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.     

Biomechanics of failed deglutitive upper esophageal sphincter relaxation in neurogenic dysphagia

Our aims were to examine the etiology and biomechanical properties of the nonrelaxing upper esophageal sphincter (UES) and the relationship between UES opening and failed relaxation. We examined the relationships among swallowed bolus volume, intrabolus pressure, sagittal UES diameter, the pharyngeal swallow response, and geniohyoid shortening in 18 patients with failed UES relaxation, 23 healthy aged controls, and 15 with Zenker's diverticulum. Etiology of failed UES relaxation was 56% medullary disease, 33% Parkinson's or extrapyramidal disease; and 11% idiopathic. Extent of UES opening ranged from absent to normal and correlated with preservation of the pharyngeal swallow response (P = 0.012) and geniohyoid shortening (P = 0.046). Intrabolus pressure was significantly greater compared with aged controls (P < 0.001) or Zenker's diverticulum (P < 0.001). The bolus volume-dependent increase in intrabolus pressure evident in controls was not observed in failed UES relaxation. The nonrelaxing UES therefore displays a constant loss of sphincter compliance throughout the full, and potentially normal, range of expansion during opening. Adequacy of UES opening is influenced by the degree of preservation of the pharyngeal swallow response and hyolaryngeal traction. In contrast, the stenotic UES displays a static loss of compliance, only apparent once the limit of sphincter expansion is reached.     

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.     

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.     

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.     

Manofluorography of deglutition after total laryngopharyngectomy

Manofluorography is a new technique for the evaluation of swallowing that provides simultaneous display of manometry and videofluoroscopy on one video screen. Data are presented from a study of deglutition in 10 patients who had prior total laryngopharyngectomy with replacement by either jejunal graft or gastric pull-up. Factors that enhance bolus passage are the presence of a widely patent graft and an intact swallowing reflex. Factors that impair bolus transit include stricture, jejunal peristalsis, impaired lingual coordination, and stenosis at the anastomotic site. The swallowing patterns of these patients serve as models of the open and closed cavity swallow and illustrate principles of manofluorographic interpretation.     

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.     

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.     

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.     

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.     

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.     

Respiration during feeding on solid food: alterations in breathing during mastication, pharyngeal bolus aggregation, and swallowing.

During feeding, solid food is chewed and propelled to the oropharynx, where the bolus gradually aggregates while the larynx remains open and breathing continues. The aggregated bolus in the valleculae is exposed to respiratory airflow, yet aspiration is rare in healthy individuals. The mechanism for preventing aspiration during bolus aggregation is unclear. One possibility is that alterations in the pattern of respiration during feeding could help prevent inhalation of food from the pharynx. We hypothesized that respiration was inhibited during bolus aggregation in the valleculae. Videofluorography was performed on 10 healthy volunteers eating solid foods with barium. Respiration was monitored concurrently with plethysmography and nasal air pressure. The timing of events during mastication, food transport, pharyngeal bolus aggregation, and swallowing were measured in relation to respiration. Respiratory cycle duration decreased during chewing (P < 0.001) but increased with swallowing (P < 0.001). During 66 recordings of vallecular bolus aggregation, there was inspiration in 8%, expiration in 41%, a pause in breathing in 17%, and multiple phases (including inspiration) in 35%. Out of 98 swallows, 47% started in the expiratory phase and 50% started during a pause in breathing, irrespective of bolus aggregation in the valleculae. Plethysmography was better than nasal manometry for determining the end of active expiration during feeding and swallowing with solid food. The hypothesis is rejected in that respiration was not inhibited during bolus aggregation. These findings suggest that airflow through the pharynx does not have a role in preventing aspiration during bolus aggregation in the oropharynx.     

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.     

Normal contractile algorithm of swallowing related muscles revealed by needle EMG and its comparison to videofluoroscopic swallowing study and high resolution manometry studies: A preliminary study

The purpose of this study was to investigate the function and importance of infrahyoid muscles with the suprahyoid muscles during swallowing, and to investigate swallowing sequences using kinematic analysis, high-resolution manometry (HRM) and electromyography (EMG). As a preliminary study, ten healthy subjects were prospectively enrolled. A needle EMG evaluated the onset latency, peak latency and duration of the suprahyoid and infrahyoid muscles. HRM measured the time intervals among the velopharynx, tongue base, and upper esophageal sphincter. We also evaluated hyoid motion using an automated kinematic analysis software® (AKAS). All of these parameters were synchronized with a tilting motion of the epiglottis. In the EMG analysis, the activations of the suprahyoid muscles developed about 300 ms earlier than that of the infrahyoid muscles. There was a significant relationship between the differences of suprahyoid and infrahyoid muscles’ latency and total duration of the hyoid motion (p < 0.05). The interval time of anterior hyoid motion has a significant correlation in the upper esophageal sphincter (UES) opening time. In conclusions, the functions of the infrahyoid muscles are also as important as that of the suprahyoid muscles for prolonged laryngeal elevation and UES opening. Moreover, kinematic analysis of videofluoroscopic swallowing study (VFSS) and HRM studies could reflect results of needle EMG study and replace EMG study.     

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.     

Pressure morphology of the relaxed lower esophageal sphincter: the formation and collapse of the phrenic ampulla

This study aimed to apply novel high-resolution manometry with eight-sector radial pressure resolution (3D-HRM technology) to resolve the deglutitive pressure morphology at the esophagogastric junction (EGJ) before, during, and after bolus transit. A hybrid HRM assembly, including a 9-cm-long 3D-HRM array, was used to record EGJ pressure morphology in 15 normal subjects. Concurrent videofluoroscopy was used to relate bolus movement to pressure morphology and EGJ anatomy, aided by an endoclip marking the squamocolumnar junction (SCJ). The contractile deceleration point (CDP) marked the time at which luminal clearance slowed to 1.1 cm/s and the location (4 cm proximal to the elevated SCJ) at which peristalsis terminated. The phrenic ampulla spanned from the CDP to the SCJ. The subsequent radial and axial collapse of the ampulla coincided with the reconstitution of the effaced and elongated lower esophageal sphincter (LES). Following ampullary emptying, the stretched LES (maximum length 4.0 cm) progressively collapsed to its baseline length of 1.9 cm (P < 0.001). The phrenic ampulla is a transient structure comprised of the stretched, effaced, and axially displaced LES that serves as a "yield zone" to facilitate bolus transfer to the stomach. During ampullary emptying, the LES circular muscle contracts, and longitudinal muscle shortens while that of the adjacent esophagus reelongates. The likely LES elongation with the formation of the ampulla and shortening to its native length after ampullary emptying suggest that reduction in the resting tone of the longitudinal muscle within the LES segment is a previously unrecognized component of LES relaxation.     

Mechanisms of airway protection during retching,vomiting, and swallowing

We investigated the mechanisms of airway protection and bolus transport during retching and vomiting by recording responses of the pharyngeal, laryngeal, and hyoid muscles and comparing them with responses during swallowing and responses of the gastrointestinal tract. Five dogs were chronically instrumented with electrodes on the striated muscles and strain gauges on smooth muscles. Retching and vomiting were stimulated by apomorphine (5-10 ug/kg iv). During retching, the hyoid and thyroid descending and laryngeal abductor muscles were activated; between retches, the hyoid, thyroid, and pharyngeal elevating, and laryngeal adductor muscles were activated. Vomiting always occurred during the ascending phase of retching and consisted of three sequential phases of hyoid and pharyngeal muscle activation culminating in simultaneous activation of all recorded elevating and descending laryngeal, hyoid, and pharyngeal muscles. Retrograde activation of esophagus and pharyngeal muscles occurred during the later phases, and laryngeal adductor was maximally activated in all phases of the vomit. During swallowing, the laryngeal adductor activation was followed immediately by brief activation of the laryngeal abductor. We concluded that retching functions to mix gastric contents with refluxed intestinal secretions and to impart an orad momentum to the bolus before vomiting. During retches, the airway is protected by glottal closure, and between retches, it is protected by ascent of the larynx and closure of the upper esophageal sphincter. The airway is protected by maximum glottal closure during vomiting. During swallowing, the airway is protected by laryngeal elevation and glottal closure followed by brief opening of the glottis, which may release subglottal pressure expelling material from the laryngeal vestibule.     

An experimental model to investigate the biomechanical determinants of pharyngeal mucosa coating during swallowing

The development of innovative experimental approaches is necessary to gain insights in the complex biomechanics of swallowing. In particular, unraveling the mechanisms of formation of the thin film of bolus coating the pharyngeal mucosa after the ingestion of liquid or semi-liquid food products is an important challenge, with implication in dysphagia treatment and sensory perceptions.The aim here is to propose an original experimental model of swallowing (i) to simulate the peristaltic motions driving the bolus from the oral cavity to the esophagus, (ii) to mimic and vary complex physiological variables of the pharyngeal mucosa (lubrication, deformability and velocity) and (iii) to measure the thickness and the composition of the coatings resulting from bolus flow. Three Newtonian glucose solutions were considered as model food boli, through sets of experiments covering different ranges of each physiological parameter mimicked.The properties of the coatings (thickness and dilution in saliva film) were shown to depend significantly on the physical properties of food products considered (viscosity and density), but also on physiological variables such as lubrication by saliva, velocity of the peristaltic wave, and to a lesser extent, the deformability of the pharyngeal mucosa.The biomechanical peristalsis simulator developed here can contribute to unravel the determinants of bolus adhesion on pharyngeal mucosa, necessary both for the design of alternative food products for people affected by swallowing disorders, and for a better understanding of the dynamic mechanisms of aroma perception.     

EMG activity in hyoid muscles during pig suckling

Infant suckling is a complex behavior that includes cycles of rhythmic sucking as well as intermittent swallows. This behavior has three cycle types: 1) suck cycles, when milk is obtained from the teat and moved posteriorly into the valleculae in the oropharynx; 2) suck-swallow cycles, which include both a rhythmic suck and a pharyngeal swallow, where milk is moved out of the valleculae, past the larynx, and into the esophagus; and 3) postswallow suck cycles, immediately following the suck-swallow cycles. Because muscles controlling these behaviors are active in all three types of cycles, we tested the hypothesis that different patterns of electromyographic (EMG) activity in the mylohyoid, hyoglossus, stylohyoid, and thyrohyoid muscles of the pig characterized each cycle type. Anterior mylohyoid EMG activity occurred regularly in every cycle and was used as a cycle marker. Thyrohyoid activity, indicating the pharyngeal swallow, was immediately preceded by increased stylohyoid and hyoglossus activity; it divided the suck-swallow cycle into two phases. Timed from the onset of the suck-swallow cycle, the first phase had a relatively fixed duration while the duration of the second phase, timed from the thyrohyoid, varied directly with cycle duration. In short-duration cycles, the second phase could have a zero duration so that thyrohyoid activity extended into the postswallow cycle. In such cycles, all swallowing activity that occurred after the thyrohyoid EMG and was associated with bolus passage through the pharynx fell into the postswallow cycle. These data suggest that while the activity of some muscles, innervated by trigeminal and cervical plexus nerves, may be time locked to the cycle onset in swallowing, the cycle period itself is not. The postswallow cycle consequently contains variable amounts of pharyngeal swallowing EMG activity. The results exemplify the complexity of the relationship between rhythmic sucking and the swallow.     

Physiology of the esophageal pressure transition zone: separate contraction waves above and below

Manometrically measured peristaltic pressure amplitude displays a well-defined trough in the upper esophagus. Whereas this manometric "transition zone" (TZ) has been associated with striated-to-smooth muscle fiber transition, the underlying physiology of the TZ and its role in bolus transport are unclear. A computer model study of bolus retention in the TZ showed discoordinated distinct contraction waves above and below. Our aim was to test the hypothesis that distinct upper/lower contraction waves above/below the manometric TZ are normal physiology and to quantify space-time coordination between tone and bolus transport through the TZ. Eighteen normal barium swallows were analyzed in 6 subjects with concurrent 21-channel high-resolution manometry and digital fluoroscopy. From manometry, the TZ center (nadir pressure amplitude) and the upper/lower margins of the pressure trough were objectively quantified. Using fluoroscopy, we quantified space-time trajectories of the bolus tail and bolus tail pressures and maximum intraluminal pressures proximal to the tail with their space-time trajectories. In every swallow, the bolus tail followed distinct trajectories above/below the TZ, separated by a well-defined spatial "jump" that terminated an upper contraction wave and initiated a lower contraction wave (3.32 +/- 1.63 cm, P = 0.0004). An "indentation wave" always formed within the TZ distal to the upper wave, increasing in amplitude until the lower wave was initiated. As the upper contraction wave tail entered the TZ, it slowed and the tail pressure reduced rapidly, while indentation wave pressure increased to normal tail pressure values at the initiation of the lower wave. The TZ was a special zone of segmental contraction. The TZ is, physiologically, the transition from an upper contraction wave originating in the proximal striated esophagus to a lower contraction wave that moves into the distal smooth muscle esophagus. Complete bolus transport requires coordination of upper/lower waves and sufficient segmental squeeze to fully clear the bolus from the TZ during the transition period.