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G Beaudoin

Publications and source records attributed to G Beaudoin.

At least 19 recordsLinked to original sources
PubMed2005

Assessment of compressive modulus, hydraulic permeability and matrix content of trypsin-treated nucleus pulposus using quantitative MRI.

A clinical strength MRI and intact bovine caudal intervertebral discs were used to test the hypotheses that (1) mechanical loading and trypsin treatment induce changes in NMR parameters, mechanical properties and biochemical contents; and (2) mechanical properties are quantitatively related to NMR parameters. MRI acquisitions, confined compression stress-relaxation experiments, and biochemical assays were applied to determine the NMR parameters (relaxation times T1 and T2, magnetization transfer ratio (MTR) and diffusion trace (TrD)), mechanical properties (compressive modulus H(A0) and hydraulic permeability k(0)), and biochemical contents (H(2)O, proteoglycan and total collagen) of nucleus pulposus tissue from bovine caudal discs subjected to one of two injections and one of two mechanical loading conditions. Significant correlations were found between k(0) and T1 (r=0.75,p=0.03), T2 (r=0.78, p=0.02), and TrD (r=0.85, p=0.007). A trend was found between H(A0) and TrD (r=0.56, p=0.12). However, loading decreased these correlations (r=0.4, p=0.2). The significant effect of trypsin treatment on mechanical properties, but not on NMR parameters, may suggest that mechanical properties are more sensitive to the structural changes induced by trypsin treatment. The significant effect of loading on T1 and T2, but not on H(A0) or k(0), may suggest that NMR parameters are more sensitive to the changes in water content enhanced by loading. We conclude that MRI offers promise as a sensitive and non-invasive technique for describing alterations in material properties of intervertebral disc nucleus, and our results demonstrate that the hydraulic permeability correlated more strongly to the quantitative NMR parameters than did the compressive modulus; however, more studies are necessary to more precisely characterize these relationships.

Animals↗
PubMed2004

Meniscal tear and extrusion are strongly associated with progression of symptomatic knee osteoarthritis as assessed by quantitative magnetic resonance imaging.

BACKGROUND: The relation between knee meniscal structural damage and cartilage degradation is plausible but not yet clearly proven. OBJECTIVES: To quantitate the cartilage volume changes in knee osteoarthritis using magnetic resonance imaging (MRI), and determine whether meniscal alteration predicts cartilage volume loss over time. METHODS: 32 patients meeting ACR criteria for symptomatic knee osteoarthritis were studied. MRI knee acquisitions were done every six months for two years. The cartilage volumes of different knee regions were measured. Three indices of structural change in the medial and lateral menisci were evaluated--degeneration, tear, and extrusion--using a semiquantitative scale. RESULTS: 24 patients (75%) had mild to moderate or severe meniscal damage (tear or extrusion) at baseline. A highly significant difference in global cartilage volume loss was observed between severe medial meniscal tear and absence of tear (mean (SD), -10.1 (2.1)% v -5.1 (2.4)%, p = 0.002). An even greater difference was found between the medial meniscal changes and medial compartment cartilage volume loss (-14.3 (3.0)% in the presence of severe tear v -6.3 (2.7)% in the absence of tear; p<0.0001). Similarly, a major difference was found between the presence of a medial meniscal extrusion and loss of medial compartment cartilage volume (-15.4 (4.1)% in the presence of extrusion v -4.5 (1.7)% with no extrusion; p<0.001). CONCLUSIONS: Meniscal tear and extrusion appear to be associated with progression of symptomatic knee osteoarthritis.

Adult↗
PubMed2004

Neural basis of emotional self-regulation in childhood.

Emotional self-regulation plays a pivotal role in socialization and moral development. This capacity critically depends on the development of the prefrontal cortex (PFC). The present functional magnetic resonance imaging study was conducted to identify the neural circuitry underlying voluntary self-regulation of sadness in healthy girls (aged 8-10). A 2 x 2 factorial design was implemented with Emotion (No Sadness vs. Sadness) and Regulation (No Reappraisal vs. Reappraisal) as factors. In the No Reappraisal conditions, subjects were instructed to react normally to neutral and sad film excerpts whereas in the Reappraisal conditions, subjects were asked to voluntarily suppress any emotional reaction in response to comparable stimuli. A significant interaction of the Emotion and Regulation factors revealed that reappraisal of sad film excerpts was associated with bilateral activations of the lateral PFC (LPFC; Brodmann areas [BA] 9 and 10), orbitofrontal cortex (OFC; BA 11), and medial PFC (BA 9 and 10). Significant loci of activations were also detected in the right anterior cingulate cortex (BA 24/32) and right ventrolateral PFC (BA 47). In an identical study previously conducted by our group in adult women [Biol Psychiatry 53 (2003) 502], reappraisal of sad film excerpts was associated with activation of the right OFC (BA 11) and right LPFC (BA 9). The greater number of prefrontal loci of activation found in children relative to adults during voluntary self-regulation of sadness may be related to the immaturity of the prefronto-limbic connections in childhood.

Behavior↗
PubMed2003

Neural correlates of sad feelings in healthy girls.

Emotional development is indisputably one of the cornerstones of personality development during infancy. According to the differential emotions theory (DET), primary emotions are constituted of three distinct components: the neural-evaluative, the expressive, and the experiential. The DET further assumes that these three components are biologically based and functional nearly from birth. Such a view entails that the neural substrate of primary emotions must be similar in children and adults. Guided by this assumption of the DET, the present functional magnetic resonance imaging study was conducted to identify the neural correlates of sad feelings in healthy children. Fourteen healthy girls (aged 8-10) were scanned while they watched sad film excerpts aimed at externally inducing a transient state of sadness (activation task). Emotionally neutral film excerpts were also presented to the subjects (reference task). The subtraction of the brain activity measured during the viewing of the emotionally neutral film excerpts from that noted during the viewing of the sad film excerpts revealed that sad feelings were associated with significant bilateral activations of the midbrain, the medial prefrontal cortex (Brodmann area [BA] 10), and the anterior temporal pole (BA 21). A significant locus of activation was also noted in the right ventrolateral prefrontal cortex (BA 47). These results are compatible with those of previous functional neuroimaging studies of sadness in adults. They suggest that the neural substrate underlying the subjective experience of sadness is comparable in children and adults. Such a similitude provides empirical support to the DET assumption that the neural substrate of primary emotions is biologically based.

Behavior Therapy↗
PubMed2003

Reliability of a quantification imaging system using magnetic resonance images to measure cartilage thickness and volume in human normal and osteoarthritic knees.

OBJECTIVE: The aim of this study was to evaluate the reliability of a software tool that assesses knee cartilage volumes using magnetic resonance (MR) images. The objectives were to assess measurement reliability by: (1) determining the differences between readings of the same image made by the same reader 2 weeks apart (test-retest reliability), (2) determining the differences between the readings of the same image made by different readers (between-reader agreement), and (3) determining the differences between the cartilage volume readings obtained from two MR images of the same knee image acquired a few hours apart (patient positioning reliability). METHODS: Forty-eight MR examinations of the knee from normal subjects, patients with different stages of symptomatic knee osteoarthritis (OA), and a subset of duplicate images were independently and blindly quantified by three readers using the imaging system. The following cartilage areas were analyzed to compute volumes: global cartilage, medial and lateral compartments, and medial and lateral femoral condyles. RESULTS: Between-reader agreement of measurements was excellent, as shown by intra-class correlation (ICC) coefficients ranging from 0.958 to 0.997 for global cartilage (P<0.0001), 0.974 to 0.998 for the compartments (P<0.0001), and 0.943 to 0.999 for the condyles(P<0.0001). Test-retest reliability of within-reader data was also excellent, with Pearson correlation coefficients ranging from 0.978 to 0.999 (P<0.0001). Patient positioning reliability was also excellent, with Pearson correlation coefficients ranging from 0.978 to 0.999 (P<0.0001). CONCLUSIONS: The results of this study establish the reliability of this MR imaging system. Test-retest reliability, between-reader agreement, and patient positioning reliability were all extremely high. This study represents a first step in the overall validation of an imaging system designed to follow progression of human knee OA.

Adult↗
PubMed2001

Effects of radiation therapy on vascular responsiveness.

The use of radiation therapy to inhibit vascular proliferative diseases has produced encouraging results in several clinical trials. However, little is known about the possible side effects of radiation on vascular responsiveness. Our goal was to study the in vitro vascular responses of the rabbit aorta to various agonists immediately after several regimens of radiation therapy administered at doses prescribed in clinical protocols and at two different dose rates. High-dose-rate radiation was administered either by brachytherapy, using a gamma source, iridium 192, or an external electron beam producing beta radiation. Low-dose-rate radiation was administered by brachytherapy using a liquid-filled balloon with the beta emitter 32P. Vascular reactivity after the various regimens of irradiation was determined using the organ bath pharmacology assay. Various agonists were applied to the rabbit aorta to produce full cumulative concentration-response curves. Radiation, administered using an external electron beam, did not alter endothelium-dependent relaxation of the aorta induced by acetylcholine. However, the use of a catheter-based system to deliver radiation disrupted the endothelial cell lining of the vessel, causing a lack of relaxation by acetylcholine. Therefore, to compare all modalities of radiation therapy on vascular responsiveness, the agonists used in this study are known to act directly on the smooth muscle. Radiation therapy had no effect on the contractile responses induced by the following agonists: phenylephrine and potassium chloride. Vascular dilatation induced by nitroglycerin, a nitric oxide donor, was unaffected by radiation therapy. The contractile response induced by des-Arg9-bradykinin, a kinin B1 receptor agonist, was significantly increased twofold to threefold by all types of irradiation under study. This enhanced response is attributable to an increase of mRNA levels coding for this receptor. In all cases, radiation therapy did not alter the effective concentration producing 50% of maximal responsiveness (EC50) and did not reduce the vascular responsiveness induced by agonists. Taken together, we conclude that radiation therapy does not hinder endothelium-independent vascular responsiveness and increases the kinin B1 receptor-mediated vasoconstriction.

Acetylcholine↗
PubMed1999

Frontal cortex and the programming of repetitive tapping movements in man: lesion effects and functional neuroimaging.

Two studies examined the contribution of human frontal cortical areas to the programming of trains of repetitive movements. The first study compared the performance of patients with unilateral frontal excisions, unilateral temporal excisions and controls on the speed of initiation of discrete vs. sequential tapping movements to visual stimuli. The frontal group showed normal initiation times in single taps and a normal execution (pace and accuracy) in sequential taps but they were slower than the other groups at initiating sequential taps indicating a sequence programming problem for repetitions of a single response. A second study examined the functional anatomy of single and sequential taps in eight control subjects using fMRI. Subjects performed flexion/extension movements of the right thumb at either 1 movement/s or as trains of four closely spaced movements at a rate of 1 train/4 s. Statistical analyses revealed that primary sensorimotor cortex and a dorsolateral premotor cortex region were activated in both conditions. Medial frontal activation was not significant in discrete movements but was clearly present in sequential movements and involved SMA and cingulate regions bilaterally. In addition, two other dorsolateral premotor foci of activation were observed in the sequential taps condition. Results from these two experiments converge toward establishing a significant role of dorsolateral and medial premotor regions in the programming of trains of repetitive responses.

Adult↗
PubMed1998

The functional neuroanatomy of major depression: an fMRI study using an emotional activation paradigm.

An important issue regarding the neural basis of major depression is whether the functional brain changes associated with the affect disturbance seen in this syndrome are similar to those that accompany transient sadness in normal subjects. To address this question, we carried out an fMRI study using an emotional activation paradigm. Brain activity associated with passive viewing of an emotionally laden film clip aimed at inducing a transient state of sadness was contrasted with that associated with passive viewing of an emotionally neutral film clip in patients suffering from unipolar depression and in normal control subjects. Results showed that transient sadness produced significant activation in the medial and inferior prefrontal cortices, the middle temporal cortex, the cerebellum and the caudate in both depressed and normal subjects. They also revealed that passive viewing of the emotionally laden film clip produced a significantly greater activation in the left medial prefrontal cortex and in the right cingulate gyrus in depressed patients than in normal control subjects. These findings suggest that these two cortical regions might be part of a neural network implicated in the pathophysiology of major depression. Taken together, these results strongly support the view that activation paradigms represent an extremely useful and powerful way of delineating the functional anatomy of the various symptoms that characterize major depression.

Adult↗
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↗