Sex differences and predictors of objective cough frequency in chronic cough

Background: Women are consistently over-represented in specialist cough clinics and known to have a more sensitive cough reflex than men. Whether female sex and other patient characteristics are associated with higher cough rates is not known. A study was conducted to determine the predictors of objective cough frequency in patients presenting to a tertiary referral clinic with chronic cough. Methods: 100 subjects (65 women) of mean (SD) age 55.8 (11.0) years and median cough duration 4 years (IQR 2.0-10.0) with unexplained chronic cough completed flow-volume loops (mean (SD) forced expiratory volume in 1 s 103 (15.2)% predicted; forced expiratory flow (FEF50) 68.8 (24.1)% predicted), methacholine challenge (42% positive), citric acid cough reflex sensitivity (C5; 0.12 M (IQR 0.06-0.50)) and the Leicester Cough Questionnaire. 24-h ambulatory cough monitoring was performed in 86 subjects; manually counted coughs were quantified as the number of explosive cough sounds per hour. Results: Women coughed significantly more than men (geometric mean 16.6 coughs/h (95% CI 13.1 to 21.0) vs 9.4 coughs/h (95% CI 6.4 to 13.9), p = 0.01)). The cough reflex was also more sensitive in women than in men (median logC5 -0.9 M vs -0.6 M, p = 0.002), but cough-related quality of life was similar in women and men (12.0 (3.6) and 12.2 (3.2), respectively, p = 0.76). Linear regression analysis showed that 38.6% of the variation in cough rate was predicted by sex (p = 0.01), logC5 (p