Gastroesophageal reflux disease (GERD) is the sole cause of chronic cough in up to 20-40% of all cases, and majority of these patients with GERD-induced cough have no classic "heartburn" symptoms. This important cause of cough can thus be difficult to detect. Non-invasive radiologic tests for GERD such as barium swallow is imperfectly sensitive in subjects with GERD-induced cough. The 24 hour pH probe, which continuously monitors esophageal pH and can correlate cough events with reflux events, is considered to be the gold standard test. However, this test is expensive, invasive, and not universally available.

The goal of the current study is to compare simultaneous measurements of esophageal pH with exhaled breath condensate pH after cough episodes, in patients with symptomatic cough. The cause of cough will be determined by a standard protocol, which includes 24 hour pH probe studies, and assessment for asthma, upper airway causes and sinus disease, and medication effects. All subjects will undergo 24 hour pH monitoring. During this monitoring period, they press an event button on the pH recording device to indicate a cough episode. After six such events, they will immediately perform an EBC collection, and EBC pH will subsequently be analyzed. Differences between pH changes in the group with cough cause by GERD will be compared to pH measurements in the group with cough but no GERD, to determine the sensitivity and specificity of pH changes for discriminating between the two groups, and optimal threshold values for pH changes in EBC.