title: Predictors of objective cough frequency in chronic obstructive pulmonary disease.
abstract: BACKGROUND
  Cough is one of the principal symptoms of chronic obstructive pulmonary disease (COPD) but the potential drivers of cough are likely to be multifactorial and poorly understood.
  
  
  OBJECTIVE
  To quantify cough frequency in an unselected group of subjects with COPD and investigate the relationships between cough, reported sputum production, smoking, pulmonary function, and cellular airway inflammation.
  
  
  METHODS
  We studied 68 subjects with COPD (mean age, 65.6 ± 6.7 yr; 67.6% male; 23 smokers; 45 ex-smokers) and 24 healthy volunteers (mean age, 57.5 ± 8.9 yr; 37.5% male; 12 smokers; 12 nonsmokers). Subjects reported cough severity, cough-specific quality of life, and sputum expectoration and performed spirometry, sputum induction, cough reflex sensitivity to capsaicin, and 24-hour ambulatory cough monitoring.
  
  
  RESULTS
  COPD current smokers had the highest cough rates (median, 9 coughs/h [interquartile range, 4.3-15.6 coughs/h]), almost double that of COPD ex-smokers (4.9 [2.3-8.7] coughs/h; P = 0.018) and healthy smokers (5.3 [1.2-8.3] coughs/h; P = 0.03), whereas healthy volunteers coughed the least (0.7 [0.2-1.4] coughs/h). Cough frequency was not influenced by age or sex and only weakly correlated with cough reflex sensitivity to capsaicin (log C5 r = -0.36; P = 0.004). Reported sputum production, smoking history, and current cigarette consumption strongly predicted cough frequency, explaining 45.1% variance in a general linear model (P < 0.001). In subjects producing a sputum sample, cough frequency was related to current cigarette consumption and percentage of sputum neutrophils (P = 0.002).
  
  
  CONCLUSIONS
  Ambulatory objective monitoring provides novel insights into the determinants of cough in COPD, suggesting sputum production, smoking, and airway inflammation may be more important than sensitivity of the cough reflex.
authors.affiliation: Respiratory Research Group, Faculty of Medicine and Human Sciences, The University of Manchester, Manchester Academic Health Science Centre, Manchester, United Kingdom.
authors.forename: Helen
authors.initials: H
authors.lastname: Sumner
authors.forename: Ashley
authors.initials: A
authors.lastname: Woodcock
authors.forename: Umme
authors.initials: U
authors.lastname: Kolsum
authors.forename: Rachel
authors.initials: R
authors.lastname: Dockry
authors.forename: Aili L
authors.initials: AL
authors.lastname: Lazaar
authors.forename: Dave
authors.initials: D
authors.lastname: Singh
authors.forename: Jørgen
authors.initials: J
authors.lastname: Vestbo
authors.forename: Jaclyn A
authors.initials: JA
authors.lastname: Smith
mesh_terms: D000368:Aged; D000704:Analysis of Variance; D002211:Capsaicin; D016022:Case-Control Studies; D003371:Cough / Q000209:etiology / Q000503:physiopathology*; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008297:Male; D008875:Middle Aged; D009504:Neutrophils / Q000166:cytology*; D029424:Pulmonary Disease, Chronic Obstructive / Q000150:complications*; D011788:Quality of Life; D012720:Severity of Illness Index; D012907:Smoking / Q000009:adverse effects / Q000503:physiopathology*; D013147:Spirometry; D013183:Sputum / Q000166:cytology*
chemical_list: D002211:Capsaicin