Airway Protective Mechanisms Research Articles

Reflex-mediated enhancement of airway protective mechanisms

The upper esophageal sphincter (UES) and lower esophageal sphincter (LES) comprise the basal mechanisms against entry of gastric content into the aerodigestive tract and the airway. There are, however, other mechanisms referred to here as “response mechanisms” that become activated after certain stimulation, such as distention of the esophagus or tactile/pressure stimulation of the pharyngeal wall, and result either in fortification of the UES barriers—i.e., esophago-UES, pharyngo-UES, and laryngo-UES contractile reflexes—or closure of the glottis—i.e., esophagoglottal and pharyngoglottal closure reflexes. In addition, there are other reflexes included among the response mechanisms—such as pharyngeal swallow and secondary peristalsis induced by pharyngeal stimulation by liquid and esophageal distention by refluxate—that result in pharyngeal and esophageal volume clearance, thus reducing the chance for contact of refluxate with the tracheal, bronchial, and glottal structures.

Introduction

Grouped into nine sections, the 31 articles in this supplement collectively offer a wide spectrum of information on the subject of gastroesophageal reflux disease (GERD). This supplement is based on the information presented at the Second Multi-Disciplinary International Symposium on Supraesophageal Complications of Reflux Disease on August 6–8, 1998, in Seattle, Washington. The discussion begins with four updates on mechanisms for protecting the airway against aspiration of gastric content. In the first update, the isolation of a mechanism that prevents herniation in swallow-related esophageal shortening and that, when dysfunctional, also may contribute to reflux esophagitis reopens the question of hiatus hernia and its relation to reflux esophagitis. The information in the second update is a functional classification of eight reflex-mediated airway-protective mechanisms identified in patients without GERD. Turning to lung response to aspiration and studies of patients with cystic fibrosis, the third update includes information about two more protective mechanisms: neutralization of acid and water transport, drawing specific attention to bicarbonate secretion impairment as a potential contributor to reflux injuries. The last update is an examination of secondary esophageal peristalsis in patients with GERD. As does the first update, this one postulates that a defect in esophageal sensation is responsible for low response to reflux.

Optimal patterns of care in patients with chronic obstructive pulmonary disease.

An intimate relationship exists between the physiological processes of respiration and swallowing at all levels of neuromotor control and peripheral function in healthy adults. Little is known regarding the potential alterations in these patterns in patients with chronic obstructive pulmonary disease (COPD), yet the impact of swallowing impairment and aspiration on the health outcomes of patients with COPD may be significant. COPD is a common comorbidity in patients with head and neck cancer and neurological disorders seen by swallowing clinicians, and warrants consideration during swallowing treatment. This article summarizes reports of alterations in the nutritional status, airway protective mechanisms, and swallowing efficiency that potentially contribute to or exacerbate the chronic and debilitating pulmonary condition. Care guidelines are given for modification of eating and swallowing behavior to optimize the health status of the patient with COPD. The need for controlled clinical trials for validation of the impact of these care guidelines on clinical outcomes is explained.

Sedation with promethazine profoundly affects spontaneous airway protection in sleeping neonatal piglets.

1. Phenothiazine use in infants has been implicated in apparent life-threatening events, sleep apnoea and Sudden Infant Death Syndrome. 2. The aim of this study was to investigate the cumulative effects of a commonly used antihistamine medication containing promethazine on airway protective mechanisms and cardiorespiratory responses in 42 healthy neonatal piglets (21 naturally sleeping, 21 sedated sleeping). 3. Sedated piglets were given 1.5 mg/kg, p.o., promethazine 2 h prior to each recording session. Control animals slept naturally with no sedative given. On three consecutive days in all piglets, physiological recordings were made during sleep; on at least one of these days, simultaneous physiological and radiological observations were made. 4. Following sedation, sleep time and time in active sleep were increased significantly (P < 0.01). The spontaneous occurrence of swallowing, arousal, body movement, gastrooesophageal reflux and apnoea was compared between naturally and sedated sleeping piglets. Sedation with promethazine significantly decreased the spontaneous occurrence of swallowing (P < 0.05) and arousal (P < 0.05) and increased the occurrence of both central (P < 0.05) and obstructive sleep apnoea (P < 0.0001). 5. By the third day, a cumulative effect of promethazine was seen; the rate of swallowing and body movement significantly decreased (P < 0.01). 6. In summary, a low dose of promethazine profoundly altered sleep characteristics, airway protective mechanisms and cardiorespiratory responses in normal healthy sleeping piglets. Continued use of promethazine over several days may attenuate airway protective mechanisms to a potentially life-threatening degree. Our findings support continued caution in the use of promethazine-containing medications for the sedation of infants.

Reflex Mediated Airway Protective Mechanisms Against Retrograde Aspiration

Reflex Mediated Airway Protective Mechanisms Against Retrograde Aspiration

Mechanisms of swallowing and airway protection in infant mammals (Sus domesticus and Macaca fascicularis)

Protection of the airway, necessary for continued respiration, is a problem for mammals because of the relative positions of the oesophageal and laryngeal openings in the pharynx. In human infants, and all other mammals, infant and adult, the epiglottis contacts the posterior surface of the soft palate, providing a continuous passage from the nasopharynx to larynx. The function and movements of the epiglottis during swallows are debated as to whether the epiglottis bends to protect the airway or remains erect and leaves the airway open during the swallow. Using high‐speed cineradiography, we examined swallows in detail for a precocious infant, Sus domesticus, the miniature pig, and the more altrical primate, Macaca fascicularis. Infant pigs swallowed in two different ways: down the midline of the oropharynx, over a bent epiglottis, and laterally, around an erect epiglottis, and presumably open airway. The epiglottis of infant macaques never bent, and milk always travelled laterally, through the pyriform recesses and around the larynx. The macaque airway was closed superiorily, however, when the soft palate sealed against the posterior pharyngeal wall. A hypothesis that could account for this pattern of swallowing involves an ontogenetic change from swallows travelling laterally through the pyriform recesses in young infants to swallows travelling over a bent epiglottis in more mature infants. This change would accompany maturation associated with weaning and the need to protect the airway from the larger and less fluid boluses of masticated solid food.

Laryngeal activity during swallow, phonation, and the Valsalva maneuver: an electromyographic analysis.

To better understand the mechanisms of airway protection during swallow, the authors of this study performed an electromyographic (EMG) analysis on the thyroarytenoid (TA) and interarytenoid (IA) muscles during a variety of tasks. The tasks included high, low, and comfortable pitch phonation, the Valsalva maneuver, saliva swallow, and 5- and 10-mL water swallows. Raw EMG signals were analyzed to obtain root mean square data, which correspond to a relative magnitude of muscle activation. The data show that both TA and IA muscles generate a similar level of relative activation, with the greatest electrical activity observed during swallow tasks followed by the Valsalva maneuver and phonation. The duration, onset, offset, and pattern of activity during the swallowing tasks also showed close synchronization between the two muscles. These data can be used in designing therapy for voice disorders and pharyngeal dysphagia.

The radionuclide salivagram in children with pulmonary disease and a high risk of aspiration

Purpose. We wanted to demonstrate the utility of the radionuclide salivagram in assessing children whose underlying medical problems suggest that aspiration of oral contents is a factor contributing to otherwise unexplained lung disease or recurrent pneumonias. Materials and methods. Following sublingual administration of 300 &mu;Ci (11.1 MBq) of technetium-99m sulfur colloid in a drop of saline, serial images were obtained for 60 min and evaluated for entrance of tracer into the major airways and lung parenchyma. Thirty-four studies were performed on 31 patients (age: 3 weeks - 16.7 years, mean 5.5 years) with recurrent pneumonias or unexplained lung disease. All had medical conditions, most frequently neurological, predisposing to aspiration. Results. Pulmonary aspiration was detected in eight patients. All positive studies demonstrated aspirated tracer distal to the tracheal bifurcation, either in bronchi or in bronchi and lung parenchyma. Aspiration was bilateral in six cases. Clearance of aspirated tracer was noted in one patient. Conclusion. The salivagram is an effective tool for demonstrating aspiration of oral contents and the level to which aspirated fluid penetrates the tracheobronchial tree. Additionally, by allowing for the evaluation of clearance of aspirated tracer, the salivagram may provide information on the status of airway-protective mechanisms.

A Method for Simultaneous Physiological and Radiographic Recordings from Sleeping Neonatal Piglets

A healthy neonatal piglet model was developed to investigate the effects of simulated gastro-esophageal reflux (GER) on airway protective mechanisms in different sleep states. Piglets were chosen for the model because there are similarities in esophageal morphology, development of the cardiorespiratory system and sleep-wakefulness cycle between the piglet and the human infant. Unanesthetized piglets were instrumented and trained to sleep in a radiolucent, temperature-controlled box. Physiologic recordings of sleep (electroencephalogram, 'ear-o-gram', behavioral observations), cardiorespiratory function (end-tidal CO2, O2 saturation, heart rate, respiratory movements), swallowing (pharyngeal or esophageal pressures) and GER (signaled by a fall in esophageal pH) were displayed and stored on a computer. An image intensifier was used for radiographic observations. The outputs from the computer and image intensifier were synchronized and recorded on videotape. The method enabled simultaneous physiologic and radiographic observations to be made during the simulation of GER by the injection of normal NaCl, distilled water or HCl (pH 2 and 3) into either the pharynx or different sites in the esophagus. The piglet model appears to accurately reflect the normal physiologic responses of the healthy sleeping neonate.

Mechanisms of airway protection after pharyngeal fluid infusion in healthy sleeping piglets

The airway protective mechanisms evoked after infusion of fluids into the pharynx were examined in the intact and healthy newborn piglet during sleep. Thirteen healthy normothermic piglets (3-6 days of age) were examined on 4 consecutive days during sleep. The fluids infused (0.05-1.5 ml) were 0.9% saline, distilled water, and HCl (pH 3 and pH 2). Respiratory rate, heart rate, oxygen saturation (SaO2), swallowing, and arousal were compared pre- and postinfusion during active (AS) and quiet sleep (QS) for each test fluid. The most common response in AS and QS was swallowing (90%) and then arousal (24%); however, no apnea occurred, and respiratory rate and SaO2 were always maintained. A significant difference occurred between HCl infusions of pH 2 and pH 3; at pH 2, the frequency of swallows and latency to the first swallow were reduced (P < 0.05) and the frequency of arousal was reduced in AS compared with that in QS (P < 0.01). Airway protection after pharyngeal fluid stimulation is achieved primarily by swallowing and arousal, without any effect on respiratory rate and SaO2. Attenuation of protective mechanisms occurred, however, when the infusate was at pH 2.

Airway protective mechanisms: current concepts.

There are at least eight mechanisms identified that result either in volume clearance of the pharynx and esophagus (secondary peristalsis and pharyngeal swallow) or prevent entry of the gastric content into the esophagus and pharynx (LES and UES), accentuate these barriers (esophago-UES and pharyngo-UES contractile reflexes), or induce closure of the vocal cords and introitus to the trachea (esophagoglottal and pharyngoglottal reflexes). The sum effect of various combinations of these mechanisms is suggested to help prevent retrograde aspiration. In other words, airway protective mechanisms against retrograde aspiration are multifactorial and involve delicate interaction between upper GI and upper airway tracts. Although the existence of these mechanisms in normal volunteers has been documented, their function in patients with retrograde aspiration and supraesophageal complications of gastroesophageal reflux disease currently awaits investigation.

Mechanisms of airway protection and upper esophageal sphincter opening during belching.

The mechanisms of airway protection, upper esophageal sphincter (UES) opening, and their coordination during belching were studied with a concurrent videoendoscopic, videofluoroscopic, and manometric technique. Analysis of videoendoscopic recordings revealed that glottal function during gastric and esophageal belching was similar and consisted of vocal cord adduction resulting in closure of intoitus to trachea, followed by anterior-caudad movement of the glottis, followed by slitlike or triangular UES opening. When a belch episode was associated with an intragastric pressure increase, in addition to the above features, there was approximation of arytenoids to the base of the epiglottis before the UES opened. Duration of vocal cord closure during belches induced by 40 ml intraesophageal air injection was significantly longer than belches induced by 20 ml (P less than 0.01). Vocal cord closure preceded the UES opening invariably. Analysis of videofluoroscopic recordings showed that hyoid bone movement during belching had a distinctive pattern different from its movement during swallowing. UES opening started generally when the hyoid bone was pulled anteriorly. Anterior hyoid excursion of 0.78 +/- 0.1 cm during belching was significantly shorter than its excursion of 1.8 +/- 0.09 cm during swallowing (P less than 0.01). We conclude that glottal closure is an integral component of both esophageal and gastric belch reflexes that prevents aspiration of regurgitated material into the airway. Glottal closure mechanism during belching has two tiers of closure: 1) vocal cord closure and 2) aryepiglottic approximation. Glottal and UES functions are closely coordinated during belching, and finally, during belching, UES is pulled open after its relaxation.

Esophagoglottal closure reflex: A mechanism of airway protection

Abrupt esophageal distention occurs commonly during gastroesophageal reflux, thereby generating a circumstance favorable to esophagopharyngeal regurgitation and laryngeal aspiration of gastric refluxate. The aims of the present study were to examine the glottal response to esophageal distention by air and regional esophageal distention by a balloon. Fifteen healthy volunteers (age, 25 ± 5 years) were studied while they were in an upright position. Using concurrent videoendoscopy and manometry, glottal and upper esophageal sphincter (UES) responses to abrupt esophageal distention by air injection (10–60 mL) and balloon distention (1.5, 2.0, and 2.5 cm) were recorded simultaneously. In addition, 6 subjects were studied with concurrent synchronized videofluoroscopy. Results showed that esophageal distention by air at a threshold volume of 10–60 mL caused vocal cord closure. The UES response to this threshold volume was variable. Volumes larger than the threshold value caused complete UES relaxation and belching. In addition to vocal cord closure, belching was accompanied by anterior movement of the glottis. On videofluoroscopy, the hyoid bone moved anteriorly in association with belching, but not with vocal cord closure without belching. Proximal esophageal distention by the balloon also provoked vocal cord closure. This response was less consistent for balloon distention in the middle and distal esophagus. It is concluded that (a) esophageal distention by either air or a balloon evokes a glottal closure mechanism, thereby suggesting the existence of an esophagoglottal reflex; (b) this reflex is elicited most easily by distention of the proximal esophagus; (c) glottal and UES responses to esophageal distention are independent from each other; and (d) the esophagoglottal closure reflex may play an important role in preventing laryngeal aspiration of acid due to gastroesophageal reflux accompanied by acid regurgitation into the pharynx.

Survival data base: central nervous system injury.

Introduction This report will reviewpublished studies of clinical outcome of patients with brain injuries that result in coma. Because coma impairs both airway protective reflexes and central ventilatory control mechanisms, the assumption willbe made that comatose patients routinely require mechanical ventilatory support. Therefore, studies describing clinical outcome in comatose patients are assumed to be pertinent to the issue of withdrawal of mechanical ventilatory support. We will review published survival statistics in coma of several diversecauses and, when appropriate, will also comment on the availability of factors that allow a poor clinical outcome in individual cases to be predicted accurately.

Airway protective and abdominal expulsive mechanisms in infantile regurgitation.

To define the expulsive and airway protective mechanisms involved in infantile regurgitation, we studied 15 infants (9 premature and 6 mature infants) with histories of frequent postfeeding regurgitation. In 13 infants we recorded pharyngeal pressure, pH, nasal and oral airflow, and abdominal respiratory movements. In two additional infants we recorded gastric pressure. In eight infants observations were made without intrapharyngeal recording devices. Distinctive abdominal regurgitation movements (RMs) immediately preceded 84% of regurgitation episodes. These RMs were characterized by one or more large brief increases in abdominal girth. In the two infants with gastric pressure recordings, large increases in gastric pressure, with duration and frequency characteristics similar to the RMs, immediately preceded regurgitation episodes. Thus, in contrast to the generally accepted concept that flow of gastric contents out of the stomach is passive during infantile regurgitation, we documented an active expulsive mechanism similar to that of vomiting in the adult. In all regurgitation episodes, upper airway closure occurred at the onset of the regurgitation movement. One or more swallows occurred immediately following RMs and prior to airway reopening in 97% of regurgitation episodes. Brief respiratory pauses occurred during regurgitation in all premature infants and occasionally in mature infants. Nasal regurgitation, coughing, and sneezing occasionally accompanied regurgitation episodes. Thus upper airway closure and swallowing prior to airway reopening were the most frequently observed airway protective mechanisms during regurgitation. Brief respiratory pauses, sneezing, and coughing may be secondary airway protective mechanisms. Nasal regurgitation likely represents immaturity of airway protective mechanisms.

Pulmonary protective mechanisms in human infants.

The flow of oral and nasal secretions into the pharynx is a recognized source of pulmonary aspiration during sleep in infants and adults alike. Such aspiration probably accounts for many cases of bacterial pneumonia. In infants, swallowing occurs frequently in sleep, and the rate of swallowing appears to be far greater than that of the sleeping adult. Such swallowing during sleep appears to be the major mechanism whereby oral and nasal secretions are transported to the digestive tract. Certain aspects of those swallows, such as "swallow-breaths" and their coordination with the respiratory cycle, have been documented. A brief period of airway closure is always seen during such nonfeeding swallows. Nonfeeding swallows are usually seen during mixed and obstructive apneic spells in preterm infants. The underlying reflex mechanisms responsible for such swallows during apnea are unclear. During ordinary postfeeding regurgitation, upper airway closure and swallowing occur in close temporal sequence. These events appear to be major mechanisms of airway protection during regurgitation. In certain infants, regurgitation and prolonged apnea often occur simultaneously. The mechanism underlying their association is unclear but may involve laryngeal chemoreceptors.