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Biomedical subjects

D Pless

Publications and source records attributed to D Pless.

6 recordsLinked to original sources
PubMed2004

[Non-invasive, multi detector row (MDR) CT based computational fluid dynamics (CFD) analysis of hemodynamics in infrarenal abdominal aortic aneurysm (AAA) before and after endovascular repair].

PURPOSE: Simulation, description and analysis of dynamic pressure in infrarenal abdominal aortic aneurysms (AAA) before and after endovascular repair. MATERIALS AND METHODS: During March 1996 and May 2001, 13 patients with AAA underwent endovascular treatment. The MDR-CT scans of these patients were used for the non-invasive analysis of the hemodynamics in the aorta with CFD software before and after endovascular repair. One pre-interventional and three post-interventional CT scans were analyzed for each patient. RESULTS: Compared to the pre-interventional simulation, endovascular treatment led to an average dynamic pressure decrease of 1057 Pa in 10 of 13 patients. During the subsequent course, the median of the dynamic pressure decreased in 8 of 13 patients. Vulnerable regions initially identified as high-pressure regions, like the docking area or the second stent limb, adapted to the pressure in the surrounding tissue in the course of time. CONCLUSION: CFD-based blood flow simulation offers the opportunity to analyze dynamic pressure in AAA before and after endovascular repair and allows a prognostic statement as to the possible homogenization of the pressure in abdominal stent-grafts.

Aortic Aneurysm, Abdominal↗
PubMed2004

Numerical simulation of air temperature and airflow patterns in the human nose during expiration.

Recovery of heat and water during expiration is an important but not yet fully understood function of the nose. The presented study investigated cooling of the expiratory air for heat recovery within the human nose applying numerical simulation. A numerical simulation in a bilateral three-dimensional model of the human nose based on computed tomography was employed. Temperature distribution and airflow patterns during expiration were displayed. Cooling of the expiratory air primarily takes place in the areas of inferior and middle turbinate. Areas of the highest decrease in temperature are characterized by turbulent airflow with vortices of low velocity. Numerical results showed good concordance with experimental in vivo temperature measurements. Heating of inspired air not only depends on inspiration but also on expiration. Cooling the warm expiratory air may be regarded as an important factor for heat recovery. Furthermore, the results demonstrate the close relation between heat exchange and airflow patterns.

Exhalation↗
PubMed2001

[Precision in standardized Iso-C-Arm based navigated boring of the proximal femur].

C-arm navigation is a new tool in computer assisted surgery. The aim of this study is to evaluate the accuracy of Iso-C-arm based drill holes in the proximal femur. In nine artificial proximal femura, two holes with an angle of 135 degrees and 100 degrees in relation to the shaft axis were drilled in the direction of the femoral head. The defined target of the 3.2 mm drillings was a 4 mm steel ball, which had previously been placed and fixed at the cranial center of the femoral head. All the drillings were standardized with a navigated drilling machine fixed to a frame which only allowed movement of the system in the direction of the drill. During navigation the positions of the drill before commencement and at the deepest point of the canal were recorded. After drilling all specimens were evaluated by CT, and the coordinates of the center of the start and the end of the drilled hole and the center of the ball were determined. Using vector calculation, the smallest distance between the straight line, defined by the center of the starting point and the end point of the drill hole, and the center of the ball was calculated. Additionally, the coordinates of the intersection between the perpendicular to the center of the ball and the straight line were determined (xv, yv, zv), to evaluate the direction of misplacement of the drilled canal in relation to the target. For the 135 degrees drill holes, a median of 2.5 mm for the smallest distance between the straight line, given by the center of the start and the end of the hole, and the center of the ball was investigated (range 1.6-3.7 mm). For the 100 degrees holes the median was 3.1 mm (range 1.8-4.2 mm). The main plane of deviation in all of the 135 degrees holes was posteriorly, whereas in the 100 degrees holes posterior deviation occurred in four cases, cranial in three cases, and in one case each caudal and anterior deviation occurred. In our opinion, the accuracy of fluoroscopy based navigation applied in the region of the proximal femur is sufficient and reproducible. This technique can be used for implant placement at the proximal femur in the future.

Equipment Design↗
PubMed1999

Characterization of the UDP-glucuronosyltransferases involved in the glucuronidation of an antithrombotic thioxyloside in rat and humans.

To investigate the glucuronidation on the hydroxyl group of carbohydrate-containing drugs, the in vitro formation of glucuronides on the thioxyloside ring of the antithrombotic drug, LF 4.0212, was followed in rat and human liver microsomes and with recombinant UDP-glucuronosyltransferases (UGT). The reaction revealed a marked regioselectivity in rat and humans. Human liver microsomes glucuronidated the compound mainly on the 2-hydroxyl position of the thioxyloside ring, whereas rat was able to form glucuronide on either the 2-, 3-, or 4- hydroxyl group of the molecule, although to a lower extent. LF 4.0212 was a much better substrate of human UGT than the rat enzyme (Vmax/Km 30.0 and 0.06 microl/min/mg, respectively). Phenobarbital, 3-methylcholanthrene, and clofibrate enhanced the glucuronidation of LF 4.0212 on positions 2, 3, and 4 of the thioxyloside ring, thus indicating that several UGT isoforms were involved in this process. The biosynthesis of the 2-O-glucuronide isomer was catalyzed by the human UGT1A9 and 2B4, but not by UGT1A6 and 2B11. By contrast, the rat liver recombinant UGT1A6 and 2B1 failed to form the 2-O-glucuronide isomers. From all the recombinant UGTs tested, none catalyzed the formation of the 3-O-glucuronide isomer. Interestingly, glucuronidation on the 4-position was found in all the metabolic competent V79 cell lines considered, including the nontransfected V79 cells, suggesting the presence of an endogenous UGT in fibroblasts able to actively glucuronidate the drug. This activity, which was nonsensitive to the inhibitory effect of 7,7,7-triphenylheptanoic acid, a potent UGT inhibitor, could reflect the existence of a different enzyme.

Animals↗
PubMed1997

Arginine 52 and histidine 54 located in a conserved amino-terminal hydrophobic region (LX2-R52-G-H54-X3-V-L) are important amino acids for the functional and structural integrity of the human liver UDP-glucuronosyltransferase UGT1*6.

The hepatic UDP-glucuronosyltransferase UGT1*6 is actively involved in the glucuronidation of short and planar phenols in humans. Based on the irreversible inhibition of the enzyme on chemical modification by 2,3-butanedione and diethyl pyrocarbonate, the roles of His54 and Arg52 were investigated by oligonucleotide site-directed mutagenesis. These amino acids belong to a consensus sequence LX2-R52-G-H54-X3-V-L located in a conserved hydrophobic region of the variable amino-terminal domain of UGT. Arg52 was replaced by alanine (mutant R52A), and His54 was replaced by alanine or glutamine (mutants H54A and H54Q). The immunological and catalytic properties of UGT1*6 and mutants were examined after stable expression in V79 cell lines. Immunoblots and immunoprecipitation studies revealed that the mutant and UGT1*6 proteins were expressed in the microsomal membranes in similar amounts. However, replacement of His54 by glutamine led to a complete loss of activity toward 4-methylumbelliferone, and the Vmax value was decreased 4-5-fold in the mutants R52A and H54A compared with the wild-type enzyme. The dissociation constants that characterize the binding of 4-methylumbelliferone and UDP-glucuronic acid to UGT1*6 were not greatly affected by the mutations. Interestingly, H54Q was not recognized by specific antibodies to the amino-terminal portion of UGT1*6, thereby indicating that this amino acid was critical to antibody recognition. In contrast, the mutants R52A and H54A could not be differentiated from the wild-type protein by pH optimum or thermal denaturation. Furthermore, these mutants were still sensitive to irreversible inhibition by diethyl pyrocarbonate and 2,3-butanedione, with second-order inactivation constant values similar to those obtained for UGT1*6. Altogether, the strict conservation of His54 and Arg52 and the mutational analysis of these residues suggest that these amino acids in the hydrophobic amino-terminal consensus sequence LX2-R52-G-H54-X3-V-L are important for the function and the structure required for optimal catalytic efficiency of UGT1*6.

Animals↗