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.     

Relationship between esophageal muscle thickness and intraluminal pressure: an ultrasonographic study

A number of studies show a close temporal relationship between the rate of change in muscle thickness as detected by high-frequency intraluminal ultrasonography (HFIUS) and intraluminal pressure measured by manometry. There is a marked variability in esophageal contraction amplitude from one swallow to another at a given level in the esophagus and along the length of the esophagus. Furthermore, peristaltic pressures are higher in the distal compared with the proximal esophagus. The goal of this study was to evaluate the relationship between the baseline and peak muscle thickness and the contraction amplitude during swallow-induced contractions along the length of the esophagus. Fifteen normal subjects were studied using simultaneous esophageal pressures and HFIUS or HFIUS alone. Recordings were made during baseline and standardized swallows in the lower esophageal sphincter (LES) and at 2, 4, 6, 8, and 10 cm above the LES. HFIUS images were digitized, and esophageal muscle thickness and peak contraction amplitudes were measured. In the resting state, muscle thickness is higher in the LES compared with the rest of the esophagus. Baseline muscle thickness is also significantly higher at 2 cm vs. 10 cm above the LES. In a given subject and among different subjects, there is a good relationship between peak muscle thickness and peak peristaltic pressures (r = 0.55) at all sites along the length of the esophagus. The positive correlation between pressure and muscle thickness implies that the mean circumferential wall stress is fairly uniform from one swallow to another, irrespective of the contraction amplitude.     

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.     

Effect of dry swallows and wet swallows of different volumes on esophageal peristalsis.

The effect of dry swallows and wet swallows of various volumes on esophageal function was studied in normal subjects. An intraesophageal transducer assembly was used to measure the dynamics of esophageal peristalsis. The strength of esophageal contraction (amplitude) following a 1-ml liquid bolus was similar to that following a dry swallow but was significantly less than that following a wet swallow of a larger volume. There was no difference in strength of esophageal squeeze following swallows ranging from 2 to 20 ml. In addition, a wet swallow was associated with slower wave speed, greater duration of the contraction wave, and later time of appearance of the peristaltic wave in the distal esophagus than a dry swallow. Futhermore, the incidence of peristalsis was greater with a wet swallow than a dry swallow. The results of our studies indicate that although the act of swallowing alone in man initiates peristalsis, afferent information contributes to the regulation of primary peristalsis.     

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.     

Suppression of Abdominal Motor Activity during Swallowing in Cats and Humans

Diseases affecting pulmonary mechanics often result in changes to the coordination of swallow and breathing. We hypothesize that during times of increased intrathoracic pressure, swallow suppresses ongoing expiratory drive to ensure bolus transport through the esophagus. To this end, we sought to determine the effects of swallow on abdominal electromyographic (EMG) activity during expiratory threshold loading in anesthetized cats and in awake-healthy adult humans. Expiratory threshold loads were applied to recruit abdominal motor activity during breathing, and swallow was triggered by infusion of water into the mouth. In both anesthetized cats and humans, expiratory cycles which contained swallows had a significant reduction in abdominal EMG activity, and a greater percentage of swallows were produced during inspiration and/or respiratory phase transitions. These results suggest that: a) spinal expiratory motor pathways play an important role in the execution of swallow, and b) a more complex mechanical relationship exists between breathing and swallow than has previously been envisioned.     

Barium swallows after free jejunal transfer: should they be performed routinely?

Fistula formation after free jejunal transfer for pharyngoesophageal reconstruction is a serious complication with potentially critical consequences. Barium swallow is used postoperatively to check for anastomotic competence before feeding but has been unreliable as a predictor of leak at our institution. The objective of this study was to evaluate the role of routine postoperative barium swallow in 41 consecutive jejunal transfers. Thirty-nine patients who underwent 41 consecutive free jejunal transfers had a routine barium swallow performed between postoperative days 12 and 17. Radiologic findings and clinical outcome were evaluated and correlated. All barium swallows were reviewed by a single experienced radiologist in a blinded fashion. One total and one partial flap failure necessitated a second free jejunal transfer. Pharyngocutaneous fistulae developed after nine free jejunal transfers, of which the barium swallow was normal in four (44 percent) and showed a leak in five (56 percent). In the 32 free jejunal transfers with no clinical leaks, 6 (19 percent) had radiologic leakage of contrast. Thus, barium swallow was normal in 30 patients and showed leakage in 11 patients. Normal barium swallow correlated with uncomplicated clinical course in 26 of 30 cases. In the remaining four cases (13 percent), however, a delayed fistula developed, which was secondary to flap necrosis in one case (negative predictive value 87 percent). On the other hand, radiologic leaks corroborated clinical fistula in 5 of 11 cases (45 percent), whereas no fistula developed in 6 cases (positive predictive value 46 percent). Of the five patients with clinical fistulae, four had early leaks (within 1 week), and the barium swallow did not provide additional information. The fifth patient developed a delayed leak 2 weeks after the barium swallow. Review of these barium swallows at the time of this study reversed the initial report of leakage in three patients, improving the predictive value to 63 percent. These patients had an uncomplicated clinical course. The positive predictive value of clinical assessment alone was 63 percent. We conclude that barium studies following free jejunal transfers can be difficult to interpret, but an experienced radiologist can improve their accuracy. A normal barium swallow, however, does not ensure an uneventful clinical course. Similarly, radiologic leaks do not imply a clinical complication of fistula. Clinical judgment should therefore be exercised in initiating oral intake after free jejunal transfer. Barium swallow should be used only as an adjunct to aid in patient management.     

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.     

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.     

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.     

Study of intestinal flow by combined videofluoroscopy, manometry, and multiple intraluminal impedance

Assessment of patterns of flow in the small bowel is difficult. Multiple intraluminal impedance has been recently used for study of flow dynamics in the esophagus. Our aims were 1) to validate multiple intraluminal impedance by correlating impedance events with intestinal flow as detected by fluoroscopy and 2) to determine intestinal flow patterns in the fasting and postprandial period and their correspondence with manometry. First, six healthy subjects underwent simultaneous video-fluoroscopic, manometric, and impedance recording from the duodenum. Videofluoroscopy was used to validate impedance patterns corresponding with barium flow in the fasting and postprandial periods. Next, 16 healthy subjects underwent prolonged simultaneous recording of impedance and manometry in both periods. Most flow events were short (10 cm or less), with antegrade flow being the most common. Correspondence between impedance and videofluoroscopy increased with increasing length of barium flow. Impedance corresponded better with flow, at any distance, than manometry. However, impedance and manometric events, when analyzed separately as index events, always corresponded with fluoroscopic flow. The fasting and postprandial periods showed comparable patterns of flow, with frequent, highly propulsive manometric and impedance sequences. Motility index was positively and significantly associated with length of impedance events. Phase 3 of the migrating motor complex could be easily recognized by impedance. Multiple intraluminal impedance can detect intestinal flow events and corresponds better with fluoroscopic flow than manometry.     

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.     

Coordination of swallowing and respiration in unconscious subjects

We investigated the coordination of swallowing and breathing in 11 unconscious patients with an endotracheal tube in place during the recovery period from general anesthesia. Swallows occurred during both the inspiratory and expiratory phases with no preponderant occurrence during either phase. When a swallow occurred during inspiration, the inspiration was interrupted immediately and was followed by expiration, but the durations of both inspiration and expiration were progressively increased as the time from the onset of inspiration to the onset of swallowing was progressively delayed. A swallow coinciding with the expiratory phase progressively prolonged the duration of the expiration that had been interrupted as the timing of swallowing was progressively delayed. Repeated swallows invariably and in a predictable manner caused changes in the breathing pattern. Thus when the frequency of regularly repeated swallows was relatively high, the breathing pattern was characterized by regular, shallow, and rapid breaths. When the frequency of regularly repeated swallows was relatively low, the breathing pattern was characterized by regular, deep, and slow breaths. When the frequency of repeated swallows was irregular, the breathing patterns were characterized by inconsistent changes in tidal volume and respiratory frequency. Our results indicate that, in unconscious subjects, some mechanisms integrating respiration and swallowing are operative and responsible for changes in breathing patterns during swallowing.     

The coordination and interaction between respiration and deglutition in young pigs

The anatomical pathways for inspired air and ingested food cross in the pharynx of mammals, implying that breathing and swallowing must be separated either in space or in time. In this study we investigated the time relationship between swallowing and respiration in young pigs, as a model for suckling mammals. Despite the high morphological position of the larynx in young mammals, allowing liquid to pass in food channels lateral to the larynx, respiration and swallowing are not wholly independent events. Although, when suckling on a veterinary teat, the swallows occurred at various points in the respiratory cycle, there was always a period of apnea associated with the swallow. Finally, an increase in the viscosity of the milk altered this coordination, changing respiratory cycle length and also restricting the relative rate at which swallows occurred in some parts of the respiratory cycle. These results suggest that the subsequent changes in respiratory activity at weaning, associated with passage of a solid bolus over the larynx, is preceded by the ability of the animal to alter coordination between respiration and swallowing for a liquid bolus. Accepted: 29 September 1997     

Axial stretch: A novel mechanism of the lower esophageal sphincter relaxation

Swallow and esophageal distension-induced relaxations of the lower esophageal sphincter (LES) are associated with an orad movement of the LES because of a concurrent esophageal longitudinal muscle contraction. We hypothesized that the esophageal longitudinal muscle contraction induces a cranially directed mechanical stretch on the LES and therefore studied the effects of a mechanical stretch on the LES pressure. In adult opossums, a silicon tube was placed via mouth into the esophagus and laparotomy was performed. Two needles with silk sutures were passed, 90 degrees apart, through the esophageal walls and silicon tube, 2 cm above the LES. The tube was withdrawn, and one end of each of the four sutures was anchored to the esophageal wall and the other end exited through the mouth to exert graded cranially directed stretch on the LES by using pulley and weights. A cranially directed stretch caused LES relaxation, and with the cessation of stretch there was recovery of the LES pressure. The degree an d duration of LES relaxation increased with the weight and the duration of stretch, respectively. The mean LES relaxation in all animals was 77.7 +/- 4.7%. The required weight to induce maximal LES relaxation differed in animals (714 +/- 348 g). N(G)-nitro-L-arginine, a nitric oxide inhibitor, blocked the axial stretch-induced LES relaxation almost completely (from 78 to 19%). Our data support the presence of an axial stretch-activated inhibitory mechanism in the LES. The role of axial stretch in the LES relaxation induced by swallow and esophageal distension requires further investigation.     

The incidence of American swallow bugs (Oeciacus vicarius) in barn swallow (Hirundo rustica) colonies in northeast Texas

The American swallow bug (Oeciacus vicarius) is an important ectoparasite of cliff swallows (Petrochelidon pyrrhonota) and is known to harbor several types of arbovirus. A recent study in northeast Texas suggested that O. vicarius might occur in barn swallows (Hirundo rustica) at rates much higher than previously thought. The purpose of this study was to determine the extent to which barn swallows in northeast Texas are parasitized by O. vicarius and how well this parasite is adapting to this novel host. A sample of 498 nests at 54 colonies was inspected for O. vicarius. Forty colonies (74.1%) were infected, while 310 nests (62.2%) were infected. Large colonies were more likely to be infected than small colonies. Colonies that also contained cliff swallows were more likely to be infected than colonies without cliff swallows. Infection levels in barn swallow nests were comparable to those reported for cliff swallows, though age and sex class ratios differed. Demographic changes among swallow species, including range expansions, increased colony sizes, and more frequent interspecific nesting associations have likely facilitated the movement of O. vicarius from the cliff swallow into a novel host, the barn swallow.     

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.     

Common cavity pressure during gastroesophageal reflux: reassessment using simultaneous pressure, impedance, and ultrasound imaging

An increase in intraesophageal pressure during transient lower esophageal sphincter (LES) relaxation [referred to as common cavity (CC) pressure] is thought to be a marker of gastroesophageal reflux (GER). Multiluminal impedance (MII) measurement is a sensitive marker of reflux entry into the esophagus during GER. We recorded GER using esophageal pressure, pH, impedance, and intraluminal ultrasound (US) images to understand the genesis of the esophageal CC pressure. Nine normal subjects underwent simultaneous MII/pH/pressure and US image recording of the esophagus for 2 h following a standardized meal. MII and pressure transducers were located at 5 and 15 cm above the LES. The US transducer and pH sensors were also placed at 5 cm above the LES. Refluxate entry into the esophagus by MII criteria was determined relative to the onset of CC pressure wave. Esophageal lumen cross-sectional area (CSA) and muscle CSA during GER were determined from the US images. Eighty liquid GER episodes identified using MII criteria, of which 55 were clearly associated with CC pressure waves, were analyzed. The GER reached 15 cm above LES in 49 of 55 (89%) by MII criteria, but the CC pressure wave was observed at 5 and 15 cm during all episodes. The propagation of the CC pressure wave was simultaneous between 5 and 15 cm during 49 of 55 (89%) of the GER episodes, but reflux entry by MII criteria was retrograde during 53 of 55 (96%) of these episodes. During 5 air-reflux episodes, MII showed a simultaneous reflux entry between the 5- and 15-cm site, however, the CC pressure preceded reflux entry during all of these episodes. There was poor correlation between the luminal CSA and the magnitude of CC pressure (R(2) = 0.144). US images revealed a close temporal correlation between CC pressure and the increase in esophageal muscle thickness and muscle CSA (markers of longitudinal muscle contraction). Disassociation between CC pressure and MII-detected reflux suggests that the onset of CC pressure is not due to GER. We speculate that longitudinal muscle contraction plays an important role in the genesis of CC pressure.     

The impact of continuous positive airway pressure on the lower esophageal sphincter

The lower esophageal sphincter (LES) is the primary barrier to gastroesophageal reflux. Reflux is associated with periods of LES relaxation, as occurs during swallowing. Continuous positive airway pressure (CPAP) has been shown to reduce reflux in individuals with and without sleep apnea, by an unknown mechanism. The aim of this study was to determine the effect of CPAP on swallow-induced LES relaxation. Measurements were made in 10 healthy, awake, supine individuals. Esophageal (Pes), LES (Ples), gastric (Pg), and barrier pressure to reflux (Pb = Ples - Pg) were recorded using a sleeve catheter during five swallows of 5 ml of water. This was repeated at four levels of CPAP (0, 5, 10, and 15 cmH(2)O). Pressures were measured during quiet breathing and during the LES relaxation associated with a swallow. Duration of LES relaxation was also recorded. During quiet breathing, CPAP significantly increased end-expiratory Pes, Ples, Pg, and Pb (P < 0.05). The increase in Pb was due to a disproportionate increase in Ples compared with Pg (P < 0.05). During a swallow, CPAP increased nadir Ples, Pg, and Pb and decreased the duration of LES relaxation (4.1 s with 0-cmH(2)O CPAP to 1.6 s on 15-cmH(2)O CPAP, P < 0.001). Pb increased with CPAP by virtue of a disproportionate increase in Ples compared with Pg. This may be due to either reflex activation of LES smooth muscle, or nonspecific transmission of pressure to the LES. The findings suggest CPAP may make the LES less susceptible to reflux by increasing Pb and decreasing the duration of LES relaxation.