Background and purpose: The pressures generated within the upper esophageal sphincter (P-UES) and lower esophageal sphincter (P-LES) reflect the integrity of these barriers to gastroesophageal and pharyngoesophageal reflux, respectively. This study sought to describe the effects of sleep, respiration and posture on the function of the LES and the LES and the pressure differentials developed across them.Methods: Ten healthy volunteers (7M, 3F: 38 +/- 10 yr) without a history of sleep-disordered breathing or reflux underwent overnight polysomnography with simultaneous measurement of P-LES and P-UES using a purpose-built sleeve device (Dentsleeve). Posture was recorded but not controlled.Results: Subjects slept for 4.3 +/- 1.6 h. Compared to waking values, both end-inspiratory and end-expiratory PUES were significantly less during slow wave sleep (SWS) (p < 0.05). However, P-LES was unaffected by sleep stage. During wakefulness and all stages of sleep, both P-UES and P-LES were greater at end-inspiration than end-expiration (p < 0.05). Similar relationships were observed whether subjects were supine or in the lateral decubitus position.Conclusion: Sleep decreases the effectiveness of the UES to act as a barrier to pharyngoesophageal reflux, particularly during slow wave sleep (SWS). UES pressure varies with respiration, with minimal values observed during expiration. Hence, barrier function of the UES appears most impaired during SWS, in the expiratory phase of the respiratory cycle. The LES pressure and its barrier pressure also vary with respiration, being least during expiration. However, unlike the UES, the function of the LES was unaffected by sleep. (C) 2006 Elsevier B.V. All rights reserved.