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

Biomechanical behavior and histological organization of the three-layered passive esophagus as a function of topography

The zero-stress state of the mucosa-submucosa and two muscle esophageal layers has been delineated, but their multi-axial response has not, because muscle dissection may not leave tubular specimens intact for inflation/extension testing. The histomechanical behavior of the three-layered porcine esophagus was investigated in this study, through light microscopic examination and uniaxial tension, with two-dimensional strain measurement in pairs of orthogonally oriented specimens. The two-dimensional Fung-type strain–energy function described suitably the pseudo-elastic tissue response, affording faithful simulations to our data. Differences in the scleroprotein content and configuration were identified as a function of layer, topography, and orientation, substantiating the macromechanical differences found. In view of the failure and optimized material parameters, the mucosa-submucosa was stronger and stiffer than muscle, associating it with a higher collagen content. A notable topographical distribution was apparent, with data for the abdominal region differentiated from that for the cervical region, owing to the existence of inner muscle with a circumferential arrangement and of outer muscle with a longitudinal arrangement in the former region, and of both muscle layers with oblique arrangement in the latter region, with thoracic esophagus being a transition zone. Tissue from the mucosa-submucosa was stronger and stiffer longitudinally, relating with a preferential collagen reinforcement along that axis, but more extensible in the orthogonal axis. </jats:p

The influence of indomethacin co-administration on ofloxacin levels in plasma and cerebrospinal fluid in rats

The possible increase of ofloxacin levels in serum and cerebrospinal fluid (CSF) by concomitant indomethacin administration was investigated in 120 healthy adult rats. The animals were administered intramuscular doses of ofloxacin 30 mg/kg alone (Group A, n = 60) or with indomethacin 2 mg/kg (Group B, n = 60). Blood and CSF samples were obtained from both groups at 30, 45, 60 and 90 min post-administration. Concentrations of ofloxacin were estimated using a microbiological assay. Co-administration of indomethacin did not affect plasma levels of ofloxacin significantly; however, higher levels were found in all CSF samples after co-administration with indomethacin, particularly after 90 min with 0.59 mug/ml versus zero median values when only ofloxacin was administered (P = 0.05). No central nervous system adverse effects were observed clinically. No correlation between levels of ofloxacin in plasma and CSF could be established either in rats administered only ofloxacin or in rats administered both drugs. The presented pharmacokinetic findings revealed that co-administration of ofloxacin and indomethacin may result in protracted quinolone levels in the CSF. However, the absence of significant correlation between concentrations of ofloxacin in plasma and CSF upon co-administration of indomethacin, as well as of central nervous system adverse effects, make the probability of an epileptogenic interaction between them unlikely. These results merit further clinical evaluation. (C) 2004 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved

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