A comparison of objective and subjective measures of cough in asthma

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 log10 C2 ( r = –0.39; P = .03) but not log10 C5 ( 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.