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. We aimed to determine the predictors of objective cough frequency in chronic cough patients presenting to a tertiary referral clinic.
Methods: 100 subjects [mean age 55.8yrs (SD±11.0), 65 female, median cough duration 4yrs (IQR 2.0-10.0yrs)] with unexplained chronic cough, completed flow-volume loops (FEV1 103% predicted (SD±15.2), FEF50; 68.8% predicted, SD±24.1), methacholine challenge (42 % positive), citric acid cough reflex sensitivity [C5; 0.12M (IQR 0.06-0.50M)] and the Leicester Cough Questionnaire. 24-hour ambulatory cough monitoring was performed in 86 subjects; manually counted coughs were quantified as the number of explosive cough sounds per hour.
Results: Females coughed significantly more than males [geometric mean 16.6 coughs/hr (95%CI 13.1-21.0) versus 9.4coughs/hr (95% CI 6.4-13.9), p=0.01)]. The cough reflex was also more sensitive in females than males (median logC5 -0.9M versus -0.6M, p=0.002) but cough related quality of life was similar (females 12.0 (±3.6) versus males 12.2 (±3.2), p=0.76). Linear regression analysis showed 41% of the variation in cough rate was predicted by sex (p=0.01), logC5 (p= <0.001) and age (p=0.003) but not lung function or bronchial hyper-reactivity.
Conclusions: Ambulatory objective cough monitoring provides novel insights into factors modulating chronic cough. These findings suggest that effects of sex and age must be taken into account in the study of cough and when designing clinical trials testing novel anti-tussive agents.