Gastroesophageal reflux (GER) is common in those with asthma, with 77% of asthmatics complaining of heartburn, with 41% experiencing reflux-associated respiratory symptoms. Likewise, 24% of those with asthma that is difficult to control have "clinically silent" GER. There are no studies examining nocturnal reflux symptoms in asthmatics. Esophageal dysmotility is also common, and abnormal esophageal acid contact times on 24h esophageal pH tests were found in 82% of asthmatics examined consecutively. Most asthmatics with GER also have abnormal esophageal acid contact times while in the supine position, reflecting sleep time. Endoscopic evidence of esophagitis was found in 43% of asthmatics. Two mechanisms of bronchoconstriction induced by esophageal acid have been proposed: a vagally mediated reflex, by which esophageal acid in the distal esophagus causes reflex bronchoconstriction, and microaspiration. Although there is conflicting evidence, distal esophageal acid causes a decrease in peak expiratory flow rates, an increase in respiratory resistance, and an increase in minute ventilation. If microaspiration is present, there is further augmentation of this airway response. Although only a few studies have been performed in those with nocturnal asthma with GER, one study in a pediatric population showed that esophageal acid infusions caused more airway responses at 04:00 than at 24:00. Also, asthmatic children with nocturnal asthma symptoms have a higher reflux score, with a positive correlation between reflux score and nighttime-associated wheezing. Despite these findings in children, a study performed in sleeping adults with nocturnal asthma noted no alterations in airflow resistance with esophageal acid, concluding that GER contributed little to the nocturnal worsening of asthma. There are also gastroesophageal circadian issues that may influence GER in asthmatics. Gastric acid secretion peaks at approximately 21:00, and gastric emptying is delayed when a meal is given at 20:00 versus 08:00. Esophageal acid clearance is delayed significantly during sleep, and acid clearance occurs during arousals. Upper esophageal sphincter (UES) pressure also decreases with sleep onset, which may predispose to microaspiration. Further research is needed to clarify what role nocturnal reflux has on nocturnal asthma and airway inflammation and whether circadian rhythm factors alter airway responses to esophageal acid.