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Biomedical subjects

Gérard Finet

Publications and source records attributed to Gérard Finet.

10 recordsLinked to original sources
PubMed2006

Silent coronaropathy: usefulness of dobutamine stress echocardiography in ischemic stroke.

BACKGROUND: Several testing options are available to detect asymptomatic coronary artery disease (CAD). Dobutamine stress echocardiography (DSE) has been reported to increase the sensitivity and specificity of stress testing to detect CAD. Most studies concerned patients with known or suspected CAD who have a high pretest probability of disease. We aimed to perform a preliminary evaluation of DSE in atherothrombotic stroke. METHODS: Patients with transient ischemic attack or nondisabling ischemic stroke attributable to an atherothrombotic source were prospectively recruited. Patients with a history of angina pectoris or electrocardiographic signs of previous myocardial infarction were excluded. DSE was considered positive when regional reduction or deterioration of myocardial thickening developed in 1 segment. Coronary angiography was performed in patients with positive DSE. RESULTS: Sixty-four patients were recruited. Analysis of DSE was possible in 60 patients. Overall the test provided clinically useful information in 60/64 patients studied (>90%). DSE was positive in 9 patients (15%). Coronary angiography was performed in 8 patients, high-grade focal lesions were found in 3 patients, and 5 patients showed diffuse atheroma. Univariate logistic regression analysis showed that the main factor predictive of a positive DSE was the presence of an aortic arch atheroma (p = 0.003). Multivariate logistic regression analysis showed that two factors had an independent predictive value of positive DSE: aortic arch atheroma (p = 0.007) and dyslipidemia (p = 0.09). CONCLUSION: DSE may improve prevention of further vascular events in patients with an atherothrombotic source of ischemic stroke. This screening may be of particular benefit to patients with an aortic arch atheroma.

Adult↗
PubMed2006

Large tube section is the key to successful coronary thrombus aspiration: findings of a standardized bench test.

Thrombus removal by aspiration is one of the adjunctive techniques used to avoid embolization during PCI for acute myocardial infarction. Numerous devices are now available, but little is known about the mechanical rationale used in comparing them. The aim of the present study was to determine parameters to obtain optimal thrombus aspiration (TA). Heparin- and antiplatelet-free blood samples were aspirated into 3 mm diameter standardized glass tubes to create a 30 mm long thrombus. Thrombus formation took place at room temperature over a period of 6 or 12 hr. Various catheters were tested using a variable vacuum device: three with right-angle distal tip (0.038'', 0.067'', and 0.070'') and one with a beveled distal (length of the beveled, 0.054''; inner diameter catheter, 0.040''). The single endpoint was complete thrombus aspiration. A total of 103 TAs were presented for the four catheters. For 6- or 12-hr-old thrombus for a given catheter, there was no significant difference in vacuum pressure required to succeed TA (P = 0.47). For 6- or 12-hr-old thrombus, the larger the contact area is, the lower the pressure needed to aspirate the thrombus. Moreover, a beveled distal tip length (0.054'') does not make it possible to succeed TA at a lower pressure. The main factor for successful TA for thrombi > or = 6 hr is inner diameter and not immediate thrombus contact area.

Chi-Square Distribution↗
PubMed2005

Postconditioning the human heart.

BACKGROUND: In animal models, brief periods of ischemia performed just at the time of reperfusion can reduce infarct size, a phenomenon called postconditioning. In this prospective, randomized, controlled, multicenter study, we investigated whether postconditioning may protect the human heart during coronary angioplasty for acute myocardial infarction. METHODS AND RESULTS: Thirty patients, submitted to coronary angioplasty for ongoing acute myocardial infarction, contributed to the study. Patients were randomly assigned to either a control or a postconditioning group. After reperfusion by direct stenting, control subjects underwent no further intervention, whereas postconditioning was performed within 1 minute of reflow by 4 episodes of 1-minute inflation and 1-minute deflation of the angioplasty balloon. Infarct size was assessed by measuring total creatine kinase release over 72 hours. Area at risk and collateral blood flow were estimated on left ventricular and coronary angiograms. No adverse events occurred in the postconditioning group. Determinants of infarct size, including ischemia time, size of the area at risk, and collateral flow, were comparable between the 2 groups. Area under the curve of creatine kinase release was significantly reduced in the postconditioning compared with the control group, averaging 208 984+/-26 576 compared with 326,095+/-48,779 (arbitrary units) in control subjects, ie, a 36% reduction in infarct size. Blush grade, a marker of myocardial reperfusion, was significantly increased in postconditioned compared with control subjects: 2.44+/-0.17 versus 1.95+/-0.27, respectively (P<0.05). CONCLUSIONS: This study suggests that postconditioning by coronary angioplasty protects the human heart during acute myocardial infarction.

Adult↗
PubMed2005

An extended modeling of the micropipette aspiration experiment for the characterization of the Young's modulus and Poisson's ratio of adherent thin biological samples: numerical and experimental studies.

The micropipette aspiration (MA) experiment remains a quite widely used micromanipulation technique for quantifying the elastic modulus of cells and, less frequently, of other biological samples. However, moduli estimations derived from MA experiments are only valid if the probed sample is non-adherent to the rigid substrate. This study extends this standard formulation by taking into account the influence of the sample adhesion. Using a finite element analysis of the sample aspiration into the micropipette, we derived a new expression of the aspirated length for linear elastic materials. Our results establish that (i) below a critical value, the thickness h of the probed sample must be considered to get an accurate value of its Young's modulus (ii) this critical value depends both on the Poisson's ratio and on the sample adhesivity. Additionally, we propose a novel method which allows the computation of the intrinsic Young's modulus of the adherent probed sample from its measured apparent elasticity modulus. Thanks to the set of computational graphs we derived from our theoretical analysis, we successfully validate this method by experiments performed on polyacrylamide gels. Interestingly, the original procedure we proposed allows a simultaneous quantification of the Young's modulus and of the Poisson's ratio of the adherent gel. Thus, our revisited analysis of MA experiments extends the application domain of this technique, while contributing to decrease the dispersion of elastic modulus values obtained by this method.

Acrylic Resins↗
PubMed2005

On the potential of the Lagrangian speckle model estimator to characterize atherosclerotic plaques in endovascular elastography: in vitro experiments using an excised human carotid artery.

Endovascular ultrasound (US) elastography (EVE) was introduced to supplement endovascular US echograms in the assessment of vessel lesions and for endovascular therapy planning. Indeed, changes in the vascular tissue stiffness are characteristic of vessel wall pathologies and EVE appears as a very appropriate imaging technique to outline the elastic properties of vessel walls. Recently, a model-based approach was proposed to assess tissue motion in EVE. It specifically consists of a nonlinear minimization algorithm that was adapted to speckle motion estimation. Regarding the theoretical framework, such an approach considers the speckle as a material property; this assumption then led to the derivation of the optical flow equations, which were suitably combined with the Lagrangian speckle model estimator to provide the full 2-D polar strain tensor. In this study, the proposed algorithm was validated in vitro using a fresh excised human carotid artery. The experimental setup consisted of a cardiovascular imaging system (CVIS) US scanner, working with a 30-MHz mechanical rotating single-element transducer, a digital oscilloscope and a pressuring system. A sequence of radiofrequency (RF) images was collected while incrementally adjusting the intraluminal static pressure steps. The results showed the potential of this 2-D algorithm to characterize and to distinguish an atherosclerotic plaque from the normal vascular tissue. Namely, the geometry as well as some mechanical characteristics of the detected plaque were in good agreement with histology. The results also suggested that there might exist a range of intraluminal pressures for which plaque detectability is optimal.

Algorithms↗
PubMed2004

Evolution of spontaneous atherosclerotic plaque rupture with medical therapy: long-term follow-up with intravascular ultrasound.

BACKGROUND: Ruptured coronary atheromatous plaque is generally considered to involve a high risk of subsequent clinical events. Few data are available on the natural evolution of non-culprit-lesion ruptured plaque. We therefore used serial intravascular ultrasound (IVUS) to study how such lesions, detected in the context of a first acute coronary syndrome with elevated troponin I levels, develop. METHODS AND RESULTS: Fourteen patients with 28 distinct plaque ruptures (2+/-1 per patient) without significant associated stenosis (minimal lumen cross-sectional area >4 mm2) were included and systematically treated with 40 mg statin and antiplatelet agent (clopidogrel and aspirin for > or =9 months). Mean clinical and IVUS follow-up was 22+/-13 months (median, 22 months). No clinical event related to the lesion under study occurred. On final IVUS examination, half (14 of 28) of the ruptured plaques had healed, and the degree of stenosis tended to diminish (stenosis, 22+/-17% versus 29+/-17% at baseline; P=0.056). No healing-prediction criterion could be identified. CONCLUSIONS: Nearly 2 years of follow-up found that spontaneous coronary atheromatous plaque rupture without significant stenosis detected on first acute coronary syndrome healed without significant plaque modification in 50% of cases with medical therapy.

Aged↗
PubMed2004

Biomechanical interaction between cap thickness, lipid core composition and blood pressure in vulnerable coronary plaque: impact on stability or instability.

BACKGROUND: A 'thin' fibrous cap atheroma is the typical morphological characteristic of vulnerable plaque. Yet the very pathological studies that have provided these descriptions have also shown the actual prediction of plaque rupture to be rather less exact. Other relevant characteristics must be involved in the mechanisms of plaque rupture--blood pressure loading (P) and the material properties of the soft atheromatous core--as predictors of the distribution of the peak circumferential stress (PCS) locations. METHODS AND RESULTS: We used a computational structural analysis based on three typical in-vivo intravascular ultrasound images of fibrous cap atheroma in which we decreased the cap thickness (CTh). With different soft atheromatous core Young's moduli (Ecore), 414 simulations were performed under eight different physiological loading blood pressures. The transition from plaque stability to plaque instability was defined by a threshold of 300 kPa and is a feature of vulnerability. It was found that (1) irrespective of plaque geometry and composition, CTh < 60 microm exposed the plaque to PCSs in excess of 300 kPa; (2) the exponential variations in PCS with change in CTh and Ecore values show that very slight structural changes are enough to tilt a vulnerable plaque from stability to instability or vice versa; and (3) the relationship between P and PCS is proportional with P acting as trigger or as protector. CONCLUSION: The present study shows why, in clinical practice, mere morphological detection by imaging techniques of thin-cap fibro-atheroma is not in itself enough for the prediction of future rupture.

Blood Pressure↗
PubMed2004

Adapting the Lagrangian speckle model estimator for endovascular elastography: theory and validation with simulated radio-frequency data.

Intravascular ultrasound (IVUS) is known to be the reference tool for preoperative vessel lesion assessments and for endovascular therapy planning. Nevertheless, IVUS echograms only provide subjective information about vessel wall lesions. Since changes in the vascular tissue stiffness are characteristic of vessel pathologies, catheter-based endovascular ultrasound elastography (EVE) has been proposed in the literature as a method for outlining the elastic properties of vessel walls. In this paper, the Lagrangian Speckle Model Estimator (LSME) is formulated for investigations in EVE, i.e., using a polar coordinate system. The method was implemented through an adapted version of the Levenberg-Marquardt minimization algorithm, using the optical flow equations to compute the Jacobbian matrix. The theoretical framework was validated with simulated ultrasound rf data of mechanically complex vessel wall pathologies. The results, corroborated with Ansys finite element software, demonstrated the potential of EVE to provide useful information about the heterogeneous nature of atherosclerotic plaques.

Animals↗
PubMed2002

The 6sigma quality approach for quantitative arteriography performance improvement.

Quantitative angiography is a medical application where the user requires tools whose operational results in term of accuracy, precision, robustness and reliability must be extensively assessed and validated for clinical use. In this study, the 6sigma methodology has been applied to analyze the performances of the General Electric QA software method. In particular, the catheter calibration procedure was identified as the weakest function in term of sensitivity to procedure parameters, like point-spread-function, field-of-view, catheter dimensions. It was therefore improved by following a design for 6sigma scheme, and the main parameters that govern the QA accuracy and precision were put under quantifiable control.

Calibration↗