Physiology and treatment of cough

A new method for objectively evaluating nocturnal cough in adults

BACKGROUND

For the management of cough diseases in adults, an objective method of evaluating nocturnal cough is required.

METHODS

In Study 1, a cough monitoring system was evaluated using 25 adult volunteers. In Study 2, the cough monitoring system was validated using 20 samples from 10 adult patients with cough diseases obtained overnight. In hospitalized patients, our original cough monitoring system with a microphone and accelerometer was used. At the same time, coughs were recorded using a video camera with digital sound recording. The number of coughs in each 8-h video-audio recording was counted manually by three trained observers. All cough data were printed out, and the basal number of cough events, using both the printed-out data and video-audio recordings, were then calculated by three observers.

RESULTS

In Study 1, the cough monitoring system demonstrated good agreement with the number of coughs counted by examiners (sensitivity 99.2%, specificity 98.9%). In Study 2, there was significant agreement in the counts of natural coughs between our system and the video-audio method (p < 0.0001) and between our system and the basal cough events (p < 0.0001).

CONCLUSIONS

Our method demonstrated excellent agreement with the video-audio recording method in adults and is considered extremely useful for the objective monitoring of overnight cough in adult patients with cough diseases.

Infant aspiration and associated signs on clinical feeding evaluation

OBJECTIVES

Few studies have examined clinical signs of aspiration in infants <51 weeks post-menstrual age (PMA) for whom the laryngeal cough reflex is not fully developed. This retrospective study explored 1) the association between signs of aspiration on a clinical feeding evaluation (CFE) and/or comorbid conditions with aspiration (silent or overt) on a modified barium swallow study (MBS) for infants in this age range, 2) the association between lower respiratory infection (LRI) and aspiration on MBS, and 3) the sensitivity and specificity of detecting aspiration according to signs on CFE and the evaluating speech-language pathologist's (SLP) years of experience.

METHODS

A retrospective review of charts of patients with MBS completed January 1, 2012-December 31, 2014 was performed. Patients were included if they were <51-weeks PMA at the time of MBS and had a CFE conducted no more than seven days prior to the MBS. Patient age, comorbidities, and MBS and CFE details were collected. The impact of CFE findings, patient age, comorbid syndromes/associations, and aerodigestive diagnoses on the odds of demonstrating silent aspiration (SA) or overt aspiration during MBS with thin liquids was determined using logistic regression, and the sensitivity and specificity of CFE for identifying SA was calculated.

RESULTS

Results from 114 patients indicated that 46 (40 %) of the infants had SA and nine (8 %) had overt aspiration on MBS. Notable signs on CFEs were cough (36 %), oxygen desaturations (33 %), and chest congestion (32 %). On multiple regression analysis there was increased odds of SA on MBS with at least one clinical sign on CFE (OR: 24.3, p = 0.02), chronic lung disease, (OR: 18.2, p = 0.01), and airway abnormalities (OR: 2.94, p = 0.01). Cough on CFE was associated with increased odds of overt aspiration on MBS (OR: 5.69, p = 0.04). Neither SA nor overt aspiration were significantly associated with LRI. Sensitivity and specificity of CFE for correctly identifying the presence of SA were 98 % and 15 %, respectively; experience of the SLP was not a contributing factor.

CONCLUSION

Further study is required to determine if specific signs on CFE are predictive of aspiration.

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 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.

Metabolism, pharmacokinetics and selected pharmacodynamic effects of codeine following a single oral administration to horses

OBJECTIVE

To describe the pharmacokinetics and selected pharmacodynamic variables of codeine and its metabolites in Thoroughbred horses following a single oral administration.

STUDY DESIGN

Prospective experimental study.

ANIMALS

A total of 12 Thoroughbred horses, nine geldings and three mares, aged 4-8 years.

METHODS

Horses were administered codeine (0.6 mg kg-1) orally and blood was collected before administration and at various times until 120 hours post administration. Plasma and urine samples were collected and analyzed for codeine and its metabolites by liquid chromatography-mass spectrometry, and plasma pharmacokinetics were determined. Heart rate and rhythm, step counts, packed cell volume and total plasma protein were measured before and 4 hours after administration.

RESULTS

Codeine was rapidly converted to the metabolites norcodeine, codeine-6-glucuronide (C6G), morphine, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G). Plasma codeine concentrations were best represented using a two-compartment model. The Cmax, tmax and elimination t½ were 270.7 ± 136.0 ng mL-1, 0.438 ± 0.156 hours and 2.00 ± 0.534 hours, respectively. M3G was the main metabolite detected (Cmax 492.7 ± 35.5 ng mL-1), followed by C6G (Cmax 96.1 ± 33.8 ng mL-1) and M6G (Cmax 22.3 ± 4.96 ng mL-1). Morphine and norcodeine were the least abundant metabolites with Cmax of 3.17 ± 0.95 and 1.42 ± 0.79 ng mL-1, respectively. No significant adverse or excitatory effects were observed.

CONCLUSIONS AND CLINICAL RELEVANCE

Following oral administration, codeine is rapidly metabolized to morphine, M3G, M6G, C6G and norcodeine in horses. Plasma concentrations of M6G, a presumed active metabolite of morphine, were comparable to concentrations reported previously following administration of an analgesic dose of morphine to horses. Codeine was well tolerated based on pharmacodynamic variables and behavioral observations.

Coughing in Small Animal Patients

Cough is one of the most common complaints in human medicine. In veterinary medicine cough is equally frequent and plays a significant role in an owner's perception of their pet's quality of life. In human and veterinary medicine, therapy for chronic cough is often ineffective. The complexity of the cough pathway and species differences have made it difficult to develop an effective antitussive agent for veterinary patients. The few effective antitussive agents currently available are associated with significant adverse effects. Fortunately, several promising drugs currently being studied in human clinical trials may offer options for use of novel antitussive therapies in small animal patients. This article reviews current understanding about cough pathophysiology, diagnostic strategies used to uncover underlying etiology of cough, and examines available options for controlling cough, including novel antitussive therapies used in human medicine.

A case of pseudomembranous tracheitis caused by Mycoplasma pneumoniae in an immunocompetent patient

Pseudomembranous tracheitis (PMT) is a rare condition characterized by pseudomembrane formation in the tracheobronchial tree that may be associated with infectious and noninfectious processes. However, PMT attributed to Mycoplasma pneumoniae (M. pneumoniae), a common atypical respiratory infectious pathogen, has not been reported till date. Here, we report about a 29-year-old woman with complaints of severe persistent cough and radiographic deterioration despite antibiotics administration for pneumonia at an outside facility. She was finally diagnosed as having PMT with bilateral diffuse bronchiolitis caused by M. pneumoniae infection. The diagnosis was made based on a bronchoscopic finding of a pseudomembrane that partially covered the membranous portion of the upper and middle trachea, a positive polymerase chain reaction (PCR) test with bronchial aspirate, and a positive serological test for M. pneumoniae without detection of any other causative pathogen through an extensive workup. Her symptoms and radiographic findings improved in response to moxifloxacin and corticosteroid treatment. This case is a rare presentation of M. pneumoniae infection complicating PMT in a young adult without any known risk factors.

Management of Respiratory Disorders and the Pharmacist's Role: Cough, Colds, and Sore Throats and Allergies (Including Eyes)

Complaints pertaining to the upper respiratory tract, such as the common cold and allergies, are a common reason for presentation to community pharmacies. This chapter explores the common cold and influenza and associated symptoms, including cough, congestion, rhinorrhea, sore throat, diarrhea, pain, and fever. This chapter will aid pharmacists in identifying the characteristics and pharmacological and nonpharmacological management of these conditions. Allergies of the nose and eyes are another common ailment encountered in the community pharmacy, and this chapter assists pharmacists in reaching a differential diagnosis and strategies to manage these conditions.

Comparison of the effects of pretreatment intravenous fentanyl or intravenous lidocaine on suppression of fentanyl-induced cough in children: a randomized, double-blind, controlled clinical trial

Background and aim

The injection of fentanyl usually causes coughing during induction of anesthesia. Based on a few studies about effects of lidocaine and the fact there is no study concerning the effect of fentanyl on fentanyl-induced cough in pediatric patients, the aim of this study was to compare the effectiveness of low dose of fentanyl with lidocaine in prevention of fentanyl-induced cough in children.

Methods

This randomized double-blind controlled clinical trial study was conducted at Motahari Hospital between February and August 2017 in Urmia (Iran). One hundred patients, aged 2–10 years, of class I or II ASA status who were candidates for elective herniorrhaphy under general anesthesia were enrolled in this study. They were randomly divided into three groups. One minute before the administration of 2 μg/kg fentanyl during induction of general anesthesia, Group I received 1.0 mg/kg lidocaine (n=33), Group II received 0.5 μg/kg fentanyl (n=34) and Group III received normal saline as a control group (n=33). The data were analyzed by STAT version 13. The incidence and severity of cough were determined across groups by using ANOVA and Chi-square tests. Multiple logistic regression was also used to examine the association between the outcome of cough incidence and clinical interventions as the exposures after adjusting for study covariates.

Results

The highest incidence of cough was found in the Group III (54.5%) versus 32.4% and 21.1% in Group II and Group I subsequently (p=0.02). We have also found significant difference in the incidence of cough among group one and three (p=0.005), and among group two and three (p=0.045). No statistically significant difference has been detected between group one and two. The severity of cough was significantly higher in Group III compared to Groups I and II (p=0.01). The time of onset of cough was similar across groups. No side effects were reported after intervention in this study

Conclusion

This study found that pretreatment with fentanyl 0.5mg/kg or 1mg/kg lidocaine is an effective approach to reducing the incidence and severity of fentanyl-induced cough in children.

Trial registration

The trial was registered at the Iranian Registry of Clinical Trials (http://WWW.irct.ir) with IRCT number: IRCT2016112027677N5.

Funding

This study was not granted or funded by any institution.

Computational Modelling of Cough Function and Airway Penetrant Behavior in Patients with Disorders of Laryngeal Function

Objective/Hypothesis

Patients with laryngeal disorders often exhibit changes to cough function contributing to aspiration episodes. Two primary cough variables (peak cough flow: PCF and compression phase duration: CPD) were examined within a biomechanical model to determine their impact on characteristics that impact airway compromise.

Study Design

Computational study

Methods

A Computational Fluid Dynamics (CFD) technique was used to simulate fluid flow within an upper airway model reconstructed from patient CT images. The model utilized a finite‐volume numerical scheme to simulate cough‐induced airflow, allowing for turbulent particle interaction, collision, and break‐up. Liquid penetrants at 8 anatomical release locations were tracked during the simulated cough. Cough flow velocity was computed for a base case and four simulated cases. Airway clearance was evaluated through assessment of the fate of particles in the airway following simulated cough.

Results

Peak‐expiratory phase resulted in very high airway velocities for all simulated cases modelled. The highest velocity predicted was 49.96 m/s, 88 m/s, and 117 m/s for Cases 1 and 3, Base case, and Cases 2 and 4 respectively. In the base case, 25% of the penetrants cleared the laryngeal airway. The highest percentage (50%) of penetrants clearing the laryngeal airway are observed in Case 2 (with −40% CPD, +40% PCF), while only 12.5% cleared in Case 3 (with +40% CPD, −40% PCF). The proportion that cleared in Cases 1 and 4 was 37.5%.

Conclusion

Airway modelling may be beneficial to the study of aspiration in patients with impaired cough function including those with upper airway and neurological diseases. It can be used to enhance understanding of cough flow dynamics within the airway and to inform strategies for treatment with “cough‐assist devices” or devices to improve cough strength.

Level of Evidence

N/A.

Therapeutic effects of naringin in a guinea pig model of ovalbumin-induced cough-variant asthma

Naringin, a well known component isolated from Exocarpium Citri Grandis, has significant antitussive effects. Recently, Naringin exhibited novel anti-inflammatory effect in chronic inflammatory diseases. In this work, we firstly evaluated the effects of naringin on enhanced cough, airway hyper-responsiveness (AHR), and airway inflammation in an ovalbumin-induced experimental cough-variant asthma (CVA) model in guinea pigs. We investigated the effect of naringin (18.4 mg/kg, per os, single dose or consecutively) on cough to inhaled capsaicin after challenge with an aerosolized antigen in actively sensitized guinea pigs. The effect of naringin on AHR to inhaled methacholine was evaluated 24 h after cough determination. Airway inflammation was assessed via bronchoalveolar lavage fluid (BALF) cytology and lung histopathology. Naringin, given consecutively, significantly reduced ovalbumin-induced enhanced cough and AHR, inhibited the increases in the leukocytes, interleukin-4 (IL-4), IL-5, and IL-13 in BALF compared with the model group. Moreover, the pathologic changes in lung tissues were clearly ameliorated by naringin treatment. These results suggest that naringin may be a beneficial agent for CVA treatment.

Efficacy of procaterol combined with inhaled budesonide for treatment of cough-variant asthma

BACKGROUND AND OBJECTIVE

Procaterol, a selective, short-acting beta-2 adrenoceptor agonist, is effective in treating 'classical' asthma, but its efficacy for cough-variant asthma (CVA) is unknown. We evaluated the efficacy and safety of procaterol combined with budesonide for CVA.

METHODS

A prospective, randomized, double-blind, placebo-controlled, multicenter trial in China was conducted. One hundred and fifty-nine patients diagnosed with CVA (aged 18-75 years) were randomly divided into two groups to receive twice daily for 8 weeks, inhaled budesonide 100 μg plus either oral procaterol 25 μg or placebo. Primary and secondary efficacy variables were cough symptom severity scores and Leicester Cough Questionnaire (LCQ) life quality scores. Adverse events were also assessed.

RESULTS

The budesonide/placebo and budesonide/procaterol groups contained 80 and 78 participants (one excluded for later diagnosis of eosinophilic bronchitis), respectively, with similar baseline characteristics. Daily cough score declined during treatment in both groups and was lower in the budesonide/procaterol group at 8 (0.44 vs 0.73) and 10 (0.36 vs 0.69) weeks (P < 0.05). Compared with the budesonide/placebo group, the proportion of patients with a reduction of 3 points or greater (66% vs 42%) and that of patients scoring 0 points (63% vs 51%) was higher in the budesonide/procaterol group for daily cough scores (P < 0.05). At 8 weeks, LCQ score improvement was superior in the budesonide/procaterol group (38.94 ± 19.24 vs 32.71 ± 18.92; P < 0.05).

CONCLUSION

Procaterol combined with budesonide was well tolerated and effective at improving cough symptoms and quality of life in patients with CVA.

PCR based bronchoscopic detection of common respiratory pathogens in chronic cough: a case control study

BACKGROUND

Viral respiratory tract infection is the most frequent cause of acute cough and is reported at onset in about one third of patients with chronic cough. Persistent infection is therefore one possible explanation for the cough reflex hypersensitivity and pulmonary inflammation reported in chronic cough patients.

METHODS

Bronchoscopic endobronchial biopsies and bronchoalveolar lavage cell counts were obtained from ten healthy volunteers and twenty treatment resistant chronic cough patients (10 selected for lavage lymphocytosis). A screen for known respiratory pathogens was performed on biopsy tissue. Chronic cough patients also underwent cough reflex sensitivity testing using citric acid.

RESULTS

There was no significant difference in incidence of infection between healthy volunteers and chronic cough patients (p = 0.115) or non-lymphocytic and lymphocytic groups (p = 0.404). BAL cell percentages were not significantly different between healthy volunteers and chronic cough patients without lymphocytosis. Lymphocytic patients however had a significantly raised percentage of lymphocytes (p < 0.01), neutrophils (p < 0.05), eosinophils (p < 0.05) and decreased macrophages (p < 0.001) verses healthy volunteers. There was no significant difference in the cough reflex sensitivity between non-lymphocytic and lymphocytic patients (p = 0.536).

CONCLUSIONS

This study indicates latent infection in the lung is unlikely to play an important role in chronic cough, but a role for undetected or undetectable pathogens in either the lung or a distal site could not be ruled out.

TRIALS REGISTRATION

Current Controlled Trials ISRCTN62337037 & ISRCTN40147207.

Characteristics of Chinese patients with cough in primary care centre

Background

Cough is one of the most common respiratory symptoms and is well characterized in specialized cough clinics with high success rates of diagnosis and treatment. However, there is a paucity of data regarding cough in primary care settings. The present study aimed at investigating clinical epidemiology of cough through a national study of two questionnaire surveys sent to primary care physicians in China.

Methods

Approximately 18,000 subjects recruited were having daytime or night symptoms of cough and diagnoses of respiratory disease from February 2005 to April 2006 as Survey 1 and from June 2007 to December 2007 as Survey 2. Patients suffering from respiratory malignancy, hyperthyroidism, hypertension, heart disease, diabetes, severe hypohepatia or renal dysfunction, pregnancy, possible pregnancy or lactation, neutropenia were not eligible. Information regarding demography, history of allergies, symptomatic profile, treatment and curative effects for cough was elicited.

Results

8216 questionnaires were collected in Survey 1 and 9711 in Survey 2. The mean values of ages were 25.7 and 22.3 years old, respectively. Symptoms included expectoration (74% and 76%), wheeze (59% and 74%), breathlessness (22% and 26%), chest pain (9% and 13%) and fever (15% and 18%). About 15% and 23% patients had hypersusceptibility, of whom 6% to 17% had a family history. More than 50% of the cases had histories of allergic rhinitis, asthma, conjunctivitis or atopic dermatitis. Asthma, COPD, and bronchitis were dominant etiologies of cough. Procaterol or the combination of antibiotics and steroids were used as the treatment.

Conclusion

Causes and outcomes of cough differed with ages and time in this particular national study, while successful and precise diagnosis and management of cough in primary care settings need to be further improved in China.

Recommendations for the proper use of nonprescription cough suppressants and expectorants in solid-organ transplant recipients

OBJECTIVE

To describe the pharmacology and safety of oral over-the-counter cough suppressants and expectorants and to present recommendations for the use of these agents in solid-organ transplant recipients based on the potential for adverse drug reactions or drug-disease interactions.

DATA SOURCES AND EXTRACTION

Data from journal articles and other sources describing the pharmacology and safety of over-the-counter cough suppressants and expectorants, drug-drug interactions with immunosuppressive agents, and drug-disease state interactions are reviewed.

DATA SYNTHESIS

Potential and documented drug-drug interactions between immunosuppressive agents and over-the-counter cough medications guaifenesin, dextromethorphan, diphenhydramine, and codeine were evaluated on the basis of pharmacokinetic and pharmacodynamic principles. Interactions between these cough medications and the physiological changes in the body following transplantation also were examined.

CONCLUSION

Diphenhydramine requires additional monitoring when used to treat cough in transplant recipients owing to its anticholinergic properties and the potential for interactions with cyclosporine. Dextromethorphan can be used in most transplant recipients, although greater caution should be exercised if the patient has undergone liver transplant or has liver impairment. Guaifenesin can be used in transplant recipients but should be used with caution in patients receiving kidney or lung transplants and in patients with renal impairment. Codeine combined with guaifenesin is another option for cough and can be used in most transplant patients although those with reduced renal function should be monitored carefully for adverse events.

Recommendations for the Proper Use of Nonprescription Cough Suppressants and Expectorants in Solid-Organ Transplant Recipients

Objective

To describe the pharmacology and safety of oral over-the-counter cough suppressants and expectorants and to present recommendations for the use of these agents in solid-organ transplant recipients based on the potential for adverse drug reactions or drug-disease interactions.

Data Sources and Extraction

Data from journal articles and other sources describing the pharmacology and safety of over-the-counter cough suppressants and expectorants, drug-drug interactions with immunosuppressive agents, and drug-disease state interactions are reviewed.

Data Synthesis

Potential and documented drug-drug interactions between immunosuppressive agents and over-the-counter cough medications guaifenesin, dextromethorphan, diphenhydramine, and codeine were evaluated on the basis of pharmacokinetic and pharmacodynamic principles. Interactions between these cough medications and the physiological changes in the body following transplantation also were examined.

Conclusion

Diphenhydramine requires additional monitoring when used to treat cough in transplant recipients owing to its anticholinergic properties and the potential for interactions with cyclosporine. Dextromethorphan can be used in most transplant recipients, although greater caution should be exercised if the patient has undergone liver transplant or has liver impairment. Guaifenesin can be used in transplant recipients but should be used with caution in patients receiving kidney or lung transplants and in patients with renal impairment. Codeine combined with guaifenesin is another option for cough and can be used in most transplant patients although those with reduced renal function should be monitored carefully for adverse events.

Validation of a Pediatric Cough Questionnaire

We conducted a study to determine if a five-item pediatric cough questionnaire (PCQ) is a valid and reliable means of measuring cough-specific quality of life in children. The five questions, which are answered by the child's parent or caregiver, cover cough frequency (Q1), sleep disturbance of the child (Q2), sleep disturbance of the parent (Q3), cough severity (Q4), and the degree of bothersomeness to the child (Q5). Each of the five items was scored on a 6-point Likert scale. The PCQ was administered three times. The first occurred when the parent telephoned to schedule an appointment for the child at a pediatric pulmonology outpatient clinic for a chief complaint of cough. The second PCQ was administered within 2 weeks of the first but before any treatment had been instituted so that test-retest reliability could be assessed. Each child was then diagnosed and treated in accordance with standard care practices. The third PCQ was administered 3 weeks after the second to determine if it would accurately reflect the parent's perception of how the child's cough had changed following treatment. Also, at the second and third encounters, parents were asked to provide their global assessment of whether their child's cough had improved, worsened, or stayed the same since the previous encounter. The parents of 120 children (70 boys and 50 girls; mean age: 6.8 yr) completed all three PCQs. Test-retest reliability was established (p < 0.001) for each of the five PCQ questions by Spearman correlation analysis (Q1: r = 0.5; Q2: r = 0.38; Q3: r = 0.42; Q4: r = 0.53; Q5: r = 0.5). Other statistical analyses confirmed the PCQ's internal consistency, discriminant validity, and convergent validity. Based on our findings, we conclude that the PCQ is a valid and reliable instrument with which to follow children with chronic cough longitudinally.

Changes in health-related quality of life and clinical implications in Chinese patients with chronic cough

Background

Chronic cough has negative effects on quality of life. However, the changes in health-related quality of life and clinical implications remain unclear in Chinese patients with chronic cough.

Methods

A standard Chinese version of Leicester cough questionnaire (LCQ) was developed by an established translation procedure and its repeatability was assessed in a preliminary study involving 20 untreated patients with stable chronic cough. The quality of life was measured with the Short form-36 health survey and compared between 110 patients with chronic cough and 90 healthy volunteers. The changes in health-related quality of life were evaluated in the patients with chronic cough with the LCQ just before the specific treatment was initiated and a week after the cough had resolved completely. Cough threshold with inhaled capsaicin, expressed as the lowest concentration of capsaicin required for the induction of ≥5 coughs, was also measured.

Results

The repeatability of the Chinese version of the LCQ was validated at a four day interval with the intraclass correlation coefficients of 0.89-0.94 for total and domain score (n = 20). The scores of the Short form-36 health survey were significantly lower in patients with chronic cough than those in healthy volunteers. In general, there was no significant difference in overall quality of life between different causes of chronic cough or genders although embarrassment, frustration and sleep disturbance were more common in female patients, as indicated by the LCQ. However, the successful treatment of cough obviously increased the total scores of the LCQ from 14.2 ± 2.7 to 19.5 ± 1.9 (t = 13.7, P < 0.0001). There was a significant correlation between the total score of the LCQ and physical (r = 0.39, P < 0.0001) or mental (r = 0.30, P < 0.001) component summary of the Short form-36 health survey but not between the LCQ and capsaicin cough threshold.

Conclusion

The quality of life is significantly impaired in Chinese patients with chronic cough. The Chinese version of the LCQ is a valid measure of cough related quality of life and is repeatable and responsive.

Peripheral mechanisms II: the pharmacology of peripherally active antitussive drugs

Cough is an indispensable defensive reflex. Although generally beneficial, it is also a common symptom of diseases such as asthma, chronic obstructive pulmonary disease, upper respiratory tract infections, idiopathic pulmonary fibrosis and lung cancer. Cough remains a major unmet medical need and although the centrally acting opioids have remained the antitussive of choice for decades, they have many unwanted side effects. However, new research into the behaviour of airway sensory nerves has provided greater insight into the mechanisms of cough and new avenues for the discovery of novel non-opioid antitussive drugs. In this review, the pathophysiological mechanisms of cough and the development of novel antitussive drugs are reviewed.

TRPV1 antagonists as potential antitussive agents

Cough is an important defensive pulmonary reflex that removes irritants, fluids, or foreign materials from the airways. However, when cough is exceptionally intense or when it is chronic and/or nonproductive it may require pharmacologic suppression. For many patients, antitussive therapies consist of OTC products with inconsequential efficacies. On the other hand, the prescription antitussive market is dominated by older opioid drugs such as codeine. Unfortunately, "codeine-like" drugs suppress cough at equivalent doses that also often produce significant ancillary liabilities such as GI constipation, sedation, and respiratory depression. Thus, the discovery of a novel and effective antitussive drug with an improved side effect profile relative to codeine would fulfill an unmet clinical need in the treatment of cough. Afferent pulmonary nerves are endowed with a multitude of potential receptor targets, including TRPV1, that could act to attenuate cough. The evidence linking TRPV1 to cough is convincing. TRPV1 receptors are found on sensory respiratory nerves that are important in the generation of the cough reflex. Isolated pulmonary vagal afferent nerves are responsive to TRPV1 stimulation. In vivo, TRPV1 agonists such as capsaicin elicit cough when aerosolized and delivered to the lungs. Pertinent to the debate on the potential use of TRPV1 antagonist as antitussive agents are the observations that airway afferent nerves become hypersensitive in diseased and inflamed lungs. For example, the sensitivity of capsaicin-induced cough responses following upper respiratory tract infection and in airway inflammatory diseases such as asthma and COPD is increased relative to that of control responses. Indeed, we have demonstrated that TRPV1 antagonism can attenuate antigen-induced cough in the allergic guinea pig. However, it remains to be determined if the emerging pharmacologic profile of TRPV1 antagonists will translate into a novel human antitussive drug. Current efforts in clinical validation of TRPV1 antagonists revolve around various pain indications; therefore, clinical evaluation of TRPV1 antagonists as antitussive agents will have to await those outcomes.

High-dose inhaled beclomethasone treatment in patients with chronic cough: a randomized placebo-controlled study

BACKGROUND

It is important to determine whether chronic cough is associated with asthma and can be helped by treatment with inhaled corticosteroids.

OBJECTIVE

To compare the effects of beclomethasone and placebo in patients with chronic cough for at least 8 weeks after excluding those with cough due to postnasal drip and gastroesophageal reflux disease.

METHODS

A prospective, randomized, double-blind, placebo-controlled study comprising 64 patients was performed for 2 weeks. The active group received metered-dose inhaler chlorofluorocarbon-beclomethasone (1,500 microg/d), and the placebo group received identical-appearing placebo inhalers. All the participants completed a respiratory questionnaire and underwent bronchoprovocation testing (BPT) with methacholine and allergy skin testing. The primary outcome measure was a decrease in daily cough scores (symptom diary and visual analog scale) during the 2-week treatment period.

RESULTS

The active group comprised 44 patients and the placebo group 20 patients. Cough duration averaged 20 weeks. At the end of treatment 82% of the active group and 15% of the placebo group had complete resolution of cough. In the active group 22 patients (50%) had positive BPT results, and in the placebo group 10 patients (50%) had positive results. There was no correlation between treatment response and responses on the respiratory questionnaire, allergy skin testing, or BPT.

CONCLUSION

Therapy with high-dose inhaled beclomethasone provided an excellent response in a subgroup of patients with chronic cough that did not correlate with atopy or airway hyperresponsiveness.

Reliability and validity of a Dutch version of the Leicester Cough Questionnaire

Background

Chronic cough is a common condition with a significant impact on quality of life. Currently, no health status measure specific for chronic cough exists in the Netherlands. Thus we developed a Dutch version of the Leicester Cough Questionnaire (LCQ) and tested its scaling and clinical properties.

Methods

The LCQ was adapted for Dutch conditions following a forward-backward translation procedure. All patients referred to our cough clinic between May 2004 and February 2005 completed five questionnaires, the LCQ, the modified Borg score for cough, the Short-Form 36 (SF-36), the Hospital Anxiety and Depression Scale (HADS) and the Global Rating of Change (GRC) upon presentation, after two weeks and after 6 months. Concurrent validation, internal consistency, repeatability and responsiveness were determined.

Results

For the concurrent validation the correlation coefficients (n = 152 patients) between the LCQ and the other outcome measures varied between 0.22 and 0.61. The internal consistency of the LCQ (n = 58) was high for each of the domains with a Crohnbach's alpha coefficient between 0.77 and 0.91. The two week repeatability of the LCQ in patients with no change in cough (n = 48) was high with intraclass correlation coefficients varying between 0.86 and 0.93. Patients who reported an improvement in cough (n = 140) after 6 months demonstrated significant improvement on each of the domains of the LCQ.

Conclusion

The Dutch version of the LCQ is a valid and reliable questionnaire to measure (changes of) health status in patients with chronic cough.

Chronic cough: how do cough reflex sensitivity and subjective assessments correlate with objective cough counts during ambulatory monitoring?

BACKGROUND

Cough reflex sensitivity, subjective estimates of cough frequency and cough-related quality of life have been used to assess cough and monitor treatment responses. The relationships between these measures and objective cough monitoring remain unclear and the usefulness of subjective assessments remains questionable.

SUBJECTS

62 patients with chronic cough (39 women) were studied. Mean age of patients was 54.9 (SD 12.2) years, with a median duration of cough of 5.5 (range 1-30) years.

METHODS

Cough reflex sensitivity testing (C5; citric acid) was performed in all patients before fully ambulatory day-time and night-time cough recordings. Patients scored the frequency and severity of their cough (Visual Analogue Scales (VAS) and 0-5 score) for each recording period and completed a cough-related quality-of-life questionnaire, Leicester Cough Questionnaire (LCQ). Ambulatory cough recordings were manually counted and reported in terms of cough seconds per hour (cs/h). Cough rates were log(10) transformed for analysis.

RESULTS

The median time spent coughing was 11.36 (range 1.06-46) cs/h with median day rates of 15.59 (range 2-74.8) cs/h and median night rates of 2.94 (range 0-26.67) cs/h. An inverse relationship was seen between day cough rates and log(10) C5 (r = -0.452, p< or =0.001). Subjective cough scores and visual analogue scales were only moderately associated with objective time spent coughing, with night-time being scores more strongly associated than day-time scores. The strongest correlation with objective cough frequency was cough-related quality of life (LCQ), (r = -0.622, p< or =0.001), mediated through the psychological domain.

CONCLUSIONS

Subjective measures of cough and cough reflex sensitivity are only moderately related to objective time spent coughing, and hence cannot be used as surrogate markers for objective cough-frequency measurements. Cough-related quality of life (LCQ) is most strongly related to objectively counted cough, and may be a useful adjunct to objective measures in the assessment of cough.

Sulfur-dioxide exposure increases TRPV1-mediated responses in nodose ganglia cells and augments cough in guinea pigs

The objective of the present experiments was to study the effects of pulmonary inflammation induced by subacute Sulfur-dioxide (SO(2)) exposure on capsaicin-induced responses in isolated primary vagal sensory neurons and cough. Additionally, we examined the effects of SO(2) exposure on respiratory function and lung histology. All experiments were conducted 24 h after 4 days of subacute SO(2) (1000 ppm, 3 h/day for 4 days) exposure. In in vitro experiments, intracellular Ca(2+) concentrations were measured in single nodose ganglia cells isolated from SO(2) treated and control guinea pigs, using a fluorescence-based methodology. In nodose ganglia cells from SO(2)-exposed animals, intracellular Ca(2+) responses evoked by capsaicin (1 x 10(-7) and 1 x 10(-6) M) were significantly augmented (87% and 59%, respectively) compared to nodose ganglia from control animals. In vivo experiments, cough responses induced by a submaximal dose of aerosolized capsaicin (30 microM) were increased approximately 50% in SO(2) exposed animals compared to control animals. The enhanced cough response produced by SO(2) was inhibited by the corticosteroid, dexamethasone (10 mg/kg, p.o. b.i.d for 4 days and 10 mg/kg, p.o. once on day 5). In separate experiments, guinea pigs exposed to SO(2) displayed a decrease in respiratory frequency and minute ventilation and an increase in enhanced pause (PenH), a surrogate measure for pulmonary obstruction. Associated with the SO(2)-induced increase in cough and changes in respiratory parameters was an increase in BAL neutrophils. BAL neutrophil counts were 5+/-4 and 691+/-141 cells x 10(3)/ml for air and SO(2)-exposed animals, respectively. The neutrophillic inflammation induced by SO(2) was attenuated by dexamethasone treatment. Finally, staining for collagen, smooth muscle and goblet cells showed inflammation, remodeling and goblet cell metaphasia in the SO(2)-exposed animals. Our results demonstrate that SO(2) exposure enhances TRPV1 receptor function at the level of the nodose ganglia. This effect occurs in parallel with an increase sensitivity of the cough response to capsaicin.

The automatic recognition and counting of cough

Background

Cough recordings have been undertaken for many years but the analysis of cough frequency and the temporal relation to trigger factors have proven problematic. Because cough is episodic, data collection over many hours is required, along with real-time aural analysis which is equally time-consuming.

A method has been developed for the automatic recognition and counting of coughs in sound recordings.

Methods

The Hull Automatic Cough Counter (HACC) is a program developed for the analysis of digital audio recordings. HACC uses digital signal processing (DSP) to calculate characteristic spectral coefficients of sound events, which are then classified into cough and non-cough events by the use of a probabilistic neural network (PNN). Parameters such as the total number of coughs and cough frequency as a function of time can be calculated from the results of the audio processing.

Thirty three smoking subjects, 20 male and 13 female aged between 20 and 54 with a chronic troublesome cough were studied in the hour after rising using audio recordings.

Results

Using the graphical user interface (GUI), counting the number of coughs identified by HACC in an hour long recording, took an average of 1 minute 35 seconds, a 97.5% reduction in counting time. HACC achieved a sensitivity of 80% and a specificity of 96%. Reproducibility of repeated HACC analysis is 100%.

Conclusion

An automated system for the analysis of sound files containing coughs and other non-cough events has been developed, with a high robustness and good degree of accuracy towards the number of actual coughs in the audio recording.

Cough in the community: a cross sectional survey and the relationship to gastrointestinal symptoms

BACKGROUND

The prevalence and severity of chronic cough in the community is uncertain. In a large population of representative normal subjects, we explored the relationship between self-reported cough severity and frequency, and factors known to be related to the aetiology of chronic cough. In particular, we have examined the relative association between cough and symptoms of gastrointestinal disease.

METHODS

A cross-sectional survey was undertaken in 36 general practices with subjects randomly selected from practice computer databases. Baseline lifestyle and demographic characteristics were recorded. Participants were asked how often in the previous 2 months they had experienced bouts or spasms of coughing. Cough symptom status was dichotomised into symptomatic using a cut off of bouts or spasms of coughing at a frequency of between once a week and once a day or above. Gastrointestinal data were collected using validated methodology.

RESULTS

Questionnaires were sent to 6416 subjects and 4003 (62%) responded. The prevalence of chronic cough was 12%, and was severe in 7%. Following multivariate analysis, regurgitation (OR 1.71; 99% CI 1.20 to 2.45) and irritable bowel syndrome (OR 2.00; 99% CI 1.47 to 2.72) were strong predictors of cough. Smoking (OR 1.61; 99% CI 1.18 to 2.19), declining social class (OR 1.63; 99% CI 1.04 to 2.57), and quality of life at baseline (OR 1.63; 99% CI 1.13 to 2.35) were also significantly associated.

CONCLUSION

Chronic cough is a common symptom in the general population. Its strong association with gastrointestinal disease may have aetiological significance.

Cough sensitivity in pure cough variant asthma elicited using continuous capsaicin inhalation

BACKGROUND

Cough variant asthma has recently been described, mainly as airway inflammation in relation to bronchial asthma, but the relationship between the two types of asthma remains unclear. Further studies of cough receptor sensitivity are necessary to fully characterize cough variant asthma.

METHODS

We assessed the relevance of testing cough sensitivity using an Astograph with continuous capsaicin inhalation, and compared the results with those obtained using intermittent inhalation. We showed the clinical applicability of testing cough sensitivity (0.156-80 microM capsaicin; five or more coughs, 1 minute of continuous inhalation at each concentration) using this method. We compared cough sensitivity among patients with pure cough variant asthma who did not develop bronchial asthma after an observation period of at least 1 year, patients with bronchial asthma and healthy individuals.

RESULTS

The continuous cough sensitivity test using the Astograph was reproducible and reliable. Cough sensitivity in patients with pure cough variant asthma was significantly higher than that in healthy individuals.

CONCLUSIONS

The cough sensitivity of patients with cough variant asthma is not necessarily identical to that of healthy individuals.

Effect of neuromuscular electrical stimulation on cough capacity and pulmonary function in patients with acute cervical cord injury

OBJECTIVE

To assess the effectiveness of neuromuscular electrical stimulation (NMES) on cough capacity and prevention of pulmonary complication in patients with acute cervical cord injury.

DESIGN

A randomized controlled trial.

SUBJECTS

Twenty-six tetraplegic patients with cervical spinal cord injury, 13 in the NMES therapy group and 13 in the control group.

METHODS

NMES was applied to the clavicular portion of the pectoralis major and abdominal muscle. Pulmonary function tests were performed before and after therapy, and at 3 months and 6 months follow-up. The pulmonary complications in this 6-month follow-up period were also recorded.

RESULTS

After the 4-week therapy, and at 3 months and 6 months follow-up testing, patients in the NMES therapy group displayed significant improvement in their peak expiratory flow, forced expiratory volume in 1 second, forced vital capacity, maximal expiratory pressure and maximal inspiratory pressure, compared with those in the control group (p<0.05). Patients in the NMES therapy group also had fewer pulmonary complications in the follow-up period.

CONCLUSION

NMES over the pectoralis and abdominal muscles might improve cough capacity and pulmonary function in cervical spinal cord injury with tetraplegia. This improvement might last for 6 months. With this improvement, pulmonary complications were reduced.

A new tool to assess and monitor the burden of chronic cough on quality of life: Chronic Cough Impact Questionnaire

INTRODUCTION

Chronic cough, one of the most frequent causes for a patient to consult a medical practitioner, limits the course of normal activities in everyday life of the patient affected (work, physical activities, social relations, night sleep). By now, there are few validated questionnaires for the evaluation of the impact of this symptom in the patient's quality of life (QoL). For this reason, we created a new questionnaire for the assessment of QoL in patients affected by chronic cough (Chronic Cough Impact Questionnaire, CCIQ).

MATERIALS AND METHODS

In the development procedure of CCIQ an initial questionnaire of 40 items was compiled and given to a first pool of 170 patients, each coming to our attention because of chronic cough; then the 25 most significant items were detected and converted into questions evaluating the answers on a Likert scale of five steps. Consequently, this final questionnaire underwent a validation procedure to assess its construct validity, internal consistency, reliability, and responsiveness. 95 patients (44.2% F, 55.8% M) were evaluated (age 53.69 +/- 11.7 years).

RESULTS

Following a statistical analysis, CCIQ showed a four-dimensional structure and good levels of internal consistency for the extracted factors: sleep/concentration (79.98), relationship (86.98), daily life impact (69.04), and mood (65.41). In stable conditions CCIQ showed a good reliability, ranged between 0.67 and 0.88. Responsiveness to clinical changes was accomplished.

DISCUSSION

These results provide evidence that CCIQ has specificity enough for being a valid tool for detecting the relative burden of cough on subjective well-being, and for obtaining a global evaluation both of chronic cough impact and of treatments for it, taking into account the patient's point of view. The CCIQ was easily and quickly filled in by the patients while waiting, and it was accepted by the patients.

The antitussive effect of placebo treatment on cough associated with acute upper respiratory infection

OBJECTIVE

The objective of this study was to determine the effects of a placebo treatment on cough in patients with cough associated with acute upper respiratory tract infection (URTI).

METHODS

Patients with dry or slightly productive cough associated with a history of URTI were recruited. Cough frequency (CF) over 15 minutes was recorded by means of a microphone connected to a pen recorder. Cough suppression time (CST) was recorded when patients were instructed by means of a red light to try not to cough. Patients received either a single dose of vitamin E (placebo treatment) or no treatment. CF and CST were recorded before and 15 minutes after treatment.

RESULTS

Twenty-seven patients were randomized to placebo treatment and 27 to the no-treatment group (mean age 22.6 years). The median difference between post- and pretreatment CF was -3 in the no-treatment group and -18 in the placebo group (p = .0003). There was a significant increase in CST in the placebo group compared with no treatment (p = .027).

CONCLUSIONS

The results demonstrate that placebo treatment has significant antitussive activity. This placebo effect may be related to generation of central neurotransmitters such as endogenous opioids.

Chronic cough in children: recent advances

Recurrent cough in children is a very common symptom of respiratory disease. Most children who cough, however, have normal pulmonary function. This article presents a diagnostic framework for chronic cough and a recommended management plan in order to avoid over investigation and over treatment of a generally benign and self-remitting condition. Pathophysiology of cough and recent advances in treatment options are also included.

Passage à la chronicité d’une toux : quels mécanismes ?

INTRODUCTION

In some situations such as post-virus or post whooping cough, a non productive subacute cough may occur without apparent local inflammation, epithelium abnormalities or bronchoconstriction. This subacute or chronic cough represents a real syndrome (cough disease) due to the central nervous system (CNS) and its ortho and parasympathic outputs. At the CNS level, functional disturbancies and neosynaptogenesis can be described, with the intervention of the NMDA-type glutamatergic receptors.

STATE OF ART

The neurons located in the expiratory area of the breathing center (Pre-Boetzinger complex of the lower brainstem) present exagerated responses to stimuli, due to the repetitive stimulation of the NMDA receptors; this phenomenon is similar to long-term-potentiation (LTP), the molecular basis of learning, memory and neosynaptogenesis. The cough reflex is thus amplified and rapidly chronic and would justify any pharmacological intervention at the NMDA-receptors level.

PERSPECTIVES

More recently 5TH4 receptors have been implied in the control of respiration; an overexpression of these receptors in the Pre-Boetzinger area could contribute to an increase of the cough reflex.

CONCLUSION

The present review aims at summarizing the main rationale target to pharmacologically block the chronic cough.

Idiopathic chronic cough and organ-specific autoimmune diseases: a case–control study

The marked female predominance in cases of idiopathic chronic cough and its association with mild chronic lymphocytic airway inflammation suggests an underlying autoimmune process. We set out to test the hypothesis that idiopathic chronic cough is associated with other organ-specific autoimmune diseases in a case control study. Twenty-two patients with idiopathic chronic cough and 65 community-matched controls for age and sex who responded to a self-administered questionnaire were asked about the presence of autoimmune disease, other medical problems and drug history. All subjects were invited to have a blood test for an autoimmune screen. Thirteen out of 22 (59%) patients with idiopathic chronic cough and eight out of 65 (12%) age- and sex-matched controls reported organ-specific autoimmune disease (odds ratio 8.8; 95% confidence interval 2.4-31.8, P<0.001). Organ-specific autoantibodies were present in a significantly higher proportion of cases than controls (40% vs. 13%; P = 0.047). These findings suggest a relationship between idiopathic chronic cough and organ-specific autoimmunity.

Effect of carbocysteine on cough reflex to capsaicin in asthmatic patients

AIMS

Cough, one of the main symptoms of bronchial asthma, is a chronic airway inflammatory disease with functionally damaged bronchial epithelium. Recently, we established an animal model with cough hypersensitivity after antigen challenge and clearly showed the protective effect of carbocysteine in this model. This study was designed to investigate the clinical effect of carbocysteine for cough sensitivity in patients with bronchial asthma.

METHODS

The effects of the two orally active mucoregulatory drugs, carbocysteine and ambroxol hydrochloride, on cough response to inhaled capsaicin were examined in 14 patients with stable asthma. Capsaicin cough threshold, defined as the lowest concentration of capsaicin eliciting five or more coughs, was measured as an index of airway cough sensitivity.

RESULTS

Geometric mean values of the cough threshold at run-in (baseline) and after 4 weeks' treatment of placebo, 1500 mg day-1 of carbocysteine and 45 mg day-1 of ambroxol hydrochloride were 12.8 micro M (95% confidence interval [CI] 5.5, 29.6), 11.0 micro M (95% CI 4.4, 27.5), 21.0 micro M (95% CI 8.8, 50.2) and 11.6 micro M (95% CI 5.8, 23.3), respectively. The cough threshold for carbocysteine was significantly greater than those of ambroxol hydrochloride (P = 0.047) and placebo (P = 0.047), respectively.

CONCLUSIONS

These findings indicate that carbocysteine administration may be a novel therapeutic option for asthmatic patients, especially with cough variant asthma.

Development of a symptom specific health status measure for patients with chronic cough: Leicester Cough Questionnaire (LCQ)

BACKGROUND

Chronic cough is a common condition which has a significant impact on quality of life. Assessment and management are hampered by the absence of well validated outcome measures. The development and validation of the Leicester Cough Questionnaire (LCQ), a self-completed health related quality of life measure of chronic cough, is presented.

METHODS

Patients with chronic cough were recruited from outpatient clinics. The development of the LCQ consisted of three phases: phase 1 (item generation); phase 2 (item reduction, allocation of items to domains and validation of questionnaire); phase 3 (repeatability and responsiveness testing of final version of questionnaire).

RESULTS

Phase 1: Literature review, multidisciplinary team meeting and 15 structured interviews with chronic cough patients generated 44 items (LCQ1) with a 7 point Likert response scale. Phase 2: 104 chronic cough outpatients completed the LCQ1 along with an importance rating for each item. The clinical impact factor method was used for item reduction to 19 items (LCQ2: final version). These items were divided into three domains (physical, psychological and social) following expert opinion. Internal reliability, as assessed using Cronbach's alpha coefficients, varied between 0.79 and 0.89. Concurrent validity was high when the LCQ2 (n=56) was compared with a cough visual analogue score (r=-0.72). There was a moderate relationship with response to the St George's Respiratory Questionnaire (r=-0.54) and SF36 total score (r=0.46). Phase 3: Two week repeatability (n=24) was high with intraclass correlation coefficients for domains varying between 0.88 and 0.96. Responsiveness in nine patients whose cough was successfully treated varied within domains from an effect size of 0.84 to 1.75.

CONCLUSION

The LCQ is a valid, repeatable 19 item self-completed quality of life measure of chronic cough which is responsive to change. It should be a useful tool in clinical trials and longitudinal studies.

The powerful placebo in cough studies?

Placebo treatment has been reported to improve subjective and objective measures of disease in up to 30-40% of patients with a wide range of clinical conditions. A review of 8 clinical trials on the effects of antitussive medicines on cough associated with acute upper respiratory tract infection shows that 85% of the reduction in cough is related to treatment with placebo, and only 15% attributable to the active ingredient Treatment with a cough medicine can be viewed as consisting of three components: pharmacological, physiological (demulcent) and placebo. The placebo effect is related to belief in the effectiveness of the treatment and this idea must in some way influence the central control of cough. Studies on the placebo effect of analgesics indicate that the placebo effect may be mediated by endogenous opioid neurotransmitters and this may explain the analgesic potency of opioid medicines such as morphine. In the present paper a model is proposed to explain the antitussive effects of placebo treatment on the basis of endogenous opioid neurotransmitters. With active pharmacological ingredients contributing only 15% to the effects of cough treatment it seems reasonable to conduct more research on the other components of treatment such as placebo.

Cough provocation tests: their clinical value

Cough provocation testing was originally developed for testing new anti-tussive agents and still remains a mandatory tool in their development. The methodology has been developed into single breath and multiple breath techniques. Neither has been fully validated; however, single breath techniques have been used in a number of patient series of more than 100 patients. These studies show that the cough reflex is more sensitive in patients with cough and becomes normal on recovery. Studies in the common cold and in angiotensin converting enzyme inhibitor-associated cough suggest that this may be cause and effect. These results point to a utility for cough provocation testing in epidemiology but not in routine clinical practice. The one exception in clinical practice is in the assessment of patient post stroke where it is a better method, than voluntary cough testing, for assessing damage to the cough reflex. Other than use in epidemiology it remains an invaluable tool in hypothesis testing.

Central pathways for cough in man--unanswered questions

Central processing of afferent cough impulses occurs in a putative 'cough centre' in the dorsal medulla where the reflex is subject to considerable cortical control. Little is known about the central neurotransmitters and mediators which mediate cough in humans. Previous animal and human studies suggest that the antitussive effect of opiates may be mediated at central 5-HT receptors. In three studies in healthy human volunteers, we have investigated the potential role of central cholinergic and dopaminergic receptors in the mediation of cough, and the potential role of 5-HT receptors in the antitussive action of opiates. Intravenous administration of atropine or physostigmine had no effect on capsaicin-induced cough. Similarly, oral administration of L-dopa, bromocriptine or haloperidol had no effect on capsaicin-induced cough. Compared with saline, intravenous morphine significantly suppressed capsaicin-induced cough and increased drowsiness. Compared with placebo, pretreatment with oral pizotifen significantly attenuated the antitussive effect of morphine, but not the sedative effect. This suggests that in humans, an agonist action at 5-HT2 and/or 5-HT1 receptors may be involved in the antitussive effect of morphine, but not its sedative effect. Further knowledge of central cough pathways in humans must await the availability of more selective receptor agonists and antagonists for human studies. This offers the promise of effective antitussive therapy. The challenge is to find an antitussive agent which can return the abnormal sensitivity of the cough reflex to normal, without adverse effects.