title: Response of the upper esophageal sphincter to esophageal distension is affected by posture, velocity, volume, and composition of the infusate.
abstract: OBJECTIVE
  Studies of the pressure response of the upper esophageal sphincter (UES) to simulated or spontaneous gastroesophageal reflux have shown conflicting results. These discrepancies could result from uncontrolled influence of variables such as posture, volume, and velocity of distension. We characterized in humans the effects of these variables on UES pressure response to esophageal distension.
  
  
  METHODS
  We studied 12 healthy volunteers (average, 27 ± 5 years old; 6 male) using concurrent esophageal infusion and high-resolution manometry to determine UES, lower esophageal sphincter, and intraesophageal pressure values. Reflux events were simulated by distal esophageal injections of room temperature air and water (5, 10, 20, and 50 mL) in individuals in 3 positions (upright, supine, and semisupine). Frequencies of various UES responses were compared using χ(2) analysis. Multinomial logistical regression analysis was used to identify factors that determine the UES response.
  
  
  RESULTS
  UES contraction and relaxation were the overriding responses to esophageal water and air distension, respectively, in a volume-dependent fashion (P < .001). Water-induced UES contraction and air-induced UES relaxation were the predominant responses among individuals in supine and upright positions, respectively (P < .001). The prevalence of their respective predominant response significantly decreased in the opposite position. Proximal esophageal dp/dt significantly and independently differentiated the UES response to infusion with water or air.
  
  
  CONCLUSIONS
  The UES response to esophageal distension is affected by combined effects of posture (spatial orientation of the esophagus), physical properties, and volume of refluxate, as well as the magnitude and rate of increase in intraesophageal pressure. The UES response to esophageal distension can be predicted using a model that incorporates these factors.
authors.affiliation: Gastroenterology and Hepatology, Department of Medicine, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, USA.
authors.forename: Arash
authors.initials: A
authors.lastname: Babaei
authors.forename: Kulwinder
authors.initials: K
authors.lastname: Dua
authors.forename: Sohrab Rahimi
authors.initials: SR
authors.lastname: Naini
authors.forename: Justin
authors.initials: J
authors.lastname: Lee
authors.forename: Omar
authors.initials: O
authors.lastname: Katib
authors.forename: Ke
authors.initials: K
authors.lastname: Yan
authors.forename: Raymond
authors.initials: R
authors.lastname: Hoffmann
authors.forename: Reza
authors.initials: R
authors.lastname: Shaker
mesh_terms: D000328:Adult; D000388:Air; D016009:Chi-Square Distribution; D049631:Esophageal Sphincter, Upper / Q000502:physiology*; D005260:Female; D006801:Humans; D016014:Linear Models; D016015:Logistic Models; D008297:Male; D008365:Manometry / Q000379:methods*; D008954:Models, Biological; D009119:Muscle Contraction; D009126:Muscle Relaxation; D016017:Odds Ratio; D056888:Patient Positioning; D010477:Perfusion; D011187:Posture; D011237:Predictive Value of Tests; D011312:Pressure; D016683:Supine Position; D014867:Water / Q000008:administration & dosage*; D014922:Wisconsin; D055815:Young Adult
chemical_list: D014867:Water