Possible Mechanisms of Influence of Esophageal Acid on Airway Hyperresponsiveness

Airway hyperresponsiveness is among the defining phenomena in asthma. In this article, 3 mechanisms are reviewed to explain how gastroesophageal reflux (GER) may influence airway hyperresponsiveness. First, microaspiration may cause not only direct tissue injury, but may also trigger vagal reflexes. Second, acid infusion of the esophagus in a dog model and in humans has been shown to result in vagally mediated reflexes leading to bronchoconstriction. These reflexes have been studied using immunohistochemical techniques. Third, neuroinflammatory reflexes have been found to play a role in airway responses through the release of tachykinins, including substance P and neurokinin A. Combined, these 3 mechanisms may lead to an increase in vagal efferent impulses that can cause or augment airway hyperresponsiveness. Studies indicate that there is an increase in airway responsiveness in asthma patients who have documented GER. Further, based on the reported number of reflux episodes occurring during 24-hour pH monitoring, airway hyperresponsiveness to methacholine challenge tends to increase as GER worsens.