between aspiration and seven other variables indicative of pharyngeal stage dysphagia. Additionally, we looked at the relationship between aspiration and oral stage dysphagia. Multiple logistic regression analysis identified five independent predictors of aspiration that were significant at the p = 0.05 level: vallecular stasis, reduced hyoid elevation, deviant epiglottic function, diffuse hypopharyngeal stasis, and delayed initiation of the pharyngeal stage of the swallow. A linear trend was observed in that, as the severity of vallecular stasis, pyriform sinus stasis, diffuse hypopharyngeal stasis, or delayed initiation of the pharyngeal stage of the swallow increased, the proportion of patients who aspirated also increased. A stepwise logistic regression model furnished estimates of the odds ratio for each independent variable and can be used by clinicians to calculate the risk of aspiration in patients who demonstrate pharyngeal stage dysphagia.

Effects of age, gender, bolus volume, and bolus viscosity on oropharyngeal pressure during swallowing

Oropharyngeal pressure during swallowing was studied in a total of 40 healthy adult males and females in two age groups (21-27 yr and 62-75 yr). Effects of bolus volume, bolus viscosity, age, and gender were analyzed, and dry and bolus swallows were compared. The duration of the intrabolus pressure, reflecting the pressure exerted by the tongue on the bolus and preceding the generation of the pharyngeal pressure, was significantly affected by bolus volume. The duration of oropharyngeal pressure was affected by age, gender, and bolus type (bolus vs. dry swallow). Peak oropharyngeal pressure was not affected by any of the test factors, although there was a tendency for older subjects to have higher pressures than young subjects.

The relationship of vallecular residue to oral involvement, reduced hyoid elevation, and epiglottic function

The purpose of this investigation was to identify certain variables that may result in vallecular residue after swallowing. The relationship between vallecular residue and oral-stage dysphagia, reduced hyoid elevation, and movement of the epiglottis was assessed in 330 patients referred to the speech pathology section for evaluation of oropharyngeal swallowing function. Patients with vallecular residue were more likely to have oral involvement or deviant epiglottic function, characterized by an absence of epiglottic inversion or incomplete inversion, than patients without vallecular residue. Although the primary focus of the study was between vallecular residue and the other select variables, the interrelationships among the three other variables were also studied. Patients with deviant epiglottic function were more likely to have oral involvement, reduced hyoid elevation, or vallecular residue than patients without deviant epiglottic function and patients with reduced hyoid elevation were more likely to have oral involvement than those with normal hyoid elevation. Multivariate analysis revealed that the relationship between oral involvement and deviant epiglottic function, present in the bivariate analysis, was not significant when controlling for other relationships in the model. The relationship between primary medical diagnostic category and the presence/absence of vallecular residue as well as the other dichotomous variables varied between and within diagnostic categories.

Tetanic response of the cricothyroid muscle

Tetanic response of canine cricothyroid muscle tissue was investigated through a series of experiments conducted in vitro. Two separate portions of the cricothyroid muscle, namely the pars recta and pars oblique, were studied. Samples of the muscle were dissected from dog larynges excised a few minutes before death and kept in Krebs-Ringer solution at a temperature of 37 degrees +/- 1 degrees C and a pH of 7.4 +/- 0.05. Tetanic contraction of the muscle samples was obtained by field stimulation to the muscle through a pair of parallel-plate platinum electrodes and with a train of square pulses of 0.1-millisecond duration and 85-V amplitude. Isometric force responses of the pars recta and pars oblique muscles were obtained electronically with a dual servo system (ergometer). The effect of tissue elongation on the active and passive responses was quantified by stimulation of the sample during cyclic elongation. Both active and passive responses as a function of elongation were obtained on the same sample.

The effects of a maxillary speech-aid prosthesis for the combined tongue and mandibular resection patient

The purpose of this investigation was to develop a protocol for the fabrication of a prosthesis that would improve speech in individuals who have undergone complete removal of the tongue and mandible. A 60-year-old man was suffering from severe xerostomia and was unable to produce intelligible speech. Speech analysis without the prosthesis revealed a profound articulatory disorder. With the prosthesis, xerostomia was eliminated and the subject had fewer articulatory errors of severity. Improvement in speech intelligibility was significant at p less than 0.001.

Use of the electroglottograph for measurement of temporal aspects of the swallow: preliminary observations

The electroglottograph (EGG) is a non-invasive, electrical impedance device that was developed for observing vocal fold contract during phonation. After a thorough study of the frequency response characteristics of the EGG, we found that the EGG output can be used to identify maximum laryngeal displacement and the duration of laryngeal movement during swallowing. With a small intranasal pressure transducer placed beneath the velum and the EGG electrodes placed externally on the thyroid cartilage, additional information on the temporal aspects of the swallow can be measured. The EGG has direct clinical application when teaching such techniques as the safe swallow and Mendelsohn maneuver and it is useful as a research technique when using repeated measures designed to study the swallow reflex.

Tetanic contraction in vocal fold muscle

Active properties of canine vocalis muscle tissue were investigated through a series of experiments conducted in vitro. Samples of the vocalis muscle were dissected from dog larynges excised a few minutes before death and kept in Krebs solution at a temperature of 37 +/- 1 degree C and a pH of 7.4 +/- 0.05. Isometric and isotonic tetanic responses of the vocalis muscle were obtained electronically with a Dual Servo System (ergometer). Isometric tension was recorded at various levels of elongation and stimulation rate. Isotonic shortening was recorded at various levels of force, and shortening velocity was obtained by numerical analysis of recorded data. It was found that fused tetanus occurred at stimulation rates of about 90 Hz, where the isometric tetanic force saturates. Repeated stimulation of the muscle in vitro not only caused nonrecoverable fatigue in the tissue, but also decreased its passive tension. The combined active and passive isometric tension increased with elongation of the muscle. Results of isometric active responses were normalized with respect to average passive response. This normalization allowed for better comparison between tetanic contraction and twitch contraction. It was found that maximum tetanic contraction was 6.4 times greater than maximum twitch contraction obtained in a previous study. A tetanic contraction period was defined and investigated for eight samples of vocalis muscle tissue from different dogs. The tetanic contraction period showed a linear increasing trend with strain.

Comparative study of the physiological properties of the vocalis and cricothyroid muscles

Viable tissue samples of the vocalis muscle and pars recta portion of the cricothyroid muscle were dissected from the excised larynges of middle-aged, male, mixed breed dogs. The samples were maintained in an aerated Krebs-Ringer solution and curarized. Temperature and pH were controlled. Field stimulation was performed with parallel-plate platinum electrodes. Using a dual mode ergometer, in vitro measurements were made at increased levels of strain. Least-squares regression analyses were performed on contraction times and 50% relaxation times as a function of strain. Results of this investigation indicated important differences in the active and passive properties of the pars recta portion of the cricothyroid and the vocalis muscle. The mean contraction time of the vocalis muscle was 24 ms and that of the cricothyroid muscle, 33.5 ms. The mean half relaxation time was 20 ms for the vocalis muscle and 30 ms for the cricothyroid. The twitch contraction and half relaxation times of the vocalis remained independent of strain, whereas those of the cricothyroid showed strong positive dependence on strain level. Differences in the passive properties of the two muscles were also evidenced; the vocalis muscle was found to be stiffer at all levels of strain.

Elasticity of canine vocal fold tissue

Stress-strain curves were obtained from vocalis muscle tissue that was kept viable in an aerated Krebs-Ringer solution after excision of the larynx from live dogs. Results are compared to similar curves obtained from dead tissue and suggest that vocal fold elasticity depends on the level of strain, the elapsed time after elongation, the condition of the tissue, and the choice of rest length for strain computation. Tables of Young's moduli for various conditions are given.