Identification of acid reflux cough using serial assays of exhaled breath condensate pH

John Hunt¹ , Yuanlin Yu¹ , James Burns² , Benjamin Gaston¹ , Lina Ngamtrakulpanit¹ , Dorothy Bunyan¹ , Brian K Walsh¹ , Alison Smith¹ and Stephanie Hom¹

¹Division of Pediatric Respiratory Medicine, Box 800386, University of Virginia, Charlottesville, Virginia 22908, USA

²Center for Laryngeal Surgery and Voice Rehabilitation, Massachusetts General Hospital, One Bowdoin Square, Boston, MA 02114, USA

author email corresponding author email

Cough 2006, 2:3doi:10.1186/1745-9974-2-3


Published:	11 April 2006

Abstract

Background

Chronic cough is a common problem, frequently caused or exacerbated by acid reflux. Diagnosis of acid reflux cough is haphazard currently, often relying on long therapeutic trials of expensive medications. We tested the hypothesis that the most relevant mechanistic component of acid reflux in chronic cough is when it rises to the level of the airway where acid can potentially be aspirated. We further wished to determine if multi-sample exhaled breath condensate (EBC) pH profiles can identify chronic cough patients likely to respond to proton pump inhibitor therapy.

Methods

59 subjects were recruited for this study. Initially we examined EBC pH (gas-standardized with Argon) in the setting of 15 experimental pharyngeal acid challenges to determine duration of EBC acidification. Subsequently, we enrolled 22 healthy subjects to determine a normal multi-sample exhaled breath condensate pH profile over 1–3 days. We additionally obtained multi-sample EBC pH profiles in 22 patients with chronic cough. These samples were timed to occur after coughing episodes. Exhaled breath condensate pH was measured after gas standardization.

Results

We found that exhaled breath condensate pH is substantially reduced for approximately 15 minutes after pharyngeal acid load. Healthy subjects rarely have any low EBC pH values (defined as < 7.4 based on a normative reference range from 404 healthy subjects). Patients with chronic cough who subsequently responded well to proton pump inhibition (n = 8) invariably had one or more cough episodes associated with EBC acidification. No patient who had normal EBC pH with each of their cough episodes reported a clinically relevant response to proton-pump inhibition.

Conclusion

Patients whose cough responds to proton pump inhibition have transient exhaled breath condensate acidification with coughing episodes, supporting the role of airway acidification in reflux-triggered cough. Multi-sample EBC pH profiles, involving samples collected immediately subsequent to a coughing episode, may be useful appropriately to direct therapy to those patients with cough who have relevant acid reflux.