BRONCHOCONSTRICTION-TRIGGERED COUGH IN CONSCIOUS GUINEA PIGS

Prevalence and causes of chronic cough in Japan

BACKGROUND

Chronic cough is one of the most common symptoms of respiratory diseases and can adversely affect patients' quality of life and interfere with social activities, resulting in a significant social burden. A survey is required to elucidate the frequency and treatment effect of chronic cough. However, clinical studies that cover all of Japan have not yet been conducted.

METHODS

Patients who presented with a cough that lasted longer than 8 weeks and visited the respiratory clinics or hospitals affiliated with the Japan Cough Society during the 2-year study period were registered.

RESULTS

A total of 379 patients were enrolled, and those who did not meet the definition of chronic cough were excluded. A total of 334 patients were analyzed: 201 patients had a single cause, and 113 patients had two or more causes. The main causative diseases were cough variant asthma in 92 patients, sinobronchial syndrome (SBS) in 36 patients, atopic cough in 31 patients, and gastroesophageal reflux (GER)-associated cough in 10 patients. The time required to treat undiagnosed patients and those with SBS was significantly longer and the treatment success rate for GER-associated cough was considerably poor.

CONCLUSIONS

We confirmed that the main causes of chronic cough were cough variant asthma, SBS, atopic cough, and their complications. We also showed that complicated GER-associated cough was more likely to become refractory. This is the first nationwide study in Japan of the causes and treatment effects of chronic cough.

Bronchial thermoplasty improves cough hypersensitivity and cough in severe asthmatics

BACKGROUND

Cough is a troublesome symptom of asthma because it is associated with disease severity and poor asthma control. Bronchial thermoplasty (BT) may be effective in improving cough severity and cough-related quality of life in severe uncontrolled asthma.

OBJECTIVE

To evaluate the efficacy of BT for cough in severe uncontrolled asthma.

METHODS

Twelve patients with severe uncontrolled asthma were enrolled in this study between 2018 May and March 2021 and arbitrarily divided into cough-predominant [cough severity Visual Analog Scale (VAS) ≥ 40 mm, n = 8] and typical asthma (cough VAS <40 mm, n = 4) groups. Clinical parameters, such as capsaicin cough sensitivity [C-CS: the concentrations to inhaled capsaicin required to induce at least two (C2) and five (C5) coughs], lung function, and type-2-related biomarkers (fractional nitric oxides and absolute eosinophil counts) and cough-related indices [cough severity VAS and the Leicester Cough Questionnaire (LCQ)] were evaluated before and 3 months after performing BT.

RESULTS

BT significantly improved both cough-related indices and C-CS in the cough-predominant group. Changes in C-CS were significantly correlated with changes in the LCQ scores (C5: r = 0.65, p = 0.02 for all patients, and r = 0.81, p = 0.01 for the cough-predominant group).

CONCLUSIONS

BT may be effective for cough in severe uncontrolled asthma by improving C-CS. However, further larger cohort studies are necessary to confirm the effect of BT for cough in asthma.

CLINICAL TRIAL REGISTRATION

This study was registered in the UMIN Clinical Trials Registry (Registry ID UMIN: 000031982).

Narrative Review of the Mechanisms and Treatment of Cough in Asthma, Cough Variant Asthma, and Non-asthmatic Eosinophilic Bronchitis

Chronic cough is a debilitating condition affecting 10-12% of the general population and is one of the leading causes for referral to secondary care. Many conditions have been associated with chronic cough, including asthma, gastro-esophageal reflux disease and upper airways cough syndrome. Inflammatory airway conditions including cough variant asthma (CVA) and non-asthmatic eosinophilic bronchitis (NAEB) contribute to a significant proportion of presentations with chronic cough, with differing diagnostic criteria and different responses to commonly used asthma therapy for their respective diagnoses. Mechanistic studies in both animal models and humans have identified increased neuronal sensitivity and subsequent central sensitization. These mechanisms include inflammatory-mediated nociceptor sensitization and alterations of afferent nerve terminal excitability, phenotypic changes in the vagal afferent neurons over time, and central neuroplasticity resulting from increased synaptic signalling from peripheral afferents. The aim of this review is to discuss the mechanisms, neurophysiology, and management approaches currently available for patients presenting with chronic cough with underlying asthma, CVA, and NAEB and to shed a light on areas of further research required to elucidate the mechanisms of cough in this patient population.

The Japanese respiratory society guidelines for the management of cough and sputum (digest edition)

Cough and sputum are common complaints at outpatient visits. In this digest version, we provide a general overview of these two symptoms and discuss the management of acute (up to three weeks) and prolonged/chronic cough (longer than three weeks). Flowcharts are provided, along with a step-by-step explanation of their diagnosis and management. Most cases of acute cough are due to an infection. In chronic respiratory illness, a cough could be a symptom of a respiratory infection such as pulmonary tuberculosis, malignancy such as a pulmonary tumor, asthma, chronic obstructive pulmonary disease, chronic bronchitis, bronchiectasis, drug-induced lung injury, heart failure, nasal sinus disease, sinobronchial syndrome, eosinophilic sinusitis, cough variant asthma (CVA), atopic cough, chronic laryngeal allergy, gastroesophageal reflux (GER), and post-infectious cough. Antibiotics should not be prescribed for over-peak cough but can be considered for atypical infections. The exploration of a single/major cause is recommended for persistent/chronic cough. When sputum is present, a sputum smear/culture (general bacteria, mycobacteria), cytology, cell differentiation, chest computed tomography (CT), and sinus X-ray or CT should be performed. There are two types of rhinosinusitis. Conventional sinusitis and eosinophilic rhinosinusitis present primarily with neutrophilic inflammation and eosinophilic inflammation, respectively. The most common causes of dry cough include CVA, atopic cough/laryngeal allergy (chronic), GER, and post-infectious cough. In the last chapter, future challenges and perspectives are discussed. We hope that the clarification of the pathology of cough hypersensitivity syndrome will lead to further development of "pathology-specific non-specific therapeutic drugs" and provide benefits to patients with chronic refractory cough.

Methacholine-induced cough as an indicator of bronchodilator-responsive cough

BACKGROUND

Cough variant asthma (CVA) is the most common cause of chronic cough and responds well to bronchodilator therapy. Previous studies on methacholine -induced cough have shown that heightened cough response due to bronchoconstriction is a feature of CVA. The aim of this study was to assess Mch-induced cough as an indicator of bronchodilator-responsive cough (BRC).

METHODS

This was a single-center retrospective study of prolonged/chronic cough cases who underwent evaluation via spirometry, FeNO and bronchial challenge testing using Mch and capsaicin (C5). Resultant bronchoconstriction after Mch challenge was assessed by flow-volume curves measuring the expiratory flow of the partial flow-volume curve 40% above residual volume (PEF₄₀) and FEV₁. BRC was defined as a decrease in cough with bronchodilator therapy by 30% or more on a visual analog scoring scale.

RESULTS

Of the 100 patients evaluated, 63 were diagnosed with BRC. Mch-induced cough at a decrease in PEF₄₀ of 35% (PC₃₅-PEF₄₀) was predictive of BRC on AUROC analysis with an AUC of 0.82 (95% CI 0.73-0.90) and cut-off of 24. The AUC for C5, FeNO and PC₂₀-FEV₁ were 0.65, 0.47, and 0.58, respectively.

CONCLUSION

Compared to C5, FeNO and PC₂₀-FEV₁, Mch-induced cough better supports a diagnosis of BRC.

Repeated bronchoconstriction attenuates the cough response to bronchoconstriction in naïve guinea pigs

BACKGROUND

Cough variant asthma (CVA) is recognized as a precursor of bronchial asthma (BA). However, the cough response to bronchoconstriction differs between these similar diseases. Repeated bronchoconstriction and the resulting imbalance of endogenous lipid mediators may impact the cough response.

METHODS

We investigated the influence of repeated bronchoconstriction on the cough response to bronchoconstriction using naïve guinea pigs. Bronchoconstriction was induced for 3 consecutive days and changes in the cough response and lipid mediators, such as PGE₂, PGI₂, and cysteinyl-LTs (Cys-LTs), in BAL fluid (BALF) were assessed. We investigated the effect of endogenous PGI₂ on the cough response by employing a PGI₂ receptor antagonist. In order to investigate the cough response over a longer period, we re-evaluated the cough response 2 weeks after repeated bronchoconstriction.

RESULTS

The number of coughs induced by bronchoconstriction were significantly decreased by repeated bronchoconstriction. The levels of PGE₂, PGI₂, and Cys-LTs, and the ratio of PGI₂/PGE₂ were significantly increased, following repeated bronchoconstriction. This decrease in the cough response was suppressed by pretreatment with a PGI₂ receptor antagonist. Two weeks after repeated bronchoconstriction, the cough response returned to the same level as before repeated bronchoconstriction along with a concomitant return of lipid mediators, such as PGE₂, PGI₂, and Cys-LTs and the ratio of PGI₂/PGE₂.

CONCLUSIONS

Our results suggest that repeated bronchoconstriction and the resulting imbalance of endogenous lipid mediators contribute to the difference in cough responses to bronchoconstriction in CVA and BA.

Determinants of response to bronchodilator in patients with cough variant asthma- A randomized, single-blinded, placebo-controlled study

BACKGROUND

Not all patients with cough variant asthma (CVA) show responsiveness to bronchodilators (RB) in clinic. Whether there are specific clinical and pathophysiological features can indicate RB in patients with CVA needs further investigation. Thus, we aimed to investigate the RB in patients with CVA and associated factors.

METHODS

Forty-two CVA patients were randomized in a 2:1 ratio to receive oral bambuterol hydrochloride (10 mg, once daily, for 3 days) or matched placebo, 36 patients (24 with bronchodilator and 12 with placebo) completed the study eventually. RB was considered when cough visual analogue scale (VAS) score decreased 30% or more after 3 days treatment. The baseline clinical and pathophysiological characteristics between patients with RB and patients without RB were compared. CRS was presented with the lowest concentration of capsaicin inducing at least 5 coughing (C5).

RESULTS

The responsive rate of patients with bronchodilator was significantly higher than that with placebo (62.5% vs 16.7%, p < 0.01). Patients with RB showed a significant greater mean decline of FEV₁% predicted after bronchial provocation (26.7% vs 22.4%, p < 0.05) and higher geometric mean of sputum eosinophils (1.37 vs 0.69, p < 0.05) as compared with these without RB. No significant differences in sputum neutrophil, Log C5 were found between patients with RB and patients without RB. There was a moderate correlation between the decline of FEV₁% pred and RB (r_s = 0.443, p < 0.05). The regression analysis showed that nocturnal cough was a predictor of RB (OR, 7.33, 95% CI: 1.11-48.26, p = 0.038). No adverse events were reported by all of the patients after the study.

CONCLUSION

More than one-third of patients with CVA do not respond to bronchodilator treatment, indicating that the response to bronchodilator should not be a diagnostic requirement of CVA. CVA patients with higher airway responsiveness will more likely respond to bronchodilator. Cough of CVA might be elicited by different mechanisms, which suggests that CVA could be divided into two phenotypes according to the response to bronchodilators.

Response to bronchodilator and clinical, pathophysiological features in patients with nonasthmatic eosinophilic bronchitis

INTRODUCTION

Whether nonasthmatic eosinophilic bronchitis (NAEB) shows response to bronchodilator (RB) remains unclear.

OBJECTIVES

To investigate the RB and its relationship with clinical and pathophysiological features in NAEB.

METHODS

Fifty-one patients with NAEB were assigned in a 2:1 ratio to receive oral bambuterol hydrochloride (n = 34, 10 mg, once daily, for 3 days) or matched placebo (n = 17) randomly, of whom 48 patients (32 with bronchodilator and 16 with placebo) completed the study. Sputum induction, spirometry and cough reflex sensitivity were measured. RB was considered when cough Visual analogue scale (VAS) score decreased 30% or more after treatment. Cough reflex sensitivity was defined as the lowest concentration of capsaicin inducing five coughings or more (C5), and presented as Log C5.

RESULTS

The responsive rate of patients with bronchodilator was significantly higher than that with placebo (34.4% vs 6.3%, P < 0.05). The VAS score decreased significantly in patients with bronchodilator (median: 6.0-3.0, P < 0.01). There was a significantly higher median Log C5 (2.7 vs 1.3, P < 0.05), and a higher trend of decline in FEV₁ % predicted and MMEF% predicted after bronchial provocation in patients with RB as compared with patients without RB. No significant differences in baseline percentages of sputum eosinophil were found between patients with RB and that without RB.

CONCLUSIONS

One third of patients with NAEB respond well to bronchodilator treatment, which are related with lower cough reflex sensitivity and increased airway responsiveness. The relationship between NAEB and asthma needs to be investigated further.

Clinical Characteristics of Cough Frequency Patterns in Patients with and without Asthma

BACKGROUND

Cough is a frequent symptom of asthma. Cough frequency (CoFr) monitoring devices are now available to objectively measure cough counts and offer a novel endpoint to assess asthma. However, little is known about CoFr in asthma.

OBJECTIVE

The aims were, first, to determine whether unique features of CoFr exist in asthmatic and nonasthmatic patients and, secondly, to evaluate relationships between CoFr and pathophysiological parameters of asthma.

METHODS

In the current study, 73 asthmatic and 63 nonasthmatic patients suffering from persistent cough were enrolled. At study entry, the Leicester Cough Questionnaire (LCQ health status), cough visual analog scale (VAS), Leicester Cough Monitor (LCM), fractional exhaled nitric oxide (FeNO) measurements, and spirometry were performed. In asthmatic patients, the bronchial hyperresponsiveness (BHR) test was conducted if applicable. In 28 asthmatic and 17 nonasthmatic patients, LCQ, VAS, and LCM were examined before and after treatment.

RESULTS

CoFr during nighttime (asleep) was significantly higher in asthmatic patients than in nonasthmatic patients. Twenty-four-hour CoFr significantly decreased after appropriate treatment and was correlated with changes in VAS and LCQ in all patients. The improvement in cough in asthmatic patients was greater during nighttime than during daytime (awake). CoFr in asthmatic patients was significantly correlated with BHR, but not with FeNO.

CONCLUSIONS

In asthmatic patients, nocturnal CoFr can be associated with BHR, was significantly higher before treatment, but improved more after treatment compared with nonasthmatic patients. Monitoring nocturnal CoFr may provide unique and valuable information on making an early prediction of therapeutic effects in asthma.

Role of prostaglandin I2 in the bronchoconstriction-triggered cough response in guinea pigs

Purpose/Aim of the study: Methacholine chloride (MCh) inhalation causes bronchoconstriction and cough. Following MCh-induced bronchoconstriction, metabolic products of prostaglandin I₂ (PGI₂) increase in bronchoalveolar lavage fluid (BALF), suggesting that PGI₂ plays a role in the cough response. Accordingly, we used an experimental guinea pig model to evaluate the role of PGI₂ in the bronchoconstriction-triggered cough response.

MATERIALS AND METHODS

Experiment 1: The concentration of PGF_1α, a stable metabolite of PGI₂, in BALF was assessed in animals exposed to nebulized MCh and animals exposed to nebulized saline. Experiment 2: Bronchoconstriction and cough were assessed in 3 groups of animals after MCh inhalation (a saline group, low-dose PGI₂ group, and high-dose PGI₂ group). Enhanced pause (Penh) was used as a measure of bronchoconstriction. Experiment 3: Bronchoconstriction and cough were assessed in 3 groups of animals (groups administered saline, a low dose of a specific antagonist of the PGI₂ receptor (IP antagonist), and a high dose of a specific IP antagonist).

RESULTS

The PGF_1α concentration in BALF was significantly higher in the bronchoconstriction group than in the control group. In animals administered high-dose PGI₂, the MCh-induced increase in Penh was significantly suppressed, and the number of coughs induced by bronchoconstriction was significantly decreased. In animals treated with a high dose of an IP antagonist, the MCh-induced increase in Penh was not affected, and the number of coughs increased.

CONCLUSIONS

Our results suggest that PGI₂ ameliorates a bronchoconstriction-triggered cough. The measurement and administration of PGI₂ may assist in the diagnosis and treatment, respectively, of the cough response triggered by bronchoconstriction.

Pattern of Response to Bronchial Challenge with Histamine in Patients with Non-Atopic Cough-Variant and Classic Asthma

Background: The aim of this study was to establish whether non-atopic patients with cough variant asthma (CVA) have different pattern of response to direct bronchoconstrictors than non-atopic patients with classic asthma (CA). Method: A total of 170 patients of both sexes with stable CVA and CA were screened for the study and 153 were included. Patients with proven atopy were not included and 17 patients with worsening of their condition or with verified bronchial obstruction during screening were excluded. All included patients performed spirometry and underwent a bronchial challenge with histamine according to long-standing protocol in our laboratory. Results: Significantly higher frequency of bronchial hyper-responsiveness (BHR) was found in patients with CA than in patients with CVA (63.9% vs. 44.9%, respectively; p < 0.05). Sensitivity was significantly lower in patients with CVA (p < 0.05), while no significant difference was found in maximal response and responsiveness. Only patients with positive challenge tests were included in the analysis. Conclusion: Adult non-atopic patients with CVA and CA have a pattern of response to non-specific bronchial stimuli similar to atopic patients with same conditions, with the exception of similar maximal response, which may reflect the efficacy of previous treatment. We believe that further studies are needed to clarify the mechanisms involved in airway response to non-specific stimuli in CVA and CA, especially in non-atopic patients. Further studies should also clarify whether this response pattern has any implications on clinical presentation or on treatment options.

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.

Role of prostaglandin E2 in bronchoconstriction-triggered cough response in guinea pigs

A feature of cough variant asthma is a heightened cough response to bronchoconstriction. The mediators of this response are unknown. This study was designed to elucidate the role of lipid mediators in bronchoconstriction-triggered cough response in an experimental animal model. We examined the influence of bronchoconstriction on cell components and mediators including prostaglandin E₂ (PGE₂) in bronchoalveolar lavage fluid (BALF). We studied the cough response to bronchoconstriction (CRB) by measuring the correlation between the increase in enhanced pause (Penh), an index of bronchoconstriction, and cough counts induced by methacholine (Mch) inhalation in conscious guinea pigs. We then examined the effects of intraperitoneal pretreatment with 16, 16-dimethyl-prostaglandin E₂ (dm-PGE₂) on CRB and cough counts. The total number of cells and cell components in the BALF were not influenced by bronchoconstriction. While levels of PGE₂, prostaglandin I₂, and cysteinyl leukotrienes were significantly increased, levels of prostaglandin D₂, thromboxane B₂, and substance P in the BALF were not. Dm-PGE₂ significantly decreased the Mch-induced increase in Penh. Following bronchoconstriction by additional Mch inhalation, dm-PGE₂ produced an increase in CRB and cough counts in a dose-dependent manner. Additionally, the heightened CRB following dm-PGE₂ treatment was suppressed by pretreatment with PGE₂ receptor (E-prostanoid EP) -1 and EP-3 antagonists in a dose-dependent manner, but not by EP-2 and EP-4 antagonists. The EP-1 antagonist also decreased cough counts. These results suggest that PGE₂ acts as an exacerbating factor for bronchoconstriction-triggered cough. EP1 and EP3 may provide new therapeutic targets for cough variant asthma.

The measurement of cough response to bronchoconstriction induced by methacholine inhalation in healthy subjects: An examination using the Astograph method

BACKGROUND

We demonstrated that heightened cough response to bronchoconstriction is a fundamental feature of cough variant asthma (CVA). To evaluate this physiological feature of CVA in daily clinical practice, it is necessary to clarify the cough response to bronchoconstriction in healthy subjects. We evaluated cough response to methacholine (MCh)-induced bronchoconstriction in healthy subjects. A forced oscillometry technique was used to measure airway resistance changes with Mch.

METHODS

Healthy never-smokers (21 men, 20 women; mean 22.3 ± 3.7 years) participated. None had a >3-week cough history, clinically significant respiratory or cardiovascular disorders, or disorders that might put subjects at risk or influence the study results or the subjects' ability to participate. Twofold increasing concentrations of Mch chloride diluted in phosphate-buffered saline (0.039 to 160 mg/mL) were inhaled from nebulizers at 1-minute intervals during subjects' tidal breathing after the baseline respiratory resistance (Rrs) was recorded. Mch inhalation continued until Rrs reached twice the baseline value and forced expiratory volume in 1 second (FEV₁) decreased to <90% of baseline value. Spirometry was measured before Mch inhalation and immediately after Rrs had increased twofold. Coughs were counted during and for 30 minutes after Mch inhalation. The cough reflex sensitivity to capsaicin was also examined.

RESULTS

The number of coughs was 11.1 ± 14.3 (median, 7.0; range, 0 to 71; reference range, 0 to 39.7). There was no significant difference in the cough response between the sexes. The reproducibility of the cough response to bronchoconstriction was sufficient. No correlation existed between the bronchoconstriction-induced cough response and capsaicin cough-reflex sensitivity.

CONCLUSIONS

Using the Astograph method, cough response to bronchoconstriction could be measured easily, safely and highly reproducibly in healthy subjects.

Bronchodilator therapy for chronic cough

Experimental studies indicate that airway calibre increases the sensitivity of the afferents involved in the cough reflex but it has proved difficult to demonstrate that airway calibre increases the sensitivity of the afferents involved in the cough reflex. Therefore, bronchodilators might have a role, although rather minor, in the treatment of cough. However, although bronchodilators represent the standard of care in the treatment of airway obstruction associated with asthma or COPD, controversy persists regarding the mechanism(s) by which these agents alleviate cough. Furthermore, the available evidence indicates that the effects of bronchodilators on cough are rather inconsistent in humans and casts doubt on the appropriateness of the common practice of using bronchodilators in the treatment of patients with cough without any other evidence of airway obstruction. Regrettably, appropriate long-term trials specifically aimed at evaluating the clinical efficacy of bronchodilators in pathologic cough have not yet been performed. Therefore, properly executed clinical studies of bronchodilators in various types of acute and chronic pathologic cough are required.

Bronchoconstriction-triggered cough in atopic cough: A retrospective study

BACKGROUND

Atopic cough (AC) and cough variant asthma (CVA) were identified as major causes of chronic non-productive cough in a Japanese study. A characteristic feature of CVA is the presence of a heightened cough response to bronchoconstriction. On the other hand, the cough response to bronchoconstriction in AC remains unclear.

METHODS

Methacholine (Mch)-induced cough in AC was measured and compared with that in CVA. Diagnoses of AC and CVA were made based on patient history, physical examination, response to bronchodilator therapy, cough reflex sensitivity to capsaicin, spirometry, and airway responsiveness to methacholine.

RESULTS

Thirteen AC patients and 12 CVA patients in whom the criteria were met were recruited to the study. After inhalation of Mch at PC35-PEF40 that means milder bronchoconstriction than PC20-FEV1, cough was triggered a few times in AC. [cough number: 1/ 32 min (0-40)]. Conversely, significantly greater number of coughs was provoked in CVA, compared with AC [cough number: 35.5/ 32 min (25-125), p < 0.05].

CONCLUSIONS

The cough response to bronchoconstriction is reduced in AC compared to CVA. This feature may be useful in the diagnosis of chronic cough.

Peripheral neural circuitry in cough

Cough is a reflex that serves to protect the airways. Excessive or chronic coughing is a major health issue that is poorly controlled by current therapeutics. Significant effort has been made to understand the mechanisms underlying the cough reflex. The focus of this review is the evidence supporting the role of specific airway sensory nerve (afferent) populations in the initiation and modulation of the cough reflex in health and disease.

Antitussive drugs--past, present, and future

Cough remains a serious unmet clinical problem, both as a symptom of a range of other conditions such as asthma, chronic obstructive pulmonary disease, gastroesophageal reflux, and as a problem in its own right in patients with chronic cough of unknown origin. This article reviews our current understanding of the pathogenesis of cough and the hypertussive state characterizing a number of diseases as well as reviewing the evidence for the different classes of antitussive drug currently in clinical use. For completeness, the review also discusses a number of major drug classes often clinically used to treat cough but that are not generally classified as antitussive drugs. We also reviewed a number of drug classes in various stages of development as antitussive drugs. Perhaps surprising for drugs used to treat such a common symptom, there is a paucity of well-controlled clinical studies documenting evidence for the use of many of the drug classes in use today, particularly those available over the counter. Nonetheless, there has been a considerable increase in our understanding of the cough reflex over the last decade that has led to a number of promising new targets for antitussive drugs being identified and thus giving some hope of new drugs being available in the not too distant future for the treatment of this often debilitating symptom.

Heightened cough response to bronchoconstriction in cough variant asthma

BACKGROUND AND OBJECTIVE

The pathophysiology of cough variant asthma (CVA) is poorly understood. We compared bronchoconstriction-triggered cough between CVA patients and normal control (NC) subjects.

METHODS

There were two protocols in the study. We measured bronchial responsiveness to methacholine (MCh) and counted the number of coughs in nine CVA patients and seven NC subjects (study A). Using partial and full flow-volume curves, expiratory flow of the partial flow-volume curve at 40% above residual volume level (PEF40) and FEV(1) were used to measure bronchoconstriction. Mild bronchoconstriction was defined as a 35% fall in PEF40 (PC(35) -PEF40), and more severe bronchoconstriction as a 20% fall in FEV1 (PC20) -FEV(1) ). In study B, the same measurements were obtained in six CVA patients before and after therapy.

RESULTS

In study A, more coughs were provoked at PC35 -PEF40 in CVA patients (median, 60 coughs/32 min post challenge; range, 12-135) than in NC subjects (median, 0/32 min; range, 0-13; P < 0.05). At PC20 -FEV1 , more coughs were provoked in CVA patients (median, 60/32 min; range, 12-150) than in NC subjects (median, 20/32 min; range, 0-54; P < 0.05). In study B, the six CVA patients who underwent re-examination after treatment had less coughs at PC35 -PEF40 (median, 3/32 min; range, 0-14) and PC(20) -FEV1 (median, 13/32 min; range, 3-26) after therapy than before therapy (median, 54/32 min; range, 33-125 and 52/32 min, 45-96, respectively; P < 0.05).

CONCLUSIONS

We identified heightened cough response to bronchoconstriction as a feature of CVA.

Reversibility of the pulmonary function based on the partial flow-volume curve predicts the efficacy of bronchodilator therapy for treating chronic cough

OBJECTIVE

Partial expiratory flow-volume curves have the potential to detect mild bronchoconstriction because they are not affected by the modulatory effects of deep inspiration. The aim of this study was to investigate the relationship between the efficacy of bronchodilator therapy (BDT) in treating the cough and to assess the increase in the expiratory flow of the partial flow-volume curve at 40% above the residual volume level (PEF40) caused by treatment with a short-acting beta-2 agonist (SABA) in patients with chronic nonproductive cough.

METHODS

We measured the reversibility of PEF40 caused by a SABA in 42 patients with chronic nonproductive cough at visit 1 (day 0). The patients received BDT for six days. The visual analogue scale (VAS) was used to assess the efficacy of BDT in treating coughing at visit 2 (day 7) (0 mm, 'no cough;' 100 mm, 'no change in coughing').

RESULTS

Reversibility of the PEF40 was correlated (r=0.690, p<0.001) with the VAS score determined at visit 2 and was higher in the patients with cough variant asthma (CVA) (44.9 ± 18.3%) than in those with atopic cough (13.4 ± 10.4%) (p<0.01).

CONCLUSION

Reversibility of the PEF40 predicted the efficacy of BDT in patients with chronic nonproductive cough and helped to identify patients with CVA.

Plasma substance P levels in patients with persistent cough

BACKGROUND

Substance P (SP) is involved in the pathogenesis of cough in animal models. However, few studies in humans have been reported and the roles of SP in clinical cough remain obscure.

OBJECTIVES

To clarify the relevance of plasma levels of SP in patients with persistent cough.

METHODS

We studied 82 patients with cough persisting for at least 3 weeks and 15 healthy controls. Patients were classified as having asthmatic cough (cough-variant asthma and cough-predominant asthma; n = 61) or nonasthmatic cough (n = 21; postinfectious cough, n = 6; gastroesophageal reflux disease, n = 5; idiopathic cough, n = 5, and others, n = 5). Correlations were evaluated between plasma SP levels as measured with ELISA and methacholine airway hyperresponsiveness (airway sensitivity and airway reactivity), capsaicin cough sensitivity, sputum eosinophil and neutrophil counts, and pulmonary function.

RESULTS

Plasma SP levels were significantly elevated in patients with both asthmatic and nonasthmatic cough compared with controls [31.1 pg/ml (range 18.0-52.2) and 30.0 pg/ml (range 15.1-50.3) vs. 15.4 pg/ml (range 11.3-23.7); p = 0.003 and p = 0.038, respectively] but did not differ between the two patient groups (p = 0.90). Plasma SP levels correlated with airway sensitivity (threshold dose of methacholine) in the patients with asthmatic cough (r = -0.37, p = 0.005) but not with airway reactivity, cough sensitivity, FEV1 values, or sputum eosinophil and neutrophil counts in either group.

CONCLUSIONS

Increased levels of SP in plasma are associated with persistent cough in humans and might be related to airway sensitivity in asthmatic cough.

Cough and Asthma

Cough is the most common complaint for which patients seek medical attention. Cough variant asthma (CVA) is a form of asthma, which presents solely with cough. CVA is one of the most common causes of chronic cough. More importantly, 30 to 40% of adult patients with CVA, unless adequately treated, may progress to classic asthma. CVA shares a number of pathophysiological features with classic asthma such as atopy, airway hyper-responsiveness, eosinophilic airway inflammation and various features of airway remodeling. Inhaled corticosteroids remain the most important form of treatment of CVA as they improve cough and reduce the risk of progression to classic asthma most likely through their prevention of airway remodeling and chronic airflow obstruction.

Bronchoconstriction-triggered cough is impaired in typical asthmatics

BACKGROUND AND OBJECTIVE

Cough is an essential innate protective behavior, which is experienced by even healthy individuals. The mechanism of cough triggered by bronchoconstriction is not yet clear. The aim of this study was to investigate the relation between bronchoconstriction and cough caused by methacholine (Mch) inhalation in typical asthmatics and normal healthy subjects.

METHODS

We measured bronchial responsiveness to Mch and counted the number of coughs induced by Mch inhalation in 15 typical asthmatics and 20 normal subjects.

RESULTS

After inhalation of Mch at the concentration causing 20% or more decrease in forced expiratory volume in 1 second (FEV(1)) (PC(20)-FEV(1)), coughs were provoked in normal subjects (number of cough: 22.5/32 min, range: 3.3-45). Conversely, coughs were hardly provoked in typical asthmatics (median number of cough: 2/32 min, range: 0-4).

CONCLUSIONS

Although typical asthmatics have increased airway responsiveness, their cough response to bronchoconstriction is impaired.