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 = .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.
Respiratory Research Group, Faculty of Medicine and Human Sciences, The University of Manchester, Manchester Academic Health Science Centre, Manchester, England.
Samantha
S
Decalmer
Applied Immunobiology and Transplantation Research Group, Institute of Cellular Medicine, University of Newcastle-upon-Tyne, Newcastle-upon-Tyne, England.
Rachel
R
Stovold
Respiratory Research Group, Faculty of Medicine and Human Sciences, The University of Manchester, Manchester Academic Health Science Centre, Manchester, England; Division of Gastroenterology and Hepatology, College of Medicine, Mayo Clinic, Jacksonville, FL.
Lesley A
LA
Houghton
Applied Immunobiology and Transplantation Research Group, Institute of Cellular Medicine, University of Newcastle-upon-Tyne, Newcastle-upon-Tyne, England.
Jeff
J
Pearson
Applied Immunobiology and Transplantation Research Group, Institute of Cellular Medicine, University of Newcastle-upon-Tyne, Newcastle-upon-Tyne, England.
Chris
C
Ward
Respiratory Research Group, Faculty of Medicine and Human Sciences, The University of Manchester, Manchester Academic Health Science Centre, Manchester, England; National Institute for Health Research Translational Research Facility in Respiratory Medicine, University Hospital of South Manchester, Manchester, England.
Angela
A
Kelsall
Respiratory Research Group, Faculty of Medicine and Human Sciences, The University of Manchester, Manchester Academic Health Science Centre, Manchester, England.
Helen
H
Jones
Respiratory Research Group, Faculty of Medicine and Human Sciences, The University of Manchester, Manchester Academic Health Science Centre, Manchester, England.
Kevin
K
McGuinness
Respiratory Research Group, Faculty of Medicine and Human Sciences, The University of Manchester, Manchester Academic Health Science Centre, Manchester, England; National Institute for Health Research Translational Research Facility in Respiratory Medicine, University Hospital of South Manchester, Manchester, England.
Ashley
A
Woodcock
Respiratory Research Group, Faculty of Medicine and Human Sciences, The University of Manchester, Manchester Academic Health Science Centre, Manchester, England. Electronic address: jacky.smith@manchester.ac.uk.
Jaclyn A
JA
Smith
D000328:Adult; D001992:Bronchoalveolar Lavage Fluid / Q000737:chemistry; D001999:Bronchoscopy; D002908:Chronic Disease; D003371:Cough / Q000175:diagnosis / Q000453:epidemiology / Q000209:etiology*; D017097:Electric Impedance; D004739:England / Q000453:epidemiology; D050782:Esophageal pH Monitoring; D004947:Esophagus; D005260:Female; D005500:Follow-Up Studies; D005764:Gastroesophageal Reflux / Q000150:complications* / Q000175:diagnosis / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D015994:Incidence; D008297:Male; D008875:Middle Aged; D013183:Sputum / Q000737:chemistry