Laryngospasm and diaphragmatic arrest in immature dogs after laryngeal acid exposure: a possible model for sudden infant death syndrome

Apneic response to fentanyl in adult rats: Role of laryngeal afferents

Intravenous (systemic) bolus injection of fentanyl (FNT) reportedly induces an immediate vagal-mediated apnea; however, the precise origin of vagal afferents responsible for this apnea remains unknown. We tested whether intralaryngeal (local) application of FNT would also trigger an apnea and whether the apneic response to both local and systemic administration of FNT was laryngeal afferent-mediated. Cardiorespiratory responses to FNT were recorded in anesthetized male adult rats with and without bilateral sectioning of the superior laryngeal nerve (SLNx) or peri-SLN capsaicin treatment (SLNcap) to block local C-fiber signal conduction. Opioid mu-receptor (MOR)-immunoreactivity was detected in laryngeal C- and myelinated neurons. We found that local and systemic administration of FNT elicited an immediate apnea. SLNx, rather than SLNcap, abolished the apneic response to local FNT application though MORs were abundantly expressed in both laryngeal C- and myelinated neurons. Importantly, SLNx failed to affect the apneic response to systemic FNT administration. These results lead to the conclusion that laryngeal afferents' MORs are responsible for the apneic response to local, but not systemic, administration of FNT.

Peripheral Neuroplasticity of Respiratory Chemoreflexes, Induced by Prenatal Nicotinic Exposure: Implication for SIDS

Sudden Infant Death Syndrome (SIDS) occurs during sleep in seemingly healthy infants. Maternal cigarette smoking and hypoxemia during sleep are assumed to be the major causal factors. Depressed hypoxic ventilatory response (dHVR) is observed in infants with high risk of SIDS, and apneas (lethal ventilatory arrest) appear during the fatal episode of SIDS. Disturbance of the respiratory center has been proposed to be involved, but the pathogenesis of SIDS is still not fully understood. Peripherally, the carotid body is critical to generate HVR, and bronchopulmonary and superior laryngeal C-fibers (PCFs and SLCFs) are important for triggering central apneas; however, their roles in the pathogenesis of SIDS have not been explored until recently. There are three lines of recently accumulated evidence to show the disorders of peripheral sensory afferent-mediated respiratory chemoreflexes in rat pups with prenatal nicotinic exposure (a SIDS model) in which acute severe hypoxia leads to dHVR followed by lethal apneas. (1) The carotid body-mediated HVR is suppressed with a reduction of the number and sensitivity of glomus cells. (2) PCF-mediated apneic response is largely prolonged via increased PCF density, pulmonary IL-1β and serotonin (5-hydroxytryptamine, 5-HT) release, along with the enhanced expression of TRPV1, NK₁R, IL1RI and 5-HT₃R in pulmonary C-neurons to strengthen these neural responses to capsaicin, a selective stimulant to C-fibers. (3) SLCF-mediated apnea and capsaicin-induced currents in superior laryngeal C-neurons are augmented by upregulation of TRPV1 expression in these neurons. These results, along with hypoxic sensitization/stimulation of PCFs, gain insight into the mechanisms of prenatal nicotinic exposure-induced peripheral neuroplasticity responsible for dHVR and long-lasting apnea during hypoxia in rat pups. Therefore, in addition to the disturbance in the respiratory center, the disorders of peripheral sensory afferent-mediated chemoreflexes may also be involved in respiratory failure and death denoted in SIDS victims.

A Comparative Assessment of the Diagnosis of Swallowing Impairment and Gastroesophageal Reflux in Canines and Humans

Swallowing impairment is a highly prevalent and clinically significant problem affecting people and dogs. There are myriad causes of swallowing impairment of which gastroesophageal reflux is the most common in both species. Similarities in anatomy and physiology between humans and canines results in analogous swallowing disorders including cricopharyngeus muscle achalasia, esophageal achalasia, hiatal herniation, and gastroesophageal reflux with secondary esophagitis and esophageal dysmotility. Accordingly, the diagnostic approach to human and canine patients with swallowing impairment is similar. Diagnostic procedures such as swallowing fluoroscopy, high-resolution manometry, pH/impedance monitoring, and endolumenal functional luminal imaging probe can be performed in both species; however, nasofacial conformation, increased esophageal length, and the difficulty of completing several of these procedures in awake dogs are inherent challenges that need to be considered. Human patients can convey their symptoms and respond to verbal cues, whereas veterinarians must rely on clinical histories narrated by pet owners followed by comprehensive physical examination and observation of the animal eating different food consistencies and drinking water. Dogs may also be unwilling to drink or eat in the hospital setting and may be resistant to physical restraint during diagnostic procedures. Despite the species differences and diagnostic challenges, dogs are a natural animal model for many oropharyngeal and esophageal disorders affecting people, which presents a tremendous opportunity for shared learnings. This manuscript reviews the comparative aspects of esophageal anatomy and physiology between humans and canines, summarizes the diagnostic assessment of swallowing impairment in both species, and discusses future considerations for collaborative medicine and translational research.

Laryngeal inflammation in the sudden infant death syndrome

OBJECTIVE

Sudden infant death syndrome (SIDS) is marked by 'the sudden death of an infant that is unexpected by history and remains unexplained after a thorough forensic autopsy and a detailed death scene investigation'. The cause is unknown. Excessive subglottic submucosal glandular tissue and excessive sulphated mucus glycoprotein in the larynges of SIDS babies have been previously reported from our institution. We now report on laryngeal immunohistology.

METHODS

Larynges from 7 children who died from Sudden Infant Death Syndrome (SIDS) at under 16 weeks of age were examined immunohistologically and compared to those from 8 age- matched control infants who died from other causes.

RESULTS

The SIDS babies had increased inflammatory changes in the laryngeal epithelium and sub- epithelium with raised numbers of cells staining for elastase (p<0.01), EG2(a marker for activated eosinophils) (p<0.01) and CD4(p<0.05) suggesting that some SIDS deaths involve preceding inflammation.

CONCLUSIONS

Although death may be sudden and unexpected it appears that, at least in some SIDS victims, there is a preceding inflammatory process in the larynx which may allow hyper-reactivity of laryngeal reflexes and consequent apnoea. This observation concurs with others in the SIDS literature and offers a field for further research and possible prevention.

Laryngeal and tracheal afferent nerve stimulation evokes swallowing in anaesthetized guinea pigs

  We describe swallowing reflexes evoked by laryngeal and tracheal vagal afferent nerve stimulation in anaesthetized guinea pigs. The swallowing reflexes evoked by laryngeal citric acid challenges were abolished by recurrent laryngeal nerve (RLN) transection and mimicked by electrical stimulation of the central cut ends of an RLN. By contrast, the number of swallows evoked by upper airway/pharyngeal distensions was not significantly reduced by RLN transection but they were virtually abolished by superior laryngeal nerve transection. Laryngeal citric acid-evoked swallowing was mimicked by laryngeal capsaicin challenges, implicating transient receptor potential vanilloid 1 (TRPV1)-expressing laryngeal afferent nerves arising from the jugular ganglia. The swallowing evoked by citric acid and capsaicin and evoked by electrical stimulation of either the tracheal or the laryngeal mucosa occurred at stimulation intensities that were typically subthreshold for evoking cough in these animals. Swallowing evoked by airway afferent nerve stimulation also desensitized at a much slower rate than cough. We speculate that swallowing is an essential component of airway protection from aspiration associated with laryngeal and tracheal afferent nerve activation.

Reflux and aerodigestive tract diseases

Gastroesophageal reflux disease can present with a wide variety of extraesophageal symptoms. In particular, the type of disease characterized predominately by laryngopharyngeal reflux may be difficult to diagnose because of the absence of regurgitation or heartburn. The available battery of diagnostic tools is often insufficient to confirm a diagnosis of reflux, so the diagnosis is often made by elimination. In many cases, treatment with proton pump inhibitors will relieve symptoms and respiratory complications, despite the persistence of non-acidic reflux. Such treatment is often employed to "confirm" the diagnosis, as measured by patient response. Many diseases have been related to this condition in the literature. The authors review knowledge about these manifestations and their relationship with refluxed gastric content. Physiopathology, symptoms and treatment are reviewed in order to clarify our understanding of laryngopharyngeal reflux diseases and related manifestations.

Laryngopharyngeal Reflux : Larynx on Fire

Laryngopharyngeal Reflux (LPR) is a commonly occurring and recently described clinical entity due to the retrograde flow of gastric contents into the pharynx. It accounts for many symptoms of upper airway including hoarseness, chronic throat irritation and globus sensation. The sensitive laryngeal mucosa is prone to damage by the combination of acid and pepsin. The inflammatory changes that follow are presumed to cause the symptoms and predispose the individual to laryngeal disorders. Diagnosis can usually be made clinically based on symptoms and laryngeal signs but a 24 hour pH metry is essential to establish diagnosis. Treatment centres on lifestyle modifications, vocal hygiene measures and long term use of proton pump inhibitors. Recent research in this field may lead to a better understanding of the pathophysiology of the disease and change the way LPR is managed.

Differential diagnosis of paradoxical vocal fold movement

PURPOSE

To present the differential diagnosis of paradoxical vocal fold movement (PVFM) and its distinguishing features.

METHODS

The authors provide an overview of PVFM by drawing from 30 years of clinical and research experience, and relating that experience to literature in this area.

CONCLUSION

PVFM is characterized by inappropriate adduction of the vocal folds during inspiration. PVFM is an uncommon and sometimes confusing cause of airway obstruction. The resultant obstruction may be intermittent or continuous, mild or severe. Most patients with PVFM have a specific etiology--inflammatory, neurological, neoplastic, iatrogenic, or psychological--that influences type of treatment and outcome.

Neonatal apnea: what's new?

Apnea of prematurity (AOP) remains a major clinical problem in present day neonatology that warrants frequent evaluations and imposes challenges in therapeutic strategies. Although the pathogenesis of AOP is poorly understood, it is probably a manifestation of physiologic immaturity of breathing control rather than a pathologic disorder. Immature breathing responses to hypoxia, hypercapnia and exaggerated inhibitory pulmonary reflexes in preterm infants might also contribute to the occurrence or severity of AOP. Recent data suggest a role for genetic predisposition. Although typically resolve with maturation, the role of bradycardia and desaturation episodes associated with AOP in the development of sleep disorder breathing and neurodevelopmental delay needs further clarification. Pharmacological treatment with methylxanthines and CPAP remain the mainstay for treatment of AOP. However, recent studies have implicated central inhibitory neuromodulators including prostaglandins, GABA and adenosine in its pathogenesis, the fact that might provide future specific targets for treatment. This review will summarize new insights involving these issues as well as others involving the pathogenesis, treatment strategies and consequences of apnea in premature infants.

Review article: The laryngological manifestations of reflux disease; why the scepticism?

BACKGROUND

Despite increasing clinical and experimental evidence of its existence, otolaryngological manifestations of reflux disease remain controversial, concerning diagnosis as well as treatment.

AIM

Proper understanding of laryngopharyngeal reflux disease (LPRD).

METHOD

Review of literature.

RESULTS

Scepticism concerning LPRD is based upon differences between gastro-oesophageal reflux disease and LPRD; lack of specificity and sensitivity of diagnostic tests to confirm LPRD; non-specificity of laryngological symptoms, which are difficult to distinguish from other causes of upper respiratory tract inflammation; non-specificity of laryngological signs in laryngoscopy, with high intra- and inter-observer variability in evaluation; diagnosis of LPRD is essentially only based on a combination of diagnostic signs and symptoms, which cannot be attributed to other pathology; slow, or sometimes lack of, response of LPRD symptoms to proton pump inhibitor (PPI) medication and lack of evidence concerning efficacy of PPIs in placebo-controlled trials.

CONCLUSIONS

LPRD remains a diagnosis by exclusion and resolution of symptoms following 4-month trial of 40 mg PPI twice daily is, for all practical purposes, considered proof of the initial diagnosis. However, non-response does not exclude LPRD as PPIs have no influence on noxious non-acid components of the refluxate.

Activation of central adenosine A2A receptors enhances superior laryngeal nerve stimulation-induced apnea in piglets via a GABAergic pathway

Activation of the laryngeal mucosa results in apnea that is mediated through, and can be elicited via electrical stimulation of, the superior laryngeal nerve (SLN). This potent inhibitory reflex has been suggested to play a role in the pathogenesis of apnea of prematurity and sudden infant death syndrome, and it is attenuated by theophylline and blockade of GABAA receptors. However, the interaction between GABA and adenosine in the production of SLN stimulation-induced apnea has not been previously examined. We hypothesized that activation of adenosine A2A receptors will enhance apnea induced by SLN stimulation while subsequent blockade of GABAA receptors will reverse the effect of A2A receptor activation. The phrenic nerve responses to increasing levels of SLN stimulation were measured before and after sequential intracisternal administration of the adenosine A2A receptor agonist CGS ( n = 10) and GABAA receptor blocker bicuculline ( n = 7) in ventilated, vagotomized, decerebrate, and paralyzed newborn piglets. Increasing levels of SLN stimulation caused progressive inhibition of phrenic activity and lead to apnea during higher levels of stimulation. CGS caused inhibition of baseline phrenic activity, hypotension, and enhancement of apnea induced by SLN stimulation. Subsequent bicuculline administration reversed the effects of CGS and prevented the production of apnea compared with control at higher SLN stimulation levels. We conclude that activation of adenosine A2A receptors enhances SLN stimulation-induced apnea probably via a GABAergic pathway. We speculate that SLN stimulation causes endogenous release of adenosine that activates A2A receptors on GABAergic neurons, resulting in the release of GABA at inspiratory neurons and subsequent respiratory inhibition.

Peripheral arterial chemoreceptors and sudden infant death syndrome

Sudden infant death syndrome (SIDS) is the major cause of death in infants between 1 month and 1 year of age. Two particular concerns are that (1) premature or low birth weight (<2500-g) infants have a 2- to 40-fold greater risk of dying of SIDS (depending on the sleep position) than infants born at term and of normal birth weight, and that (2) the proportion of premature infants dying of SIDS has increased from 12 to 34% between 1988 and 2003. Hypo- and hypersensitivity of peripheral arterial chemoreceptors (PACs) may be one biological mechanism that could help to explain the epidemiological association between the increased incidence of SIDS in formerly premature infants. Because premature infants are often exposed to the extremes of oxygen stress during early postnatal development, they are more likely to have a maladaptive response of PACs later in their lives. As the first line of defense that mediates an increase in ventilation to a hypoxic challenge during wakefulness and sleep, PACs also mediate arousal responses during sleep in response to an asphyxial event that is often associated with upper airway obstruction. In most mammalian species, PACs are not fully developed at birth and thus are vulnerable to plasticity-induced changes mediated by environmental exposures such as the extremes of oxygen tension. Hypoxic or hyperoxic exposure during early postnatal development can lead to hyposensitive or hypersensitive PAC responses later in life. Although baseline chemoreceptor activity may not be the cause of an initial hypoxic or asphyxial event, the level of peripheral chemoreceptor drive does modulate the (1) time to arousal, (2) resumption of airflow during airway obstruction, (3) escape behaviors during rebreathing, and (4) cardiorespiratory responses that result from activation of the laryngeal chemoreflex. The laryngeal chemoreflex can be stimulated by reflux of gastric contents above the upper esophageal sphincter, or an increase in nasopharyngeal secretions from upper respiratory tract infections--events that contribute to some cases of SIDS. In this review, evidence is presented that both hypo- and hypersensitivity of PACs may be disadvantageous to the premature infant who is placed in an at risk environment for the occurrence of hypoxemia/asphyxia event thereby predisposing the infant to SIDS.

Review article: supra-oesophageal manifestations of gastro-oesophageal reflux disease and the role of night-time gastro-oesophageal reflux

Gastro-oesophageal reflux disease (GERD) has been associated with a variety of supra-oesophageal symptoms, including asthma, laryngitis, hoarseness, chronic cough, frequent throat clearing and globus pharyngeus. GERD may be overlooked as the underlying mechanism for these symptoms because typical GERD symptoms may be absent, despite abnormal oesophageal acid exposure. Two basic mechanisms linking GERD with laryngeal symptoms have been proposed: direct contact of gastric acid with the upper airway, in some cases due to micro-aspiration, and a vagovagal reflex triggered by acidification of the distal portion of the oesophagus. Gastro-oesophageal reflux (GER) during sleep is believed to be an important mechanism for the development of supra-oesophageal complications of GERD, such as asthma and idiopathic pulmonary fibrosis (IPF). Several physiological changes during sleep, including prolonged oesophageal acid contact time, decreased upper oesophageal sphincter pressure, increased gastric acid secretion, decreased salivation, decreased swallowing and a decrease in conscious perception of acid, render an individual more susceptible to reflux-induced injury. Supra-oesophageal symptoms often improve in response to aggressive acid-suppressive therapy. However, many unanswered questions remain regarding the appropriate approach to diagnosis and treatment of patients with GERD-related supra-oesophageal symptoms. In this article we review the relationship between supra-oesophageal symptoms and GERD and, where possible, highlight the evidence supporting the role of night-time reflux as a contributing factor to these symptoms.

Paroxysmal laryngospasm: a typical but underrecognized supraesophageal manifestation of gastroesophageal reflux?

Thirty-five consecutive adult patients with paroxysmal laryngospasm (LS) and with unimpaired vocal fold mobility were prospectively studied for coexisting gastroesophageal reflux disease (GERD). Nineteen patients reported frequent (>3 episodes a week) LS episodes (FLS patients) and 16 patients reported occasional LS episodes (OLS patients). All patients underwent an extensive otorhinolaryngological (ORL) examination, upper gastrointestinal (GI) endoscopy, ambulatory 24-hr dual-channel esophageal pH monitoring, and esophageal manometry. In addition, a subset of LS patients also underwent ambulatory duodenogastroesophageal reflux (DGER) monitoring. Patients with daily LS used the symptom marker during pH monitoring indicating separate LS episodes. All FLS patients and 14 OLS patients (87%) had a diagnosis of GERD. Only 10 patients (29%) experienced heartburn and/or regurgitation. Compared to OLS patients, FLS patients generally had more severe GERD as indicated by a higher prevalence of a hiatus hernia, higher distal and proximal esophageal acid exposure times, and higher values of DGER. In six FLS patients, 21 LS episodes (91%) occurred simultaneously with acid reflux, indicating a causal association between LS and GER. On antireflux therapy consisting of omeprazole, 20 mg bid, or lansoprazole, 30 mg oid, and lifestyle measures, LS ceased completely in all patients within 6 weeks. The present study not only demonstrates the role of GER in the pathogenesis of LS and the effectiveness of antireflux therapy, but also suggests that LS in adult patients with unimpaired vocal fold mobility might be considered a typical, although most frequently unrecognized, supraesophageal manifestation of GER.

Supra-oesophageal manifestations of gastro-oesophageal reflux disease

Since the early 1960s, many studies have been published that consider the possible relationship between gastro-oesophageal (acid) reflux (GORD) and various other complaints, including dental erosions, ear, nose and throat problems, chronic cough and asthma. Although a high coincidence of GORD and these supra-oesophageal complaints have been noted, there is no consensus on the pathophysiology and management of such complications. In this article we review the literature published between 1966 and 2000 on this subject. We also analyse the available information on the incidence, pathophysiological mechanisms, diagnostic approach and therapeutic options in the various subgroups of disorders.

Gastroesophageal reflux and the upper airway

EER is a disorder commonly seen in otolaryngologic practice and differs from GERD in its clinical manifestations, pathophysiology, and response to treatment. Its association with numerous disorders in children should lead otolaryngologists to consider this diagnosis in all patients with voice, airway, and swallowing complaints.

Laryngopharyngeal reflux and laryngeal web formation in patients with pediatric recurrent respiratory papillomas

OBJECTIVE

To determine whether treatment of laryngopharyngeal reflux reduces the laryngeal soft tissue complications encountered in surgery for recurrent respiratory papillomas.

STUDY DESIGN

Retrospective chart review.

METHODS

Retrospective chart review of all pediatric patients treated for laryngeal recurrent respiratory papillomas between 1984 and 1999 was performed. Thirty-one such patients were identified. Twenty-four were at "high risk" for developing complications based on the number of operating suite visits and the presence of disease at the anterior commissure. Twelve patients underwent 24-hour double pH probe testing.

RESULTS

Overall, 13 of 31 patients (42%) developed laryngeal webs. No other soft tissue complications were encountered. Of the patients who had pH probe testing, 12 of 12 (100%) had at least one pharyngeal episode of acid exposure. Of the "high-risk" patients, 10 were treated for reflux and only 2 of 10 (20%) developed webs. Eleven of 14 (79%) of the "high-risk" patients who were not treated for reflux developed webs. The difference in rate of web formation between patients treated for reflux and those not treated for reflux was statistically significant (P =.011).

CONCLUSIONS

Antireflux treatments for patients undergoing surgery for laryngeal recurrent respiratory papillomas may reduce the soft tissue complications, especially scarring and web formation. Prophylactic antireflux therapy may be warranted in any patient undergoing surgery during which laryngeal mucosal disruption is anticipated.