“Right Ventricle Speckle Tracking in Bronchopulmonary Dysplasia: One Year Follow Up”

Purpose: Bronchopulmonary dysplasia is still a main problem in preterm infants. The screening of secondary right ventricle (RV) failure concern neonatologist and pediatric cardiologists. Measurements of right ventricle deformation through speckle tracking analysis in echocardiography could help to early diagnosis.Methods: A prospective longitudinal study was carried out over 28 months at a tertiary care pediatric cardiology reference center. Under 32 weeks’ pre-term infants were eligible for the study. Twenty-eight days after birth, all enrolled patients were included in one group: no bronchopulmonary dysplasia (NO-BPD) or bronchopulmonary dysplasia (BPD). At 36 PMA, BPD patients were included in one group according to severity categorization (mild, moderate, severe). At three time points echocardiogram measurements were performed. Right ventricle strain was studied using speckle tracking analysis and it was compared with classical function parameters between groups and along time. Results: Fifty patients were enrolled in the study, 22 on NO-BPD group and 28 on BPD group (16 mild, 8 moderate, 4 severe). RV strain showed no statistical differences between groups. However, BDP group showed worse RV function than NO-BPD group, both in speckle tracking analysis and in classical parameters. During de follow-up, an improvement trend is shown in RV strain. Conclusions: RV longitudinal strain and strain rate derived by speckle tracking is feasible in preterm infants. Although it seems to be a good correlation between RV strain and BPD severity, authors cannot conclude it. More studies should be carried out to investigate the optimum echocardiographic screening model of RV dysfunction in BPD patients.

Normal Ranges of Right Atrial Strain and Strain Rate by Two-Dimensional Speckle-Tracking Echocardiography: A Systematic Review and Meta-Analysis

Background: Normal range values of right atrial (RA) phasic function markers are essential for the identification of normal and abnormal values, comparison with reference values, and the clinical meaning of obtained values. Accordingly, we aimed to define the normal range values of RA phasic function markers obtained by 2D speckle-tracking echocardiography through a meta-analysis and determine the main sources of heterogeneity among reported values.Methods: PUBMED, SCOPUS, and EMBASE databases were searched for the following keywords: “right atrial/right atrium” and “strain/speckle/deformation” and “echocardiography.” Studies were selected that included a human healthy adult group without any cardiovascular diseases or risk factors and that were written in the English language. For the calculation of each marker of RA phasic functions, a random-effect model was used. Meta-regression was employed to define the major sources of variabilities among reported values.Results: Fifteen studies that included 2,469 healthy subjects were selected for analysis. The normal range values for RA strain and strain rate were 42.7% (95% CI, 39.4 to 45.9%) and 2.1 s−1 (95% CI, 2.0 to 2.1 s−1) during the reservoir phase, respectively, 23.6% (95% CI, 20.7 to 26.6%) and −1.9 s−1 (95% CI, −2.2 to −1.7 s−1) during the conduit phase, correspondingly, and 16.1% (95% CI, 13.6 to 18.6%) and −1.8 s−1 (95% CI, −2.0 to −1.5 s−1) during the contraction phase, respectively. The sources of heterogeneity for the normal range of these markers were the number of participants, the type of software, the method of global value calculation, the right ventricular fractional area change, the left ventricular (LV) ejection fraction, the RA volume index, sex, the heart rate, the diastolic blood pressure, the body mass index, and the body surface area.Conclusions: Using 2D speckle-tracking echocardiography, we defined normal values for RA phasic function markers and identified the sources of heterogeneity as demographic, anthropometric, hemodynamic, and echocardiography factors.Systematic Review Registration:https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42021236578, identifier: CRD42021236578.

The Presence of the Temporal Horn Exacerbates the Vulnerability of Hippocampus during Head Impacts

Hippocampal injury is common in traumatic brain injury (TBI) patients, but the underlying pathogenesis remains elusive. In this study, we hypothesize that the presence of the adjacent fluid-containing temporal horn exacerbates the biomechanical vulnerability of the hippocampus. Two finite element models of the human head were used to investigate this hypothesis, one with and one without the temporal horn, and both including a detailed hippocampal subfield delineation. A fluid-structure interaction coupling approach was used to simulate the brain-ventricle interface, in which the intraventricular cerebrospinal fluid was represented by an arbitrary Lagrangian-Eulerian multi-material formation to account for its fluid behavior. By comparing the response of these two models under identical loadings, the model that included the temporal horn predicted increased magnitudes of strain and strain rate in the hippocampus with respect to its counterpart without the temporal horn. This specifically affected cornu ammonis (CA) 1 (CA1), CA2/3, hippocampal tail, subiculum, and the adjacent amygdala and ventral diencephalon. These computational results suggest the presence of the temporal horn is a predisposing factor for the prevalence of hippocampal injury, advancing the understanding of hippocampal injury during head impacts. A corresponding analysis in an imaging cohort of collegiate athletes found that temporal horn size negatively correlates with hippocampal volume in the same subfields, suggesting a possible real-world correlation whereby a larger temporal horn may be associated with decreased hippocampal volume. Our biomechanical and neuroimaging effort collectively highlight the mechanobiological and anatomical interdependency between the hippocampus and temporal horn.

Experimental and Modeling Studies on the Stress Relaxation Behaviour of Ti-6Al-4V Alloy

The transient mechanical behavior of materials during stress relaxation has evoked interest in manufacturing applications because of the effect of stress relaxation on formability enhancement. However, most of the previous studies have focused on advanced high strength steels and aluminum alloys. Limited transient stress relaxation studies have been conducted on titanium alloys in order to understand the influence of stress relaxation on forming behavior. Titanium alloys are widely used in aerospace components because of their high strength to weight ratios and excellent fatigue strengths. However, room temperature formability of Ti alloys is an important concern, which restricts their widespread use in various applications. To address these challenges, the present study is aimed to understand the role of transient stress relaxation on formability of Ti alloys. Toward this end, stress relaxation of a dual phase titanium alloy (Ti-6Al-4V) has been investigated experimentally. Stress relaxation tests were performed by interrupting uniaxial tensile tests in the uniform deformation regime for a pre-defined strain and hold time after which tests were continued monotonically until fracture. Single step, room temperature stress relaxation experiments were performed systematically to study the effect of hold time, pre-strain, and strain rate on mechanical properties. The stress relaxation phenomenon was found to contribute positively to the ductility improvement. The mechanisms responsible for enhancing the formability are discussed. The experimentally obtained stress vs. time data were analyzed using a advanced constitutive model for stress relaxation available in literature.

Feasability of Diaphragmatic Speckle Tracking In Intensive Care Units

Background: Diaphragmatic dysfunction is a common condition in intensive care units (ICU). Its presence correlates with prolonged weaning from mechanical ventilation and mortality. Diaphragmatic excursion (EXdi) and thickening fraction (TFdi) are the 2 main measures currently described in diaphragmatic ultrasound, but each has its limitations. Strain and strain rate are already used cardiac sonography and could be of interest in the assessment of diaphragmatic function in ICU. The aim of this work was to evaluate the feasibility of diaphragmatic strain and strain rate in ICU and to describe their distribution, reproducibility and agreement with existing parameters. Methods: All patients who underwent a T-tube weaning test were prospectively included. Ultrasound loops were recorded on each side of the patient during the last 30 minutes of the weaning test. Two operators measured strain, strain rate, EXdi, and TFdi blind to each other in post-treatment analysis. Results: Thirty patients were analyzed. The median values for strain and strain rate were -6.74% and -0.23.s-1 on the left side and -8.17% and -0.22.s-1 on the right side. Concerning strain and strain rate, intra-class coefficients showed systematically a very good reliability between operators. Conclusion: Diaphragmatic strain and strain rate measurements appeared feasible in an ICU environment and seemed reproducible and not strongly correlated with EXdi and TFdi. An improvement of the analysis software is needed to improve the ease of interpretation. The interest of these parameters in clinical practice should be explored in forthcoming studies.

A Machine Learning Approach to Investigate the Uncertainty of Tissue-Level Injury Metrics for Cerebral Contusion

Controlled cortical impact (CCI) on porcine brain is often utilized to investigate the pathophysiology and functional outcome of focal traumatic brain injury (TBI), such as cerebral contusion (CC). Using a finite element (FE) model of the porcine brain, the localized brain strain and strain rate resulting from CCI can be computed and compared to the experimentally assessed cortical lesion. This way, tissue-level injury metrics and corresponding thresholds specific for CC can be established. However, the variability and uncertainty associated with the CCI experimental parameters contribute to the uncertainty of the provoked cortical lesion and, in turn, of the predicted injury metrics. Uncertainty quantification via probabilistic methods (Monte Carlo simulation, MCS) requires a large number of FE simulations, which results in a time-consuming process. Following the recent success of machine learning (ML) in TBI biomechanical modeling, we developed an artificial neural network as surrogate of the FE porcine brain model to predict the brain strain and the strain rate in a computationally efficient way. We assessed the effect of several experimental and modeling parameters on four FE-derived CC injury metrics (maximum principal strain, maximum principal strain rate, product of maximum principal strain and strain rate, and maximum shear strain). Next, we compared the in silico brain mechanical response with cortical damage data from in vivo CCI experiments on pig brains to evaluate the predictive performance of the CC injury metrics. Our ML surrogate was capable of rapidly predicting the outcome of the FE porcine brain undergoing CCI. The now computationally efficient MCS showed that depth and velocity of indentation were the most influential parameters for the strain and the strain rate-based injury metrics, respectively. The sensitivity analysis and comparison with the cortical damage experimental data indicate a better performance of maximum principal strain and maximum shear strain as tissue-level injury metrics for CC. These results provide guidelines to optimize the design of CCI tests and bring new insights to the understanding of the mechanical response of brain tissue to focal traumatic brain injury. Our findings also highlight the potential of using ML for computationally efficient TBI biomechanics investigations.

Atrial Strain by Feature-Tracking Cardiac Magnetic Resonance Imaging in Takotsubo Cardiomyopathy. Features, Feasibility, and Reproducibility

Objectives: The purpose of this study was to investigate whether there may be a bi-atrial dysfunction in Takotsubo syndrome (TS) during the transient course of the disease, using cardiac magnetic resonance imaging feature tracking (CMR-FT) in analyzing bi-atrial strain. Method: Eighteen TS patients and 13 healthy controls were studied. Reservoir, conduit, and booster bi-atrial functions were analyzed by CMR-FT. The correlation between LA and RA strain parameters was assessed. Intra- and inter-observer reproducibility was evaluated for all strain and strain rate (SR) parameters using intraclass correlation coefficients (ICCs) and Bland-Altman analysis. Results: Atrial strain were feasible in all patients and controls. Takotsubo patients showed an impaired LA Reservoir strain (∊s), LA Reservoir strain rate (SRs), LA and RA Conduit strain(∊e), LA and RA conduit strain rate (SRe) in comparison with controls (P < 0.001 for all of them), while no differences were found as to LA and RA booster deformation parameters (∊a and SRa). Analysis of correlation showed that LA ∊s, SRs, ∊e, and SRe were positively correlated with corresponding RA strain measurements (P < 0.001, r = 0.61 and P = 0,03, r = 0,54, respectively). Reproducibility was good to excellent for all atrial strain and strain rate parameters (ICCs ranging from 0,50 to 0,96). Conclusion: Atrial strain analysis using CMR-FT may be a useful tool to reveal new pathophysiological insights in Takotsubo cardiomyopathy. Additional studies, with a larger number of patients, are needed to confirm the possible role of these advanced CMR tools in characterizing TS patients.

Elasto-thermoviscoplastic finite element analyses of cold upsetting and forging processes of S25C steel with dynamic strain aging considered

A practical methodology is presented to characterize the thermoviscoplastic flow stress at larger strain over the temperature range of cold metal forming using tensile and compression tests. Its importance is emphasized for non-isothermal finite element (FE) analysis of automatic multi-stage cold forging (AMSCF) process where maximum strain and strain rate exceed around 3.0 and 200/s, respectively. The experimental compressive flow stress is first characterized using traditional bilinear C-m model with high accuracy. It is employed for describing the closed-form function model to extrapolate the experimental flow stress over the experimentally uncovered ranges of state variables. The strain effect on the flow stress is then improved using the experimental tensile flow stress accurately calculated at large strain and room temperature. A complicated flow behavior of S25C characterized by its dynamic strain aging features is expressed by the presented methodology, which is utilized to analyze the test upsetting and AMSCF processes by the elasto-thermoviscoplastic finite element method for revealing the effects of flow stresses on the process.