Muscle mechanics and modeling of the esophagus during swallowing

Underlying this thesis is the application of basic mechanics to study esophagel bolus transport. Two different yet related analyses were performed to analyze the physiology of the esophageal muscle layers during swallowing.; A model is developed to extract the active and passive components of circular muscle tension from concurrent manometric and videofluoroscopic data. Local differential equations of motion are integrated across the esophageal wall to yield global equations of equilibrium which relate total tension within the esophageal wall to intraluminal pressure and wall geometry. The model equations are applied to a region of the esophagus in which active muscle contraction is inhibited to quantify the passive muscle properties. This passive model is used along with the global equations to separate total esophageal muscle tension into active and passive components.; We first analyze the sensitivities of the model and perform parametric studies of esophageal muscle mechanics using analytically derived distributions of luminal geometry and intra-luminal pressure. Two specific aspects are studied: (1) longitudinal muscle mechanics including longitudinal shortening: and longitudinal muscle fiber stress and (2) stresses within the extracellular collagen matrix. The model is then applied to in vivo manofluoroscopic data to characterize the pattern of active circular muscle contraction during human swallowing. We find that normal peristalsis occurs as a series of transitions between localized "peaked" contractions and broad segmental contractions. The specifics are different for each individual, but consistent within an individual.; In a different study, we present the first local analysis of longitudinal shortening using concurrent ultrasonography and manometry. Conservation of volume implies that changes in the axial separation of two closely spaced material points is inversely proportional to changes in the muscle cross-sectional area, which we measure from the ultrasound images. Concurrent with this measure of longitudinal muscle contraction, circular muscle contraction is inferred from intraluminal pressure. Our results suggest that circular and longitudinal muscle layers act in concert during bolus transport. Longitudinal muscle contraction may play a physiological role in bolus transport, whereby active circular muscle tension is increased by a local increase in circular muscle fiber density due to longitudinal shortening.