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.     

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.     

Antagonistic effects of vasotocin and isotocin on the upper esophageal sphincter muscle of the eel acclimated to seawater

The effects of isotocin (IT) and vasotocin (VT), which are fish analogues of mammalian oxytocin and vasopressin respectively, were examined in the isolated upper esophageal sphincter (UES) muscle. IT relaxed and VT constricted the UES muscle in a concentration-dependent manner. The relaxation by IT and the contraction by VT were completely blocked by H-9405 (an oxytocin receptor antagonist) and by H-5350 (a V₁-receptor antagonist), respectively, suggesting that the eel UES possesses both IT and VT receptors. Truncated fragments of VT did not show any significant effects, indicating that all nine residues are essential for the VT and IT actions. IT may relax the UES muscle through enhancing cAMP production, since similar relaxation was also observed after treatment with 3-isobutyl-1-methylxantine, forskolin and 8-bromoadenosine, 3′, 5′-cyclic mono-phosphate (8BrcAMP). Although 8-bromoguanosine, 3′, 5′-cyclic monophosphate also relaxed the UES, its effect was less than 1/3 of that 8BrcAMP, suggesting minor contribution of nitric oxide (NO) in the relaxation of the UES muscle. Both peptides seem to act directly on the UES muscle, not through release of other substances from the epithelial cells, since similar relaxation and contraction were observed even in the scraped UES preparations. When IT and VT were intravenously administrated (in vivo experiments), the drinking rate of the seawater eel was enhanced by IT and was inhibited by VT. These effects correspond to the in vitro results described above, relaxation by IT and contraction by VT in the UES muscle. The significance of the relaxing effect by IT is discussed with respect to controlling the drinking behavior of the eel.     

The upper esophageal sphincter in the cat: the role of central innervation assessed by transient vagal blockade

Studies were performed on four cats to assess the role of extrinsic innervation via the cervical nerve trunks in the control of upper esophageal sphincter function. Transient vagal nerve blockade was accomplished by cooling the cervical vagosympathetic nerve trunks previously isolated in skin loops on each side of the neck. Upper esophageal sphincter pressure was measured using a multilumen oval manometry tube and a rapid pull-through technique. The upper esophageal sphincter response to cervical intraesophageal balloon distention and acid perfusion was assessed. The feline upper esophageal sphincter has a distinct asymmetric pressure profile, whereby anterior pressure greater than posterior pressure greater than left pressure greater than right pressure. Bilateral vagal nerve blockade lowered the mean upper esophageal sphincter pressure from 18.5 +/- 1.5 to 12.0 +/- 2.8 mmHg (1 mmHg = 133.3 Pa) (p less than 0.001), with a significant reduction in pressure in all four quadrants. Intraesophageal balloon distention and acid perfusion both produced a significant increase in upper esophageal sphincter pressure. Bilateral vagal nerve blockade completely abolished the response of the upper esophageal sphincter to balloon distention and acid perfusion. We conclude that normal upper esophageal sphincter tone in the cat is partially mediated by excitatory neural input via the cervical nerve trunks, presumably via the recurrent laryngeal nerves; and cervical intraesophageal balloon distention and acid perfusion produce reflex contraction of the upper esophageal sphincter, which is dependent on neural pathways via the cervical vagal nerve trunks, but the relative contribution of afferent and efferent pathways remains unknown.     

Post- and pre-synaptic action of isotocin in the upper esophageal sphincter muscle of the eel: its role in water drinking

Isotocin is a fish analogue of the mammalian hormone oxytocin. To elucidate sites of action of isotocin (IT) in the upper esophageal sphincter (UES) muscle, a key muscle in swallowing, IT was applied after treatment with tetrodotoxin (TTX). Even after blocking nerve activity with TTX, IT relaxes the UES muscle in a concentration-dependent manner, suggesting that IT receptor(s) is present on the muscle cells. Similar relaxation was also obtained by application of 3-isobutyl-1-methylxanthine (IBMX), forskolin (FSK) and 8-bromo-adenosine, 3′,5′-cyclic monophosphate (8BrcAMP) after pretreatment with TTX, suggesting that the relaxing effect (postsynaptic action) of IT may be mediated by cAMP. In contrast to such relaxing effect, IT enhanced the UES contraction induced by repetitive electrical field stimulation (EFS). Such enhancement was blocked by an IT receptor antagonist, suggesting that this effect is also mediated by IT receptor(s). Similar enhancement was also induced by IBMX, FSK and 8BrcAMP, suggesting the enhancing effect is also mediated by cAMP. However, no enhancing effect of IT was observed when the muscle was stimulated by carbachol, or after treatment with curare or TTX, denying the postsynaptic modulatory action of IT and suggesting presynaptic action for IT, i.e., accelerating acetylcholine release. Summarizing these results, role of IT in precisely regulating the drinking rate in the seawater eel is discussed.     

Cholinergic innervation to the upper esophageal sphincter muscle in the eel,with special reference to drinking behavior

To elucidate innervation in the upper esophageal sphincter (UES) muscle of the eel, a key muscle in swallowing, repetitive electrical field stimulation (EFS; 30 mA, 40 V, 300 micros, 10 Hz, 10 trains) was employed. Anatomically, the eel UES muscle consists of striated fibers. The EFS-induced contraction of the UES was completely blocked by tetrodotoxin and curare, and abolished in Ca2+ -free Ringer solution. These results suggest that the EFS stimulates nerve fibers specifically and releases acetylcholine as a neurotransmitter. In fact, acetylcholine and carbachol constricted the UES in a concentration-dependent manner. Even after blocking neuronal firing with tetrodotoxin, acetylcholine constricted the UES muscle, suggesting the existence of acetylcholine receptors on the UES muscle cells. Both EFS- and carbachol-evoked contractions of the UES were blocked by curare at a lower concentration than by atropine or hexamethonium, suggesting that the acetylcholine receptor is nicotinic. Even in Ca2+ -free Ringer solution, a direct current stimulus (2 s duration) constricted the UES muscle to an extent similar to that in the presence of Ca2+, indicating that the muscle contraction itself does not need extracellular Ca2+, i.e., the muscle can be constricted by a release of Ca2+ from the sarcoplasmic reticulum.     

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.     

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.     

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.     

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.     

Stimulus-dependent pacemaker activity in the distal canine lower esophageal sphincter

Electrical and mechanical properties of the distal canine lower esophageal sphincter were studied in vitro to investigate possible means of inducing pacemaker activity. Both direct excitation and block of potassium conductance were investigated. The acetylcholine analog, carbachol, induced tissue depolarization and increase in tone but no electrical slow waves. Tetraethylammonium (TEA) chloride induced depolarization and evoked continuous spiking activity and increase in tone. BaCl did not depolarize the tissue but low amplitude spiking activity developed and increased tone. The putative potassium channel blocker, aminacrine at 2 X 10(-4) M, induced electrical slow wave activity in the distal lower esophageal sphincter, with or without superimposed spikes, accompanied by phasic contractile activity. This activity closely resembled the spontaneous pacemaker activity observed previously in the proximal lower esophageal sphincter. The aminacrine-induced activity was abolished by calcium influx blockers. Aminacrine, but not TEA or BaCl, abolished the nonadrenergic nerve-mediated inhibitory junction potentials. In conclusion, block of inhibitory innervation, and induction of electrical slow waves as a control mechanism for phasic contractile activity, seems to require blockade of an aminacrine- but not TEA-sensitive potassium conductance.     

Atypical localization of myenteric neurons in the opossum lower esophageal sphincter

This study investigated sphincter-body differences in neuronal density and morphometry between the esophageal sphincter and body with a view to determining whether previously reported differences are authentic. The anatomical limits of the opossum lower esophageal sphincter were correlated with its physiological behavior by manometric demarcation. Following this, peeled whole mounts and paraffin and cryosections were used to study the morphology and morphometry of the esophageal myenteric plexus. Thirty animals were used and seven quantitated. The plexus of the esophageal body was located as usual in a plane between the longitudinal and circular muscle, which coincided with the plane of cleavage when these muscle layers were peeled apart for studying the plexus in whole mounts. In contrast, the plexus was located in several planes in the lower esophageal sphincter, which had no cleavage plane. Therefore, peeling the sphincter removes neurons and yields falsely low counts, making peel preparations of this region unsuitable for neuronal quantitation. In paraffin sections, the neuron density in the esophageal body 7 cm above the sphincter was 6,353 +/- 850/cm2, but decreased significantly to 2,254 +/- 353/cm2 at the 1-cm segment. In the lower esophageal sphincter, the neuronal count increased again to 8,530 +/- 1,606/cm2. Flash-frozen cryosections, which produced neuronal morphology similar to the in vivo condition, showed that there was no difference in neuronal size between esophageal body and sphincter. These studies show that atypical myenteric plexus localization causes spuriously low neuronal counts reported in the lower esophageal sphincter and that reported neuronal size differences are technique-dependent.     

MAPK mediates PKC-dependent contraction of cat esophageal and lower esophageal sphincter circular smooth muscle

Esophageal (ESO) circular muscle contraction and lower esophageal sphincter (LES) tone are PKC dependent. Because MAPKs may be involved in PKC-dependent contraction, we examined ERK1/ERK2 and p38 MAPKs in ESO and LES. In permeabilized LES muscle cells, ERK1/2 antibodies reduced 1,2-dioctanoylglycerol (DG)- and threshold ACh-induced contraction, which are PKC dependent, but not maximal ACh, which is calmodulin dependent. LES tone was reduced by the ERK1/2 kinase inhibitor PD-98059 and by the p38 MAPK inhibitor SB-203580. In permeable ESO cells, ACh contraction was reduced by ERK1/ERK2 and p38 MAPK antibodies and by PD-98059 and SB-203580. ACh increased MAPK activity and phosphorylation of MAPK and of p38 MAPK. The 27-kDa heat shock protein (HSP27) antibodies reduced ACh contraction. HSP27 and p38 MAPK antibodies together caused no greater inhibition than either one alone. p38 MAPK and HSP27 coprecipitated after ACh stimulation, suggesting that HSP27 is linked to p38 MAPK. These data suggest that PKC-dependent contraction in ESO and LES is mediated by the following two distinct MAPK pathways: ERK1/2 and HSP27-linked p38 MAPK.     

Localization and inhibitory actions of galanin at the feline lower esophageal sphincter

Intrinsic reflexes of the lower esophageal sphincter (LES) are mediated by specific arrangements of excitatory and inhibitory nerves. We have previously described an excitatory reflex at the feline LES mediated by a bombesin-like peptide (BN) which causes release of substance P (SP) to directly contract the LES. Galanin is a neurotransmitter in the enteric nervous system which colocalizes in neurons containing vasoactive intestinal peptide (VIP). The aims of this study were to determine: (1) the distribution of galanin at the feline LES; (2) the effect of galanin on basal LES tone; (3) the effect of galanin on agonist-induced LES contractions by BN, SP and bethanechol; and (4) the effect of galanin on LES relaxation induced by esophageal distension and exogenous VIP. Galanin-like immunoreactivity (galanin-LI) was localized in neurons that were widely distributed throughout the LES and adjacent organs. Galanin-LI was most abundant in the circular muscle, muscularis mucosa and myenteric plexus of the LES. In anesthetized cats, intra-arterial galanin had no effect on basal LES pressure in a dose range of 10⁻¹¹ to 10⁻⁶ g/kg. Galanin (510⁻⁷ g/kg) reduced the LES contractile response to SP by 65 ± 8% (P = 0.0001). This galanin-mediated inhibition of SP was not blocked by tetrodotoxin. Galanin similarly decreased the LES contractile response to BN (63 ± 7%, P = 0.005) and bethanechol (55 ± 17%, P = 0.012). Galanin had no effect on the LES relaxation induced by esophageal distension or exogenous VIP. We conclude: (1) galanin-LI is present in neurons at the feline LES; (2) galanin has no effect on basal sphincter tone, but inhibits contractions of the LES by both direct and indirect agonists; and (3) galanin does not effect the LES relaxation induced by esophageal distension or VIP.     

Simultaneous registration of rheographic and manometric parameters of the inferior esophageal sphincter in the cat

The aim of the present study was to detect simultaneously hemodynamic parietal events and intraluminal pressure of the Lower Esophageal Sphincter (LES), with particular regards to cyclic changes due to systo-diastolic cardiac activity. A probe for combined Intraluminal Manometric Plethysmography (IMP) and Intraluminal Impedence Plethysmography (IIP) was used. It was a Swan Ganz bipolar pacing catheter, modified by removing the latex balloon from the tip. The exposed side-hole (diameter smaller than 0.5 mm) was utilized as a terminal orifice for an infused manometry system. It was preliminarly essayed in bench tests. A perfusion rate of 1.75 ml/min was chosen as it did not induce significant elevations of the pressure base-line and allowed detection of pressure rise rates up to 300 mm Hg/s. The two metallic rings, originally designed for intracardiac stimulation, were used as low resistance electrodes to record impedence variations. Since very small shifts of recording electrodes induce important artifacts, the present experiments were carried out on curarized cats. In these conditions, artificial ventilation could be temporarily stopped to avoid any artifact due to respiration mechanics. The proposed method seems to be satisfactory enough for simultaneous acquisition of IIP and IMP data at LES level. Recordings of IIP allow to reveal changes in parietal blood content which could chiefly be referred to lamina propria and submucosa districts. On the other hand, IMP cyclic fluctuations would signal variations of total sphincteric tension, likely depending on hemodynamic events in all vascular beds of the wall. In our opinion, a more extensive analysis of IMP and IIP waves, as well as of reciprocal relationships between rheografic and manometric parameters, may provide very useful knowledges on sphincteric physiology.     

Prostaglandins and myogenic control of tension in lower esophageal sphincter in vitro.

Active tension is produced by the lower esophageal sphincter (LES) of North American opossum in vitro by a myogenic mechanism. Strips of LES, but not those from the esophageal body, contracted to prostaglandin (PG)F2 alpha, stable expoxymethano derivatives of PGH2 and to thromboxane B2. Stable endoperoxides were more than 500 times more potent than PGF2 alpha. PGI2 and 6-keto PGF1 alpha were weak relaxants of LES strips. LES strips transformed arachidonic acid into contractile substances. This transformation was prevented by agents which interfere with PG synthesis by inhibiting cyclo-oxygenase [indomethacin (IDM), 5,8,11,14-eicosatetraynoic acid (ETA) or thromboxane synthetase [imidazole]. Tranylcypromine 500 microgram/ml also inhibited contractions to arachidonic acid. These agents also reduced muscle tone, so that endogenous PG formation may contribute to active tension in the LES. ETA and IDM increased tone before inhibiting it, and this effect was prevented by prior treatment with ETA or imidazole. There may also be an endogenous PG which inhibits LES tone. The possibility that this may be PGI2 is discussed.