PubMed Health⌕ Search

Biomedical subjects

G Beaudoin

Publications and source records attributed to G Beaudoin.

11 recordsLinked to original sources
PubMed1992

A nonlinear analysis of pulsatile blood flow applied to investigate shear stress in arterial prostheses.

Although the main function of an arterial graft is to restore distal blood flow, there is evidence that certain local parameters of blood flow, particularly wall shear stresses, are important in determining the graft's long-term patency. Wall shear stresses were associated with intimal hyperplasia, intimal proliferation, and endothelial cell development, morphology, and attachment. Here we present a detailed method which permits the investigation of the wall shear stress acting on arteries and prostheses in dogs. The theory takes into account the nonlinear terms of the Navier-Stokes equations as well as the nonlinear behaviour and large deformation of the arterial wall. It is based on the numerical resolution of the nonlinear equations by the Crank-Nicolson method which was selected for its unconditional stability. Through the locally measured values of the pressure, pressure gradient, radius and flow rate, the velocity distribution and wall shear stress at a given location along the artery or the prosthesis, can be determined. Complete results on the same dog are presented for the distal aorta and for the middle of a chemically processed prosthesis, implanted as substitute in the thoracic aorta.

Animals↗
PubMed1989

In vivo biostability of four types of arterial grafts with impervious walls; their haemodynamic and pathological characteristics.

We describe the haemodynamic and pathological characteristics of four types of four impervious arterial prostheses, two alloplastic (Mitrathane and Gore-Tex), and two chemically processed bovine heterografts (Solcograft and Solco P). They were implanted in the thoracic aortae of dogs for durations of 24 hours, 48 hours, one week, two weeks, one month, three months and six months. Haemodynamic analyses showed no relation between the shear rate index, I.gamma, and compliance, CD. The observed shear rates are 6.5 times lower than those likely to damage the endothelial cell layer. Macroscopic and microscopic observations of explanted grafts showed the presence of obstructive thrombi at the anastomoses of Mitrathane grafts as early as one week. Gore-Tex grafts develop in the area of anastomoses parietal-thrombi which reorganize and become covered with pseudo-endothelial cells. The bovine heterografts show a similar behaviour. However, whereas Solcograft has an irregular thin wall, Solco P had improved characteristics except in the graft implanted for three months which demonstrated, some manufacturing weaknesses. Both types showed the development of anastomotic pannus covered with endothelial-like cells. All grafts, whether alloplastic or chemically processed, suffered from an absence of healing of the middle part of the prosthesis. The cause of this problem will be found in the analysis of the biochemical and enzymatic reactations between the material used and its physiological surrounding.

Anastomosis, Surgical↗
PubMed1989

Plasma filtration in Couette flow membrane devices.

This report investigates the effects of transmembrane pressure (ptm), rotation speed, and membrane characteristics on the performance of a rotating membrane device for separating plasma from whole blood. This device consists of 58 cm2 polymeric membrane rotating at high speed (3,000-4,000 r/min) inside a concentric cylinder and produces a Couette type flow in a gap 0.9 mm thick. Blood enters tangentially at the top, exits tangentially at bottom, and plasma is collected by an axial duct. It is found that this device yields maximum filtration velocities (plasma filtration flux per unit area) in the range of 0.5-0.8 cm/min, which are 10-20 times larger than those obtained by using hollow fiber plasma filters. This high performance is not due to the effect of centrifugal forces on red blood cells but rather to the very high shear rates, on the order of 20,000 sec-1, generated in the gap by toroidal flow instabilities (Taylor vortices). When a 0.8 micron pore size Nuclepore (polycarbonate) membrane is used, the filtration velocity presents a narrow peak of 0.6 cm/min at ptm = 10 mm Hg at 3,000 r/min and decreases to 0.35 cm/min at larger ptm. With a 0.5-micron pore nylon membrane the filtration speed increases continuously with ptm and reaches a plateau of 0.5 cm/min.

Cell Separation↗
PubMed1988

Hydrophilic microporous polyurethane versus expanded PTFE grafts as substitutes in the carotid arteries of dogs. A limited study.

A novel, microporous, hydrophilic polyether urethane-urea (PEUU) vascular graft was compared with expanded PTFE in the canine carotid artery. At implantation times ranging from 4 h to 6 months, all the PEUU grafts were found to be occluded while of the PTFE grafts, only those implanted for 1 week and 6 months were blocked. Histopathological analysis of the explanted grafts and their capsules revealed an ongoing inflammatory reaction at the anastomotic sites of the PEUU grafts.

Animals↗
PubMed1987

Physicochemical characterization of a hydrophilic microporous polyurethane vascular graft.

There is still a need for a viable small-diameter synthetic vascular graft. The expanded PTFE device appears to be the best presently available, but is still inferior to the autologous saphenous vein. Recently, a novel microporous, small-diameter vascular graft fabricated from Mitrathane, a polyether urethane urea (PEUU), has been developed. In this article, we report the findings of an in vitro evaluation of the morphological, mechanical, and chemical properties of this new device. The results are compared with those of established vascular prostheses made from alternative materials including expanded PTFE and bovine heterograft, and with natural blood vessels. The PEUU graft displays good mechanical properties in spite of the presence of some structural defects or anomalies. In particular it compares favorably to the expanded PTFE device by providing both superior radial compliance and improved suture tearing strength.

Animals↗
PubMed1986

The virgin, modified, human, umbilical vein graft: morphologic characteristics and mechanical properties.

The authors used macrophotography, endoscopy, roentgenography, light microscopy, and transmission and scanning electron microscopy to assess the morphologic characteristics of 37 virgin, human, umbilical vein grafts. The specimens showed deep longitudinal folds (22%) and multiple transverse folds of the intimal surface (27%), irregularity of wall thickness (41%) and intimal breakdown exposing thrombogenic layers of the vein wall to blood (19%). The mechanical properties also studied were dynamic compliance, Young's modulus, breaking strength and breaking strain. The mean dynamic compliance was 6.44 X 10(-4) mm Hg-1 (SD = 2.02 X 10(-4) mm Hg-1, i.e., 31%), which is in agreement with results of others. The specimens showed great variability in Young's modulus, breaking strength and breaking strain. The structural deficiencies and variable mechanical properties of human umbilical vein grafts require investigation to determine their effect on patency rates due to increased thrombogenicity and thus to establish whether there are potential hazards associated with their use.

Biomechanical Phenomena↗
PubMed1985

[Physical characteristics of stripping veins preserved at 4 degrees C and usable as artery substitutes].

The mechanical behavior of varicosis veins harvested during stripping and preserved at 4 degrees C has been investigated by measuring the compliance, the yield strain, the yield stress and the longitudinal Young's modulus. No relationship has been demonstrated between those parameters and external factors such as age, sex, storage duration and bacteremic contamination. The mechanical behavior of such veins is unpredictable. Therefore, it is mandatory to proceed through individual and non-destructive quality control tests to obtain a selection of grafts suitable for implantation. Moreover, implantation should be oriented towards patients who are able to visit the hospital frequently since the healing capacity of the venous homograft is unpredictable.

Arteries↗
PubMed1985

[Stripped veins for secondary vascular access in hemodialysis. Pathologic study of the grafts after surgical excision].

The suitability of stripping vein homografts as AV fistulae for intermittent hemodialysis has been evaluated. Microscopic investigation of stored veins indicated the superiority of cryopreservation over refrigeration. A systematic study of 12 venous homograft fistulae surgically excised from hemodialysis patients revealed that the homograft walls are the sites of both connective tissue proliferation and of mural degeneration. It was also noted that the implants failed in the short term (less than 1 yr) mainly due to stenosis, in the medium term (1 yr-3 yrs) mainly due to aneurysmal dilatation and for a variety of reasons beyond 3 years. It was concluded that when suitably selected, handled and stored, stripping vein homografts are a viable alternative to treated human umbilical or bovine heterografts as blood access fistulae if no autograft is available.

Arteriovenous Shunt, Surgical↗
PubMedDate not supplied

Effect of membrane characteristics on the performance of Couette rotating plasma separation devices.

The concept of a cylindrical membrane rotating at high speed inside a concentric cylinder (Couette flow device) has proved to be very efficient for plasma separation from whole blood. The authors show that its high filtration velocity (about 0.5-0.6 cm/min) is due to the presence of Taylor vortices in the blood-filled annular gap, which greatly increase the shear rates, but not radial migration of formed elements under centrifugal forces. The variation of filtrate velocity with transmembrane pressure (ptm) markedly depends upon the type of membrane. With a 0.8 micron polycarbonate membrane and bovine blood at 40% hematocrit, the filtration velocity reaches a peak equal to 0.6 cm/min at 3,000 rpm, then decreases to 80 mmHg, reaching a plateau of 0.35 cm/min independent of ptm. With a nylon membrane of 0.5 micron pores under the same conditions, the filtration velocity does not present a peak, but rises continuously to reach a 90 mmHg plateau equal to 0.5 cm/min. Similar behavior, but with lower plateaus, is also obtained with polycarbonate membranes at pore sizes below 0.4 microns. At 3,000 rpm, hemolysis occurs if ptm exceeds 750 mmHg, far above the operating range.

Blood Flow Velocity↗
PubMedDate not supplied

High efficiency plasmapheresis using rotating membrane device.

We report here an experimental investigation of the effects of inlet blood pressure and rotation speed on the performance of a rotating membrane device for plasmapheresis commercialized by Hemascience. The good performance of this device can be explained by a combination of high shear rate, centrifugation of red cells and platelets away from the membrane and large secondary flows.

Blood Flow Velocity↗