Effects of HCl-pepsin laryngeal instillations on upper airway patency-maintaining mechanisms

Duodenal Contents Reflux-Induced Laryngitis in Rats: Possible Mechanism of Enhancement of the Causative Factors in Laryngeal Carcinogenesis

Objectives:

The main factors considered responsible for the onset of laryngeal cancer are tobacco smoking and alcohol abuse. Recently, gastroesophageal reflux has also been implicated as a causative factor in several laryngeal disorders, including laryngeal cancer. However, the significance of gastroesophageal reflux in laryngeal cancer is controversial.

Methods:

We investigated the histologic features of the esophagus and larynx in a rat model of reflux of the duodenal contents. Cell proliferation was also evaluated in laryngeal samples by detection of Ki67 antigen.

Results:

In this reflux model, laryngitis with infiltration of inflammatory cells and proliferation of small mucous glands was evident from 10 weeks after operation, and basal cell hyperplasia around the epiglottis and hyperplastic changes in the larynx were detected at 30 weeks. No dysplastic or malignant lesions were detected in the laryngeal samples within the duration of the experiment, in spite of detection of malignancy in 31.3% of lesions in esophageal samples at 30 weeks. The Ki67 index at each week was significantly higher than that of the control animals.

Conclusions:

Previous studies have shown smoking and alcohol abuse to have refluxogenic effects. Reflux of duodenal contents causes laryngitis. Reflux does not appear to be an independent risk factor for laryngeal carcinogenesis, but it may enhance the acknowledged etiologic risk factors, namely, smoking and alcohol abuse, by promoting cell proliferation.

Acute Neonatal Respiratory Failure

Acute respiratory failure requiring assisted ventilation is one of the most common reasons for admission to the neonatal intensive care unit. Respiratory failure is the inability to maintain either normal delivery of oxygen to the tissues or normal removal of carbon dioxide from the tissues. It occurs when there is an imbalance between the respiratory workload and ventilatory strength and endurance. Definitions are somewhat arbitrary but suggested laboratory criteria for respiratory failure include two or more of the following: PaCO₂ > 60 mmHg, PaO₂ < 50 mmHg or O₂ saturation <80 % with an FiO₂ of 1.0 and pH < 7.25 (Wen et al. 2004).

Simulated reflux decreases vocal fold epithelial barrier resistance

OBJECTIVES/HYPOTHESIS

The vocal fold epithelium provides a barrier to the entry of inhaled and systemic challenges. However, the location of the epithelium makes it vulnerable to damage. Past research suggests, but does not directly demonstrate, that exposure to gastric reflux adversely affects the function of the epithelial barrier. Understanding the nature of reflux-induced epithelial barrier dysfunction is necessary to better recognize the mechanisms for vocal fold susceptibility to this disease. Therefore, we examined the effects of physiologically relevant reflux challenges on vocal fold transepithelial resistance and gross epithelial and subepithelial appearance.

STUDY DESIGN

Ex vivo, mixed design with between-group and repeated-measures analyses.

METHODS

Healthy, native porcine vocal folds (N = 52) were exposed to physiologically relevant acidic pepsin, acid-only, or pepsin-only challenges and examined with electrophysiology and light microscopy. For all challenges, vocal folds exposed to a neutral pH served as control.

RESULTS

Acidic pepsin and acid-only challenges, but not pepsin-only or control challenges significantly reduced transepithelial resistance within 30 minutes. Reductions in transepithelial resistance were irreversible. Challenge exposure produced minimal gross changes in vocal fold epithelial or subepithelial appearance as evidenced by light microscopy.

CONCLUSIONS

These findings demonstrate that acidic environments characteristic of gastric reflux compromise epithelial barrier function without gross structural changes. In healthy, native vocal folds, reductions in transepithelial resistance could reflect reflux-related epithelial disruption. These results might guide the development of pharmacologic and therapeutic recommendations for patients with reflux, such as continued acid-suppression therapy and patient antireflux behavioral education.

Monitoring of gastric acid suppression in patients with extraesophageal reflux disease

OBJECTIVE

Response to acid suppressive therapy varies in patients with extraesophageal esophageal reflux disease (EERD). Inadequate suppression of gastric acid may contribute to the observed differences in the response to the treatment. The aim of this study was to evaluate suppression of gastric acid in EERD patients being treated with acid suppressive therapy.

METHODS

Charts of patients with EERD who underwent dual channel 24h esophageal pH monitoring while receiving acid suppressive therapy between January 2002 and June 2004 were reviewed. Suppression of gastric acid was determined based on the number of acid reflux episodes, esophageal acid exposure, and acid clearance time.

RESULTS

Twenty patients (12 male, 8 female, age range: 2-19 years) were identified. Esophageal pH monitoring was within normal limits, documenting complete acid suppression in nine patients (45%). Increased numbers of acid reflux episodes were observed in seven patients. In four patients, the number of acid reflux episodes was normal in spite of incomplete acid suppression. However, other abnormal pH monitoring parameters included delayed acid clearance in three patients and increased acid exposure time in three. The majority of patients also showed alkaline reflux.

CONCLUSION

Esophageal pH monitoring documented incomplete acid suppression in this group of infants, children, adolescents and teens with EERD. Monitoring of gastric acid suppression can be useful in guiding the follow-up of EERD patients who receive acid suppressive therapy.

Neural and hydroxyl radical mechanisms underlying laryngeal airway hyperreactivity induced by laryngeal acid-pepsin insult in anesthetized rats

Laryngopharyngeal or gastroesophageal reflux is associated with laryngeal airway hyperreactivity (LAH), but neither the cause-effect relationship nor the underlying mechanism has been elucidated. Here we established a rat model with enhanced laryngeal reflex reactivity induced by laryngeal acid-pepsin insult and investigated the neural and hydroxyl radical (*OH) mechanisms involved. The laryngeal segments of 103 anesthetized rats were functionally isolated while animals breathed spontaneously. Ammonia vapor was delivered into the laryngeal segment to measure laryngeal reflex reactivity. We found that the laryngeal pH 5-pepsin treatment doubled the reflex apneic response to ammonia, whereas laryngeal pH 7.4-pepsin, pH 2-pepsin, and pH 5-denatured pepsin treatment had no effect. Histological examination revealed limited laryngeal inflammation and epithelial damage after pH 5-pepsin treatment and more severe damage after pH 2-pepsin treatment. In rats that had received the laryngeal pH 5-pepsin treatment, the apneic response to ammonia was abolished by either denervation or perineural capsaicin treatment (PCT; a procedure that selectively blocks capsaicin-sensitive afferent fibers) of the superior laryngeal nerves, but was unaffected by perineural sham treatment. LAH was prevented by laryngeal application of either dimethylthiourea (DMTU; a *OH scavenger) or deferoxamine (DEF; an antioxidant for *OH), but was unaltered by the DMTU vehicle or iron-saturated DEF (ineffective DEF). LAH reappeared after recovery from PCT, DMTU, or DEF treatment. We conclude that 1) laryngeal insult by pepsin at a weakly acidic pH, but not at acidic pH, can produce LAH; and 2) LAH is probably mediated through sensitization of the capsaicin-sensitive laryngeal afferent fibers by a *OH mechanism.

Prevalence of gastroesophagopharyngeal acid reflux events: an evidence-based systematic review

OBJECTIVES

To identify variables contributing to discrepant gastroesophagopharyngeal acid reflux (GEPR) findings and to critically assess the prevalence of GEPR in healthy individuals and patients with reflux laryngitis (RL).

STUDY DESIGN

Quantitative systematic review.

METHODS

Pharyngeal pH monitoring studies of healthy individuals and patients with RL were identified through a MEDLINE search of publications between 1966 and 2003. Pooled results of the measured pharyngeal acid exposure characteristics and the prevalence of GEPR events were analyzed. Statistical comparisons were performed using a chi 2 test.

RESULTS

The study included 181 controls and 184 RL patients. Subjects' age ranged from 19 to 85 years. Gastroesophagopharyngeal acid reflux events were detected at 1, 2, and 4 cm above upper esophageal sphincter (UES) and 0.5 cm below arytenoids, with varying rates. The prevalence of GEPR ranged from 0% to 83% in controls and 27% to 86% in RL. After excluding the healthy subjects with abnormal esophageal acid exposure, prevalence of GEPR decreased from 35% to 17% (P<or=.002). Gastroesophagopharyngeal acid reflux in RL was significantly more prevalent than in the entire group of controls as well as in controls without abnormal esophageal acid exposure (P<or=.001).

CONCLUSIONS

The prevalence of GEPR in controls and patients with RL varies in the studied 4 areas above the UES. The percentage of the subjects with GEPR increased as the probe was located more closely to the UES. Differences in demographic characteristics of the subjects, interventions used to select subjects, and pharyngeal pH monitoring techniques were identified as factors possibly contributing to inconsistent pharyngeal pH monitoring findings. The documented differences in methodology of existing studies make comparison of the studies difficult.

Gastroesophageal reflux, asthma, and mechanisms of interaction

Gastroesophageal reflux (GER) is a potential trigger of asthma. The esophagus and lung interact through a variety of mechanisms. Esophageal acid-induced bronchoconstriction can be provoked by a vagally mediated reflex, whereby acid in the distal esophagus produces airway responses; by neural enhancement of bronchial reactivity, whereby esophageal acid augments airway hyperresponsiveness; or by microaspiration, in which small amounts of esophageal acid in the upper airway cause significant airway responses. Interestingly, even in the microaspiration model, the vagus nerve plays a significant role. Neurogenic inflammation in the lung may occur with either vagally mediated mechanisms or with microaspiration. The prevalence of reflux symptoms, esophagitis, and abnormal esophageal acid contact time is higher in patients with asthma than in control populations. Potential mechanisms, whereby asthma may predispose to the development of GER, include autonomic dysregulation, an increased pressure gradient differential between the thorax and the abdomen, a high prevalence of hiatal hernia, alterations in crural diaphragm function, and bronchodilator medication use. Further research will help define how the esophagus and lung interact.

Reflexes from airway rapidly adapting receptors

Rapidly adapting receptors (RARs) occur throughout the respiratory tract from the nose to the bronchi. They have thin myelinated nerve fibres, an irregular discharge and adapt rapidly to a maintained volume stimulus, but often slowly to a chemical stimulus. They are polymodal, responding to mechanical and chemical irritant stimuli, and to many inflammatory and immunological mediators. RARs show very varied sensitivities to different stimuli, and diverse reflex responses. Those in the larynx are usually called 'irritant' receptors. They probably cause cough, the expiration reflex and other laryngeal reflexes: cardiovascular, mucus secretion, bronchoconstrictor and laryngoconstrictor. Those in the trachea and larger bronchi are very mechanosensitive; they cause cough, bronchoconstriction and airway mucus secretion. Those in the larger bronchi are more chemosensitive; they may cause cough, but also stimulate hyperventilation, augmented breaths, mucus secretion, bronchoconstriction and laryngeal closure. Most of the stimuli to RARs also affect other airway receptors, especially those with C-fibre afferents, and the total reflex response will be the additive affect of all these reflexes.

Laryngopharyngeal reflux: state of the art diagnosis and treatment

Gastroesophageal reflux has been implicated in the pathogenesis of a wide variety of otolaryngologic disorders. Patients with otolaryngologic disorders associated with gastroesophageal reflux infrequently have the classic symptoms of gastroesophageal reflux, such as heartburn. Clinical presentation of laryngopharyngeal reflux is commonly characterized by chronic intermittent symptoms. A meticulous synthesis of the information obtained from a complete otolaryngologic examination, diagnostic tests, and response to treatment is essential for the efficient management of patients with otolaryngologic disorders associated with laryngopharyngeal reflux.

Larynx vs. esophagus as reflexogenic sites for acid-induced bronchoconstriction in dogs

Bronchoconstriction in asthmatic patients is frequently associated with gastroesophageal reflux. However, it is still unclear whether bronchoconstriction originates from the esophagus or from aspiration of the refluxate into the larynx and larger airway. We compared the effect of repeated esophageal and laryngeal instillations of HCl-pepsin (pH 1.0) on tracheal smooth muscle activity in eight anesthetized and artificially ventilated dogs. Saline was used as control. We used pressure in the cuff of an endotracheal tube (Pcuff) as a direct index of smooth muscle activity at the level of the larger airways controlled by vagal efferents. The Pcuff values of the first 60 s after instillations were averaged, and the difference from the baseline values was evaluated. Changes in Pcuff were significantly greater with laryngeal than with esophageal instillations (P = 0.0166). HCl-pepsin instillation into the larynx evoked greater responses than did saline (P = 0.00543), whereas no differences were detected with esophageal instillations. Repeated laryngeal exposure enhanced the responsiveness significantly (P < 0. 001). Our data indicate that the larynx is more important than the esophagus as a reflexogenic site for the elicitation of reflex bronchoconstriction in response to acidic solutions.