Reviews and feature article
A comparison of objective and subjective measures of cough in asthma

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Background

Cough is widely recognized as a key symptom in the diagnosis and the monitoring of asthma, but little is known about how best to assess cough in asthma.

Objective

To determine how objective cough rates correlate with subjective measures of cough in asthma.

Methods

We studied 56 subjects, median age 42.0 years (range, 28.5-71), 34 (60.7%) female, with asthma. Subjects performed cough reflex sensitivity testing (concentration of citric acid causing 2 and 5 coughs [C2 and C5]), 24-hour fully ambulatory cough recordings, subjectively scored the severity of their cough (visual analog scales and 0-5 score) and completed a cough-related quality of life questionnaire (Leicester Cough Questionnaire). Ambulatory cough recordings were manually counted and reported in cough seconds per hour (cs/h).

Results

The median time spent coughing was 2.6 cs/h (range, 0.0-14.2), with subjects spending more time coughing by day (median, 3.9 cs/h [0.0-18.5]) than by night (median, 0.3 cs/h [0.0-8.7]; P < .001). A weak inverse relationship was seen between day cough rates and log10C2 (r = –0.39; P = .03) but not log10C5 (r = –0.08; P = .65). Objective time spent coughing was also weak-moderately associated with subjective cough scores and visual analog scales, and most strongly correlated with cough-related quality of life (r = –0.54; P < .001).

Conclusion

Subjective measures of cough and cough reflex sensitivity are poor surrogates for objective cough frequency in asthma. When designing studies to assess interventions for cough in asthma, we advocate a combination of both objective measures of cough and cough-related quality of life.

Section snippets

Subjects

To study a wide range of asthma severity, we recruited subjects from 2 sources at a regional respiratory unit (North West Lung Centre, Manchester, United Kingdom): a database of asthma volunteers and respiratory outpatient clinics (including a severe asthma clinic). Inclusion criteria were the diagnosis of asthma by a specialist pulmonologist and a positive methacholine challenge test (except in those with severe asthma). Healthy volunteers were also recruited to allow for comparisons of cough

Subjects

We studied 56 subjects with asthma (median age, 42.0 years [range, 28.5-71], 34 [60.7%] female; Table II). Eleven (19.6%) subjects were exsmokers with a median smoking history of 1.5 pack-years (range, 0.3-6.0). Inhaled corticosteroids (ICSs) were taken by 32 (57.1%) subjects, and 3 (5.4%) were taking oral corticosteroids (median dose, 20 mg [7-30]). One subject was maintained with 8-weekly intramuscular triamcinolone injections. Bronchial hyperreactivity to methacholine was demonstrated in 49

Discussion

This study is the first to examine the relationships between objective and subjective measures of cough in subjects with classic asthma, not selected for the symptom of cough. The correlations between objective cough frequency and subjective measures of cough in asthma are at best moderate, and the relationship with citric acid cough reflex sensitivity is only weak for the less commonly used C2 endpoint. The best relationship with objective cough rates was seen for cough-related quality of

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  • Cited by (0)

    Supported by the North West Lung Research Centre Endowment Fund.

    Disclosure of potential conflict of interest: J. A. Smith is a consultant for Schering- Plough, receives grant support from Schering-Plough, and is an inventor on a cough-monitoring patent owned by the University Hospital of South Manchester Trust, patent licensed to Vitalograph Ltd. A. A. Woodcock is a consultant for GlaxoSmithKline, Chiesi, and Schering-Plough; receives grant support from Schering-Plough and AstraZeneca; and is a co-inventor of an ambulatory cough monitor patent owned by the University Hospital of South Manchester and licensed by Vitalograph Ltd. The rest of the authors have declared that they have no conflict of interest.

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