The potential role of gastroesophageal reflux in asthma.
Gastroesophageal reflux disease (GERD) afflicts approximately 20% of adults in the United States on a weekly basis and 40% on a monthly basis, and is also a trigger for asthma. The prevalence of GERD is higher in asthmatics compared to control groups, with 77% of asthma patients having reflux symptoms and 82% of asthmatics having abnormal esophageal acid contact times on 24-hour esophageal pH testing. Esophageal acid elicits respiratory responses including decreases in airflow, oxygen saturation, and increases in respiratory resistance, minute ventilation, and respiratory rate. Mechanisms of esophageal acid-induced bronchoconstriction include a vagally-mediated reflex, heightened bronchial reactivity, and microaspiration. Esophageal acid also produces airway neurogenic inflammatory responses with the release of substance P, tachykinins, nitric oxide, and other cytokines. Predisposing factors to GERD development in asthmatics include autonomic dysregulation, an increased pressure gradient between the thorax and the abdomen, a high prevalence of hiatal hernia, and altered crural diaphragm function. Theophylline may also potentiate GERD. Therapy of GERD improves asthma outcome. In combined studies examining 326 medically treated asthma patients, asthma symptoms improved in 69% of patients. Surgical therapy trials in 417 asthma patients show asthma symptoms improved in 79%. Management strategies for GERD in asthmatics with reflux symptoms include utilizing an empiric trial of a proton pump inhibitor for three months while measuring asthma outcomes. Since GERD may be clinically ''silent'' in asthma patients, consider 24-hour esophageal pH testing in severe asthma patients who do not have GERD symptoms. Future research will develop the association between asthma and GERD.
Pulmonary Division, Allergy and Critical Care Medicine, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA. sharding@uab.edu
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