The effect of mechanoreceptor stimulation of the laryngopharynx on the oesophago-gastric junction

Cricoid Pressure Controversies

Since cricoid pressure was introduced into clinical practice, controversial issues have arisen, including necessity, effectiveness in preventing aspiration, quantifying the cricoid force, and its reliability in certain clinical entities and in the presence of gastric tubes. Cricoid pressure–associated complications have also been alleged, such as airway obstruction leading to interference with manual ventilation, laryngeal visualization, tracheal intubation, placement of supraglottic devices, and relaxation of the lower esophageal sphincter. This review synthesizes available information to identify, address, and attempt to resolve the controversies related to cricoid pressure. The effective use of cricoid pressure requires that the applied force is sufficient to occlude the esophageal entrance while avoiding airway-related complications. Most of these complications are caused by excessive or inadequate force or by misapplication of cricoid pressure. Because a simple-to-use and reliable cricoid pressure device is not commercially available, regular training of personnel, using technology-enhanced cricoid pressure simulation, is required. The current status of cricoid pressure and objectives for future cricoid pressure–related research are also discussed.

Towards minimally invasive monitoring for gastroenterology - An external Squamocolumnar Junction Locator

Transient lower oesophageal sphincter relaxations (TLOSRs) occur frequently and are the main mechanism of acid reflux. The only means of currently detecting TLOSRs is intra-luminal manometry and the probes themselves may stimulate TLOSRs. The squamo-columnar junction moves 4-5 centimeters proximally during TLOSRs and this provides a means of detecting such episodes. The objective of this work is to develop a sensor system capable of detecting the movement of a miniature magnet attached to the squamo-columnar junction from outside the body and thus allow detection of TLOSRs without the artifact associated with intraluminal detection probes. A GaAs Hall effect sensor was selected and an alternating current supply was developed with a combination of filters and a Phase Sensitive Detector, to detect the magnet. The oscillation frequency of the current was chosen in order to reduce electronic noise, and filtering outside this frequency means the signal to noise ratio was greatly improved. The phase sensitive detector was employed to accurately convert the amplitude of the sensor's output to a DC signal. With the addition of paired Flux Concentrators increases the range up to 10.2 centimetres, an improvement of 580% over commercial Hall effect sensors. The AC circuit and flux concentrator device far exceeds the sensitivity of the current Hall effect sensors supplied in the market, by rejecting noise and providing accurate measurement over significantly larger distances. The development of this sensor has applications beyond this specific medical device.

High-resolution solid-state manometry of the effect of rocuronium on barrierpressure

BACKGROUND

The pressure in the lower esophageal sphincter (LES) is partly dependent on striated muscles derived from the crural portion of the diaphragm. The effect of neuromuscular blockade on the integrity of the esophagogastric junction is not well studied. We conducted a prospective interventional study to determine the effect of rocuronium on the barrier pressure (LES pressure - intragastric pressure) of the esophagogastric junction. We also studied the effect of positive pressure ventilation on the barrier pressure after neuromuscular blockade with rocuronium.

METHODS

Fourteen patients classified as American Society of Anesthesiologists classification system (ASA) I or II (aged 18-75 years) who presented for elective surgery (11 cholecystectomy, 3 inguinal hernia) participated in the study. Esophageal manometry was performed during anesthetization with propofol, fentanyl, and sevoflurane. The LES pressure was studied prior to anesthesia, after anesthesia induction during spontaneous breathing with laryngeal mask airway, after administration of rocuronium (0.6 mg/kg), and during positive pressure ventilation.

RESULTS

Muscle relaxation with rocuronium showed no significant changes in barrier pressure when comparing the pressure immediately before rocuronium administration with the pressure obtained after rocuronium administration at the time point of 0% train-of-four (TOF). Conversion to positive pressure ventilation did not change the barrier pressure with inspiration or expiration. The greatest decrease in barrier pressure was measured after inducing anesthesia when comparing pressures during inspiration (P < 0.01).

CONCLUSIONS

Neuromuscular blockade with rocuronium and conversion from spontaneous breathing to positive pressure ventilation does not decrease the barrier pressure during anesthesia induction.

Cough challenge tests involving mechanical stimulation of the cervical trachea in patients with cough as a leading symptom

BACKGROUND AND OBJECTIVE

Challenge tests involving chemical stimulation by inhalation of capsaicin or citric acid are currently used to assess cough sensitivity. We investigated the clinical usefulness of cough challenge tests based on mechanical stimulation.

METHODS

A total of 347 patients (126 men and 221 women) were enrolled in the study, including 161 patients with asthma, 116 with cough-variant asthma, 27 with acute upper respiratory tract viral infections, 25 with acute bronchitis, four with pneumonia, three with chronic bronchitis and 11 with cough of unknown aetiology. Three modes of mechanical stimulation were assessed: the cervical trachea was compressed softly with the fingers several times (tracheal compression test); the trachea was stretched by retroflexion of the neck for 5 s (tracheal stretch test); and a vibrating tuning fork was placed on the cervical trachea for 20 s (tuning fork test). The relationships between phonation-induced cough and the results of these tests were assessed.

RESULTS

The cough detection rate was 27.7% with the tracheal compression test, 39.8% with the tracheal stretch test and 36.9% with the tuning fork test. An itchy sensation with or without cough was noted by about 50% of subjects undergoing each of the tests. Provocation of cough and an itchy sensation during each test was significantly more frequent in subjects with phonation-induced cough. Tests were usually negative after improvement of the cough with treatment.

CONCLUSIONS

Mechanical stimulation of the cervical trachea is a feasible cough challenge test that may be useful for evaluating disease activity.

Effects of cricoid pressure and remifentanil on the esophageal sphincters using high-resolution solid-state manometry

BACKGROUND

Cricoid pressure has been shown to decrease the pressure in the lower esophageal sphincter (LES), increasing the risk of aspiration. Whether this reaction is due to pain associated with the application of cricoid pressure has not been studied. The aim of this study was to compare the effects of cricoid pressure with those of peripheral pain on pressures in the LES, and to study whether remifentanil influences these effects. Data from the upper esophageal sphincter (UES) are also described.

METHODS

Continuous solid-state manometry was performed in 14 healthy volunteers. Initially, the effect of remifentanil (target-controlled infusion with a plasma target concentration of 5.0 ng/ml) was studied, and thereafter, the effects of cricoid pressure and peripheral pain stimulation (cold stimulation). Finally, these two interventions were repeated under ongoing remifentanil infusion.

RESULTS

Remifentanil decreased the LES pressure significantly [ΔP-6.5 mmHg, 95% confidence interval (95% CI) -1.7 to -11.2]. Cricoid pressure application decreased the LES pressure significantly (ΔP-3.7 mmHg, 95% CI -1.4 to 6.1), whereas peripheral pain did not (ΔP 1.2 mmHg, 95% CI -3.5 to 1.1). Under ongoing remifentanil infusion, no cricoid pressure-induced LES relaxation was observed. Cricoid pressure induced high pressures in the area of the UES, 215.7 (±91.2) mmHg without remifentanil vs. 219.4 (±74.2) mmHg with remifentanil.

CONCLUSIONS

Remifentanil as well as cricoid pressure per se induced decreases in LES pressure. However, cricoid pressure-induced changes of the barrier pressure were not significant whether induced with or without an infusion of remifentanil.

Clinical history in gastroesophageal cough

Gastroesophageal disease, a common cause of chronic cough, is often poorly recognised. We reviewed the presenting history of 47 chronic cough patients who had been proven to have gastroesophageal disease by oesophageal function testing. Fourty-seven patients (26 female), were enroled. Symptoms which were most common included: cough on phonation, on rising from bed, associated with certain foods or with eating in general. Symptoms known to be associated with laryngopharyngeal reflux, such as throat clearing, dysphonia, globus and dysphagia were also associated. Heartburn or indigestion was present in 63% of those questioned. These data show that symptoms associated with reflux in chronic coughers differ from those commonly perceived to be characteristic of classical heartburn-associated reflux. These data suggest that, contrary to previous reports, a symptom complex which is characteristic of reflux cough can be identified.

The effects of cricoid pressure, remifentanil, and propofol on esophageal motility and the lower esophageal sphincter

Cricoid pressure is the gold standard during the induction of anesthesia when there is a risk of aspiration of gastric contents. However, the effect of cricoid pressure during the different steps of complete anesthesia induction has not been studied. The purpose of this study was to investigate the effects of cricoid pressure, remifentanil, and propofol on lower esophageal sphincter (LES) and esophageal motility. We recorded LES pressure (LESP) and calculated barrier pressure ([BrP] = LESP - gastric pressure) in 10 healthy volunteers using a Dent sleeve device. There was a significant decrease in LESP and BrP when a cricoid pressure of 30 N was performed in the awake volunteers (P < 0.05). However, this effect was not seen during the infusion of remifentanil 0.2 microg . kg(-1) . min(-1). Remifentanil per se or together with a bolus dose of propofol 1 mg/kg IV did not induce any statistical change in LESP or BrP. Remifentanil abolished spontaneous esophageal motility and completely eliminated the experience of discomfort induced by cricoid pressure. In conclusion, cricoid pressure of 30 N induced a decrease of LESP and BrP in awake volunteers. These effects were not seen during the remifentanil infusion. This shows the importance of when to apply cricoid pressure during rapid-sequence induction.

Laryngo-upper esophageal sphincter contractile reflex in humans deteriorates with age

BACKGROUND & AIMS

Recent studies have shown the existence of several reflex connections between the aerodigestive and upper gastrointestinal tracts. Our aim was to study the effect of laryngeal stimulation on upper esophageal sphincter (UES) pressure and to determine the reproducibility of this effect.

METHODS

We studied 14 young and 10 elderly healthy nonsmoker volunteers and 7 patients with UES dysphagia using a concurrent manometric and video endoscopic technique. Three levels of laryngeal air stimulation were studied: 6 mm Hg/50 ms, 10 mm Hg/50 ms, and 6 mm Hg/2 s. Ten young subjects were studied twice.

RESULTS

For 6-mm Hg/2-s and 6-mm Hg/50-ms duration stimuli, the frequency of UES response to air stimulation as evidenced by mucosal deflection (response/deflection ratio) in the elderly volunteers was significantly lower compared with that of young subjects (P < 0.05). The response/deflection ratio of the 6-mm Hg/2-s stimulus was significantly higher than those induced by stimuli of shorter duration (P < 0.01). Poststimulation UES pressure was significantly higher than prestimulation pressure (P < 0.05) in both groups. The magnitude of the increase in poststimulation UES pressure in the elderly volunteers was similar to that of the young subjects. Findings were similar in repeated studies. Four of 7 dysphagic patients exhibited an abnormal response.

CONCLUSIONS

Afferent signals originating from the larynx reproducibly induce contraction of the UES: the laryngo-UES contractile reflex. This reflex is elicited most reliably by 6-mm Hg/2-s air stimulation. Frequency elicitation of this reflex decreases significantly with age while the magnitude of change in UES pressure remains unchanged, indicating a deleterious effect of aging on the afferent arm of this reflex. This reflex is altered in some dysphagic patients.

Gastroesophageal reflux disease and baclofen: is there a light at the end of the tunnel?

Transient lower esophageal sphincter relaxations (TLESRs) are rapid and prolonged relaxations of the lower esophageal sphincter (LES) that are not associated with swallowing. They are the mechanism by which most gastroesophageal reflux episodes occur in normal people and in patients with esophagitis. Transient LES relaxations appear to be mediated by a vagovagal reflex initiated by gastric distention. Baclofen is a g-aminobutyric acid (GABA) derivative that inhibits the production of TLESRs by acting as a GABA(B) receptor agonist at one or more loci along the vagovagal reflex arc. Animal and human studies suggest that baclofen decreases the number of reflux events and amount of esophageal acid exposure. Baclofen or another GABA(B) receptor agonist may be clinically useful in treatment of gastroesophageal reflux disease.

Normal physiology of the aerodigestive tract and its effect on the upper gut

There is a close functional relation between the aerodigestive tract and the upper gastrointestinal tract. The pharynx and larynx are involved in respiration, speech, and deglutition. This article reviews the effects of reflexes emanating from the pharynx and larynx on the esophagus and its sphincters, as well as the effects of reflexes emanating from the esophagus on the larynx. Principally, reciprocal reflexes within these 2 regions result in protection of the airway against aspiration from above and below, either by swallowed or refluxed material. However, other reflexes appear to facilitate reflux of gastric content into the esophagus and inhibit esophageal motor function.

Patterns of esophageal inhibition during swallowing, pharyngeal stimulation, and transient LES relaxation. Lower esophageal sphincter

Lower esophageal sphincter (LES) relaxation and esophageal body inhibition co-occur during esophageal peristalsis but not necessarily during pharyngeal stimulation or transient LES relaxation (tLESR). This study examined these relationships and the impact on reflux. Nine young volunteers were studied. An artificial high-pressure zone (HPZ) was established, and pH was recorded 8 and 5 cm proximal to the LES. Pharyngeal stimulation was by water injection and gastric distension with liquid or gas. Peristalsis, pharyngeal stimulation, and spontaneous events were recorded. Swallowing relaxed the LES in 100% of trials (the HPZ in 80%) and caused no reflux. Pharyngeal stimulation relaxed the LES in two-thirds of trials, had no effect on the HPZ, and caused no reflux. Gastric distension was associated with 117 tLESRs, 48% with acid reflux, and 32% with gas reflux; there was no effect on the HPZ. We conclude that LES relaxation is a necessary but not sufficient condition for reflux. LES relaxation and esophageal body inhibition are independent events that may be concurrent (swallowing) or dissociated (tLESR).

Peripheral mechanisms affecting the lower esophageal sphincter tone

LES tone is influenced by central and peripheral mechanisms. Peripheral factors influencing the LES tone include inhibitory reflexes originating from the stomach, esophagus, pharynx, and larynx. Although the role of LES relaxation and its associated reflux events induced by gastric distention has been extensively studied, the LES relaxations triggered by stimulation of the aerodigestive tract have only recently been the focus of systematic investigation and have resulted in documentation of the intricate reflex relationship between the upper gastrointestinal tract and the aerodigestive tract.