The impact of continuous positive airway pressure on the lower esophageal sphincter

Abstract

The lower esophageal sphincter (LES) is the primary barrier to gastroesophageal reflux. Reflux is associated with periods of LES relaxation, as occurs during swallowing. Continuous positive airway pressure (CPAP) has been shown to reduce reflux in individuals with and without sleep apnea, by an unknown mechanism. The aim of this study was to determine the effect of CPAP on swallow-induced LES relaxation. Measurements were made in 10 healthy, awake, supine individuals. Esophageal (Pes), LES (Ples), gastric (Pg), and barrier pressure to reflux (Pb ϭ Ples Ϫ Pg) were recorded using a sleeve catheter during five swallows of 5 ml of water. This was repeated at four levels of CPAP (0, 5, 10, and 15 cmH 2O). Pressures were measured during quiet breathing and during the LES relaxation associated with a swallow. Duration of LES relaxation was also recorded. During quiet breathing, CPAP significantly increased end-expiratory Pes, Ples, Pg, and Pb (P Ͻ 0.05). The increase in Pb was due to a disproportionate increase in Ples compared with Pg (P Ͻ 0.05). During a swallow, CPAP increased nadir Ples, Pg, and Pb and decreased the duration of LES relaxation (4.1 s with 0-cmH 2O CPAP to 1.6 s on 15-cmH2O CPAP, P Ͻ 0.001). Pb increased with CPAP by virtue of a disproportionate increase in Ples compared with Pg. This may be due to either reflex activation of LES smooth muscle, or nonspecific transmission of pressure to the LES. The findings suggest CPAP may make the LES less susceptible to reflux by increasing Pb and decreasing the duration of LES relaxation. lower esophageal sphincter relaxation; esophageal function; gastroesophageal reflux GASTROESOPHAGEAL REFLUX IS common, with ϳ20% of the general community reporting reflux symptoms on a weekly basis (19). Nocturnal reflux has been reported to occur in 9 -11% of the population (9) and may be particularly harmful to the esophagus because of the associated prolonged acid clearance time (5). Obstructive sleep apnea (OSA) is an aggravating factor for nocturnal reflux, presumably because of the development during obstructive events of pressure gradients across the lower esophageal sphincter (LES) that favor reflux.The LES is a high-pressure zone located between the esophagus and stomach, which acts as a barrier to reflux. Pressure within the sphincter is generated by contraction of esophageal smooth muscle and of the crural diaphragm during inspiration.Baseline LES pressure (Ples) fluctuates with respiration, increasing during inspiration as a consequence of diaphragm contraction. In normal, healthy individuals, relaxation of the LES is initiated by swallowing and lasts until the esophageal peristaltic contraction reaches the sphincter segment. Such relaxation is essential to allow passage of the swallowed bolus from the esophagus to the stomach, but may also result in stomach contents entering the esophagus. The LES may also relax in the absence of esophageal peristaltic contraction. Such transient LES relaxations, which usually occur in response to gastric distension (12), underlie ...

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