Mechanisms of cough

Levodropropizine for children and adolescents with acute post-viral cough: an evidence-based choice

Acute post-viral cough is a common symptom, usually mild-moderate and self-resolving. However, acute cough may be particularly annoying, affecting sleep, and quality of life, also of the family. Thus, treatment is deemed necessary. Antitussive remedies may be pharmacological or non-pharmacological. Antitussive drugs are either central or peripheral. Central drugs are burdened with significant side effects and can cause abuse, especially in adolescents. Levodropropyzine, on the other hand, is an effective peripheral drug, as demonstrated by two meta-analyses, and has an optimal safety profile. Non-pharmacological remedies tend to be safe, but few substances have a documented degree of efficacy. Therefore, when managing children and adolescents with a post-viral cough, the practical approach may be based on levodropropizine use, which is preferable when the cough is particularly persistent and disturbs sleep.

Neuromodulators in Acute and Chronic Cough in Children: An Update from the Literature

Cough is one of the most common reasons leading to pediatric consultations, negatively impacting the quality of life of patients and caregivers. It is defined as a sudden and forceful expulsion of air from the lungs through the mouth, typically triggered by irritation or the stimulation of sensory nerves in the respiratory tract. This reflex is controlled by a neural pathway that includes sensory receptors, afferent nerves, the brainstem's cough center, efferent nerves, and the muscles involved in coughing. Based on its duration, cough in children may be classified as acute, lasting less than four weeks, and chronic, persisting for more than four weeks. Neuromodulators have shown promise in reducing the frequency and severity of cough by modulating the neural pathways involved in the cough reflex, although they require careful monitoring and patient selection to optimize the outcomes. This review aims to examine the rationale for using neuromodulators in the management of cough in children.

Patient-reported experiences with refractory or unexplained chronic cough: a qualitative analysis

BACKGROUND

Chronic cough, defined as a cough lasting 8 or more weeks, affects up to 10% of adults. Refractory chronic cough (RCC) is a cough that is uncontrolled despite comprehensive investigation and treatment of comorbid conditions while unexplained chronic cough (UCC) is a cough with no identifiable cause despite extensive evaluation of comorbid conditions. RCC and UCC are often poorly controlled. Understanding individuals' lived experience of the symptoms and impacts of these conditions may guide therapeutic strategies.

OBJECTIVES

The primary objectives of this study were to assess respondents' perceptions of the key symptoms of RCC and UCC and the impacts of RCC and UCC and their symptoms on well-being, health-related quality of life, work productivity, and social relationships.

DESIGN

Qualitative study.

METHODS

This study enrolled 30 adults with physician-diagnosed RCC or UCC. Two trained qualitative researchers conducted individual, in-depth telephone interviews using a semi-structured interview guide. Interviews were audio-recorded, transcribed, coded, and systematically analyzed to identify content themes.

RESULTS

A total of 15 respondents with RCC and 15 with UCC were included in the study. Many respondents had RCC or UCC for a long duration (median 9 years, range: 0-24). Half of the respondents reported having a coughing episode at least once daily. Only 40% of respondents reported that medication had improved their symptoms. In over half of the respondents, RCC or UCC hindered communication, caused embarrassment, frustration, and worry, and lowered quality of life. Perceptions of meaningful treatment benefits in RCC or UCC varied widely across respondents.

CONCLUSION

RCC and UCC remained poorly managed in many individuals and were associated with a wide range of symptoms and cough triggers that hindered daily activities and reduced emotional well-being. Understanding individuals' lived experiences may inform the development of RCC and UCC therapeutic strategies.

Spontaneous Expulsion of Foreign Body Bronchus: Understanding the Mechanism

Foreign Body (FB) aspiration pose a challenge to the otolaryngologist of its early diagnosis along with safe removal. Almost all airway foreign bodies require bronchoscopy and removal. Very rarely, spontaneous expulsion of bronchial FB may happen. We are reporting one such case of spontaneous expulsion of a metallic FB from right main bronchus in a fourteen-year-old boy. The mainstay of treatment for FB bronchus is bronchoscopic removal. Spontaneous expulsion occurs very rarely & may be associated with life threatening complications. Impaction of FB in sub glottis may lead to sudden choking & death. In this report we also have tried to provide insight into the physics and physiological mechanism facilitating spontaneous expulsion of a bronchial foreign body.

Pharmacological activities and pharmacokinetics of liquiritin: A review

ETHNOPHARMACOLOGICAL RELEVANCE

Liquiritin is a flavonoid derived from Radix et Rhizoma Glycyrrhizae, which is a widely used traditional Chinese medicine with the effects of invigorating spleen qi, clearing heat, resolving toxins, and dispelling phlegm to stop coughs.

AIM OF THE STUDY

In this review,the pharmacokinetics and pharmacological activities of liquiritin have been summarized.

MATERIALS AND METHODS

The information on liquiritin up to 2021 was collected from PubMed, Web of Science, Springer Link, and China National Knowledge Infrastructure databases. The key words were "liquiritin", "nerve", "tumor", "cardiac", etc. RESULTS: The absorption mechanism of liquiritin conforms to the passive diffusion and first-order kinetics while with low bioavailability. Liquiritin can penetrate the blood-brain-barrier. Besides, liquiritin displays numerous pharmacological effects including anti-Alzheimer's disease, antidepressant, antitumor, anti-inflammatory, cardiovascular protection, antitussive, hepatoprotection, and skin protective effects. In addition, the novel preparations, new pharmacological effects,and cdusafty of liquiritin are also discussed in this review.

CONCLUSION

This review provides a comprehensive state of knowledge on the pharmacokinetics and pharmacological activities of liquiritin, and makes a forecast for its research directions and applications in clinic.

Deep neuromuscular block for minimally invasive lung surgery: a protocol for a systematic review with meta-analysis and trial sequential analysis

INTRODUCTION

Minimally invasive lung surgery (MILS) gradually became the primary surgical therapy for lung cancer, which remains the leading cause of cancer death. Adequate muscle relaxation by deep neuromuscular block (NMB) is particularly necessary for MILS to provide a satisfactory surgical field. However, deep NMB for MILS remains controversial, as one-lung ventilation may provide an acceptable surgical field. Then, we will perform a protocol for a systematic review and meta-analysis to identify the efficacy of deep NMB for MILS.

METHODS AND ANALYSIS

We will search the PubMed, Cochrane Library, Embase, Ovid Medline, Web of Science, Chinese BioMedical Literature, China National Knowledge Infrastructure, VIP and Wanfang databases from inception to March 2022 to identify randomised controlled trials of adult participants undergoing MILS with deep NMB. Studies published in English or Chinese will be considered. The primary outcome will be the surgical conditions according to the surgeon's perspective. Secondary outcomes will be the incidence of perioperative events and perioperative mortality. Heterogeneity will be assessed by the χ² test and I² statistic. Data will be synthesised by both a fixed-effect and a random-effects meta-analysis, with an intention to present the random-effects result if there is no indication of funnel plot asymmetry. Otherwise, metaregression will be used. The Cochrane risk-of-bias tool, trial sequential analysis and Grading of Recommendations Assessment, Development and Evaluation will be used to assess the evidence quality and control the risks of random errors. Funnel plots and Egger's regression test will be used to assess publication bias.

ETHICS AND DISSEMINATION

Ethical approval was not required for this systematic review protocol. The results will be disseminated through peer-reviewed publications.

PROSPERO REGISTRATION NUMBER

CRD42021254016.

Therapeutic applications of capsaicin in humans to target conditions of the respiratory system: A scoping review

BACKGROUND

Various studies have explored potential therapeutic applications of capsaicin in human medicine, for example in pain, obesity, cancer, cardiovascular and respiratory disease. The aim of this scoping review was to identify and chart available evidence on therapeutic applications of capsaicin in humans using any mode of capsaicin delivery to treat conditions of the respiratory system.

METHODS

Electronic bibliographic databases (Web of Science, PubMed, Medline, ScienceDirect, Embase, Scopus) were searched from inception to 2021 to identify experimental studies reporting clinical outcomes of therapeutic applications of capsaicin. Studies with or without control group published in peer-reviewed journals were included. Animal studies, studies of human cell lines, and physiological proof of concept studies were excluded. Reviewer pairs independently double-screened 2799 search results for inclusion.

RESULTS

Twenty-three original studies were included. Capsaicin has been investigated for the treatment of non-allergic rhinitis (n = 15), nasal polyposis (n = 3), allergic rhinitis (n = 2), unexplained chronic cough (n = 2), and prevention of aspiration pneumonia (n = 1). Modes of delivery included intranasal application (nasal spray, soaked pads, solution), inhalation, ingestion, and aural ointment. Seventeen studies reported positive effects of capsaicin on clinical outcomes for rhinitis, nasal polyposis, chronic cough, and pneumonia. Sixteen studies reported on the safety of capsaicin, with no reports of significant adverse events and overall fair to good patient acceptability.

CONCLUSION

While the evidence identified in this review has limited implications for clinical practice, studies support the general safety of capsaicin as administered in these studies and highlight emerging strands of research and clinical hypotheses which warrant further examination.

WAO-ARIA consensus on chronic cough - Part II: Phenotypes and mechanisms of abnormal cough presentation - Updates in COVID-19

BACKGROUND

Chronic cough can be triggered by respiratory and non-respiratory tract illnesses originating mainly from the upper and lower airways, and the GI tract (ie, reflux). Recent findings suggest it can also be a prominent feature in obstructive sleep apnea (OSA), laryngeal hyperresponsiveness, and COVID-19. The classification of chronic cough is constantly updated but lacks clear definition. Epidemiological data on the prevalence of chronic cough are informative but highly variable. The underlying mechanism of chronic cough is a neurogenic inflammation of the cough reflex which becomes hypersensitive, thus the term hypersensitive cough reflex (HCR). A current challenge is to decipher how various infectious and inflammatory airway diseases and esophageal reflux, among others, modulate HCR.

OBJECTIVES

The World Allergy Organization/Allergic Rhinitis and its Impact on Asthma (WAO/ARIA) Joint Committee on Chronic Cough reviewed the current literature on classification, epidemiology, presenting features, and mechanistic pathways of chronic cough in airway- and reflux-related cough phenotypes, OSA, and COVID-19. The interplay of cough reflex sensitivity with other pathogenic mechanisms inherent to airway and reflux-related inflammatory conditions was also analyzed.

OUTCOMES

Currently, it is difficult to clearly ascertain true prevalence rates in epidemiological studies of chronic cough phenotypes. This is likely due to lack of standardized objective measures needed for cough classification and frequent coexistence of multi-organ cough origins. Notwithstanding, we emphasize the important role of HCR as a mechanistic trigger in airway- and reflux-related cough phenotypes. Other concomitant mechanisms can also modulate HCR, including type2/Th1/Th2 inflammation, presence or absence of deep inspiration-bronchoprotective reflex (lower airways), tissue remodeling, and likely cough plasticity, among others.

Chronic cough in adults

Cough, a defense mechanism for clearing the airways of secretions, exudate, or foreign bodies, may become a troublesome symptom. Chronic cough, one of the most frequent symptoms requiring medical attention, is often not due to identifiable causes in adults. Chronic productive cough defines chronic bronchitis, and thus is present in 100% of these patients, and frequently in patients with bronchiectasis, cystic fibrosis, and chronic infectious respiratory diseases. However, chronic cough is most frequently dry. Thus, chronic cough in adults is a difficult syndrome requiring multidisciplinary approaches, particularly to diagnose and treat the most frequent identifiable causes, but also to decide which patients may benefit by treating the central cough hypersensitivity by neuromodulatory therapy and/or non-pharmacologic treatment (speech pathology therapy). Recent guidelines provide algorithms for diagnosis and assessment of cough severity; particularly chronic cough in adults. After excluding life-threatening diseases, chronic cough due to identifiable causes (triggers and/or diseases), particularly smoking and/or the most frequent diseases (asthma, chronic bronchitis, chronic obstructive pulmonary disease, eosinophilic bronchitis, and adverse reactions to drugs [angiotensin-converting enzyme inhibitors and sitagliptin]) should be treated by avoiding triggers and/or according to guidelines for each underlying disease. In patients with troublesome chronic cough due to unknown causes or persisting even after adequate avoidance of triggers, and/or treatment of the underlying disease(s), a symptomatic approach with neuromodulators and/or speech pathology therapy should be considered. Additional novel promising neuromodulatory agents in clinical development (e.g., P2X3 inhibitors) will hopefully become available in the near future.

Identification of the Molecular Mechanisms of Peimine in the Treatment of Cough Using Computational Target Fishing

Peimine (also known as verticine) is the major bioactive and characterized compound of Fritillariae Thunbergii Bulbus, a traditional Chinese medicine that is most frequently used to relieve a cough. Nevertheless, its molecular targets and mechanisms of action for cough are still not clear. In the present study, potential targets of peimine for cough were identified using computational target fishing combined with manual database mining. In addition, protein-protein interaction (PPI), gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were performed using, GeneMANIA and Database for Annotation, Visualization and Integrated Discovery (DAVID) databases respectively. Finally, an interaction network of drug-targets-pathways was constructed using Cytoscape. The results identified 23 potential targets of peimine associated with cough, and suggested that MAPK1, AKT1 and PPKCB may be important targets of pemine for the treatment of cough. The functional annotations of protein targets were related to the regulation of immunological and neurological function through specific biological processes and related pathways. A visual representation of the multiple targets and pathways that form a network underlying the systematic actions of peimine was generated. In summary, peimine is predicted to exert its systemic pharmacological effects on cough by targeting a network composed of multiple proteins and pathways.

Upper Respiratory Tract Infection-Associated Acute Cough and the Urge to Cough: New Insights for Clinical Practice

Upper respiratory tract infection (URTI)-associated acute cough is the most common symptom both in children and adults worldwide and causes economic and social problems with significant implications for the patient, the patient's family, and the health care system. New pathogenic mechanisms in acute cough, including the urge to cough (UTC) mechanisms, have been recently identified. The brainstem neural network, pharyngeal sensory innervation, airway mechanical stimulation, inflammatory mediators, and postnasal drip actively participate in the onset and maintenance of acute cough and the urge to cough phenomenon. However, there is still no effective pharmacological treatment capable of interfering with the pathophysiologic mechanisms involved in URTI-associated acute cough. Moreover, severe adverse events frequently occur in administering such cough medications, mainly in children. New evidence has been provided concerning polysaccharides, resins, and honey as potential cough relievers with high antitussive efficiency, effect on the UTC, and minimal side effects.

Immune system in the pathogenesis of chronic cough

Chronic cough is a common symptom of various chronic diseases. However, the vast majority of individuals with conditions that are commonly associated with cough, such as asthma and GERD, do not have chronic cough. This implies that cough reflex sensitivities differ among individuals. It is known that in the pathogenesis of cough, the nervous system plays a vital role. Recently more information about the role of the immune system and its interaction with the nervous system in the pathogenesis of cough has appeared in the literature. The aim of this article is to review the most recent data about the role of the immune system in the pathogenesis of chronic cough.

An approach to the child with a wet cough

When children have a wet cough, it suggests the presence of secretions in their airways. This often has an infectious aetiology which is usually a self-limiting viral infection requiring no investigation or treatment. In those with acute wet cough it is, however, important to identify features suggestive of community acquired pneumonia or an inhaled foreign body as these causes require specific management. When there is chronic wet cough, the most common diagnoses are protracted bacterial bronchitis (PBB) and bronchiectasis. The relationship between these two conditions is complex as the development of bronchiectasis manifests as a clinical continuum in which the early features of which are indistinguishable from PBB. It is therefore important to identify PBB and chronic cough endotypes which are associated with an increased risk of bronchiectasis. This article offers a pragmatic approach to the investigation and treatment of children with wet cough. It is hoped this will limit unnecessary investigations whist aiding the prompt diagnosis of conditions needing treatment to reduce symptom burden and prevent further lung damage.

Comparison of deep or moderate neuromuscular blockade for thoracoscopic lobectomy: a randomized controlled trial

Background

Laparoscopic surgery typically requires deep neuromuscular blockade (NMB), but whether deep or moderate NMB is superior for thoracoscopic surgery remains controversial.

Methods

Patients scheduled for thoracoscopic lobectomy under intravenous anesthesia were randomly assigned to receive moderate [train of four (TOF) 1–2] or deep NMB [TOF 0, post-tetanic count (PTC) 1–5]. Depth of anesthesia was controlled at a Narcotrend rating of 30 ± 5 in both groups. The primary outcome was the need to use an additional muscle relaxant (cisatracurium) during surgery. Secondary outcomes included surgeon satisfaction, recovery time of each stage after drug withdrawal [time from withdrawal until TOF recovery to 20% (antagonists administration), 25, 75, 90, 100%], blood gas data, VAS pain grade after extubation, the time it takes for patients to begin walking after surgery, postoperative complications and hospitalization time. Results were analyzed on an intention-to-treat basis.

Results

Thirty patients were enrolled per arm, and all but one patient in each arm was included in the final analysis. Among patients undergoing moderate NMB, surgeons applied additional cisatracurium in 8 patients because of body movement and 5 because of coughing (13/29, 44.8%). Additional cisatracurium was not applied to any of the patients undergoing deep NMB (p < 0.001). Surgeons reported significantly higher satisfaction for patients undergoing deep NMB (p < 0.001, Wilcoxon rank sum test). The mean difference between the two groups in the time from withdrawal until TOF recovery of 25% or 90% was 10 min (p < 0.001). The two groups were similar in other recovery data, blood gas analysis, VAS pain grade, days for beginning to walk and mean hospitalization time.

Conclusions

Deep NMB can reduce the use of additional muscle relaxant and increase surgeon satisfaction during thoracoscopic lobectomy.

Trial registration

Chinese Clinical Trial Registry, ChiCTR-IOR-15007117, 22 September 2015.

Association of cough hypersensitivity with tracheal TRPV1 activation and neurogenic inflammation in a novel guinea pig model of citric acid-induced chronic cough

Objective

This study was performed to establish a novel model of citric acid-induced chronic cough in guinea pigs and to investigate the pathogenesis of cough hypersensitivity.

Methods

Healthy conscious guinea pigs inhaled citric acid (0.4 M) for 3 minutes twice daily for 25 days. Cough reactivity was evaluated, substance P (SP) and calcitonin gene-related peptide (CGRP) in bronchoalveolar lavage fluid were detected, and transient receptor potential cation channel subfamily V member 1 (TRPV1) protein expression in the trachea and bronchus was determined. Tracheal and bronchial tissues were examined for TRPV1.

Results

Inhalation of 0.4 M citric acid increased coughing in a time-dependent manner: coughing peaked at 15 days and reached the lowest level at 25 days. This was accompanied by similar changes in SP, CGRP, and TRPV1 protein expression. TRPV1 was mainly observed in the mucosal and submucosal layer of the trachea and bronchi. The areas of TRPV1 positivity in the trachea and bronchi of citric acid-treated animals were significantly larger than in the control group.

Conclusions

Repeated inhalation of citric acid can be employed to establish a chronic cough model in guinea pigs. Cough hypersensitivity in this model is related to tracheal TRPV1 activation and neurogenic inflammation.

Reliability and Validity of the Swedish Version of the Hull Airway Reflux Questionnaire (HARQ-S)

Introduction

Cough is a common symptom for which patients seek medical care and is defined as chronic if it has lasted for more than 8 weeks. The Hull Airway Reflux Questionnaire (HARQ) was developed with the aim of eliciting the major component of chronic cough. It comprises 14 items with a maximum total score of 70. A Swedish version (HARQ-S) has previously been developed but not yet formally validated. The aim of the present study was to validate the HARQ-S in terms of instrumental reliability and concurrent validity.

Methods

A total of 67 consecutively selected non-smoking patients with chronic cough and 91 non-smoking allegedly healthy controls were asked to answer two questionnaires, the HARQ-S and a local questionnaire, at two occasions about 3 weeks apart.

Results

The HARQ-S showed good psychometric properties. The patients had significantly higher total scores (p < 0.001) compared to the controls, and the questionnaire showed outstanding discrimination ability to distinguish between patients and controls, with an area under the receiver operating characteristic curve of 0.99. Fifty patients and 77 controls completed the HARQ-S twice, showing good test–retest agreement in all items as well as in the total scores in both groups, and without any significant differences over time.

Conclusion

The Swedish version of the HARQ is a valid and reliable questionnaire with good agreement between the two measurements in both patients and controls. The HARQ-S has good reliability and validity and can be used as a diagnostic tool in Swedish-speaking patients with chronic cough.

TRPV1 and TRPM8 in Treatment of Chronic Cough

Chronic cough is common in the population, and among some there is no evident medical explanation for the symptoms. Such a refractory or idiopathic cough is now often regarded as a neuropathic disease due to dysfunctional airway ion channels, though the knowledge in this field is still limited. Persistent coughing and a cough reflex easily triggered by irritating stimuli, often in combination with perceived dyspnea, are characteristics of this disease. The patients have impaired quality of life and often reduced work capacity, followed by social and economic consequences. Despite the large number of individuals suffering from such a persisting cough, there is an unmet clinical need for effective cough medicines. The cough treatment available today often has little or no effect. Adverse effects mostly follow centrally acting cough drugs comprised of morphine and codeine, which demands the physician's awareness. The possibilities of modulating airway transient receptor potential (TRP) ion channels may indicate new ways to treat the persistent cough "without a reason". The TRP ion channel vanilloid 1 (TRPV1) and the TRP melastin 8 (TRPM8) appear as two candidates in the search for cough therapy, both as single targets and in reciprocal interaction.

Novel montelukast sodium-loaded stable oral suspension bioequivalent to the commercial granules in rats

To develop a montelukast sodium-loaded stable oral suspension bioequivalent to the commercial granules in rats, several montelukast sodium-loaded suspensions were prepared with a suspending agent, stabilizers and anti-aggregation agents, and their stabilities were investigated by visually observing the sedimentation phenomenon and determining the concentration of the degradation product. Moreover, dissolution and pharmacokinetic studies of the optimized formulation were examined in rats compared to commercial montelukast sodium-loaded granules. Avicel RC-591 (Avicel), a suspending agent, prevented the sedimentation of these suspensions at >2.496 (w/v) per cent composition. Amongst the stabilizers tested, fumaric acid provided the lowest concentration of montelukast sulphoxide (a degradation product) in these suspensions at 40 °C, demonstrating its excellent stabilizing activity. Furthermore, as an anti-aggregation agent, glycerin gave lower amounts of degradation product than those with poloxamer 407 and Tween 80. In particular, montelukast-loaded oral suspension, an aqueous suspension containing montelukast sodium/Avicel/fumaric acid/glycerin at a concentration of 312/2496/15.6/62.4 (mg/100 ml), and the commercial granules exhibited similar dissolution profiles in 0.5% (w/v) aqueous solution of sodium lauryl sulphate. Moreover, the pharmacokinetics in rats provided by this suspension was comparable to that of the commercial granules, suggesting that they were bioequivalent. In addition, it was physically and chemically stable at 40 °C for at least 6 months. Thus, this montelukast sodium-loaded oral suspension, with bioequivalence to the commercial granules and excellent stability, could be a prospective dosage form for the treatment of asthma.

Airway Hypersensitivity, Reflux, and Phonation Contribute to Chronic Cough

BACKGROUND & AIMS

Although chronic cough is common, its etiology is often elusive, making patient management a challenge. Gastroesophageal reflux and airway hypersensitivity can cause chronic cough. We explored the relationship between reflux, phonation, and cough in patients with idiopathic chronic cough.

METHODS

We performed a blinded, cross-sectional study of nonsmoking patients with chronic cough (duration, >8 weeks) refractory to reflux treatment referred to the Digestive Disease Center at Vanderbilt University. All underwent 24-hour acoustic recording concurrently and temporally synchronized with ambulatory pH-impedance monitoring. Cough, phonation, and pH-impedance events were recorded. We evaluated the temporal relationship between cough and phonation or reflux events using Poisson and logistic regression.

RESULTS

Seventeen patients met the inclusion criteria (88% female; 100% white; median age, 63 years [interquartile age range, 52-66 years]; mean body mass index, 30.6 [interquartile range, 27.9-34.0]); there were 2048 analyzable coughing events. The probability of subsequent coughing increased with higher burdens of preceding cough, reflux, or phonation. Within the first 15 minutes after a cough event, the cough event itself was the main trigger of subsequent cough events. After this period, de novo coughing occurred with increases of 1.46-fold in association with reflux alone (95% confidence interval, 1.17-1.82; P < .001) and 1.71-fold in association with the combination of phonation and reflux events.

CONCLUSIONS

Antecedent phonation and reflux increased the rate of cough events in patients with idiopathic chronic cough. Reflux events were more strongly associated with increased rate of coughing. Our findings support the concept that airway hypersensitivity is a cause of chronic cough, and that the vocal folds may be an effector in chronic cough ClinicalTrials.gov number: NCT01263626.

Diagnosis of asthma - new theories

INTRODUCTION

Recent studies have shown a remarkably high frequency of poorly controlled asthma. Several reasons for this treatment failure have been discussed, however, the basic question of whether the diagnosis is always correct has not been considered. Follow-up studies have shown that in many patients asthma cannot be verified despite ongoing symptoms. Mechanisms other than bronchial obstruction may therefore be responsible. The current definition of asthma may also include symptoms that are related to mechanisms other than bronchial obstruction, the clinical hallmark of asthma.

AIM

Based on a review of the four cornerstones of asthma - inflammation, hyperresponsiveness, bronchial obstruction and symptoms - the aim was to present some new aspects and suggestions related to the diagnosis of adult non-allergic asthma.

CONCLUSION

Recent studies have indicated that "classic" asthma may sometimes be confused with asthma-like disorders such as airway sensory hyperreactivity, small airways disease, dysfunctional breathing, non-obstructive dyspnea, hyperventilation and vocal cord dysfunction. This confusion may be one explanation for the high proportion of misdiagnosis and treatment failure. The current diagnosis, focusing on bronchial obstruction, may be too "narrow". As there may be common mechanisms a broadening to include also non-obstructive disorders, forming an asthma syndrome, is suggested. Such broadening requires additional diagnostic steps, such as qualitative studies with analysis of reported symptoms, non-effort demanding methods for determining lung function, capsaicin test for revealing airway sensory hyperreactivity, careful evaluation of the therapeutic as well as diagnostic effect of corticosteroids and testing of suggested theories.

TRP channels and temperature in airway disease-clinical significance

Temperatures above and below what is generally regarded as "comfortable" for the human being have long been known to induce various airway symptoms, especially in combination with exercise in cold climate with temperatures below 0°C, which is naturally since exercise is followed by enhanced ventilation and thus greater amounts of inhaled cold air. The aim was to highlight the knowledge we have today on symptoms from the airways (here also including the eyes) arisen from various temperatures; the mechanisms, the pathophysiology and their clinical significance. The most common eye and airway conditions related to temperature changes are dry eye disease, rhinitis, laryngeal dysfunction, asthma, chronic obstructive pulmonary disease and chronic cough. Transient receptor potential (TRP) ion channels are probably involved in all temperature induced airway symptoms but via different pathways, which are now beginning to be mapped out. In asthma, the most persuasive hypothesis today is that cold-induced asthmatic bronchoconstriction is induced by dehydration of the airway mucosa, from which it follows that provocations with osmotic stimuli like hypertonic saline and mannitol can be used as a surrogate for exercise provocation as well as dry air inhalation. In chronic unexplained cough there seems to be a direct influence of cold air on the TRP ion channels followed by coughing and increased cough sensitivity to inhaled capsaicin. Revelations in the last decades of the ability of several airway TRP ion channels to sense and react to ambient air temperature have opened new windows for the understanding of the pathogenesis in a diversity of airway reactions appearing in many common respiratory diseases.

Chronic cough: from a complex dysfunction of the neurological circuit to the production of persistent cough

Chronic cough or cough that lasts more than 8 weeks, once a chest x-ray and spirometry are confirmed normal, is caused by an alteration in a section of the route between peripheral receptors, mainly in the upper and lower airway and oesophagus, spinal cord and the cough centre in the brain stem involving the cortex. These mechanisms of cough have their homology in the circuit of chronic pain, and on that basis, should expand future research of chronic cough. Clinically chronic cough is easy to diagnose by an excessive response or hypertussia to low-intensity stimuli or banal stimuli, which we now call hypersensitivity cough syndrome, quantified by a positive reflex cough with capsaicin or citric acid. However, hypersensitivity cough syndrome can be impossible to quantify in the laboratory when the hyper-responsiveness originates in the central nervous system. This is normally caused by excessive peripheral input or convergence of stimuli from different sources. Once central hypersensitivity is acquired, peripheral input is not as important for activation of the cough.