Chronic cough: Relationship between microaspiration, gastroesophageal reflux, and cough frequency

Background: Microaspiration is often considered a potential cause of cough. The aim of this study was to investigate the relationship between microaspiration, the degree and type of gastroesophageal reflux, and the frequency of coughing in patients with chronic cough. Methods: One hundred patients with chronic cough (mean [± SD] age, 55.8 years [± 11.0 years]; 65 women) and 32 healthy volunteers (median age, 43.5 years [interquartile range (IQR), 30-50.8 years]; 16 women) were recruited. Patients with chronic cough performed 24-h objective cough frequency with simultaneous esophageal impedance/pH monitoring and measurement of pepsin concentrations in sputum and BAL. Twelve healthy volunteers underwent bronchoscopy/BAL, and 20 underwent impedance/pH monitoring. Results: Patients with chronic cough had significantly more reflux episodes than healthy volunteers (median, 63.5 reflux episodes [IQR, 52.5-80.0] vs 59.0 [IQR, 41.8-66.0]; P = .03), although the absolute difference was small, and there was no difference in numbers of events extending into the proximal esophagus (median, 17.2% [IQR, 8.0%-26.0%] vs 20.3% [IQR, 5.1%-32.1%]; P = .36). BAL pepsin levels were also similar in chronic cough to control subjects (median, 18.2 ng/mL [range, 0-56.4 ng/mL] vs 9.25 ng/mL [range, 0-46.9 ng/mL]; P 5.27). Sputum but not BAL pepsin weakly correlated with the number of proximally occurring reflux events(r = 0.33, P = .045) but was inversely related to cough frequency(r = -0.52, P = .04). Sputum pepsin was, therefore, best predicted by combining the opposing influences of cough and proximal reflux(r = 0.50, P = .004). Conclusions: Proximal gastroesophageal reflux and microaspiration into the airways have limited roles in provoking chronic cough. Indeed, coughing appears to be protective, reducing pepsin concentration in the larger airways of patients with chronic cough. Trial registry: ISRCTN Register; No.: ISRCTN62337037; URL: www.isrctn.org.