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TECHNICAL PAPERS

The Mechanical Advantage of Local Longitudinal Shortening on Peristaltic Transport

[+] Author and Article Information
Anupam Pal, James G. Brasseur

Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA 16802

J Biomech Eng 124(1), 94-100 (Sep 24, 2001) (7 pages) doi:10.1115/1.1427700 History: Received February 16, 2001; Revised September 24, 2001
Copyright © 2002 by ASME
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References

Figures

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Longitudinal esophageal motions during peristalsis in the lower feline esophagus, from Dodds et al. 2. The axial displacements of tantalum markers with time are shown in the lower half of the esophagus by thick black lines during peristaltic transport of a liquid bolus (shaded). The changes in relative distance between markers show that a peristaltic wave of longitudinal shortening progresses distally along with the circular muscle contraction wave, as material points on the wall of the lumen move in circulatory fashion, first proximally, then distally.
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Local shortening of esophageal wall muscle in the mid-esophagus from high-frequency ultrasound measurements, from Nicosia et al. 11. The local length of a narrow longitudinal segment of the esophageal wall muscle layer (l) is plotted relative to its initial length (l0) in the resting state, centered on the time of maximum intraluminal pressure induced by circular muscle contraction. The plot is an average over 24 swallows from 4 normal subjects. Maximum average local longitudinal shortening, (l/l0)max, was about 0.35.
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Bolus geometry. (a) X-ray image of a radio-opaque bolus in the esophagus. (b) Bolus geometry applied in the mathematical model. VB is the bolus volume, λ is the bolus length, and c is the peristaltic wave speed. The bolus fluid has viscosity μ and the bolus geometry is specified by the mathematical function H which varies with axial position x and time t. A “lubrication layer” of radius ε is required at the tail of the modeled bolus (Li et al. 8). L is the total length of the bolus plus lubrication layer. The average radius of the bolus (a) is defined from VB≡πa2λ.
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Schematic showing radial and axial motions of a boundary material point as the bolus propagates from time t (solid line) to t+Δt (dashed line)
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Schematic showing parameters associated with our mathematical model of local longitudinal shortening (see Fig. 2). (l/l0)max quantifies the degree of LLS while Δ parametrizes the offset between peak contraction of longitudinal and circular muscles.
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Effect of local longitudinal shortening on average flow rate for Δ=0 and different occlusion radii ε. The dotted vertical line identifies maximum local longitudinal shortening for humans.
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Effect of local longitudinal shortening on intraluminal pressure. ε=0.5 mm;Δ=0.
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Effect of local longitudinal shortening on wall shear stress. ε=0.5 mm;Δ=0.
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Effect of local longitudinal shortening on contractile pressure. –: ε=0.5 mm which leads to peak pressure with LLS of 55.7 mmHg and [[dashed_line]]: ε=1.6 mm leading to peak pressure with LLS=20.9 mmHg[(l/l0)max=0.35,Δ=0]. Insert shows the relative insensitivity of LLS-induced pressure reduction to peak pressure at LLS for humans.
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Effect of alignment of peak longitudinal shortening with respect to peak pressure at different levels of maximum local longitudinal shortening (l/l0)max, including no shortening. The dotted vertical line corresponds to minimum contractile pressure. ε=0.5 mm.
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Effect of local longitudinal shortening on power. ε=0.5 mm;Δ=0. The dotted lines are the values in humans.

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