A novel approach to studying the relationship between subjective and objective measures of cough

Background: Currently, no data are available on the relationship between changes in objective and subjective measures of cough, the magnitude of change in cough frequency perceived by patients as clinically meaningful, or the sample sizes required to show significant changes in cough therapeutic trials. Because patients anecdotally report reductions in cough severity while undergoing esophageal testing, we aimed to address these issues by assessing objective and subjective measures of cough with and without an esophageal catheter. Methods: Twenty-four-hour cough monitoring was performed on two occasions, with and without esophageal impedance/pH monitoring in 62 patients with chronic cough (mean age 56.8 years [SD ± 10.8]; 43 women; median cough duration 3.3 years [interquartile range (IQR), 2.0-10.0]). Cough was assessed objectively measuring coughs per hour and subjectively using a numerical cough score and a visual analog scale (VAS), scored separately for day and night, and then averaged to represent each 24-h period. Results: Objective cough frequency was reduced by a median of 33.3% (IQR, -68.8% to -13.0%; P < .001) with the catheter. The averaged day and night cough scores and VAS scores also significantly decreased, but changes in these did not correlate with decreases in cough frequency. Sample-size calculations suggested that crossover designs using objective cough frequency may be preferable in therapeutic trials. Conclusions: These observations provide useful information on the reduction in objective cough frequency scored as an improvement by patients with chronic cough and offer guidance for the design and powering of future therapeutic trials. Trial registry: ISRCTN; No.: ISRCTN62337037; URL: http://www.controlled- trials.com.