Strain Rate Ratio Research Articles

Short-term effects of angiotensin receptor-neprilysin inhibitors on diastolic strain and tissue doppler parameters in heart failure patients with reduced ejection fraction: A pilot trial

ObjectiveAlthough sacubitril/valsartan has recently shown its long-term benefits on morbidity and mortality in symptomatic patients with chronic heart failure with reduced ejection fraction (HFrEF), its short-term effects on diastolic function remain uncertain. We sought to assess 30-day effects of sacubitril/valsartan on left ventricular (LV) diastolic paremeters determined by speckle tracking and tissue Doppler imaging (STI and TDI respectively) as well as their association with functional capacity change evaluated by peak oxygen uptake (VO2max) in stable patients with symptomatic HFrEF. MethodsA total of 35 patients (aged 61 ± 9 years) eligible for sacubitril/valsartan underwent a complete two-dimension (2D) echocardiographic study and a cardiopulmonary exercise test at baseline and 30 days after the initiation of therapy. ResultsSignificant improvements in ratio of trans-mitral inflow early diastolic velocity E to mitral annulus early diastolic velocity E′ (ΔΕ//Ε′ = -35.9%, p = 0.001), peak early diastolic strain rate SRE (ΔSRE = +22.5%, p = 0.024) and ratio E/SRE (ΔE/SRE = -33.2%, p = 0.025) were observed after 1-month therapy. Compared with baseline, VO2max also increased significantly by 16.7 % (p = 0.001). Baseline E/SRE and ΔE/SRE were the strongest independent predictors of VO2max improvement (beta = -0.43, p = 0.004 and beta = 0.45, p = 0.021 respectively) in the multivariate analysis. ConclusionSacubitril/valsartan was associated with early improvement in LV diastolic function determined by TDI and 2D STI. Baseline E/SRE was stronger than standard echocardiographic parameters in predicting the early benefit of sacubitril/valsartan therapy.

Effects of the strain rate and fiber blending ratio on the tensile behavior of hooked steel fiber and polyvinyl alcohol fiber hybrid reinforced cementitious composites

The strain rate effect on the tensile behavior of high performance hybrid fiber reinforced cementitious composites was evaluated according to the blending ratio of hooked steel fiber (HSF) and polyvinyl alcohol fiber (PVA). The tensile strength, strain capacity, peak toughness, and softening toughness were investigated. In the experimental result, specimen with 1.5 vol% HSF and 0.5 vol% PVA (HSF1.5PVA0.5) exhibited the highest tensile strength and softening toughness. However, the strain capacity and peak toughness were less than those of the specimen with 2.0 vol% HSF (HSF2.0). Nevertheless, HSF1.5PVA0.5 exhibited the highest dynamic increase factors (DIFs) for the tensile strength, strain capacity, and softening toughness. HSF2.0 showed a higher DIF for the peak toughness than HSF1.5PVA0.5. But HSF1.5PVA0.5 is expected to exhibit a higher DIF for the peak toughness than HSF2.0 at high strain rates (>101 s−1), because it have highest strain rate sensitivity of tensile strength and strain capacity.

Visco-elastic parasitic folding: Influences on the resulting porosity distribution

Parasitic folds represent a common structure of multi-scale multilayer folds and the resulting asymmetric S- or Z-shapes and symmetric M-shapes represent a complex strain distribution. How the strain evolution affects the resulting porosity remains unclear. In this study, a 2-D plane strain finite element modeling approach is used to simulate multi-scale, multilayer, viscoelastic buckle folds under in-situ stress and pore pressure conditions. A variety of material and model parameters (including the elastic modulus contrast, number of layers, viscosity contrast, strain rate and layer thickness ratio) are considered and their influence on the shape of parasitic folds and on the resulting porosity distribution is analyzed. This study demonstrates that the shapes of the parasitic folds depend on the buckling of both the large- and small-scale folds and are influenced by the various parameters. The numerical modeling results show a large variability in porosity changes as a result of the complex distribution of the volumetric strain during the multi-scale, multi-layer buckling process. Three regions, including the hinge and limb of the less competent layer in the M-shaped folds and the limb of the less competent layer in the Z-shaped folds, feature significant porosity changes, which vary from double the initial magnitude to almost zero. In addition, the numerical simulations provide a general understanding of the influence of the various model parameters on the resulting porosity distribution. Through the applied volumetric strain-porosity-permeability coupling, the resulting fluid flow regimes in multi-scale, multilayer buckling systems include localized pervasive and focused regimes.

P5250Diastolic strain rate ratio as determined on MRI on detecting left ventricle stiffness and predict heart failure in post-STEMI patients

Abstract Background ST-elevation myocardial infarction (STEMI) Patients suffered from progressive heart failure, for which progressive and aggravated Left ventricle stiffness was one of the major culprit. Myocardial deformation in the early diastole is largely affected by the left ventricle compliance which could partly reflect chamber stiffness and potentially predict left ventricular remodeling for post-STEMI patients. Purpose To determine the value of diastolic strain rate in detecting left ventricle stiffness and early heart failure in post-STEMI patients. Methods A number of 52 (M/F: 46/6, age: 54.27 [46.8–62.3]yrs) patients with STEMI three months ago were prospectively recruited from 2016 to 2017. Follow-up was done until 2018. The primary end points were the symptoms of heart failure (NYHA II-IV). Consent was acquired from each patient and 3.0 T MRI was arranged. Imaging analysis was performed on Cvi 42 (V5.9.3 Canada). Peak radial strain (PS) and strain rate (SR) were extracted both from 2D short- and long-axis cine images, while peak circumferential parameters only from the short axis slices and longitudinal the long axis slices. The diastolic strain rate ratios (DSRRs) were calculated as the peak early diastolic SR divided by the peak late diastolic SR, which were derived from the two peak points on the corresponding curve of time-to-SR curve in the diastole (Figure 1a). Receiver-operating characteristics curve analysis and Logistic regression test were done for statistical analysis on R project and P<0.05 was considered as significant. Results Three patients were excluded due to unsatisfied cine images. Among the 52 patients, none of the patients died or had congestive heart failure. 23/52 (44.2%) patients complained of heart failure symptoms at the one-year follow-up. No significant difference was found in LVEF and three directional peak strain values or systolic peak strain rates between the patients with and without heart failure. Patients with symptoms had lower Longitudinal PS (P=0.049), early diastolic radial SR (P=0.01798), longitudinal SR (P=0.0042), and decreased DSRR in all directions (Figure 1b). Multivariate Logistic regression test showed that only DSRR in the radial direction on the short axis (DSRR-SR) was the independent predictor of the heart failure symptoms (6.59; range, 6.71–3.68; P=0.026). ROC analysis demonstrated that the DSRR-SR of 2.35 had sensitivity 91.3% and specificity 58.6% for the prediction of heart failure (Figure 1c). Figure 1 Conclusion DSRR especially DSRR-SR was more sensitive to left ventricle stiffness change and help predict the progression of heart failure for Post-STEMI patients. Further studies were needed to verify the its association with other cardiovascular clinical events. Acknowledgement/Funding the National Natural Science Foundation of China (81600299,81471721, 81471722, 81771887, and 81771897,);

Non-axisymmetric Homann stagnation-point flow of a viscoelastic fluid towards a fixed plate

Abstract We have investigated the non-axisymmetric Homann stagnation-point flow of a viscoelastic fluid over a rigid plate. In a recent paper Weidman (2012) has modified Homann’s stagnation point flow and made it non-axisymmetric over a rigid plate. Now if the fluid is non-Newtonian a new family of asymmetric stagnation-point flows arises depending on the shear to strain-rate ratio γ ( = b ∕ a ) and the viscoelastic parameter k . Here a , b are the strain rate and shear rate of the stagnation-point flow. The governing momentum equations are solved numerically using fourth order Runge–Kutta method with shooting technique. The effect of the various parameters on the wall shear stress parameters, the dimensionless velocities, the displacement thicknesses and the velocity distributions are analysed. Numerical results of wall shear stress and displacement thicknesses are compared with their large value behaviours and those behaviours give a good agreement with the corresponding numerical solutions.

A comparative study of three ultrasonic elastographic methods for the differentiation and diagnosis of benign and malignant breast masses

Background: To evaluate the application of three elastography methods including real-time tissue elasticity imaging (RTE), strain rate ratio elasticity imaging (SR), and acoustic radiation force elastic imaging (ARFI) in two ultrasound instruments for the diagnosis of benign and malignant breast lesions. Materials and Methods: The authors examined 97 breast nodules of 97 patients who were ready to undergo adenomammectomy. For each patient, RTE was applied to determin nodule properties by level 5 score method, SR was applied to measure the strain rate ratio of targeted nodules, and the surrounding mammary glands at the same level, ARFI was applied to measure internal and marginal shear wave velocity (SWV) values of targeted nodules. Results: The sensitivity and specificity of RTE, SR, the internal SWV values, and marginal SWV values were more than 80% in diagnosing breast nodules. Area under the curve of RTE, SR, the internal SWV values, and the marginal SWV values in diagnosis of benign and malignant breast nodules were 0.923, 0.934, 0.934 and 0.916, respectively. No significant differences were found among the four values for the diagnosis efficiency. Conclusions: RTE, SR, and ARFI are all highly valuable in diagnosing benign and malignant breast nodules.

Machine Learning Enabled Prediction of Mechanical Properties of Tungsten Disulfide Monolayer.

One of two-dimensional transition metal dichalcogenide materials, tungsten disulfide (WS2), has aroused much research interest, and its mechanical properties play an important role in a practical application. Here the mechanical properties of h-WS2 and t-WS2 monolayers in the armchair and zigzag directions are evaluated by utilizing the molecular dynamics (MD) simulations and machine learning (ML) technique. We mainly focus on the effects of chirality, system size, temperature, strain rate, and random vacancy defect on mechanical properties, including fracture strain, fracture strength, and Young’s modulus. We find that the mechanical properties of h-WS2 surpass those of t-WS2 due to the different coordination spheres of the transition metal atoms. It can also be observed that the fracture strain, fracture strength, and Young’s modulus decrease when temperature and vacancy defect ratio are enhanced. The random forest (RF) supervised ML algorithm is employed to model the correlations between different impact factors and target outputs. A total number of 3600 MD simulations are performed to generate the training and testing dataset for the ML model. The mechanical properties of WS2 (i.e., target outputs) can be predicted using the trained model with the knowledge of different input features, such as WS2 type, chirality, temperature, strain rate, and defect ratio. The mean square errors of ML predictions for the mechanical properties are orders of magnitude smaller than the actual values of each property, indicating good training results of the RF model.

The Dynamic Mechanics Behavior on Triaxial Compression of the Recycled Aggregate Concrete

The tests under triaxial compression states were conducted on recycled aggregate concrete (RAC) by different stress ratios (-0.1: -0.1: -1; -0.1: -0.25: -1; -0.1: -0.5: -1; -0.1: -0.75: -1; -0.1: -1: -1) at the strain rates of 10-5/s, 10-4/s, 10-3/s, and 10-2/s. This study was accomplished in the servo-hydraulic multi-axial testing system. The experimental phenomena and failure modes of recycled aggregate concrete under triaxial compression are described, the results of triaxial compressive strength of recycled aggregate concrete are presented, the effects of the strain rate and stress ratio on the triaxial compressive strength of recycled aggregate concrete are studied. This paper built a new dynamic strength criterion. The strength criterion describes the characteristics of structural RAC at different stress ratios and strain rates. The feature of the model is that it can consider the influence of strain rates.

Co-extrusion of Zircaloy-2 and Zr-Sn alloy for double clad tube manufacturing: Numerical simulation and experimental validation

Zircaloy-2 cladding in boiling water nuclear reactors is prone to brittle failure due to pellet-cladding interaction (PCI). The simultaneous effects of stress corrosion cracking and cladding stresses are the main failure mechanisms which limit the life of fuel clad tubes. Zircaloy-2 clad tube, with the inner surface lined with dilute Zr-0.3 wt %Sn layer is a potential and effective protection against PCI failure. Due to the difference in flow behavior of two dissimilar alloys (softer in the core and harder in the sleeve), the manufacturing of double-clad tubes requires proper selection of process parameters. In the present study, manufacturing process has been developed at actual scale to produce metallurgically bonded Zr-Sn lined Zr-2 double clad. Further, this paper systematically brings out the billet assembly methodology using copper jacketing and vacuum degassing. The constraints present in defect-free metallurgical bonding have been overcome by a series of industrial co-extrusion trials of Zr-Sn and Zr-2 composite billet assembly suggested by FEM-based simulation. The co-extrusion process parameters such as strain rate (ram speed), temperature and co-extrusion ratio were suitably optimized using FEM-based analysis of co-extrusion. The metallurgical bond integrity, microstructure evolution and liner thickness variation were characterized by FEG-SEM. The interface between Zr-2 and Zr-Sn was found to be continuous.

Research on the impact response and model of hybrid basalt-macro synthetic polypropylene fiber reinforced concrete

This paper experimentally studied the impact behavior of hybrid basalt-macro synthetic polypropylene fiber reinforced concrete under impact loads (101–102 /s) with a split Hopkinson pressure bar (SHPB) device. The fiber content of basalt fiber (BF) was 0.05%, 0.075% and 0.1% and that of macro synthetic polypropylene fiber (SF) was 0.15%, 0.25%, 0.35% and 0.5%. Both static and impact tests were conducted to investigate the effect of strain rate and fiber hybrid ratio on the dynamic performance of the hybrid FRC, i.e. impact strength, dynamic increase factor (DIF), impact strain and toughness. The test results indicate that the hybrid FRC is strain-rate sensitive and a proper fiber hybrid ratio can improve the impact performance of concrete. DIF and lgε̇ are linearly related, whereas the impact strain, toughness and strain rate present quadratic polynomial relationship. Both BF and SF can enhance the impact strength of concrete. However, BF has a better enhancement effect than SF in terms of improving impact strength but not as good as SF in improving impact toughness. Also, appropriate BF and SF hybrid ratio can enhance the impact strength and toughness of concrete but excess fiber content has a weakening effect. In this study, the optimal fiber hybrid ratio was 0.075%–0.35% (BF-SF) which had the best impact resistance. Finally, a damage dynamic constitutive model suitable for the hybrid FRC was proposed to fit the test curves from SHPB test based on Zhu-Wang-Tang (ZWT) constitutive model.

Differential diagnosis value of ultrasound elastography in Hashimoto's thyroiditis with benign and malignant nodules

Objective To investigate the differential diagnosis value of ultrasound elastography in Hashimoto's thyroiditis with benign and malignant nodules. Methods From January 2013 to December 2015, 21 patients(25 nodules) with Hashimoto's thyroiditis and malignant nodules and 52 patients(76 nodules) with benign nodules in Jiangshan Hospital of Traditional Chinese Medicine were studied.All nodules were detected by color Doppler ultrasound and ultrasound elastography. Results The proportion of boundaries clear, morphological rules, non-low-echo, no calcification or coarse calcifications, RI value <0.70, blood flow grade 0-Ⅰin patients with malignant nodules(32.0%, 24.0%, 12.0%, 40.0%, 32.0%, 24.0%) were lower than those of the benign group(80.3%, 51.3%, 47.4%, 97.4%, 60.5%, 51.3%)(χ2=20.245, 5.682, 9.928, 44.228, 6.153, 5.682, P=0.000, 0.017, 0.002, 0.000, 0.013, 0.017). The sensitivity, specificity and diagnostic accuracy of two-dimensional color Doppler ultrasound in diagnosing Hashimoto's thyroiditis with malignant and benign nodules were 68.0%, 75.0% and 73.2%, respectively.The ultrasound elastography ≥Ⅲ grade level was as the predictor of malignant nodules, the sensitivity, specificity and diagnostic accuracy of ultrasound elastography in diagnosing Hashimoto's thyroiditis with benign and malignant nodules were 88.0%, 69.7% and 74.3%, respectively.The ultrasound elastography strain rate ratio=5.13 was the cut-off point, the ultrasound elastography strain rate ratio in diagnosing Hashimoto's thyroiditis with benign and malignant nodules, the sensitivity was 76.0%, the specificity was 92.1%, the diagnostic accuracy was 88.1%. Conclusion Ultrasound elastography grading and ultrasound elastography strain rate have certain value in the differential diagnosis of Hashimoto's thyroiditis with malignant and benign nodule. Key words: Hashimoto disease; Thyroid neoplasms; Thyroid nodule; Ultrasounography; Sensitivity and Specificity

The role of strain rate, local extinction, and hydrodynamic instability on transition between attached and lifted swirl flames

The coupling between fluid strain rate, local flame extinction, hydrodynamic instability, and flame lift-off was studied in premixed swirl flames using multi-kHz repetition-rate OH* chemiluminescence (CL), OH planar laser induced fluorescence (PLIF), and stereoscopic particle image velocimetry (S-PIV). Over 50 different combinations of fuel composition (CH4/H2 ratio), equivalence ratio, and reactant preheat temperature were studied, allowing systematic variation of the reactant-to-product density ratio, laminar flame speed, and Lewis number. Depending on the test conditions, the flame could either be stably attached to the nozzle, stably lifted, or intermittently transitioning between attached and lifted states. Transition between stabilization states was linked with the transition between convective instability and absolute instability at the flame base; formation of an m=1 (m denotes the azimuthal wavenumber) globally unstable wave was associated with the lifted flame, which was manifested by a helical precessing vortex core (PVC). The minimum bulk velocity at which the flame was stably lifted was linearly correlated with the laminar flame extinction strain rate, while none of the other commonly reported key parameters governing hydrodynamic instability was able to collapse the data alone. Hence, lift-off was associated with a relatively constant Damköhler number based on the bulk fluid strain rate and extinction strain rate. The roles of local strain and extinction on the transition process were further elucidated by the cases with intermittent lift-off/reattachment. The probability of the flame being in the lifted state was roughly linearly correlated with the degree of local extinction at the flame base while the flame was still in the attached state. Moreover, this probability also was linearly related to the ratio of fluid-dynamic strain rate to extinction strain rate, but not the fluid-dynamic strain rate itself. These results demonstrate the importance of predicting extinction and hydrodynamic stability for predicting the attachment state of swirl flames.

Influence of the Strain Rate, Particle Size, and Equivalence Ratio on the Combustion of the Premixed Air–Aluminum Microparticle Mixture with a Counterflow Structure

The effects of the strain rate, equivalence ratio, and particle diameter on the combustion of a mixture of aluminum microparticles with air under fuel-lean conditions are studied in the counterflow configuration with an approximate analytical perturbation method. The flame structure is assumed to consist of three zones: preheating, flame, and post-flame zones. Reasonable agreement between the current results and experimental data is obtained in terms of the flame temperature. The dimensionless ignition and ultimate flame temperatures, place of the flame starting point, and flame thickness are obtained as functions of the strain rate for different particle diameters and equivalent ratios. The results indicate that the ignition and ultimate flame temperatures and also the flame thickness decrease with increasing strain rate. With a decrease in the strain rate, the length of the preheating zone increases. With increasing particle diameter, the flame thickness increases, whereas the ignition and ultimate flame temperatures decrease. An increase in the equivalence ratio causes an increase in the ultimate flame temperature and reduction of the preheating zone and flame thickness.

Phenomenological modelling of flow behaviour of 20MnMoNi55 reactor pressure vessel steel at cryogenic temperature with different strain rates

Abstract In the present study a phenomenological constitutive model is developed to describe the flow behaviour of 20MnMoNi55 low carbon reactor pressure vessel (RPV) steel at sub-zero temperature under different strain rates. A set of uniaxial tensile tests is done with the variation of strain rates and temperature ranging from 10−4 s−1 to 10−1 s−1 and -80 °C to −140 °C respectively. From the experimental data, family of flow curves at different temperatures and strain rates are generated and fitted exponentially. The strain rate and temperature dependence of the coefficients of the exponential flow curves are extracted from these curves and characterised through a general phenomenological constitutive coupled equation. The coefficients of this coupled equation are optimised using genetic algorithm. Finite element simulation of tensile tests at different strain rates and temperatures are done using this coupled equation in material model of Abaqus FEA software and validated with experimental results. The novelties of proposed model are: (a) it can predict precisely the flow behaviour of tensile tests (b) it is a simple form of equation where fitting parameters are both function of strain rate ratio and temperature ratio, (c) it has ability to characterize flow behaviour with decreasing subzero temperatures and increasing strain rates.

Numerical modeling for accurate prediction of strain localization in hole expansion of a steel sheet

The hole expansion of a low carbon steel sheet shows an interesting feature that localized thinning and subsequent crack initiation are observed inside the specimen, and not at the hole edge as is typically expected. The present work investigated a numerical modeling approach to predict this localization behavior within the framework of a finite element (FE) analysis. Plastic anisotropy of the sheet was taken into account using the anisotropic yield functions Yld2000-2d and Yld2004-18p for the plane stress and three-dimensional elements, respectively. Careful examination of the FE model revealed that the influence of the out-of-plane stress is very small, suggesting that shell elements can be efficiently used in the analysis. The influence of friction was also found to be negligibly small. However, the constitutive description exhibited a significant influence in that even a slight change in the yield function parameters resulted in a considerable difference in the prediction. For this reason, several sets of parameters were obtained based on the different material properties, and their influences on the hole expansion simulation were analyzed. In particular, the prediction accuracy could be greatly improved when the yield function parameters were optimized such that the flow stresses and plastic strain rate ratios in uniaxial and plane strain states were well captured.

Research on compressive impact dynamic behavior and constitutive model of polypropylene fiber reinforced concrete

The latest experimental studies indicate that polypropylene fiber is able to remarkably enhance the ability of concrete to resist impact loading and crack. This paper further studies the dynamic behavior and constitutive model of polypropylene fiber reinforced concrete (PFRC) at high strain rate. PFRC specimens with various polypropylene fiber content (0, 0.8, 1.2, 1.6, 2.0, 5.0 kg/m3) are tested by utilizing the Split Hopkinson Pressure Bar (SHPB). Both the quasi-static tests and the SHPB tests were performed to study the effect of fiber content, strain rate and water-cement (w/c) ratio on the dynamic mechanical properties of PFRC. Test results indicate that the dynamic mechanical properties of PFRC such as dynamic strength, dynamic increase factor, peak and ultimate strain, peak and ultimate toughness, are positively affected by strain rate. Polypropylene fiber can improve the impact toughness and crack resistance of concrete and it is more suitable for concrete material with a higher w/c ratio. Finally, the experimental stress-strain curves obtained in SHPB test were fitted by a damage dynamic constitutive model of PFRC on the basis of ZWT constitutive model. The great fitting results prove that the modified model can well describe the dynamic behavior of PFRC.

Combined effects of steel fiber and strain rate on the biaxial compressive behavior of concrete

Understanding the biaxial mechanical behavior of steel fiber reinforced concrete (SFRC) is of critical significance when the concrete structures are subjected to dynamic loading. This paper presents the results of an experimental investigation on the dynamic mechanical behavior of SFRC subjected to biaxial compressive loadings. Aiming at the combined effects of steel fiber and strain rate on strength criterion, a series of dynamic biaxial compressive experiments on 100 mm-length SFRC cubic specimens with various steel fiber contents (0%, 1%, 2%, and 3% by volume) were conducted by using a large dynamic triaxial servo-hydraulic testing apparatus. The specimens were loaded by biaxial compression with five stress ratios (i.e. 0:1, 0.25:1, 0.5:1, 0.75:1 and 1:1, respectively) at various strain rates ranging from 10−5/s to 10−2/s. A comprehensive dynamic biaxial strength criterion taking into account the combined effects of uniaxial strength, strain rate and stress ratio was proposed. The effect of steel fiber content and strain rate on the biaxial mechanical behavior of SFRC specimens was discussed, including the failure mode, stress-strain curve, biaxial compressive strength, dynamic strength criterion. It suggested that at given strain rate, the biaxial stress ratio is the major factor dominating the strength increment, and the incorporation of steel fiber has a remarkable enhancement on the strength for all stress ratios. Additionally, the dynamic compressive strengths of SFRC were found to increase with the increase of strain rate, while the failure pattern and dynamic ultimate strength were closely dependent on the magnitude of lateral stress exerted on the specimens. The comparison indicates that the proposed model results of dynamic strength criterion were in good agreement with the experimental data for SFRC specimens.

Cardiac autonomic and left ventricular mechanics following high intensity interval training: a randomized crossover controlled study.

Physical inactivity and sedentary behavior is associated with increased cardiovascular disease risk. Short duration high-intensity interval training (HIIT) has been shown to improve important health parameters. The aim of the present study was to assess the combined adaptations of the cardiac autonomic nervous system and myocardial functional and mechanical parameters to HIIT. Forty physically inactive and highly sedentary men completed two weeks of HIIT and control period. The HIIT protocol consisted of 3 × 30-s maximal cycle ergometer sprints against a resistance of 7.5% body weight, interspersed with 2 min of active recovery. Total power spectral density (PSD) and associated low-frequency (LF) and high-frequency (HF) power spectral components of heart rate variability were recorded. Conventional and speckle tracking echocardiography recorded left ventricular (LV) structural, functional, and mechanical parameters. HIIT produced a significant increase in total log-transformed (ln) PSD and ln HF and a significant decrease in LF/HF ratio (all P < 0.05) compared with the control period. HIIT produced significant improvements in LV diastolic function, including lateral E', estimated filling pressure (E/E' ratio), E deceleration time, and isovolumetric relaxation time ( P < 0.05 for all). Fractional shortening was the only conventional marker of LV systolic function to significantly improve ( P < 0.05). In this setting, there were significant improvements in global peak systolic strain rate, early and late diastolic strain rate, and early to late diastolic strain rate ratio, as well as apical rotation, apical systolic and diastolic rotation velocity, apical radial and circumferential strain and strain rate, LV torsion, and LV systolic and diastolic torsion velocity (all P < 0.05). A short-term program of HIIT was associated with a significant increase in cardiac autonomic modulation, demonstrated by a residual increase in cardiac vagal activity as well as significantly improved cardiac function and mechanics. This study demonstrates that HIIT may be an important stimulus to reduce the health implications associated with physical inactivity and sedentary behavior. NEW & NOTEWORTHY This is the first study to measure the combined adaptations of the cardiac autonomic nervous system and myocardial function and mechanics following high-intensity interval training (HIIT). This study demonstrates that a 2-wk HIIT intervention provides significant improvements in cardiac autonomic modulation and myocardial function and mechanics in a large cohort of young physically inactive and highly sedentary individuals. HIIT may be a powerful stimulus to reduce the health implications associated with physical inactivity and sedentary behavior.

Evaluation of Right Ventricular Function by Speckle-Tracking Echocardiography in Patients with Ankylosing Spondylitis: A Case-Control Study.

We aimed to evaluate the right ventricular (RV) systolic function in patients with ankylosing spondylitis (AS) compared to healthy subjects by using standard echocardiography and speckle-tracking echocardiography (STE) methods. This was a case-control study in which 64 patients (mean age, 55.7 ± 9.2 years; male/female, 53/11), who had AS for at least five years (mean disease duration, 7.1 ± 2.6 years) and 70 age-matched healthy subjects (mean age, 54.9 ± 8.5 years; male/female 55/15) were included. Clinical and laboratory signs of cardiac disease were recorded. The RV systolic function was assessed by standard echocardiography and two-dimensional STE method. Case and control groups did not show significant difference in terms of clinical and laboratory signs of cardiac disease. RV function parameters in standard echocardiography were statistically similar between AS patients and control subjects. However, RV parameters in STE revealed significantly impaired RV function in AS patients compared to control group. RV-free wall longitudinal strain, RV-free wall longitudinal systolic strain rate, RV-free wall longitudinal early diastolic strain rate, RV-free wall longitudinal late diastolic strain rate were lower, and RV-early diastolic strain rate/RV-late diastolic strain rate ratio was higher for the patients in the AS group (p < 0.001 for all). AS is associated with impaired RV function as shown by STE even if there is no clinical or laboratory sign of cardiac abnormality. STE is more effective than standard echocardiography to detect RV function. Therefore we suggest regular evaluation of RV function in patients with AS.

Challenges in Scale-Resolving Simulations of turbulent wake flows with coherent structures

The objective of this work is to investigate the challenges encountered in Scale-Resolving Simulations (SRS) of turbulent wake flows driven by spatially-developing coherent structures. SRS of practical interest are expressly intended for efficiently computing such flows by resolving only the most important features of the coherent structures and modelling the remainder as stochastic field. The success of SRS methods depends upon three important factors: i) ability to identify key flow mechanisms responsible for the generation of coherent structures; ii) determine the optimum range of resolution required to adequately capture key elements of coherent structures; and iii) ensure that the modelled part is comprised nearly exclusively of fully-developed stochastic turbulence. This study considers the canonical case of the flow around a circular cylinder to address the aforementioned three key issues. It is first demonstrated using experimental evidence that the vortex-shedding instability and flow-structure development involves four important stages. A series of SRS computations of progressively increasing resolution (decreasing cut-off length) are performed. An a priori basis for locating the origin of the coherent structures development is proposed and examined. The criterion is based on the fact that the coherent structures are generated by the Kelvin–Helmholtz (KH) instability. The most important finding is that the key aspects of coherent structures can be resolved only if the effective computational Reynolds number (based on total viscosity) exceeds the critical value of the KH instability in laminar flows. Finally, a quantitative criterion assessing the nature of the unresolved field based on the strain-rate ratio of mean and unresolved fields is examined. The two proposed conditions and rationale offer a quantitative basis for developing “good practice” guidelines for SRS of complex turbulent wake flows with coherent structures.