Intrabolus pressure gradient identifies pathological constriction in the upper esophageal sphincter during flow

Propulsion of a bolus through the upper esophageal sphincter (UES) is driven by a pressure drop in the direction of flow against frictional resisting force. Basic mechanics suggest that the axial rate of drop in intrabolus pressure (IBP), i.e., the intrabolus pressure gradient (IBPG), should be locally sensitive to abnormal constriction. We sought to quantify space-time patterns of IBP and IBPG that correlate with pathological disruption to transsphincteric bolus transport. High-resolution high-fidelity perfused manometry was applied concurrent with videofluoroscopy in 6 healthy controls and 10 patients with restricted UES opening and 4 bolus volumes. Pressures were interpolated spatially and displayed as space-time isocontours with bolus head and tail trajectories superimposed to identify the IBP domain. IBP and IBPG were averaged over an approximately steady period of transsphincteric flow. The axial location and magnitude of maximum IBPG were quantified for each swallow relative to the location of the abnormal restriction. We found that average hypopharyngeal IBP and locally maximal IBPG were significantly higher in the patient group (P < 0.001), whereas the maximum IBPG was insensitive to bolus volume, and the locations of maximum IBPG in the patient group were well correlated with axial locations of maximal UES constriction (r = 0.84, P < 0.01). Space-time structure of IBP and IBPG correlated qualitatively with swallow dysfunction. Because IBPG reflects pressure force driving the bolus against frictional force in the UES, IBPG reflects local changes in frictional resistance from pathological constriction during bolus flow. Consequently, the location and magnitude of IBPG reflect the existence and location of abnormal constriction, and IBP and IBPG structure reflect decompensation of the pharyngeal swallow.     

Upper esophageal sphincter impedance as a marker of sphincter opening diameter

The measurement of the physical extent of opening of the upper esophageal sphincter (UES) during bolus swallowing has to date relied on videofluoroscopy. Theoretically luminal impedance measured during bolus flow should be influenced by luminal diameter. In this study, we measured the UES nadir impedance (lowest value of impedance) during bolus swallowing and assessed it as a potential correlate of UES diameter that can be determined nonradiologically. In 40 patients with dysphagia, bolus swallowing of liquids, semisolids, and solids was recorded with manometry, impedance, and videofluoroscopy. During swallows, the UES opening diameter (in the lateral fluoroscopic view) was measured and compared with automated impedance manometry (AIM)-derived swallow function variables and UES nadir impedance as well as high-resolution manometry-derived UES relaxation pressure variables. Of all measured variables, UES nadir impedance was the most strongly correlated with UES opening diameter. Narrower diameter correlated with higher impedance (r = -0.478, P < 0.001). Patients with <10 mm, 10-14 mm (normal), and ≥ 15 mm UES diameter had average UES nadir impedances of 498 ± 39 Ohms, 369 ± 31 Ohms, and 293 ± 17 Ohms, respectively (ANOVA P = 0.005). A higher swallow risk index, indicative of poor pharyngeal swallow function, was associated with narrower UES diameter and higher UES nadir impedance during swallowing. In contrast, UES relaxation pressure variables were not significantly altered in relation to UES diameter. We concluded that the UES nadir impedance correlates with opening diameter of the UES during bolus flow. This variable, when combined with other pharyngeal AIM analysis variables, may allow characterization of the pathophysiology of swallowing dysfunction.     

Deglutitive upper esophageal sphincter relaxation: a study of 75 volunteer subjects using solid-state high-resolution manometry

This study aimed to use a novel high-resolution manometry (HRM) system to establish normative values for deglutitive upper esophageal sphincter (UES) relaxation. Seventy-five asymptomatic controls were studied. A solid-state HRM assembly with 36 circumferential sensors spaced 1 cm apart was positioned to record from the hypopharynx to the stomach. Subjects performed ten 5-ml water swallows and one each of 1-, 10-, and 20-ml volume swallows. Pressure profiles across the UES were analyzed using customized computational algorithms that measured 1) the relaxation interval (RI), 2) the median intrabolus pressure (mIBP) during the RI, and 3) the deglutitive sphincter resistance (DSR) defined as mIBP/RI. The automated analysis succeeded in confirming bolus volume modulation of both the RI and the mIBP with the mean RI ranging from 0.32 to 0.50 s and mIBP ranging from 5.93 to 13.80 mmHg for 1- and 20-ml swallows, respectively. DSR was relatively independent of bolus volume. Peak pharyngeal contraction during the return to the resting state postswallow was almost 300 mmHg, again independent of bolus volume. We performed a detailed analysis of deglutitive UES relaxation with a novel HRM system and customized software. The enhanced spatial resolution of HRM allows for the accurate, automated assessment of UES relaxation and intrabolus pressure characteristics, in both cases confirming the volume-dependent effects and absolute values of these parameters previously demonstrated by detailed analysis of concurrent manometry/fluoroscopy data. Normative values were established to aid in future clinical and investigative studies.     

A novel pattern of longitudinal muscle contraction with subthreshold pharyngeal stimulus: a possible mechanism of lower esophageal sphincter relaxation

A subthreshold pharyngeal stimulus induces lower esophageal sphincter (LES) relaxation and inhibits progression of ongoing peristaltic contraction in the esophagus. Recent studies show that longitudinal muscle contraction of the esophagus may play a role in LES relaxation. Our goal was to determine whether a subthreshold pharyngeal stimulus induces contraction of the longitudinal muscle of the esophagus and to determine the nature of this contraction. Studies were conducted in 16 healthy subjects. High resolution manometry (HRM) recorded pressures, and high frequency intraluminal ultrasound (HFIUS) images recorded longitudinal muscle contraction at various locations in the esophagus. Subthreshold pharyngeal stimulation was induced by injection of minute amounts of water in the pharynx. A subthreshold pharyngeal stimulus induced strong contraction and caudal descent of the upper esophageal sphincter (UES) along with relaxation of the LES. HFIUS identified longitudinal muscle contraction of the proximal (3-5 cm below the UES) but not the distal esophagus. Pharyngeal stimulus, following a dry swallow, blocked the progression of dry swallow-induced peristalsis; this was also associated with UES contraction and descent along with the contraction of longitudinal muscle of the proximal esophagus. We identify a unique pattern of longitudinal muscle contraction of the proximal esophagus in response to subthreshold pharyngeal stimulus, which we propose may be responsible for relaxation of the distal esophagus and LES through the stretch sensitive activation of myenteric inhibitory motor neurons.     

Space-time pressure structure of pharyngo-esophageal segment during swallowing

We applied high-resolution manometry with spatiotemporal data interpolation and simultaneous videofluoroscopy to normal pharyngeal swallows to correlate specific features in the space-time intraluminal pressure structure with physiological events and normal deglutitive transsphincteric bolus flow to define normal biomechanical properties of the pharyngo-esophageal (PE) segment. Pressures were recorded by microperfused catheter, and the two-dimensional space-time data sets were plotted as isocontours. On these were superimposed bolus trajectories, anatomic segment movements, and hyo-laryngeal trajectories from concurrent videofluoroscopy. Correlation of the highly reproducible space-time-pressure structure with radiographic images confirmed that primary deglutitive PE segment functions (pressure profile, laryngeal elevation, axial sphincter motion, timing of relaxation, contraction) are accurately discernible from single isocontour pressure visualization. Pressure during bolus flow was highly dependent on axial location within PE segment and time instant. The intrabolus pressure domain, corresponding to the space-time region between bolus head and tail trajectories, demonstrated significant bolus volume dependence. High-resolution manometry accurately, comprehensively, and highly reproducibly depicts the PE segment space-time-pressure structure and specific physiological events related to upper esophageal sphincter opening and transsphincteric flow during normal swallowing. Intrabolus pressure variations are highly dependent on position within the PE segment and time.     

Development of the movement of the epiglottis in infant and juvenile pigs

Although backward folding of the epiglottis is one of the signal events of the mammalian adult swallow, the epiglottis does not fold during the infant swallow. How this functional change occurs is unknown, but we hypothesize that a change in swallow mechanism occurs with maturation, prior to weaning. Using videofluoroscopy, we found three characteristic patterns of swallowing movement at different ages in the pig: an infant swallow, a transitional swallow and a post-weaning (juvenile or adult) swallow. In animals of all ages, the dorsal region of the epiglottis and larynx was held in an intranarial position by a muscular sphincter formed by the palatopharyngeal arch. In the infant swallow, increasing pressure in the oropharynx forced a liquid bolus through the piriform recesses on either side of a relatively stationary epiglottis into the esophagus. As the infant matured, the palatopharyngeal arch and the soft palate elevated at the beginning of the swallow, so exposing a larger area of the epiglottis to bolus pressure. In transitional swallows, the epiglottis was tilted backward relatively slowly by a combination of bolus pressure and squeezing of the epiglottis by closure of the palatopharyngeal sphincter. The bolus, however, traveled alongside but never over the tip of the epiglottis. In the juvenile swallow, the bolus always passed over the tip of the epiglottis. The tilting of the epiglottis resulted from several factors, including the action of the palatopharyngeal sphincter, higher bolus pressure exerted on the epiglottis and the allometry of increased size. In both transitional and juvenile swallows, the subsequent relaxation of the palatopharyngeal sphincter released the epiglottis, which sprang back to its original intranarial position.     

Assessment of intraluminal impedance for the detection of pharyngeal bolus flow during swallowing in healthy adults

Intraluminal impedance, a nonradiological method for assessing bolus flow within the gut, may be suitable for investigating pharyngeal disorders. This study evaluated an impedance technique for the detection of pharyngeal bolus flow during swallowing. Patterns of pharyngoesophageal pressure and impedance were simultaneously recorded with videofluoroscopy in 10 healthy volunteers during swallowing of liquid, semisolid, and solid boluses. The timing of bolus head and tail passage recorded by fluoroscopy was correlated with the timing of impedance drop and recovery at each recording site. Bolus swallowing produced a drop in impedance from baseline followed by a recovery to at least 50% of baseline. The timing of the pharyngeal and esophageal impedance drop correlated with the timing of the arrival of the bolus head. In the pharynx, the timing of impedance recovery was delayed relative to the timing of clearance of the bolus tail. In contrast, in the upper esophageal sphincter (UES) and proximal esophagus, the timing of impedance recovery correlated well with the timing of clearance of the bolus tail. Impedance-based estimates of pharyngoesophageal bolus clearance time correlated with true pharyngoesophageal bolus clearance time. Patterns of intraluminal impedance recorded in the pharynx during bolus swallowing are therefore more complex than those in the esophagus. During swallowing, mucosal contact between the tongue base and posterior pharyngeal wall prolongs the duration of pharyngeal impedance drop, leading to overestimation of bolus tail timing. Therefore, we conclude that intraluminal impedance measurement does not accurately reflect the bolus transit in the pharynx but does accurately reflect bolus transit across the UES and below.     

The role of the superior laryngeal nerve in esophageal reflexes

The aim of this study was to determine the role of the superior laryngeal nerve (SLN) in the following esophageal reflexes: esophago-upper esophageal sphincter (UES) contractile reflex (EUCR), esophago-lower esophageal sphincter (LES) relaxation reflex (ELIR), secondary peristalsis, pharyngeal swallowing, and belch. Cats (N = 43) were decerebrated and instrumented to record EMG of the cricopharyngeus, thyrohyoideus, geniohyoideus, and cricothyroideus; esophageal pressure; and motility of LES. Reflexes were activated by stimulation of the esophagus via slow balloon or rapid air distension at 1 to 16 cm distal to the UES. Slow balloon distension consistently activated EUCR and ELIR from all areas of the esophagus, but the distal esophagus was more sensitive than the proximal esophagus. Transection of SLN or proximal recurrent laryngeal nerves (RLN) blocked EUCR and ELIR generated from the cervical esophagus. Distal RLN transection blocked EUCR from the distal cervical esophagus. Slow distension of all areas of the esophagus except the most proximal few centimeters activated secondary peristalsis, and SLN transection had no effect on secondary peristalsis. Slow distension of all areas of the esophagus inconsistently activated pharyngeal swallows, and SLN transection blocked generation of pharyngeal swallows from all levels of the esophagus. Slow distension of the esophagus inconsistently activated belching, but rapid air distension consistently activated belching from all areas of the esophagus. SLN transection did not block initiation of belch but blocked one aspect of belch, i.e., inhibition of cricopharyngeus EMG. Vagotomy blocked all aspects of belch generated from all areas of esophagus and blocked all responses of all reflexes not blocked by SLN or RLN transection. In conclusion, the SLN mediates all aspects of the pharyngeal swallow, no portion of the secondary peristalsis, and the EUCR and ELIR generated from the proximal esophagus. Considering that SLN is not a motor nerve for any of these reflexes, the role of the SLN in control of these reflexes is sensory in nature only.     

Differential relaxation and contractile responses of the human upper esophageal sphincter mediated by interplay of mucosal and deep mechanoreceptor activation

BACKGROUND AND AIMS: the neural mechanisms of distension-induced esophagoupper esophageal sphincter (UES) reflexes have not been explored in humans. We investigated the modulation of these reflexes by mucosal anesthesia, acid exposure, and GABA(B) receptor activation. In 55 healthy human subjects, UES responses to rapid esophageal air insufflation and slow balloon distension were examined before and after pretreatment with 15 ml of topical esophageal lidocaine, esophageal HCl infusion, and baclofen 40 mg given orally. In response to rapid esophageal distension, UES can variably relax or contract. Following a mucosal blockade by topical lidocaine, the likelihood of a UES relaxation response was reduced by 11% (P < 0.01) and the likelihood of a UES contractile response was increased by 14% (P < 0.001) without alteration in the overall UES response rate. The UES contractile response to rapid esophageal air insufflation was also increased by 8% (P < 0.05) following sensitization by prior mucosal acid exposure. The UES contractile response, elicited by balloon distension, was regionally dependent (P < 0.05) (more frequent and of higher amplitude with proximal esophageal distension), and the response was attenuated by topical lidocaine (P < 0.05). Baclofen (40 mg po) had no effect on these UES reflexes. Abrupt gaseous esophageal distension activates simultaneously both excitatory and inhibitory pathways to the UES. Partial blockade of the mucosal mechanosensitive receptors permits an enhanced UES contractile response mediated by deeper esophageal mechanoreceptors. Activation of acid-sensitive esophageal mucosal chemoreceptors upregulates the UES contractile response, suggestive of a protective mechanism.     

Contractile and endurance properties of geniohyoid and diaphragm muscles

Despite the wealth of information about the neural control of pharyngeal dilator muscles, little is known about their intrinsic physiological properties. In the present study the in situ isometric contractility and endurance of a pharyngeal dilator, the geniohyoid muscle, were compared with properties of the diaphragm in 12 anesthetized artificially ventilated cats. The contraction time (means +/- SE) of the geniohyoid (27 +/- 2 ms) was shorter than that of the diaphragm (36 +/- 3 ms; P less than 0.0005), as was the half-relaxation time (29 +/- 2 vs. 45 +/- 4 ms; P less than 0.002). The faster contraction and relaxation of the geniohyoid compared with the diaphragm were appropriately reflected in the shape of the force-frequency curves for the two muscles, with that of the geniohyoid located to the right of the diaphragm force-frequency curve. The endurance properties of the two muscles were assessed using repetitive stimulation at 40 Hz in trains lasting 0.33 s, with one train repeated every second. The ratio of force at the end of 2 min of repetitive stimulation to initial force was 0.67 +/- 0.06 for the geniohyoid and 0.15 +/- 0.03 for the diaphragm (P less than 0.00001). After the repetitive stimulation, the muscle force generated in response to a range of stimulus frequencies was reduced to a greater extent for the diaphragm than for the geniohyoid muscle. These results indicate that the geniohyoid muscle has a faster physiological profile than does the diaphragm yet is relatively resistant to fatigue when driven at high rates.     

Utilizing intraluminal pressure differences to predict esophageal bolus flow dynamics

Successful esophageal emptying depends on the generation of a sustained intrabolus pressure (IBP) sufficient to overcome esophagogastric junction (EGJ) obstruction. Our aim was to develop a manometric analysis paradigm that describes the bolus driving pressure difference and the flow permissive time for esophageal bolus transit. Twenty normal subjects were studied with a 36-channel manometry assembly (1-cm spacing) during two 5- and one 10-ml barium swallows and concurrent fluoroscopy. Bolus domain pressure plots were generated by plotting bolus domain pressure (BDP) and EGJ relaxation pressure. BDP was defined as the pressure midway between the peristaltic ramp-up and the proximal margin of the EGJ. The flow permissive time was defined as the period where the BDP was > or = EGJ relaxation pressure. The mean BDP was 11.7 +/- 1.0 mmHg (SE), and the mean flow permissive time was 3.9 +/- 0.4 s for 5-ml swallows in normal controls. The mean BDP difference during flow was 4.0 +/- 1.0 mmHg. There was no significant difference in the fluoroscopic transit time and the flow permissive time calculated from the BDP plots (5 ml: fluoroscopy 3.4 +/- 0.2 s; BDP 3.9 +/- 0.4 s, P > 0.05). BDP plots provide a reliable measurement of IBP and its relationship with EGJ relaxation. The time available for flow can be readily delineated from this analysis, and the driving pressure responsible for flow can be accurately described and quantified. This may help predict abnormal bolus transit and the underlying mechanical properties of the EGJ.     

Variability of the Pharyngeal Phase of Swallow in the Cat

Objective

The pharyngeal phase of swallow has been thought to be a stereotypical motor behavior.

Study Design

This is a prospective, preclinical, hypothesis driven, one group by three-task design.

Methods

We sought to compare the effects of pharyngeal swabbing, water only, and water plus punctate mechanical stimulation on the spatiotemporal features of the pharyngeal phase of swallow in the cat. Swallow was elicited under these three conditions in six anaesthetized cats. Electromyographic activity was recorded from seven muscles used to evaluate swallow: mylohyoid, geniohyoid, thyrohyoid, thyroarytenoid, thyropharyngeus, cricopharyngeus, and parasternal.

Results

Pharyngeal swabbing in comparison to the other stimulus conditions, results in decreases in post-swallow cricopharyngeus activity (upper esophageal sphincter); a significant increase in parasternal (schluckatmung; swallow breath) activity; and increases in thyrohyoid (laryngeal elevator), thyroarytenoid (laryngeal adductor) and parasternal muscles burst duration. Pearson correlations were found of moderate strength between 19% of burst duration comparisons and weak to moderate relationships between 29% of burst amplitude comparisons. However, there were no positive significant relationships between phase durations and electromyogram amplitudes between any of the muscles studied during swallow.

Conclusions

The results support the concept that a stereotypical behavior, such as pharyngeal swallowing in animal models, can be modified by sensory feedback from pharyngeal mucosal mechanoreceptors. Furthermore, differences in swallow phase durations and amplitudes provide evidence that separate regulatory mechanisms exist which regulate spatial and temporal aspects of the behavior.     

Relative contribution of various airway protective mechanisms to prevention of aspiration during swallowing

Deglutitive airway protective mechanisms include glottal closure, epiglottal descent, and anterosuperior displacement of the larynx. Aspiration of swallowed material may occur during the pre-, intra-, or postpharyngeal phase of swallowing. Our objectives were to determine the relative contribution of the airway protective mechanisms during each phase of swallow in 14 decerebrated cats before and after suprahyoid myotomy, epiglottectomy, and unilateral cordectomy. After myotomy, superior excursions of the hyoid, thyroid, and cricoid cartilages and anteroposterior diameter of maximum upper esophageal spincter (UES) opening were significantly diminished, but the incidence of pharyngeal residue significantly increased (P < 0.05). No aspiration was observed in the predeglutitive period. After myotomy, the incidence of aspiration significantly increased in both intra- and postdeglutitive periods. Epiglottectomy did not alter aspiration incidence, but unilateral cordectomy resulted in a 100% incidence of intra- and postdeglutitive aspiration. In conclusion, glottal closure constitutes the primary mechanism for prevention of intra- and postdeglutitive aspiration, but laryngeal elevation may assist this function. Bolus pulsion without laryngeal distraction can open the UES, but at risk of aspiration due to decreased pharyngeal clearance. The epiglottis provides no apparent airway protection during any phase of swallowing.     

Adaptation of swallowing hyo-laryngeal kinematics is distinct in oral vs. pharyngeal sensory processing

Before a bolus is pushed into the pharynx, oral sensory processing is critical for planning movements of the subsequent pharyngeal swallow, including hyoid bone and laryngeal (hyo-laryngeal) kinematics. However, oral and pharyngeal sensory processing for hyo-laryngeal kinematics is not fully understood. In 11 healthy adults, we examined changes in kinematics with sensory adaptation, sensitivity shifting, with oropharyngeal swallows vs. pharyngeal swallows (no oral processing), and with various bolus volumes and tastes. Only pharyngeal swallows showed sensory adaptation (gradual changes in kinematics with repeated exposure to the same bolus). Conversely, only oropharyngeal swallows distinguished volume differences, whereas pharyngeal swallows did not. No taste effects were observed for either swallow type. The hyo-laryngeal kinematics were very similar between oropharyngeal swallows and pharyngeal swallows with a comparable bolus. Sensitivity shifting (changing sensory threshold for a small bolus when it immediately follows several very large boluses) was not observed in pharyngeal or oropharyngeal swallowing. These findings indicate that once oral sensory processing has set a motor program for a specific kind of bolus (i.e., 5 ml water), hyo-laryngeal movements are already highly standardized and optimized, showing no shifting or adaptation regardless of repeated exposure (sensory adaptation) or previous sensory experiences (sensitivity shifting). Also, the oral cavity is highly specialized for differentiating certain properties of a bolus (volume) that might require a specific motor plan to ensure swallowing safety, whereas the pharyngeal cavity does not make the same distinctions. Pharyngeal sensory processing might not be able to adjust motor plans created by the oral cavity once the swallow has already been triggered.     

Single motor unit recordings in human geniohyoid reveal minimal respiratory activity during quiet breathing

Maintenance of airway patency during breathing involves complex interactions between pharyngeal dilator muscles. The few previous studies of geniohyoid activity using multiunit electromyography (EMG) have suggested that geniohyoid shows predominantly inspiratory phasic activity. This study aimed to quantify geniohyoid respiration-related activity with single motor unit (SMU) EMG recordings. Six healthy subjects of normal body mass index were studied. Intramuscular EMG recordings of geniohyoid activity were made with a monopolar needle with subjects in supine and seated positions. The depth of the geniohyoid was identified by ultrasound, and the electrode position was confirmed with maneuvers to isolate activity in geniohyoid and genioglossus. Activity was recorded at 85 sites in the geniohyoid during quiet breathing (45 supine and 40 seated). When subjects were supine, 33 sites (73%) showed no activity during breathing and 10 (22%) showed tonic activity. In addition, one site showed a tonic SMU with increased expiratory discharge, and one site in another subject had one unit with expiratory phasic activity. When subjects were seated, 27 sites (68%) in the geniohyoid showed no activity, 12 sites (30%) showed tonic activity that was not respiration related, and one unit at one site showed phasic expiratory activity. The average peak discharge frequency of geniohyoid motor units was 16.2 ± 3.1 impulses/s during the "geniohyoid maneuver," which was the first part of a swallow. In contrast to previous findings, the geniohyoid shows some tonic activity but minimal respiration-related activity in healthy subjects in quiet breathing. The geniohyoid has little active role in airway stability under these conditions.     

Adult human upper esophageal sphincter contains specialized muscle fibers expressing unusual myosin heavy chain isoforms.

The functional upper esophageal sphincter (UES) is composed of the cricopharyngeus muscle (CP), the most inferior part of the inferior pharyngeal constrictor (iIPC), and the upper esophagus (UE). This sphincter is collapsed and exhibits sustained muscle activity in the resting state; it only relaxes and opens during swallowing, vomiting, and belching. The tonic contractile properties of the UES suggest that the skeletal muscle fibers in this sphincter differ from those in the limb and trunk muscles. In this study, myosin heavy chain (MHC) composition in the adult human UES muscles obtained from autopsies was investigated using immunocytochemical and immunoblotting techniques. Results showed that the adult human UES muscle fibers expressed unusual MHC isoforms such as slow-tonic (MHC-ton), alpha-cardiac (MHC-alpha), neonatal (MHC-neo), and embryonic (MHC-emb), which coexisted with the major MHCs (i.e., MHCI, IIa, and IIx). MHC-ton and MHC-alpha were coexpressed predominantly with slow-type I MHC isoform, whereas MHC-neo and MHC-emb coexisted mainly with fast-type IIa MHC. A slow inner layer (SIL) and a fast outer layer (FOL) in the iIPC and CP were identified immunocytochemically. MHC-ton- and MHC-alpha-containing fibers were concentrated mainly in the SIL, whereas MHC-neo- and MHC-emb-containing fibers were distributed primarily to the FOL. Identification of the specialized muscle fibers and their distribution patterns in the adult human UES is valuable for a better understanding of the physiological and pathophysiological behaviors of the sphincter.     

Influence of bite force and tongue pressure on oro-pharyngeal residue in the elderly

Objective: To investigate the influence of maximal bite force, maximal tongue pressure, number of mastications and swallowing on the oro‐pharyngeal residue in the elderly. Background: Oro‐pharyngeal residue in the elderly is an indication of dysphagia. Pharyngeal residue is especially critical as it may cause aspiration pneumonia, which is one of the major causes of death in elderly. Materials and methods: Videofluorographic recordings were performed on 14 elderly volunteers (six males, eight females, age range 65–93 years) without any history or symptoms of dysphagia. The subjects were instructed to consume 9 g of barium containing bread in two manners; free mastication and swallow (FMS: masticate and swallow freely), and limited mastication and swallow (LMS: swallow once after 30 chewing actions). The amount of oral and pharyngeal residue was evaluated using a 4‐point rating scale. Maximal occlusal force was measured by a pressure sensitive sheet, and maximal tongue pressure using a handy probe. Multiple regression analysis was performed to examine the influence of these items on the amount of oral and pharyngeal residue in FMS and LMS. Results: In FMS, age was found to be a factor which increased oral residue (p = 0.053), and the number of swallowing (p = 0.017) and the state of the prosthesis (p = 0.030) reduced the pharyngeal residue. In LMS, tongue pressure was a factor which reduced oral residue (p = 0.015) and increased pharyngeal residue (p = 0.008). Conclusion: It is suggested that in the elderly tongue pressure contributed to propulsion of the food bolus from oral cavity into the pharynx, and multiple swallowing contributed to the reduction in the amount of pharyngeal residue.     

Mechanical function of hyoid muscles during spontaneous breathing in cats

We assessed the mechanical behavior of the geniohyoid and sternohyoid muscles during spontaneous breathing using sonomicrometry in anesthetized cats. When the animals breathed O2, the hyoid muscles either became longer or did not change length (but never shortened) during inspiration. During progressive hyperoxic hypercapnia, transient increases in geniohyoid muscle inspiratory lengthening occurred in many animals; however, at high PCO2 the geniohyoid invariably shortened during inspiration (mean 4.9% of resting length at the end of CO2 rebreathing; P less than 0.001). The PCO2 at which geniohyoid inspiratory lengthening changed to inspiratory shortening was significantly higher than the CO2 threshold for the onset of geniohyoid electrical activity (P less than 0.01). For the sternohyoid muscle, hypercapnia caused inspiratory lengthening in 13 of 17 cats and inspiratory shortening in 4 of 17 cats; on average the sternohyoid lengthened by 1.6% of resting length at the end of CO2 rebreathing (P less than 0.01). Sternohyoid lengthening occurred in spite of this muscle being electrically active. These results suggest that the relationship between hyoid muscle electrical activity and respiratory changes in length is very complex, so that the presence of hyoid muscle electrical activity does not necessarily indicate muscle shortening, and among the geniohyoid and sternohyoid muscles, the geniohyoid has a primary role as a hypopharyngeal dilator in the spontaneously breathing cat, with the sternohyoid muscle acting in an accessory capacity.     

Relation between upper airway volume and hyoid muscle length

Previous studies have suggested that the geniohyoid and sternohyoid muscles act to enlarge the upper airway. If correct, there should be an inverse relation between upper airway volume and the length of hyoid muscles. To test this, known volumes of air were injected into or removed from the isolated sealed upper airway of eight pentobarbital sodium-anesthetized cats, and the resultant changes in geniohyoid and sternohyoid length were measured using sonomicrometry. Increases in upper airway volume shortened the geniohyoid in all cats (P less than 0.001) and shortened the sternohyoid in seven of eight cats (P less than 0.01); mean geniohyoid shortening (as a % of resting length) exceeded that of the sternohyoid. Decreases in upper airway volume lengthened the geniohyoid in all cats (P less than 0.001) but caused variable changes in sternohyoid length. Extension of the neck increased the resting lengths of both the geniohyoid (P less than 0.001) and sternohyoid (P less than 0.002). Neck flexion shortened the resting length of both hyoid muscles (P less than 0.001 for both), with the geniohyoid shortening more (as a % of resting length) than the sternohyoid (P less than 0.005). Progressive flexion of the neck from 180 to 90 degrees caused progressive increases in the ratio of changes in muscle length to changes in upper airway volume during airway inflation but did not affect this relation during airway deflation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of positional changes of anatomic structures on upper airway dilating muscle shortening during electro- and chemostimulation.

Positional changes of anatomic structures surrounding the upper airway are known to affect pharyngeal mechanics and collapsibility. We hypothesized that these alterations also affect the ability of the upper airway dilator muscles to enlarge the pharynx by altering their ability to shorten when activated. Using sonomicrometry, we evaluated in seven anesthetized dogs the effects of changes in tracheal and head position on the length of the genioglossus (GG) and the geniohyoid (GH) and the effects of these positional changes on the magnitude of shortening of the two muscles in response to electro- (ES) and chemostimulation (CS). Caudal traction of the trachea lengthened the GG and GH in all dogs, whereas cranial displacement of the trachea and flexion of the head to a vertical position shortened the muscles. Compared with the magnitude of ES-induced shortening in the neutral position, ES-induced shortening of the GG was 144.7 +/- 14.6, 49.3 +/- 4.3, and 33.5 +/- 11.6% during caudal and cranial displacement of the trachea and during head flexion, respectively. Similar effects of the positional changes were found for the GH, as well as for both muscles during respiratory stimulation with P(CO2) of 90 Torr at the end of CO(2) rebreathing, although inspiratory muscle shortening during CS reached only one-quarter to one-third of the magnitude observed during ES. We conclude that positional alterations of anatomic structures in the neck have a dramatic effect on the magnitude of shortening of the activated GG and GH, which may reduce substantially their ability to protect pharyngeal patency.