Cough challenge in the assessment of cough reflex

Clinical Parameters of the Speech-Language Pathology Assessment of the Chronic Cough: A Scoping Review

OBJECTIVE

to map the clinical parameters used in the speech-language pathology assessment of the chronic cough.

METHODS

a scoping review was performed to answer the clinical question: "What are the clinical parameters included in the speech-language pathology assessment of patients with chronic cough?" Evidence was searched by electronic and manual search. The electronic search included: MEDLINE, Cochrane Library, EMBASE, Web of Science, SCOPUS, and LILACS. Each database had a specific search strategy. The manual search included Journal of Voice, Chest, and Thorax, Brazilian Library of Theses and Dissertations, Open Grey, and Clinical Trials, in addition to scanning the references of the included studies. The extracted data considered information regarding the publication, sample, assessment, and measures used when assessing chronic cough.

RESULTS

the electronic search found 289 studies; the manual search found 1036 studies; 12 were selected for the present study. The most used assessments were: self-assessment (75%), aerodynamic analysis (66.67%), the perceptual auditory judgment of the voice quality (58.33%), acoustic analysis of the voice (41.67%), cough frequency, and cough threshold (41.67%) and electroglottography (25%).

CONCLUSIONS

the subjective instruments were used more frequently, while specific objective instruments, which are recent, were used less frequently. Complementary assessments such as vocal assessment, have been frequently used, also, with no other parameter. A lack of homogeneity was identified in the speech-language pathology assessment and measures of patients with chronic cough, thus, the comparison among studies and clinical analysis is difficult.

Chronic cough-the limitation and advances in assessment techniques

Accurate and consistent assessments of cough are essential to advance the understanding of the mechanisms of cough and individualised the management of patients. Considerable progress has been made in this work. Here we reviewed the currently available tools for subjectively and objectively measuring both cough sensitivity and severity. We also provided some opinions on the new techniques and future directions. The simple and practical Visual Analogue Scale (VAS), the Leicester Cough Questionnaire (LCQ), and the Cough Specific Quality of Life Questionnaire (CQLQ) are the most widely used self-reported questionnaires for evaluating and quantifying cough severity. The Hull Airway Reflux Questionnaire (HARQ) is a tool to elucidate the constellation of symptoms underlying the diagnosis of chronic cough. Chemical excitation tests are widely used to explore the pathophysiological mechanisms of the cough reflex, such as capsaicin, citric acid and adenosine triphosphate (ATP) challenge test. Cough frequency is an ideal primary endpoint for clinical research, but the application of cough counters has been limited in clinical practice by the high cost and reliance on aural validation. The ongoing development of cough detection technology for smartphone apps and wearable devices will hopefully simplify cough counting, thus transitioning it from niche research to a widely available clinical application.

Functional gastrointestinal disorders are associated with capsaicin cough sensitivity in severe asthma

BACKGROUND

Although sensory nerve dysfunction is related to the pathology of severe uncontrolled asthma and functional gastrointestinal disorders (FGIDs), the impact of comorbid FGIDs on the pathophysiology of severe uncontrolled asthma remains poorly understood. The aim was to clarify the physiological relationships between severe uncontrolled asthma and FGIDs.

METHODS

Fifty-two patients with severe uncontrolled asthma who visited our hospital between September 2016 and August 2019 were retrospectively analyzed. Clinical characteristics, other comorbidities including gastroesophageal reflux disease (GERD), and biomarkers such as fractional nitric oxide (FeNO) and capsaicin cough sensitivity (C-CS) before the beginning of biologics or bronchial thermoplasty, were compared between patients with and without comorbid FGIDs. C-CS was evaluated by C5 (concentration of inhaled capsaicin that induced five or more coughs), and C5 ≤2.44 μM was defined as heightened C-CS.

RESULTS

Seventeen patients had comorbid FGIDs. These patients had a lower FeNO level (21.9 ± 1.7 ppb vs. 33.9 ± 2.8 ppb, P = 0.04), a lower C5 threshold (2.24 ± 2.88 μM vs. 8.91 ± 5.5 μM, P < 0.001), a higher prevalence of comorbid GERD (64.7% vs. 31.7%, P = 0.03), and a higher prevalence of heightened C-CS (70.6% vs. 28.6%, P = 0.007) than those without FGIDs. Analysis of covariance showed a significant effect of FGIDs on C-CS in severe uncontrolled asthma without being affected by GERD.

CONCLUSIONS

Comorbid FGIDs are associated with heightened C-CS in patients with severe uncontrolled asthma, and they may be an important extra-respiratory manifestation of the airway neuronal dysfunction phenotype of severe uncontrolled asthma.

Changes in Cough Reflex Sensitivity in Children After Removal of Hypertrophied Adenoid Tissue

Purpose

The co-occurrence of adenoids and chronic cough is common in children. The goal of this research was to specify changes in cough reflex sensitivity as a result of adenoid tissue removal.

Patients and Methods

The sample group consisted of 17 children (six boys and 11 girls, aged 4–12 years, mean age 6.24 years), all of them possessing symptoms of chronic cough and adenoids, confirmed by nasal fiberoptic endoscopy. This sample group underwent cough reflex sensitivity assessment, which took place both prior to and after endoscopic adenoidectomy. The definition of the cough reflex sensitivity is the lowest capsaicin concentration that caused two (C2) or five (C5) coughs. Capsaicin aerosol in ascending concentrations (from 0.61 to 1250 µmol/L) was inhaled by a single-breath method (KoKo DigiDoser), with the addition of an inspiratory flow regulator valve (RIFR).

Results

Concentrations of capsaicin causing two (C2) and five coughs (C5) were reported. Cough sensitivity (geometric mean with 95% CI) for C2 was 31.86 (12.98–78.18) µmol/L preoperatively and 11.97 (6.16–23.26) µmol/L postoperatively (P=0.064). Cough sensitivity for C5 was 234.91 (97.19–567.77) µmol/L preoperatively and 69.13 (29.08–164.35) µmol/L postoperatively (P=0.022). The children’s pulmonary function was within the normal range.

Conclusion

In our study, adenoidectomy significantly increased cough reflex sensitivity in non-atopic children suffering from chronic cough.

Transient Receptor Potential Vanilloid Subtype 1: Potential Role in Infection, Susceptibility, Symptoms and Treatment of COVID-19

The battle against the new coronavirus that continues to kill millions of people will be still long. Novel strategies are demanded to control infection, mitigate symptoms and treatment of COVID-19. This is even more imperative given the long sequels that the disease has on the health of the infected. The discovery that S protein includes two ankyrin binding motifs (S-ARBMs) and that the transient receptor potential vanilloid subtype 1 (TRPV-1) cation channels contain these ankyrin repeat domains (TRPs-ARDs) suggest that TRPV-1, the most studied member of the TRPV channel family, can play a role in binding SARS-CoV-2. This hypothesis is strengthened by studies showing that other respiratory viruses bind the TRPV-1 on sensory nerves and epithelial cells in the airways. Furthermore, the pathophysiology in COVID-19 patients is similar to the effects generated by TRPV-1 stimulation. Lastly, treatment with agonists that down-regulate or inactivate TRPV-1 can have a beneficial action on impaired lung functions and clearance of infection. In this review, we explore the role of the TRPV-1 channel in the infection, susceptibility, pathogenesis, and treatment of COVID-19, with the aim of looking at novel strategies to control infection and mitigate symptoms, and trying to translate this knowledge into new preventive and therapeutic interventions.

Is there clinical value in performing capsaicin cough challenges in patients with severe asthma?

Over 330 million people have been diagnosed with asthma worldwide [1], of whom 5–10% are classified as severe [2]. Despite use of high doses of inhaled corticosteroids (ICS), long-acting bronchodilators (LABA) and/or maintenance oral steroid use, patients with severe asthma account for over 50% of the asthma healthcare budget [3, 4]. Largely due to exacerbations requiring hospitalisation, and cost of treatments to control disease severity, the disease burden has serious implications for their health and quality of life [3–5].

Heightened capsaicin cough sensitivity is independently associated with poor asthma control in moderate-to-severe asthma patientshttps://bit.ly/3mkbLkI

Detection of airway protective level of the cough reflex in acute stroke patients

Background

The most common respiratory complications in cerebrovascular strokes were respiratory infection, pulmonary edema, acute lung injury (ALI) acute respiratory distress syndrome (ARDS) and pulmonary embolism (PE). The inhalation cough challenge facilitates the quantification of cough.

Objectives

To detect the level of cough reflex that is enough to protect against respiratory infection in stroke patients, and to identify predictors of post-stroke respiratory infection.

Patients and methods

One hundred and one of cerebrovascular stroke patients were assessed in the first week of symptoms by National Institutes of Health Stroke Scale (NIHSS) Arabic version, Mann Assessment of Swallowing Ability (MASA), cough challenge test, cough flow meter, and A2DS2 score. Then, follow up after 1 week.

Results

Post-stroke respiratory infection was higher in older patients and those who were not working. Respiratory infection was significantly associated with high A2DS2 and NIHSS score (p value < 0.001). A highly significant increase in the levels of the inflammatory markers was detected in patients with a respiratory infection. Eighty percent of stroke patients with no cough developed a respiratory infection. The Mann total scores and the peak cough flow were lower in patients who had a respiratory infection.

Conclusion

Preserved cough reflex is essential in preventing aspirations and consequent respiratory infections.

Methods for assessing cough sensitivity

Cough sensitivity can be described as the reaction intensity of the cough reflex to different stimuli which activate chemically and mechanically sensitive vagal afferent nerves innervating airways and lungs. Measurement of cough reflex sensitivity plays an important role in revealing the underlying mechanisms of cough and evaluating the effects of pharmacological interventions. Besides, different responses to cough suppression therapies indicate the existence of cough hypersensitivity. In consideration of these factors stated above, cough sensitivity should therefore be assessed with a variety of cough challenge tests. Based on the neuroanatomical characteristics of the cough reflex, chemical challenge tests have been developed to objectively assess cough sensitivity. In cough inhalation challenges, capsaicin and citric acid are commonly used as the tussive agents to induce cough, which are validated for describing a profile of cough sensitivity to chemical irritants. Recently, mechanical methodologies have also been tried to measure the mechanical sensitivity of the cough reflex. Methodological consideration and selection are necessary for the reasonable assessment of cough sensitivity while employing cough challenges in clinical trials. Thus, in this review, we will focus on describing various methodologies of cough sensitivity measurement and, detailing some factors influencing on the accuracy of outcomes in the experimentally induced cough.

Cough, an unresolved problem in interstitial lung diseases

PURPOSE OF REVIEW

Many patients with interstitial lung diseases (ILDs), especially fibrotic ILDs, experience chronic cough. Cough has a major impact on wellbeing, affecting both physical and psychological aspects of life. The pathophysiology of cough in ILDs is poorly understood and currently no good antitussive therapy exists.

RECENT FINDINGS

Research on cough in ILDs is increasing. A recent proof-of-concept study with nebulized sodium cromoglycate for patients with idiopathic pulmonary fibrosis (IPF)-related cough showed a promising effect on cough. Observational data suggest that antifibrotic pirfenidone might reduce cough in IPF. Studies on the effect of acid inhibition on cough in ILDs show contradicting results.

SUMMARY

The first steps in analyzing new treatment options for chronic cough in patients with ILDs, especially in IPF, have been taken, but an effective treatment is still lacking.

Cough as an adverse effect on inhalation pharmaceutical products

Cough is an adverse effect that may hinder the delivery of drugs into the lungs. Chemical or mechanical stimulants activate the transient receptor potential in some airway afferent nerves (C-fibres or A-fibres) to trigger cough. Types of inhaler device and drug, dose, excipients and formulation characteristics, including pH, tonicity, aerosol output and particle size may trigger cough by stimulating the cough receptors. Release of inflammatory mediators may increase the sensitivity of the cough receptors to stimulants. The cough-provoking effect of aerosols is enhanced by bronchoconstriction in diseased airways and reduces drug deposition in the target pulmonary regions. In this article, we review the factors by which inhalation products may cause cough.

Increased Capsaicin Sensitivity in Patients with Severe Asthma Is Associated with Worse Clinical Outcome

Rationale: Capsaicin cough reflex sensitivity (C-CS) is associated with poorly controlled asthma, although its association with severe asthma remains unknown.Objectives: To determine the clinical impact of C-CS on severe asthma.Methods: We prospectively enrolled 157 patients with asthma (including 122 patients with severe asthma who were in step 4 or 5 according to the Global Initiative for Asthma 2015 guidelines) between November 2016 and October 2019. A capsaicin cough challenge was performed along with spirometry and assessment of biomarkers. The concentration required to induce at least five coughs by capsaicin was adopted as an index of C-CS. An Asthma Control Test and comorbidities were also evaluated. Associations of biomarkers with four clinical features of severe asthma made by the European Respiratory Society/American Thoracic Society guidelines (poor control [Asthma Control Test < 20; n = 58], frequent exacerbations [≥2/yr; n = 28], admissions [≥1/yr; n = 17], and airflow limitation [FEV₁% predicted < 80%; n = 30]) were assessed.Measurements and Main Results: Heightened C-CS was associated with poor asthma control, frequent exacerbations, and admissions, particularly in patients without atopy (n = 54). Meanwhile, C-CS was not related to airflow limitation. Multivariate regression analysis has revealed that heightened C-CS (at least five coughs by capsaicin ≤ 2.44 μM) was a significant risk for poor asthma control and frequent exacerbations. Regarding general factors and comorbidities, ex-smoking status, diabetes mellitus, and chronic rhinosinusitis were associated with clinical features of severe asthma (all P < 0.05).Conclusions: Heightened C-CS is a risk factor for severe asthma. The present study suggests the association of airway neuronal dysfunction with the pathophysiology of non-type 2 severe asthma.

Mechanisms underlying the stimulatory effect of inhaled sulfur dioxide on vagal bronchopulmonary C-fibres

KEY POINTS

Brief inhalation of SO₂ of concentration >500 p.p.m. triggered a pronounced stimulatory effect on vagal bronchopulmonary C-fibres in anaesthetized rats. This stimulatory effect was drastically diminished by a pretreatment with NaHCO₃ that raised the baseline arterial pH, suggesting a possible involvement of acidification of airway fluid and/or tissue generated by inhaled SO₂ . The stimulation was completely abolished by pretreatment with antagonists of both acid-sensing ion channels and transient receptor potential vanilloid type-1 receptors, indicating that this effect was caused by acid activation of these cation channels expressed in airway sensory nerves. This conclusion was further supported by the results obtained from studies in isolated rat vagal bronchopulmonary sensory neurones and also in the cough response to SO₂ inhalation challenge in awake mice. These results provide new insight into the underlying mechanism of harmful irritant effects in the respiratory tract caused by accidental exposure to a high concentration of SO₂ .

ABSTRACT

Inhalation of sulfur dioxide (SO₂ ) triggers coughs and reflex bronchoconstriction, and stimulation of vagal bronchopulmonary C-fibres is primarily responsible. However, the mechanism underlying this stimulatory effect is not yet fully understood. In this study, we tested the hypothesis that the C-fibre stimulation was caused by SO₂ -induced local tissue acidosis in the lung and airways. Single-unit activities of bronchopulmonary C-fibres in response to inhalation challenges of SO₂ (500-1500 p.p.m., 10 breaths) were measured in anaesthetized rats. Inhalation of SO₂ reproducibly induced a pronounced and sustained stimulation (lasting for 15-60 s) of pulmonary C-fibres in a concentration-dependent manner. This stimulatory effect was significantly attenuated by an increase in arterial pH generated by infusion of sodium bicarbonate (NaHCO₃ ), and completely abrogated by a combined pretreatment with amiloride (an antagonist of acid-sensing ion channels, ASICs) and AMG8910 (a selective antagonist of the transient receptor potential vanilloid type-1 receptor, TRPV1). Furthermore, in isolated rat vagal pulmonary sensory neurones, perfusion of an aqueous solution of SO₂ evoked a transient increase in the intracellular Ca²⁺ concentration; this response was also markedly diminished by a pretreatment with amiloride and AMG8910. In addition, inhalation of SO₂ consistently evoked coughs in awake mice; responses were significantly smaller in TRPV1^-/- mice than in wild-type mice, and almost completely abolished after a pretreatment with amiloride in TRPV1^-/- mice. These results suggested that the stimulatory effect of inhaled SO₂ on bronchopulmonary C-fibres was generated by acidification of fluid and/or tissue in the lung and airways, which activated both ASICs and TRPV1 expressed in these sensory nerves.

The assessment of the peak of reflex cough in subjects with acquired brain injury and tracheostomy and healthy controls

INTRODUCTION

There is no standard procedure to evaluated the peak of reflex cough flow (PCF-reflex) in the literature, which is important assessment in subjects with acquired brain injury and tracheostomy cannula. The present study aims to investigate the PCF of the reflex cough in a broad sample of healthy controls and, furthermore, the presence and the strength of voluntary and reflex cough in subjects with ABI with tracheostomy cannula.

MATERIALS AND METHODS

We recruited 147 participants including the healthy subjects (n = 105) and acquired brain injury subjects (n = 43), who underwent respiratory assessment: the Tidal Volume, Forced Vital Capacity, PCF of voluntary cough (PCF-voluntary) and PCF-reflex (using a spirometer connected with a nebulizer by a bidirectional).

RESULTS

The PCF-reflex of controls and subjects was significant lower than the PCF-voluntary (P < 0.01). The PCF-voluntary was not assessed in 26 (60.5 %) subjects due to severe cognitive deficit. In subjects without cognitive deficits (n = 17; 39.5 %), it was significantly lower than in healthy controls (p < 0.01). In contrast, the PCF-reflex was completed in all subjects and it was not significantly different from healthy controls. Furthermore, the strength of the PCF-reflex decreased with increasing inhalation numbers of nebulised air.

CONCLUSION

Reflex cough behaviour differs largely from voluntary cough and the PCF results reflect this great discrepancy. PCF-reflex could be useful parameter for assessing the airway protection whereas PCF-voluntary for measuring airway clearance.

Comparison of mannitol and citric acid cough provocation tests

RATIONALE

Citric acid has been used as a cough provocation test for decades. However, the methods of administration have not been standardized. Inhaled mannitol is a novel cough provocation test, which has regulatory approval and can be performed utilizing a simple disposable inhaler in a standardized manner.

OBJECTIVE

To compare the mannitol and citric acid cough provocation tests with respect to their ability to identify subjects with chronic cough and their tolerability.

METHODS

Subjects with chronic cough (n = 36) and controls (n = 25) performed provocation tests with mannitol and citric acid. Both tests were video recorded. Cough sensitivity was expressed as coughs-to-dose ratios (CDR) and the cumulative doses to mannitol or concentration to citric acid evoking 5 coughs (C5). Forced expiratory volume in 1 s (FEV₁), visual analogue scales (VAS), test completion rates and the total cough frequencies were analysed.

RESULTS

Mannitol and citric acid CDR both effectively separated those with cough and the control subjects (AUC 0.847 and 0.803, respectively) as did C5 (AUC 0.823 and 0.763, respectively). There was a good correlation between the cough sensitivity provoked by the two stimuli, either expressed as CDR (r = 0.65, p < 0.001) or C5 (r = 0.53, p = 0.001). Both tests were similarly tolerated in terms of VAS, although more patients discontinued the mannitol test early, primarily due to cough.

CONCLUSIONS

Mannitol and citric acid tests correlated well, equally identified subjects with chronic cough and their tolerability was similar. The feasibility issues, strict standardisation and regulatory approval may favour mannitol to be used in clinical cough research.

A systematic review of methods of citric acid cough reflex testing

INTRODUCTION

This systematic review summarises and appraises methods of citric acid cough reflex testing (CRT) documented in published literature.

METHODS

Electronic databases, MEDLINE, EMBASE, CINAHL, PsychINFO, Scopus were searched up to and including 11th February 2018. Studies reporting a method of citric acid CRT, published in peer-reviewed journals in English or Spanish, were assessed for the inclusion criteria. Of the selected studies, information on the instrumentation and CRT protocol was extracted.

RESULTS

A total of 129 studies were included. Instrumentation and protocols differed widely across studies. Reporting of methods of citric acid CRT was sub-standard, with many crucial methodological components omitted from published manuscripts, preventing their full replication.

CONCLUSIONS

Considerable methodological variability exists for citric acid CRT in published literature. The findings suggest that caution is warranted in comparing citric acid cough thresholds across studies. Full replication of previously published methods of citric acid CRT is limited due to crucial elements of the citric acid CRT protocol being omitted from published manuscripts. These findings have implications on the use of citric acid CRT in clinical and pharmaceutical studies to evaluate the effects of antitussive medications and cough therapies.

The effect of gefapixant, a P2X3 antagonist, on cough reflex sensitivity: a randomised placebo-controlled study

We evaluated the effect of gefapixant on cough reflex sensitivity to evoked tussive challenge.

In this phase 2, double-blind, two-period study, patients with chronic cough (CC) and healthy volunteers (HV) were randomised to single-dose gefapixant 100 mg or placebo in a crossover fashion. Sequential inhalational challenges with ATP, citric acid, capsaicin and distilled water were performed 1, 3 and 5 h after dosing. Mean concentrations evoking ≥2 coughs (C2) and ≥5 coughs (C5) post dose versus baseline were co-primary endpoints. Objective cough frequency (coughs·h−1) over 24 h and a cough severity visual analogue scale (VAS) were assessed in CC patients. Adverse events were monitored.

24 CC patients and 12 HV were randomised (mean age 61 and 38 years, respectively). The cough challenge threshold increased for ATP by 4.7-fold (C2, p≤0.001) and 3.7-fold (C5, p=0.007) for gefapixant versus placebo in CC patients; in HV, C2 and C5 increased 2.4-fold (C2, p=0.113; C5, p=0.003). The distilled water C2 and C5 thresholds increased significantly (p<0.001) by a factor of 1.4 and 1.3, respectively, in CC patients. Gefapixant had no effect on capsaicin or citric acid challenge. Median cough frequency was reduced by 42% and the least squares mean cough severity VAS was 18.0 mm lower for gefapixant versus placebo in CC patients. Dysgeusia was the most frequent adverse event (75% of HV and 67% of CC patients).

ATP-evoked cough was significantly inhibited by gefapixant 100 mg, demonstrating peripheral target engagement. Cough count and severity were reduced in CC patients. Distilled water may also evoke cough through a purinergic pathway.

Roles of citric acid in conjunction with saline nebulization in experimental tracheostomy in guinea pigs

PURPOSE

Tracheostomy usually accompanied by the impairment of cough reflex, which may affect the clearance of secretions and result in the occurrence and development of pulmonary inflammation. Previous research has demonstrated that citric acid could effectively evoke cough. However, there are limited data available on this topic specific to the cough stimulation method, and the roles of citric acid in tracheostomy still remain obscure. The aims of present study were to identify the potential roles of citric acid in conjunction with saline nebulization in tracheostomy in guinea pigs.

MATERIALS AND METHODS

Experimental tracheostomy model was induced in guinea pigs, and different nebulization interventions were implemented. The expression of P-selectin and platelet count were analyzed by flow cytometer and automatic globulimeter, the histological changes in trachea and lung tissue were assessed by hematoxylin and eosin staining, and the inflammatory cytokines and substance P (SP) levels in bronchoalveolar lavage fluid were evaluated by enzyme-linked immunosorbent assay.

RESULTS

Tracheostomy resulted in the disorder of trachea mucosa and cilia, the inflammatory cell infiltration in lung tissue, the increase of IL-6, TNF-α levels and the decrease of SP level. Citric acid alone increase the SP level, and the joint action of citric acid and saline nebulization further showed significantly beneficial effects on pathological, inflammatory changes and SP level.

CONCLUSIONS

Citric acid combined with saline nebulization contributes to the alleviation of tracheotomy-induced tracheal damage and pulmonary inflammation in an experimental tracheostomy model in guinea pigs. This may provide novel insights into the inflammation management and cough recovery after tracheostomy.

A service evaluation of cough reflex testing to guide dysphagia management in the postsurgical adult head and neck patient population

PURPOSE OF REVIEW

The article reviews recent literature supporting the use of cough reflex testing (CRT), and outlines a service evaluation of CRT conducted with postsurgical head and neck cancer patients. There is a growing evidence base to support the use of CRT in dysphagia management to establish laryngeal sensation and screen for silent aspiration; however, there is a lack of evidence relating to using CRT within the head and neck population.

RECENT FINDINGS

Over a 3-month period, inpatients on an ear, nose and throat/maxillofacial ward underwent CRT as part of their clinical swallow evaluation. Data from these patients were collected, including their diagnoses, CRT findings, and subsequent management. The evaluation was limited by difficulties in maintaining a supply of citric acid, accessing medics to prescribe the citric acid, and staffing levels, as administration of the CRT initially required two members of staff to be present.

SUMMARY

The service evaluation findings, alongside current evidence examining noncancer mortality rates, suggests identification of silent aspiration is important in this population. CRT was useful to rationalize instrumental assessments and was easily incorporated into the swallowing evaluation. More evidence is needed to support the use of CRT within the head and neck population.

Tiotropium Attenuates Refractory Cough and Capsaicin Cough Reflex Sensitivity in Patients with Asthma

BACKGROUND

Asthmatic cough is often refractory to standard treatments such as inhaled corticosteroids (ICS) and long-acting β₂ agonists (LABA). Tiotropium may modulate cough reflex sensitivity of acute viral cough, but its efficacy in asthmatic cough remains unknown.

OBJECTIVE

To evaluate whether tiotropium improves cough and cough reflex sensitivity in patients with asthma refractory to ICS/LABA.

METHODS

Seventeen consecutive patients with asthma with chronic cough despite the use of ICS/LABA (13 women; 43.4 ± 19.0 years; average ICS dose, 651 ± 189 μg/d; fluticasone equivalent) were additionally treated with tiotropium (5 μg/d) for 4 to 8 weeks to examine its effects on pulmonary function and capsaicin cough reflex sensitivity (cough thresholds C2 and C5). Cough severity, cough-specific quality of life, and asthma control were also evaluated using cough visual analog scales (VASs), the Japanese version of Leicester Cough Questionnaire (J-LCQ), and Asthma Control Test (ACT), respectively. Patients with an improved cough VAS score of 15 mm or more were considered responders to tiotropium.

RESULTS

Tiotropium significantly improved cough VAS, J-LCQ, and ACT scores, but not FEV₁. Changes in cough VAS score correlated with those in C2 (r = -0.58; P = .03), C5 (r = -0.58; P = .03), and ACT scores (r = -0.62; P = .02), but not in FEV₁ in the overall patients. When analyses were confined to the 11 responders, tiotropium significantly improved capsaicin cough reflex sensitivity within the subgroup (C2: P = .01 and C5: P = .02) and versus the nonresponders (C2: P = .004 and C5: P = .02).

CONCLUSION

Tiotropium may alleviate asthmatic cough refractory to ICS/LABA by modulating cough reflex sensitivity but not through bronchodilation.

Cough in idiopathic pulmonary fibrosis

Many patients with idiopathic pulmonary fibrosis (IPF) complain of chronic refractory cough. Chronic cough is a distressing and disabling symptom with a major impact on quality of life. During recent years, progress has been made in gaining insight into the pathogenesis of cough in IPF, which is most probably "multifactorial" and influenced by mechanical, biochemical and neurosensory changes, with an important role for comorbidities as well. Clinical trials of cough treatment in IPF are emerging, and cough is increasingly included as a secondary end-point in trials assessing new compounds for IPF. It is important that such studies include adequate end-points to assess cough both objectively and subjectively. This article summarises the latest insights into chronic cough in IPF. It describes the different theories regarding the pathophysiology of cough, reviews the different methods to assess cough and deals with recent and future developments in the treatment of cough in IPF.

Airway remodeling associated with cough hypersensitivity as a consequence of persistent cough: An experimental study

BACKGROUND

Chronic cough involves airway remodeling associated with cough reflex hypersensitivity. Whether cough itself induces these features remains unknown.

METHODS

Guinea pigs were assigned to receive treatment with citric acid (CA), saline (SA), or CA+dextromethorphan (DEX). All animals were exposed to 0.5M CA on days 1 and 22. On days 4-20, the CA and CA+DEX groups were exposed to CA, and the SA group to saline thrice weekly, during which the CA+DEX group was administered DEX pretreatment to inhibit cough. The number of coughs was counted during each 10-min CA or SA exposure. Terbutaline premedication was started to prevent bronchoconstriction. Bronchoalveolar lavage and pathology were examined on day 25. Average cough number for 10 CA exposures was examined as "cough index" in the CA group, which was divided into frequent (cough index>5) and infrequent (<5) cough subgroups for lavage and pathology analysis.

RESULTS

The number of coughs significantly increased in the CA group from day 13 onwards. In the CA+DEX and SA groups, the number of coughs did not differ between days 1 and 22, while average number of coughs during days 4-20 was significantly lower than at days 1 and 22. Bronchoalveolar cell profiles were similar among the four groups. The smooth muscle area of small airways was significantly greater in the frequent-cough subgroup than in the other groups (in which it was similar), and highly correlated with cough index in CA group.

CONCLUSION

Repeated cough induces airway smooth muscle remodeling associated with cough reflex hypersensitivity.

How does rhinovirus cause the common cold cough?

Cough is a protective reflex to prevent aspiration and can be triggered by a multitude of stimuli. The commonest form of cough is caused by upper respiratory tract infection and has no benefit to the host. The virus hijacks this natural defence mechanism in order to propagate itself through the population. Despite the resolution of the majority of cold symptoms within 2 weeks, cough can persist for some time thereafter. Unfortunately, the mechanism of infectious cough brought on by pathogenic viruses, such as human rhinovirus, during colds, remains elusive despite the extensive work that has been undertaken. For socioeconomic reasons, it is imperative we identify the mechanism of cough. There are several theories which have been proposed as the causative mechanism of cough in rhinovirus infection, encompassing a range of different processes. Those of which hold most promise are physical disruption of the epithelial lining, excess mucus production and an inflammatory response to rhinovirus infection which may be excessive. And finally, neuronal modulation, the most convincing hypothesis, is thought to potentiate cough long after the original stimulus has been cleared. All these hypotheses will be briefly covered in the following sections.

A randomized placebo controlled trial to evaluate the effects of butamirate and dextromethorphan on capsaicin induced cough in healthy volunteers

AIMS

The examination of cough reflex sensitivity through inhalational challenge can be utilized to demonstrate pharmacological end points. Here we compare the effect of butamirate, dextromethorphan and placebo on capsaicin-induced cough in healthy volunteers.

METHODS

In this randomized, placebo-controlled, six way crossover study the effect of dextromethrophan 30 mg, four doses of butamirate and placebo was evaluated on incremental capsaicin challenges performed at baseline and 2, 4, 6, 8, 12 and 24 h following dosing. The primary end point was the area under the curve (AUC(0,12h)) of log10 C5 from pre-dose to 12 h after dosing. Plasma butamirate metabolites were analyzed to evaluate pharmacokinetic and pharmacodynamic relationships.

RESULTS

Thirty-four subjects (13 males, median age 25 years) completed the study. Cough sensitivity decreased from baseline in all arms of the study. Dextromethorphan was superior to placebo (P = 0.01) but butamirate failed to show significant activity with maximum attenuation at the 45 mg dose. There was no apparent relationship between pharmacokinetic and pharmacodynamic parameters for butamirate.

CONCLUSIONS

We have demonstrated for the first time that dextromethorphan attenuates capsaicin challenge confirming its broad activity on the cough reflex. The lack of efficacy of butamirate could be due to formulation issues at higher doses.

Targeting TRP channels for chronic cough: from bench to bedside

Cough is currently the most common reason for patients to visit a primary care physician in the UK, yet it remains an unmet medical need. Current therapies have limited efficacy or have potentially dangerous side effects. Under normal circumstances, cough is a protective reflex to clear the lungs of harmful particles; however, in disease, cough can become excessive, dramatically impacting patients' lives. In many cases, this condition is linked to inflammatory diseases such as asthma and chronic obstructive pulmonary disease (COPD), but can also be refractory to treatment and idiopathic in nature. Therefore, there is an urgent need to develop therapies, and targeting the sensory afferent arm of the reflex which initiates the cough reflex may uncover novel therapeutic targets. The cough reflex is initiated following activation of ion channels present on vagal sensory afferents. These ion channels include the transient receptor potential (TRP) family of cation-selective ion channels which act as cellular sensors and respond to changes in the external environment. Many direct activators of TRP channels, including arachidonic acid derivatives, a lowered airway pH, changes in temperature, and altered airway osmolarity are present in the diseased airway where responses to challenge agents which activate airway sensory nerve activity are known to be enhanced. Furthermore, the expression of some TRP channels is increased in airway disease. Together, this makes them promising targets for the treatment of chronic cough. This review will cover the current understanding of the role of the TRP family of ion channels in the activation of airway sensory nerves and cough, focusing on four members, transient receptor potential vanilloid (TRPV) 1, transient receptor potential ankyrin (TRPA) 1, TRPV4, and transient receptor potential melastatin (TRPM) 8 as these represent the channels where most information has been gathered with relevance to the airways. We will describe recent data and highlight the possible therapeutic utility of specific TRP channel antagonists as antitussives in the clinic.

TRP Channels in Respiratory Pathophysiology: the Role of Oxidative, Chemical Irritant and Temperature Stimuli

There is rapidly growing evidence indicating multiple and important roles of Ca(2+)- permeable cation TRP channels in the airways, both under normal and disease conditions. The aim of this review was to summarize the current knowledge of TRP channels in sensing oxidative, chemical irritant and temperature stimuli by discussing expression and function of several TRP channels in relevant cell types within the respiratory tract, ranging from sensory neurons to airway smooth muscle and epithelial cells. Several of these channels, such as TRPM2, TRPM8, TRPA1 and TRPV1, are discussed in much detail to show that they perform diverse, and often overlapping or contributory, roles in airway hyperreactivity, inflammation, asthma, chronic obstructive pulmonary disease and other respiratory disorders. These include TRPM2 involvement in the disruption of the bronchial epithelial tight junctions during oxidative stress, important roles of TRPA1 and TRPV1 channels in airway inflammation, hyperresponsiveness, chronic cough, and hyperplasia of airway smooth muscles, as well as TRPM8 role in COPD and mucus hypersecretion. Thus, there is increasing evidence that TRP channels not only function as an integral part of the important endogenous protective mechanisms of the respiratory tract capable of detecting and ensuring proper physiological responses to various oxidative, chemical irritant and temperature stimuli, but that altered expression, activation and regulation of these channels may also contribute to the pathogenesis of respiratory diseases.

Is opiate action in cough due to sedation?

OBJECTIVES

Opiates have been used for cough suppression for centuries. It is unclear whether this antitussive action is due to their known sedative effects. We aimed to assess correlation between cough suppression and opiate usage.

METHODS

We performed a post hoc analysis of two published trials with three opioids. In study one, patients with chronic cough were treated with 4 weeks of modified release morphine sulphate (5 mg twice daily) or placebo in a double-blinded placebo-controlled fashion. Cough suppression was assessed subjectively by the Leicester Cough Questionnaire and objectively by citric acid aerosol (CAA) induced cough challenge. In study 2, normal volunteers were given single doses of placebo, codeine 30 mg or dextromethorphan 50 mg and cough suppression assessed using the CAA-induced cough challenge. Sedation was contemporaneously assessed by direct questioning.

RESULTS

There were 14 episodes of patient-reported sedation; 2 with modified release morphine sulphate, 9 with codeine and 3 with dextromethorphan. There was no correlation between change in the Leicester Cough Questionnaire or the CAA-induced cough challenge and reported sedation.

CONCLUSION

This observational study suggests that sedation is unlikely to underlie the antitussive properties of these opioids. Eliciting the mechanism of these medications in cough may be a target for future tailored drug development.

Pharmacodynamic modeling of cough responses to capsaicin inhalation calls into question the utility of the C5 end point

BACKGROUND

Inhaled capsaicin elicits cough reproducibly in human subjects and is widely used in the study of cough and antitussive therapies. However, the traditional end points C2 and C5 (the concentrations of capsaicin inducing at least 2 or 5 coughs, respectively) display extensive overlap between health and disease and therefore might not best reflect clinically relevant mechanisms.

OBJECTIVES

We sought to investigate capsaicin dose responses in different disease groups.

METHODS

Two novel capsaicin cough challenges were compared in patients with chronic cough (CC; n = 20), asthmatic patients (n = 18), and healthy volunteers (HVs; n = 20). Increasing doubling doses of capsaicin (0.48-1000 μmol/L, 4 inhalations per dose) were administered in challenge 1, whereas the order of the doses was randomized in challenge 2. A nonlinear mixed-effects model compared dose-response parameters by disease group and sex. Parameters were also correlated with objective cough frequency.

RESULTS

The model classified subjects based on maximum cough response evoked by any concentration of capsaicin (Emax) and the capsaicin dose inducing half-maximal response (ED50). HVs and asthmatic patients were not statistically different for either parameter and therefore combined for analysis (mean ED50, 38.6 μmol/L [relative SE, 28%]; mean Emax, 4.5 coughs [relative SE, 11%]). Compared with HVs/asthmatic patients, patients with CC had lower ED50 values (14.7 μmol/L [relative SE, 28%], P = .008) and higher Emax values (8.6 coughs [relative SE, 11%], P < .0001). Emax values highly correlated with 24-hour cough frequency (r = 0.71, P < .001) and were 37% higher in female compared with male subjects, regardless of disease group (P < .001).

CONCLUSIONS

Nonlinear mixed-effects modeling demonstrates that maximal capsaicin cough responses better discriminate health from disease and predict spontaneous cough frequency and therefore provide important insights into the mechanisms underlying CC.

Cough reflex testing in Dysphagia following stroke: a randomized controlled trial

BACKGROUND

Significant health issues and service delivery costs are associated with post-stroke pneumonia related to dysphagia. Silent aspiration is known to increase pneumonia and mortality in this population. The utility of cough reflex testing (CRT) for reducing pneumonia in acute stroke patients was the subject of this randomised, controlled trial.

METHODS

Patients referred for swallowing evaluation (N = 311) were assigned to either 1) a control group receiving standard evaluation or 2) an experimental group receiving standard evaluation with CRT. Participants in the experimental group were administered nebulised citric acid with test results contributing to clinical decisions. Outcomes for both groups were measured by pneumonia rates at 3 months post evaluation and other clinical indices of swallowing management.

RESULTS

Analysis of the data identified no significant differences between groups in pneumonia rate (P = 0.38) or mortality (P = 0.15). Results of CRT were shown to influence diet recommendations (P < 0.0001) and referrals for instrumental assessment (P < 0.0001).

CONCLUSIONS

Despite differences in clinical management between groups, the end goal of reducing pneumonia in post stroke dysphagia was not achieved.

Phenotyping airways disease: an A to E approach

The airway diseases asthma and chronic obstructive pulmonary disease (COPD) are heterogeneous conditions with overlapping pathophysiological and clinical features. It has previously been proposed that this heterogeneity may be characterized in terms of five relatively independent domains labelled from A to E, namely airway hyperresponsiveness (AHR), bronchitis, cough reflex hypersensitivity, damage to the airways and surrounding lung parenchyma, and extrapulmonary factors. Airway hyperresponsiveness occurs in both asthma and COPD, accounting for variable day to day symptoms, although the mechanisms most likely differ between the two conditions. Bronchitis, or airway inflammation, may be predominantly eosinophilic or neutrophilic, with different treatments required for each. Cough reflex hypersensitivity is thought to underlie the chronic dry cough out of proportion to other symptoms that can occur in association with airways disease. Structural changes associated with airway disease (damage) include bronchial wall thickening, airway smooth muscle hypertrophy, bronchiectasis and emphysema. Finally, a variety of extrapulmonary factors may impact upon airway disease, including rhinosinusitis, gastroesophageal reflux disease, obesity and dysfunctional breathing. This article discusses the A to E concept in detail and describes how this framework may be used to assess and treat patients with airway diseases in the clinic.

Acid-sensing by airway afferent nerves

Inhalation of acid aerosol or aspiration of acid solution evokes a stimulatory effect on airway C-fiber and Aδ afferents, which in turn causes airway irritation and triggers an array of defense reflex responses (e.g., cough, reflex bronchoconstriction, etc.). Tissue acidosis can also occur locally in the respiratory tract as a result of ischemia or inflammation, such as in the airways of asthmatic patients during exacerbation. The action of proton on the airway sensory neurons is generated by activation of two different current species: a transient (rapidly activating and inactivating) current mediated through the acid-sensing ion channels, and a slowly activating and sustained current mediated through the transient receptor potential vanilloid type 1 (TRPV1) receptor. In view of the recent findings that the expression and/or sensitivity of TRPV1 are up-regulated in the airway sensory nerves during chronic inflammatory reaction, the proton-evoked irritant effects on these nerves may play an important part in the manifestation of various symptoms associated with airway inflammatory diseases.

Pre-clinical studies in cough research: role of Transient Receptor Potential (TRP) channels

Cough is a protective reflex and defence mechanism in healthy individuals, which helps clear excessive secretions and foreign material from the lungs. Cough often presents as the first and most persistent symptom of many respiratory diseases and some non-respiratory disorders, but can also be idiopathic, and is a common respiratory complaint for which medical attention is sought. Chronic cough of various aetiologies is a regular presentation to specialist respiratory clinics, and is reported as a troublesome symptom by a significant proportion of the population. Despite this, the treatment options for cough are limited. The lack of effective anti-tussives likely stems from our incomplete understanding of how the tussive reflex is mediated. However, research over the last decade has begun to shed some light on the mechanisms which provoke cough, and may ultimately provide us with better anti-tussive therapies. This review will focus on the in vitro and in vivo models that are currently used to further our understanding of the sensory innervation of the respiratory tract, and how these nerves are involved in controlling the cough response. Central to this are the Transient Receptor Potential (TRP) ion channels, a family of polymodal receptors that can be activated by such diverse stimuli as chemicals, temperature, osmotic stress, and mechanical perturbation. These ion channels are thought to be molecular pain integrators and targets for novel analgesic agents for the treatment of various pain disorders but some are also being developed as anti-tussives.

Airway irritation and cough evoked by acid: from human to ion channel

Inhalation or aspiration of acid solution evokes airway defense responses such as cough and reflex bronchoconstriction, resulting from activation of vagal bronchopulmonary C-fibers and Aδ afferents. The stimulatory effect of hydrogen ion on these sensory nerves is generated by activation of two major types of ion channels expressed in these neurons: a rapidly activating and inactivating current mediated through ASICs, and a slow sustaining current via activation of TRPV1. Recent studies have shown that these acid-evoked responses are elevated during airway inflammatory reaction, revealing the potential convergence of a wide array of inflammatory signaling on these ion channels. Since pH in the airway fluid drops substantially in patients with inflammatory airway diseases, these heightened stimulatory effects of acid on airway sensory nerves may play a part in the manifestation of airway irritation and excessive cough under those pathophysiological conditions.

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.

Heightened cough sensitivity secondary to latanoprost

Chronic cough is a common symptom with significant morbidity. We report a case of a 51-year-old woman who presented with chronic cough. She recently had received a diagnosis of glaucoma and had started receiving therapy with topical latanoprost. The onset of cough coincided with the use of latanoprost. We performed a citric acid cough challenge while the patient was receiving latanoprost and repeated the challenge after therapy with the drug was stopped. The initial cough challenge revealed marked hypersensitivity of the cough reflex. After stopping therapy with latanoprost for 10 days, the cough sensitivity was reduced significantly. Within 3 days of recommending therapy with latanoprost, the cough sensitivity increased to the initial value. This case illustrates that the topical application of latanoprost can markedly increase cough sensitivity, which is reversible on stopping administration of the drug. Moreover, the case reflects the clinical manifestation of the effect of topical latanoprost therapy on cough reflex, which, to our knowledge, has never been reported in the medical literature.

The capsaicin cough reflex in patients with symptoms elicited by odorous chemicals

Patients with multiple chemical sensitivity and eczema patients with airway symptoms elicited by odorous chemicals have enhanced cough reflex to capsaicin when applying the tidal breathing method. The aims of the present study were to test whether the capsaicin induced cough reflex was enhanced when applying the single breath inhalation method in similar groups of patients with symptoms related to odorous chemicals e.g. other persons wearing of perfume; and to investigate to what extent the reporting of lower airway symptoms influenced the cough reflex. Sixteen patients fulfilling Cullen's criteria for multiple chemical sensitivity and 15 eczema patients with airway symptoms elicited by odorous chemicals were compared with 29 age-matched, healthy controls. We measured C5--the capsaicin concentration causing five coughs or more--using the single breath inhalation test. No difference was found between groups in age, body mass index or pulmonary function. The median C5 were 129 micromol/L (control group), 48 micromol/L (multiple chemical sensitivity patients), 32 micromol/L (eczema patients). The reporting of lower airway symptoms from odorous chemicals was significantly (p<0.05) correlated to increased cough reflex sensitivity to capsaicin, independent of patient group or co-existence of asthma. The results suggest that the C5 is not reliable for diagnosing MCS but C5 can be used to verify presence of lower airway symptoms related to odorous chemicals.

TRPA1 agonists evoke coughing in guinea pig and human volunteers

RATIONALE

Cough is the most frequent reason for consultation with a family doctor, or with a general or respiratory physician. Treatment options are limited and one meta-analysis concluded that over-the-counter remedies are ineffective. There is also increasing concern about their use in children. Environmental irritants such as air pollution and cigarette smoke are thought to evoke cough by stimulating airway sensory nerves; however, how this occurs is not fully understood.

OBJECTIVES

We hypothesized that the TRPA1 (transient receptor potential cation channel, subfamily A, member 1) receptor may have a role as a novel target for tussive agents given that many potential irritants have been shown to activate this channel.

METHODS

We investigated the effect of TRPA1 ligands on vagal sensory nerve activity in vitro and in guinea pig and human tussive challenge models.

MEASUREMENTS AND MAIN RESULTS

We demonstrated that TRPA1 agonists such as acrolein activate cloned human TRPA1 channels in HEK293 cells and also vagal sensory nerves in murine, guinea pig, and human tissues. A role for TRPA1 was confirmed, using specific inhibitors and tissue from Trpa1(-/-) gene-deleted animals. Finally, TRPA1 ligands evoked reproducible tussive responses in both a guinea pig model and normal volunteers.

CONCLUSIONS

This study identifies the TRPA1 receptor as a promiscuous receptor, activated by a wide range of stimuli, making it a perfect target for triggering cough and as such one of the most promising targets currently identified for the development of antitussive drugs.

Clinical cough III: measuring the cough response in the laboratory

As interest in clinical cough research grows, measurement of cough reflex sensitivity will assume an increasingly important role. With proper equipment and meticulous attention to methodological details, cough reflex sensitivity can be safely, accurately, and reproducibly determined. Such precise measurement allows the evaluation of the effect of pharmacological or nonpharmacological interventions on the sensitivity of the cough reflex, or the comparison of cough reflex sensitivity between different subject populations. In addition to the method, other vital components of optimal cough challenge testing include proper interpretation of data and appropriate selection of study populations.

Capsaicin provocation using two different inhalation devices

BACKGROUND

Sensory hyperreactivity (SHR) has been suggested as one explanation for chemically induced airway symptoms; it can be diagnosed with a capsaicin inhalation test. Previous capsaicin inhalation studies of SHR have used a Pari Boy device. This model of inhalator device has become outdated, hence it is necessary to abandon it in favour of a new device. The aim of this study was to transfer the capsaicin inhalation test using the Pari Boy device to a corresponding model using the Maxin MA3 device.

METHODS

Twenty-one patients with SHR and 44 healthy controls visited the clinic twice and underwent a randomised protocol. The participants were provoked with saline and capsaicin using one of two devices, Pari Boy and Maxin MA3. Eight patients also underwent two additional capsaicin provocations with Maxin MA3. A new series of capsaicin concentrations was chosen for Maxin MA3. The results from each device were analysed, the agreement between the two devices and the repeatability of the Maxin MA3 were evaluated.

RESULTS

Among all participants, the mean number of coughs with the Pari Boy was 5.5 (95% CI: 2.7; 8.2) after inhalation of 0.4 micromol/L capsaicin and 20.0 (95% CI: 14.1; 25.9) after 2.0 micromol/L. With the Maxin MA3, the mean number of coughs was 3.6 (95% CI: 1.3; 4.0) after 0.06 micromol/L capsaicin, and 17.8 (95% CI: 12.0; 23.6) after 0.3 micromol/L. The Maxin MA3 showed good repeatability and the agreement between the devices with the capsaicin concentrations chosen for each device was considered to be good.

Assessment of antitussive efficacy of dextromethorphan in smoking related cough: objective vs. subjective measures

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

Dextromethorphan is widely used as a cough suppressant in over the counter medications. Its efficacy in altering cough reflex sensitivity has been shown in healthy volunteers. In contrast evidence for an effect on clinically important cough is poor.

WHAT THIS STUDY ADDS

A significant decrease in evoked cough was seen with dextromethorphan compared with placebo. However, both placebo and active treatment improved subjective data to a similar degree. We doubt the validity of currently used objective tests in the investigation of antitussives.

AIMS

Using an established model of smokers cough we measured the antitussive effects of dextromethorphan compared with placebo.

METHODS

The study was a randomized, double-blind placebo controlled, crossover comparison of 22 mg 0.8 ml(-1) dextromethorphan delivered pregastrically with matched placebo. Objective and subjective measurements of cough were recorded. Subjective measures included a daily diary record of cough symptoms and the Leicester quality of life questionnaire. Cough frequency was recorded using a manual cough counter. The objective measure of cough reflex sensitivity was the citric acid, dose-response cough challenge.

RESULTS

Dextromethorphan was significantly associated with an increase in the concentration of citric acid eliciting an average of two coughs/inhalation (C2) when compared with placebo, 1 h post dose by 0.49 mM (95% CI 0.05, 0.45, geometric mean 3.09) compared with placebo 0.24 mM (geometric mean 1.74) P < 0.05 and at 2 h 0.57 mM (95% CI 0.01, 0.43, geometric mean 3.75) compared with placebo 0.34 mM (geometric mean 2.19) P < 0.05). There was a highly significant improvement in the subjective data when compared with baseline. However, there was no significant difference between placebo and active treatment. No correlation was seen between cough sensitivity to citric acid and recorded cough counts or symptoms. When both subjective and objective data were compared with screening data there was evidence of a marked 'placebo' effect.

CONCLUSIONS

The objective measure of cough sensitivity demonstrates dextromethorphan effectively diminishes the cough reflex sensitivity. However, subjective measures do not support this. Other studies support these findings, which may represent a profound sensitivity of the cough reflex to higher influences.

Cough and its importance in COPD

Patients with COPD most frequently complain of breathlessness and cough and these are both increased during exacerbations. Studies have generally focused on quality of life during end-stage disease, where breathlessness becomes dominant and cough less important. There are very little data on the frequency and severity of cough in COPD or its impact on quality of life at different stages of disease. Little is known about the factors that influence objective cough counts in COPD. Cough may be a marker for progressive disease in milder COPD patients who continue to smoke, and it may be useful in case-finding for milder disease in the community. The cough reflex sensitivity is heightened in COPD compared with healthy volunteers and similar to that in subjects with asthma. The degree of airflow obstruction does not predict cough reflex sensitivity or objective cough counts, implying an independent process. Effective treatments for cough in COPD have not yet been identified. Improved outcome measures of cough, a better understanding of cough in the natural history of COPD, and its importance to patients are needed.

Cough reflex and oral chemesthesis induced by capsaicin and capsiate in healthy never-smokers

Background

Many tussive agents are components of foods, but little is known about the relationship between cough reflex and oral chemesthesis sensitivities. We investigated the relationships between cough reflex and oral chemesthesis in individuals using two transient receptor potential vanilloid 1 (TRPV1) agonists with different potencies: capsaicin and capsiate.

Methods

Twenty-eight healthy never-smokers were allocated to evaluate cough and oral chemesthesis of capsinoids. Cough reflex sensitivities are estimated by the lowest concentrations generating five coughs by each TRPV1 agonist inhalation. Oral chemesthesis sensitivities are estimated by the lowest concentrations which generate a hot sensation when filter paper loaded with each TRPV1 agonist is placed on the tongue.

Results

There were strong correlations between capsaicin- and capsiate-induced cough reflex sensitivities, and between capsaicin- and capsiate-induced oral chemesthesis sensitivities. However, there were no significant correlations between cough reflex and oral chemesthesis sensitivities induced by both capsaicin and capsiate. The cough reflex sensitivities are significantly greater in females than in males whereas there were no gender differences in oral chemesthesis.

Conclusion

The results showed that the sensitivities of sensory afferents were different between cough reflex and oral chemesthesis, suggesting that TRPV1 sensitivities differ between organs within healthy individuals. Capsiate could be a tussigen for the cough challenge test.