Aortic Wall Elastic Properties in Case of Bicuspid Aortic Valve

Purpose of the ReviewBicuspid aortic valve (BAV) is associated with a significant risk of development of aneurysm and dissection of the ascending thoracic aorta. Development of what is called BAV associated aortopathy is particularly heterogeneous with an uncertain prognosis and with no prognostic biomarkers except for the aortic diameter. This situation leads to an important variability of the therapeutic strategy of this aortopathy. By reviewing the literature on aortic stiffness in the case of BAV, we aimed at evaluating its potential prognostic role in the development of aortic dilatation.Recent FindingsStudies evaluating aortic stiffness, with ultrasound or magnetic resonance imaging, converge toward the description of an increased segmental aortic stiffness in BAV patients regardless of age, diameter or aortic level, from the root to the arch. Even though there is a lack of longitudinal studies evaluating the progression of aortic dilatation, new data have recently shown the potential prognostic role of the maximal rate of systolic distension of the aortic wall with magnetic resonance imaging.SummaryAlthough the use of aortic distensibility calculation is a simple evaluation of stiffness that could be easily transposed in daily practice, its interpretation remains uncertain. New arterial stiffening indicators seem more promising but need a stronger validation

Precise control of thermal conductivity at the nanoscale through individual phonon-scattering barriers

International audienceThe ability to precisely control the thermal conductivity (κ) of a material is fundamental in the development of on-chip heat management or energy conversion applications. Nanostructuring permits a marked reduction of κ of single-crystalline materials, as recently demonstrated for silicon nanowires. However, silicon-based nanostructured materials with extremely low κ are not limited to nanowires. By engineering a set of individual phonon-scattering nanodot barriers we have accurately tailored the thermal conductivity of a single-crystalline SiGe material in spatially defined regions as short as ∼15 nm. Single-barrier thermal resistances between 2 and 4×10−9 m2 K W−1 were attained, resulting in a room-temperature κ down to about 0.9 W m−1 K−1, in multilayered structures with as little as five barriers. Such low thermal conductivity is compatible with a totally diffuse mismatch model for the barriers, and it is well below the amorphous limit. The results are in agreement with atomistic Green’s function simulations

Titanium-based silicide quantum dot superlattices for thermoelectrics applications

Ti-based silicide quantum dot superlattices (QDSLs) are grown by reduced-pressure chemical vapor deposition. They are made of titanium-based silicide nanodots scattered in an n-doped SiGe matrix. This is the first time that such nanostructured materials have been grown in both monocrystalline and polycrystalline QDSLs. We studied their crystallographic structures and chemical properties, as well as the size and the density of the quantum dots. The thermoelectric properties of the QDSLs are measured and compared to equivalent SiGe thin films to evaluate the influence of the nanodots. Our studies revealed an increase in their thermoelectric properties specifically, up to a trifold increase in the power factor, with a decrease in the thermal conductivity making them very good candidates for further thermoelectric applications in cooling or energy-harvesting fields

Aortic Wall Elastic Properties in Case of Bicuspid Aortic Valve

International audiencePurpose of the Review: Bicuspid aortic valve (BAV) is associated with a significant risk of development of aneurysm and dissection of the ascending thoracic aorta. Development of what is called BAV associated aortopathy is particularly heterogeneous with an uncertain prognosis and with no prognostic biomarkers except for the aortic diameter. This situation leads to an important variability of the therapeutic strategy of this aortopathy. By reviewing the literature on aortic stiffness in the case of BAV, we aimed at evaluating its potential prognostic role in the development of aortic dilatation. Recent Findings: Studies evaluating aortic stiffness, with ultrasound or magnetic resonance imaging, converge toward the description of an increased segmental aortic stiffness in BAV patients regardless of age, diameter or aortic level, from the root to the arch. Even though there is a lack of longitudinal studies evaluating the progression of aortic dilatation, new data have recently shown the potential prognostic role of the maximal rate of systolic distension of the aortic wall with magnetic resonance imaging. Summary: Although the use of aortic distensibility calculation is a simple evaluation of stiffness that could be easily transposed in daily practice, its interpretation remains uncertain. New arterial stiffening indicators seem more promising but need a stronger validation

On the relationship between the basicity of a surface and its ability to catalyze transesterification in liquid and gas phases: the case of MgO

International audienceGas or liquid phase transesterification reactions are used in the field of biomass valorization to transform some platform molecules into valuable products. Basic heterogeneous catalysts are often claimed for these applications but the role of basicity in the reaction mechanism depending on the operating conditions is still under debate. In order to compare the catalyst properties necessary to perform a transesterification reaction both in liquid and gas phases, ethyl acetate and methanol, which can be easily processed both in these two phases, were chosen as reactants. The catalyst studied is MgO, known for its basic properties and its ability to perform the reaction. By means of appropriate thermal treatments, different kinds of MgO surfaces, with different coverages of natural adsorbates (carbonates and hydroxyls groups), can be prepared and characterized by means of CO2 adsorption followed by IR spectroscopy and hept-1-ene isomerization model reaction. New results on the basicity of the natural MgO surface (covered by carbonate and hydroxyl groups) are first given and discussed. The catalytic behavior in the transesterification reaction is then determined as a function of the adsorbate coverage. It is shown that the transesterification activity in the liquid phase is directly correlated with the kinetic basicity of the surface in agreement with the mechanism already proposed in the literature. On the reverse, no direct correlation with the basicity of the surface was established with the transesterification activity in the gas phase. A very high activity, in the gas phase, was observed and discussed for the natural surface pre-treated at 623 K. Preliminary DFT modeling of ester adsorption and methanol adsorption capacity determination were performed to investigate plausible reaction routes

Segmental aortic stiffness in patients with bicuspid aortic valve compared with first-degree relatives

International audienceAims: To compare the stiffness index in patients with bicuspid aortic valve (BAV) with first-degree relatives at each segment of the thoracic ascending aorta and to compare segmental analysis of aortic stiffness in association with BAV morphotype and function.Methods: 219 patients with BAV and 148 first-degree relatives (without BAV) were consecutively included at a reference centre for BAV. Ultrasound assessment of aortic and carotid stiffness was based on the variation of the segmental arterial diameters during the cardiac cycle and on blood pressure.Results: Without adjustment, the ascending aorta of patients with BAV seemed stiffer at each segment compared with controls (stiffness index at the sinus of Valsalva: 17.0±10.9 vs 8.9±6.1, p<0.001; tubular aorta: 20.4±31.3 vs 12.7±4.8, p=0.04). However, after adjustment on aortic diameter and age, only the sinus of Valsalva remained stiffer (p<0.001), whereas the tubular aorta no longer differed (p=0.610). In patients with BAV, aortic diameters were not influenced by the valve morphotype, except for the arch, which was more dilated in the case of 1- Non coronary sinus-Right subtype of BAV : 36.1 vs 27.6 mm, p<0.001. Aortic regurgitation was associated with an increase in aortic diameters at the sinus of Valsalva (p<0.001) and the tubular aortic levels (p=0.04).Conclusion: Stiffness increase at the sinus of Valsalva level is independent of aortic dilatation in patients with BAV, contrary to the classic relationship between stiffness and dilatation found on the other segments. The relationship between stiffness and clinical impact needs to be assessed at each aortic segment

Smart ultrasound device for real-time myocardial stiffness quantification of the human heart

International audienceIntroduction: Myocardial stiffness (MS) is crucial to understand cardiac biomechanics and evaluate cardiac function. We recently demonstrated that shear wave imaging using acoustic radiation force can provide quantitative end-diastolic MS in human patients [1]. However, the dependence of shear wave velocity with myofiber orientation remained a limitation and required to perform Shear Wave Velocity (SWV) estimations from different probe orientations which is challenging in clinical practice. We propose a new approach to provide real-time quantitative assessment of MS without dependence of the probe orientation based on a dedicated smart ultrasound (US) device. Methods: A new US probe was designed and manufactured to generate acoustic radiation force along the central axis and track the SWV simultaneously along three different orientations to obtain an elliptic profile of SWS. The probe was connected to dedicated electronics and software to provide real-time end-diastolic MS with ECG gating. Validation was performed on 4 in-vitro calibrated phantoms (0.92-1.49-2.58-3.49 m/s) and on ex vivo porcine hearts. MS along and across the fibers were compared to the values measured by conventional shear wave imaging with a linear probe mounted on a rotation motor (angular step of 10°) (Aixplorer, Supersonic imaging). Finally, the in vivo feasibility and reproducibility of measuring MS of the antero-septal wall and of the right ventricular (RV) wall was assessed transthoracically on four human volunteer. Results: In vitro results on phantoms showed a good agreement with calibrated value (r2 = 0.98, std = 4.8%). Elliptic profiles on ex-vivo porcine heart showed good agreement with Aixplorer measurements acquired at different angles, with a relative difference along the long axis (LA) of: Δ=7.0%, Δ=7.1%, Δ=9% respectively for left ventricle (LV), right ventricle (RV) and septum. Finally, myocardial SWV assessment in human volunteers was obtained successfully on the RV and on the septum in late diastole. The mean MS was 1.79+/-0.15 m/s along the fiber direction, the fractional anisotropy (FA) was 0.25 +/-0.06 on septal wall in good agreement with previous results [1] and 1.06 +/-0.11 m/s along fibers orientation and a FA of 0.27 +/-0.08 on RV. Finally the beat to beat reproducibility of MS measurement was estimated to be 8.22%. Conclusion: The new smart US device allowed non-invasive quantification of anisotropic myocardial tissues in real time. Results showed the accuracy of the methods. This approach could offer a new clinical tool for the evaluation of the myocardium in cardiomyopathies and in heart failure patients

Online data analysis at the ESRF bioSAXS beamline, BM29

International audienc