45 research outputs found
A computational model of ureteral peristalsis and an investigation into ureteral reflux.
The aim of this study is to create a computational model of the human ureteral system that accurately replicates the peristaltic movement of the ureter for a variety of physiological and pathological functions. The objectives of this research are met using our in-house fluid-structural dynamics code (CgLes-Y code). A realistic peristaltic motion of the ureter is modelled using a novel piecewise linear force model. The urodynamic responses are investigated under two conditions of a healthy and a depressed contraction force. A ureteral pressure during the contraction shows a very good agreement with corresponding clinical data. The results also show a dependency of the wall shear stresses on the contraction velocity and it confirms the presence of a high shear stress at the proximal part of the ureter. Additionally, it is shown that an inefficient lumen contraction can increase the possibility of a continuous reflux during the propagation of peristalsis
Effect of impaired vasa vasorum flow on the structure and mechanics of the thoracic aorta: implications for the pathogenesis of aortic dissection
Objective: To investigate the alterations of structure and mechanical
properties of the aortic wall, resulting from impairment of vasa vasorum
Row. Methods: Eight healthy Landrace pigs were subjected to interruption
of vasa vasorum how to the upper segment of their descending thoracic
aorta. Under sterile conditions, the periaortic tissue was excised and
the contiguous intercostal arteries were ligated. Ten sham-operated pigs
were used as controls. Fifteen days postoperatively, the animals were
sacrificed and their upper descending thoracic aortas were removed.
Histology, and collagen and elastin content determination by image
analysis technique were performed. Mechanical analysis of aortic strips
was carried out with a uniaxial tension device and stress-strain curves
were obtained. Results: In contrast to normal aortic walls of the
control group, histology of the avascular aortas revealed severe
ischemic necrosis of the outer media along with abnormal straightening
of the elastin and collagen fibers, without significant collagen and
elastin content changes. The borderline between the outer ischemic and
inner non-ischemic media was sharp, and an outset of dissection was
observed at this point. Mechanical analysis showed that at the same
level of strain, the ischemic aorta was significantly stiffer at both
low (P = 0.03) and high strains (P = 0.003). Conclusions: Impairment of
blood supply to the thoracic aorta leads to abnormal morphology of
elastin and collagen fibers of the outer media, resulting in increased
aortic stiffness under a wide range of stresses. In the clinical
setting, decreased vasa vasorum flew, reportedly occurring in arterial
hypertension, may increase the stiffness of the outer media of the
thoracic aorta and produce interlaminar shear stresses, contributing to
the development of aortic dissection. (C) 2000 Elsevier Science B.V. All
rights reserved