ANALYSES OF NORMAL AND ABNORMAL ESOPHAGEAL TRANSPORT USING COMPUTER-SIMULATIONS

Mathematical modeling and computer simulations are combined with concurrent manometric and videofluoroscopic data to analyze the contractile behavior of the esophageal wall during normal and abnormal esophageal bolus transport. The study focuses on axial variations in intraluminal pressure in relationship to deformations of the esophageal wall during the transport process. Four case studies of esophageal bolus transport described by Kahrilas et al. (Gastroenterology 94: 73-80, 1988), one normal and three abnormal, are analyzed in detail by capturing the major elements of both the videofluoroscopic and concurrent manometric data in the mathematical model. In all cases a strong correlation between the deformations of the luminal wall and the axial variations of intraluminal pressure is observed. Simulation of normal bolus transport shows that, whereas only gentle variations in intrabolus pressure occur in the main body of the bolus due to weak frictional forces there, large frictional forces force a rapid rise in pressure near the bolus tail induced by circular muscle squeeze. Of particular interest is the analysis of incomplete clearance of bolus fluid in the aortic arch region. The only physically correct model consistent both with the videofluoroscopic and the manometric data implies the existence of two separate contraction waves, one above and one below the transition zone. As the proximal wave slows and decreases in strength, a new distal wave forms, pinching off bolus fluid as it propagates distally. We hypothesize that the contraction wave in the upper esophagus is associated with striated circular muscle, that this wave slows, weakens, and dies at the proximal end of the esophageal transition zone, that a separate contraction wave is born distally due to smooth muscle in that segment, and that this distal wave is responsible for transporting bolus fluid into the lower smooth muscle-dominated esophagus. We hypothesize that these ''striated'' and ''smooth'' muscle contraction waves are properly coordinated in normal bolus transport and that bolus retention in the transition zone is due to a temporal and spatial ''mismatch'' of the upper and lower peristaltic waves.