Developmental Patterning by Mechanical Signals in Arabidopsis

A central question in developmental biology is whether and how mechanical forces serve as cues for cellular behavior and thereby regulate morphogenesis. We found that morphogenesis at the Arabidopsis shoot apex depends on the microtubule cytoskeleton, which in turn is regulated by mechanical stress. A combination of experiments and modeling shows that a feedback loop encompassing tissue morphology, stress patterns, and microtubule-mediated cellular properties is sufficient to account for the coordinated patterns of microtubule arrays observed in epidermal cells, as well as for patterns of apical morphogenesis

Relationships between Specific Airway Resistance and Forced Expiratory Flows in Asthmatic Children

. The first aim was to assess the relationships between forced expiratory flows and sRaw in a large group of asthmatic children in a transversal study. We then performed a longitudinal study in order to determine whether sRaw of preschool children could predict subsequent impairment of forced expiratory flows at school age.Pulmonary function tests (sRaw and forced expiratory flows) of 2193 asthmatic children were selected for a transversal analysis, while 365 children were retrospectively selected for longitudinal assessment from preschool to school age. (% predicted) (−0.09, 95% CI, −0.20 to 0). and could be used in preschool children to predict subsequent mild airflow limitation

Description expérimentale et numérique de l'interaction entre un stent biodégradable et la paroi artérielle

PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

The influence of variability on the optimal shape of an airway tree branching asymmetrically.

International audienceThe asymmetry of the bronchial tree has been reported on numerous occasions, and bronchi in the lung bifurcate most of the time into a major and a minor daughter. Asymmetry is most probably bound to play a role on the hydrodynamic resistance and volume occupation of the bronchial tree. Thus, in this work, we search for an optimal asymmetric airway tree crossed by Poiseuille flow that would be a good candidate to model the distal conductive part of the lung. The geometry is controlled by major and minor diameter reduction factors that depend on the generation. We show that the optimal asymmetric tree has diameter reduction factors that are adimensional from the second level of bifurcation and that they are highly dependent on the asymmetric ratio that defines the relative sizes of the major and minor branches in a bifurcation. This optimization also gives access to a cost function whose particularity is to be asymmetric around its minimum. Thus, the cliff-edge hypothesis predicts that if the system suffers variability, then the best tree is shifted from the optimal. We apply a recent theoretical model of cliff-edge in order to measure the role of variability on the determination of the best asymmetric tree. Then, we compare our results with lung data of the literature. In particular, we are able to quantify the variability needed to fit the data and to give hypothesis that could explain, at least partially, the shift found between the optimal tree and the measures in the case of asymmetric bronchial trees. Finally, our model predicts that, even if the population is adapted at best, there always exist individuals whose bronchial trees are associated with larger costs comparatively to the average and who ought to be more sensitive to geometrical remodeling

PALMAZ–SCHATZ STENT-OPENING MECHANICS USING A SIMPLE APPROACH INVOLVING THE BALLOON–STENT AND STENT–ARTERY CONTACT PROBLEM: APPLICATION TO BIOPOLYMER STENTS

International audienceWe used the finite element method-based toolbox COMSOL Multiphysics to address the important question of biopolymer coronary stent mechanics. We evaluated the diameter of the stent, the immediate elastic recoil, the dogboning and the foreshortening during deployment while using an idealized model that took into account the presence of the balloon and the coronary artery wall (equivalent pressure hypothesis). We validated our model using the well-known mechanics of the Palmaz–Schatz metal stent and acquired new data concerning a poly-L-lactic acid (PLLA) stent and some other biodegradable co-polymer-based stents. The elastic recoil was relatively high (26.1% to 31.1% depending on the biopolymer used) when taking into account the presence of both the balloon and artery. The dogboning varied from 31% to 46% for the polymer stents and was 62% for the metal stent, suggesting that less arterial damage could be expected with biopolymer stents. Various strut thicknesses were tested for the PLLA stent (114, 180 and 250[Formula: see text][Formula: see text]m) and no significant improvement in elastic recoil was observed. We concluded that the stent geometry has a greater impact on the scaffolding role of the structure than the strut thickness, or even the mechanical properties of the stent

Comparison of methods of chemical loop gain measurement during tidal ventilation in awake healthy subjects

International audienceThe loop gain (LG) is defined as the ratio of a ventilatory response over the perturbation in ventilation, and it is used to analyze ventilatory control stability. The LG can be derived from minute ventilation (VE), end-tidal PCO2 (PETCO2) and PETO2 values. Several methods of LG assessment have been developed, which have never been compared. We evaluated the computability, the short term repeatability and the agreement of six published (or slightly modified) models for LG determination. These models included three unconstrained autoregressive models: univariate (VE), bivariate (VE, PETCO2) and trivariate (VE, PETCO2 and PETO2) and three analytical transfer function constrained models based on VE, VE and CO2-sensitivity, and VE, central and peripheral CO2-sensitivities, respectively. The models were tested using tidal breathing data in 37 awake healthy subjects (median age, 35 years, 23 women). Modelling failed in 11, 0, and 0 subjects for the three unconstrained models respectively, and 4, 1, and 9 subjects for the three constrained models, respectively. Bland and Altman analyses of the LG values in the medium frequencies range of two separate recordings demonstrated good repeatability for four models, excluding univariate and trivariate unconstrained models. The four repeatable models gave LG values that were in agreement (medium frequencies LG, median 0.100 to 0.210), although the constrained model based on VE systematically overestimated LG values. The variances explained by these models were around 20%. In conclusion, model-based analyses of tidal breathing were performed using different approaches that give comparable results of chemical LG and explained variance

Boundary conditions in arterial flows and evaluation of reflection indices

International audienc