Stiffness Parameters Research Articles

Effect of sodium-glucose co-transporter inhibitors on arterial stiffness in patients with type 2 diabetes mellitus

Abstract Introduction Selective sodium-glucose co-transporter 2 inhibitors (SGLT2i) reduce cardiovascular morbidity and mortality in patients with type 2 diabetes mellitus (T2DM). In addition to glucose homeostasis the impaired arterial stiffness may participate in this morbidity and mortality. Purpose The aim of this study was to investigate the effect of administration of SGLT2i therapy on arterial stiffness parameters, including aortic pulse wave velocity (PWV) and central systolic blood pressure (SBPao), which have significant prognostic value for predicting cardiovascular events. Methods Our prospective, observational study included 40 patients with T2DM (mean age: 60.3±9.9 years, 24 males). Biochemical and arterial stiffness parameters were analysed before starting SGLT2i therapy (14 patients on dapagliflozin, 25 patients on empagliflozin, 1 patient on ertugliflozin), at 3, 6 months and an average of 3.3±1.3 years follow-up period. Arterial stiffness parameters were determined using an invasively validated oscillometric based Arteriograph (AG) method. Changes in the variables and their interrelation was analysed by repeated data ANOVA and multivariate linear regression. Results Significant decrease in PWV and HgbA1c were observed 3 months after the initiation of SGLT2i therapy (PWV: 10.68±1.35 m/s vs. 10.05±1.40 m/s and HgbA1c: 7.86±0.55 vs. 6.83±0.66 %, p<0,05) and this long-term effect continued during the 3.3-years follow-up period (PWV: 9.96±1.25 m/s and HgbA1c: 7.19±0.81 %, p<0,005, Figure 1). Pearson's correlation analysis and multivariate linear regression analysis showed no association between decreased PWV and BMI, brachial diastolic blood pressure (DBPb) while significant, but weak correlation was observed with HgbA1c and brachial systolic blood pressure (SBPb) (r=0.22-0.26, p<0.05, Figure 2). SBPao results showed non-significant decrease and a subsequent non-significant long-term increase comparing to baseline during the 3.3 years follow-up. Conclusion Short and long-term SGLT2i therapy in T2DM significantly improved PWV values and this effect is independent of changes in SBPao. All these findings emphasize the clinical relevance of arterial stiffness as a biomarker in the SGLT2i induced beneficial effect on the vasculature, however further clarification, long-term evaluation needed to define the role of PWV in the prediction of cardiovascular events.Figure 1Figure 2

Thermal vibration analysis of FG-GPLRC doubly curved shells partially resting on Kerr foundation based on higher-order shear deformation theory

In this paper, we present a novel analytical approach for investigating the influence of non-homogeneous Kerr elastic foundations on the nonlinear dynamical characteristics of functionally graded graphene platelets reinforced composite (FG-GPLRC) doubly curved shells. A new aspect of this study is the investigation of various distributions of the Kerr foundation, either centrally within or along the edges of the nanocomposite shells, a model not previously explored. Three distinct distributions of graphene nanoplatelets reinforcement are examined, utilizing the rule of mixtures and the Halpin-Tsai micromechanical model. The theoretical framework is based on Reddy's third-order shear deformation theory. The equations of motion, formulated as partial differential equations, are efficiently resolved through the application of Galerkin's method. The effectiveness of this approach resides in its utilization of integration to tackle the distribution issue of the elastic foundation, all without the need for deploying intricate algorithms. The validity of our proposed method is established through meticulous comparisons with findings from prior literature. Furthermore, this paper delves into the effect of material properties, thermal conditions, boundary conditions, geometrical parameters, and four configurations of the shells on the vibrational responses. Of notable significance is our thorough investigation of the impact of variations in the distributions, stiffness, and geometrical parameters of the elastic foundation on natural frequencies and the nonlinear transient response of these shells, all of which hold great importance in structural design. We present the obtained results systematically in various formats, including tables, 2D and 3D graphs, and contour plots, providing a comprehensive overview of the research outcomes. These findings have profound implications for the field of engineering, contributing to advancements in novel structural designs and their diverse applications.

Colored noise in river level oscillations as triggering factor for unstable dynamics in a landslide model with displacement delay

In the present paper we examine the effect of the noise in river level oscillation on the landslide dynamics. The analysis is conducted in several phases. In the first phase, we analyze the multi-annual level oscillation of the Kolubara and the Ibar river (Serbia). Based on the observed dataset, we suggest a deterministic model for the river level oscillation with the additional contribution of the noise part, which we confirm to have the properties of colored noise. In the second phase of the research, we introduce the influence of the river-level oscillation, with the included effect of colored noise in the spring-block delay model of landslide dynamics. Results of the research indicate conditions under which the effect of river noise has both stabilizing and destabilizing effects on the landslide dynamics. The effect of noise intensity D and correlation time ε is systematically analyzed in interaction with delayed interaction, spring stiffness and friction parameters. It is determined that the landslide dynamics is sensitive to the change of noise intensity and that the increase of noise intensity leads to onset of unstable landslide dynamics. On the other hand, results obtained indicate that the examined model of landslide dynamics is rather robust towards the change of correlation time ε. Interaction of this parameter and some of the friction parameters leads to stabilization of landslide dynamics, which confirms the importance of the influence of the noise color in river level oscillations on the landslide dynamics.

Abstract 18373: Differential Effects of Hypertension and Aneurysm on Stiffness Properties of the Abdominal Aorta

Introduction: The serum and glucocorticoid inducible kinase-1 (SGK-1) can contribute to matrix remodeling in murine models of hypertension (HTN) and abdominal aortic aneurysm (AAA), a potential biomechanical link between these aortopathies. Utilizing aortic stiffness as a marker of pathologic remodeling. Hypothesis: We hypothesize that HTN causes an SGK-1 dependent increase in aortic stiffness to amplify AAA growth. Methods: AngiotensinII (AngII) infusion induced HTN in C57Bl/6 mice (WT;1.46mg/kg/day) with subset groups treated + periadventitial CaCl2 to induce AAA and + infusion of the specific SGK-1 inhibitor EMD638683 (2.5mg/kg/day;n=2-4 each). Abdominal aortic ultrasound was conducted on Day 0 and Day 21 to measure stiffness parameters (radial strain(RS), distensibility(D), pulse propagation velocity(PPV)). Aortic diameter (AoD) was obtained by ultrasound and systolic blood pressures (SBP) were measured by Coda tail cuff. Results: This HTN model has consistently resulted in >30% increase in SBP and AAA induction did not effect SBP. Although the WT+AngII+AAA mice had 66+8% increase in AoD, dilation was not amplified beyond that of the WT+AAA mice (72+7%, p=NS). Treatment with EMD had no impact on SBP, but did significantly reduce AAA growth (WT+AAA+EMD=29+5%; WT+AngII+AAA+EMD= 24+3%), therefore despite ongoing mechanical tension, SGK-1 inhibition abrogated a pathway necessary for degenerative remodeling. Accordingly, aortic stiffness was differentially altered in HTN versus AAA. As indictors of increased stiffness, D decreased with HTN (p<0.05 vs Day 0) and RS decreased with AAA (p<0.05 vs Day 0), but SGK-1 inhibition had no effect, indicating that the matrix remodeling driving these mechanical parameters was not SGK-1 dependent. Conversely, PPV was increased in both aortopathies (WT+AAA, WT+AngII, WT+AngII+AAA; each p<0.05 vs Day 0) but EMD infusion prevented elevation in PPV, suggesting SGK-1-dependent preservation of contractility. Conclusions: Although concurrent induction of HTN and AAA did not amplify AAA growth, these aortopathies differentially impacted aortic stiffness. Tracking PPV as an indicator of pathologic SGK-1 activity may represent a pharmacological target to abrogate dysfunctional aortic remodeling.

Correlation of Plasma Membrane Microviscosity and Cell Stiffness Revealed via Fluorescence-Lifetime Imaging and Atomic Force Microscopy.

The biophysical properties of cells described at the level of whole cells or their membranes have many consequences for their biological behavior. However, our understanding of the relationships between mechanical parameters at the level of cell (stiffness, viscoelasticity) and at the level of the plasma membrane (fluidity) remains quite limited, especially in the context of pathologies, such as cancer. Here, we investigated the correlations between cells' stiffness and viscoelastic parameters, mainly determined via the actin cortex, and plasma membrane microviscosity, mainly determined via its lipid profile, in cancer cells, as these are the keys to their migratory capacity. The mechanical properties of cells were assessed using atomic force microscopy (AFM). The microviscosity of membranes was visualized using fluorescence-lifetime imaging microscopy (FLIM) with the viscosity-sensitive probe BODIPY 2. Measurements were performed for five human colorectal cancer cell lines that have different migratory activity (HT29, Caco-2, HCT116, SW 837, and SW 480) and their chemoresistant counterparts. The actin cytoskeleton and the membrane lipid composition were also analyzed to verify the results. The cell stiffness (Young's modulus), measured via AFM, correlated well (Pearson r = 0.93) with membrane microviscosity, measured via FLIM, and both metrics were elevated in more motile cells. The associations between stiffness and microviscosity were preserved upon acquisition of chemoresistance to one of two chemotherapeutic drugs. These data clearly indicate that mechanical parameters, determined by two different cellular structures, are interconnected in cells and play a role in their intrinsic migratory potential.

Comparing corneal biomechanic changes among solo cataract surgery, microhook ab interno trabeculotomy and iStent implantation

Minimally invasive glaucoma surgery has expanded the surgical treatment options in glaucoma, particularly when combined with cataract surgery. It is clinically relevant to understand the associated postoperative changes in biomechanical properties because they are influential on the measurement of intraocular pressure (IOP) and play an important role in the pathogenesis of open-angle glaucoma (OAG). This retrospective case–control study included OAG patients who underwent cataract surgery combined with microhook ab interno trabeculotomy (µLOT group: 53 eyes of 36 patients) or iStent implantation (iStent group: 59 eyes of 37 patients) and 62 eyes of 42 solo cataract patients without glaucoma as a control group. Changes in ten biomechanical parameters measured with the Ocular Response Analyzer and Corneal Visualization Scheimpflug Technology (Corvis ST) at 3 and 6 months postoperatively relative to baseline were compared among the 3 groups. In all the groups, IOP significantly decreased postoperatively. In the µLOT and control groups, significant changes in Corvis ST-related parameters, including stiffness parameter A1 and stress‒strain index, indicated that the cornea became softer postoperatively. In contrast, these parameters were unchanged in the iStent group. Apart from IOP reduction, the results show variations in corneal biomechanical changes from minimally invasive glaucoma surgery combined with cataract surgery.

Implantation of Intracorneal Ring Segments in Keratectasia: Effects on Corneal Biomechanics in 112 Eyes.

The aim of this study was to analyze changes in corneal biomechanical properties after implantation of intracorneal ring segments (ICRSs) in keratectasia. This retrospective single-center study included 112 patient eyes that underwent femtosecond laser-assisted ICRS implantation (Intacs SK; Addition Technology Inc, Des Plaines, IL) for keratectasia. Biomechanical analysis was performed using the Ocular Response Analyzer (ORA; Reichert Inc, Depew, NY), with determination of corneal resistance factor, corneal hysteresis, and Keratoconus Match Index, as well as by Corvis ST (OCULUS, Wetzlar, Germany), with determination of stiffness parameter A1, Ambrosio relational thickness to the horizontal profile (Arth), integrated radius, deformation amplitude ratio, and stress-strain index as well as Corvis Biomechanical Index and Tomographic Biomechanical Index. Data collection was performed preoperatively and 6 months postoperatively for ORA and Corvis ST and additionally after 1 and 2 years for ORA. The corneal resistance factor decreased significantly postoperatively (5.8 ± 1.7 mm Hg) compared with preoperatively (6.75 ± 3.7 mm Hg; P = 0.021) and increased again during follow-up (6.2 ± 1.9 mm Hg; P = 0.024), without regaining preoperative values. Corneal hysteresis and Keratoconus Match Index did not change significantly. Stiffness parameter A1 ( P = 0.045) increased significantly after ICRS implantation and Arth decreased significantly from 181 ± 85 to 150 ± 92 ( P = 0.016). However, there was no significant postoperative change for others Corvis parameters. Corneal biomechanical properties showed inconsistent changes after ICRS implantation. Classical corneal biomechanical parameters (using single central air-puff tonometers) do not seem to be suitable for follow-up after ICRS implantation.

Association of severe preeclampsia and vascular damage assessed by noninvasive markers of arterial stiffness

BackgroundPreeclampsia (PE) is a hypertensive disorder of pregnancy associated with high maternal and fetal morbidity and mortality and increased future risk of cardiovascular complications. ObjectiveTo analyze whether women who have had PE with severe features in their pregnancy have higher arterial stiffness (AS) parameters than those whose PE course was without signs of severity. MethodsSixty-five women who developed PE during their gestation were evaluated, divided into two groups: PE group without severe features or non-severe PE (n=30) and PE group with severe features or severe PE (n=35). Carotid-femoral pulse wave velocity (cfPWV), central augmentation index corrected to a heart rate of 75 beats per minute (AIxc75) and central augmentation pressure (cAP) were determined one month and six months postpartum. Comparison of proportions was carried out using the chi-square test, comparison of means between groups using the Student’s t-test or the Mann–Whitney test, and comparison of means of the same group at different evolutionary moments, using the t-test or the Wilcoxon test. Correlation, with and between hemodynamic parameters, was carried out with Spearman’s correlation coefficient and the association between demographic variables, personal history and hemodynamic parameters, and altered arterial stiffness parameters was carried out using linear and logistic regression models. ResultsWomen with severe PE presented, both at 1 and 6 months postpartum, higher values of blood pressure, both central and peripheral, as well as AR and pulse amplification parameters, than those women whose PE was not severe. Central augmentation index (cAIx) values at 1 month and 6 months postpartum were higher, although not significantly, in the severe PE group compared to the non-severe PE group (24.0 (16.5–34.3) vs. 19.0% (14–29) and 24.0 (14.0–30.0) vs. 20.0% (12.3–26.8), respectively). Carotid-femoral pulse wave velocity (cfPWV) was significantly higher at both 1 and 6 months postpartum in the severe PE group compared to the non-severe PE group (10.2 (8.8−10.7) vs. 8.8m/s (8.3−9.6) and 10.0 (8.8−10.6) vs. 8.8m/s (8.3−9.3), respectively). Central systolic pressure and central pulse pressure amplification were also higher, although not significantly, in the severe PE group in comparison with the non-severe PE group. ConclusionsWomen who have had severe PE have more pronounced arterial stiffness parameters than those in whom PE was not particularly severe. The determination of cAIx and cfPWV, as a strategy for the assessment of cardiovascular risk, should be evaluated among women who have had PE.

Cross-Sectional Relationship Between Atrial Conduction Delay and Arterial Stiffness in Patients with Obstructive Sleep Apnea.

Prolonged P-wave duration (PWD), which indicates atrial conduction delay, is a potent precursor of atrial fibrillation (AF) that may be induced by obstructive sleep apnea (OSA). The cardio-ankle vascular index (CAVI), which is an arterial stiffness parameter, is elevated in patients with OSA; moreover, an increased CAVI is associated with atrial conduction delay through left atrium enlargement in association with left ventricular diastolic dysfunction. We aimed to examine the relationship between the CAVI and PWD in patients with OSA. We included patients with a sinus rhythm who underwent overnight polysomnography. We measured the PWD and CAVI on standard 12-lead electrocardiograms; further, we analyzed the relationship between PWD and CAVI. We analyzed data from 300 participants (men, 89.0%; mean age, 52.3 ± 13.1 years; and body mass index, 26.2 ± 3.9 kg/m2). The mean PWD was 104.4 ± 10.4 ms while the mean CAVI was 7.5 ± 1.5. PWD was significantly correlated with CAVI (r = 0.478, p < 0.001); additionally, PWD and CAVI were directly associated with OSA severity (p = 0.002 and p = 0.002, respectively). Multivariate regression analysis revealed an independent significant correlation of PWD and CAVI with OSA severity. In patients with OSA, an increase in arterial stiffness is associated with atrial conduction delay.

Effectiveness of a fixed combination of amlodipine/indapamide in hypertensive patients in real clinical practice

Objective. To assess the possibility of obtaining and the degree of additional antihypertensive effect, the dynamics of vascular wall stiffness parameters, vascular age indicators in patients with uncontrolled hypertension (HTN) when transferring from previous therapy to a fixed combination of amlodipine/indapamide in typical outpatient practice.Design and methods. Twenty-five patients with 1–3 degree HTN who got a prescription of a fixed combination of amlodipine/indapamide (ARIFAM 5/1,5 or 10/1,5 mg, Servier) were included in the study. The follow-up duration was 2 months and included the following methods: clinical assessment (systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate), with titration of the drug dose every two weeks; double assessment (at the beginning and at the end of the study) of arterial stiffness based on the determination of the cardio-ankle vascular index (CAVI), biological age of vessels using the VaSeraVS‑1500N volumetric sphygmography device, as well as quality of life indicators (SF‑36 questionnaire). The reliability of changes in the studied parameters during active outpatient management of patients was assessed.Results. Combined pharmacotherapy using a fixed combination of amlodipine/indapamide was well tolerated by all patients. We recorded a significant decrease in SBP on average by 31,0 ± 10,6 mmHg, DBP by 11,0 [7,0; 20,0] mmHg, and the achievement of the target SBP level at the end of the 2nd month was shown in 17 (68 %) patients, the target DBP level was found in 100 % of patients. A significant decrease in vascular wall stiffness parameters was shown as a decrease in the CAVI index (p = 0,034), a decrease in AI (p = 0,0001) and the PEP/ET ratio of the Veissler coefficient (p = 0,009), as well as in the calculated vascular age indicator (p = 0,00001). Significant (p = 0,0001) changes were recorded for most data of quality of life (SF‑36) in patients with HTN, with the exception of the social functioning scale.Conclusions. Combined pharmacotherapy of patients with 1–3 degree HTN with the inclusion of a fixed combination drug amlodipine/indapamide with prolonged release has a clear positive effect, i. e. improved hemodynamic parameters, a significant reduction in vascular stiffness, a decrease in vascular age and improved quality of life.

A calibration method for spatial error of industrial robot under variable load conditions based on double-ball rotary structure and three contact displacement sensors

A new calibration device using a double-ball rotary structure and three contact displacement sensors is proposed to measure the spatial errors of six-axis serial robot. The error model is divided into kinematics part and static stiffness part, established by Modified DH (MDH) model and virtual joint method. The MDH parameter errors are compensated by modifying the angles of each axis with Newton Raphson compensation method and ridge estimation. The stiffness parameters are also identified by the least square method. The self-designed double-ball rotary device is calibrated by coordinate measuring machine (CMM), while the three-point measuring device is calibrated by gauge block. Then, the kinematic and static stiffness calibration and compensation experiments are carried out on EPSON C4 A901 robot in turn. The spatial error under none load and 1.0 kg, 1.5 kg, 2.0 kg gravity load are measured separately. The experiment results show that the motion accuracy of the robot is improved to the range from 0.0163 mm to 0.0236 mm under the gravity load conditions between weights of 1.0 kg and 2.0 kg. Finally, by comparing the measuring results from the laser displacement sensor and laser interferometer, the measurement accuracy of each axis of the self-designed device is equivalent to the laser displacement sensor and the laser interferometer in micron range.

The relationship of systemic and pulmonary arterial parameters with HFpEF scores (H2 FPEF, HFA-PEFF) and diastolic dysfunction parameters in heart failure patients with preserved ejection fraction.

We aimed to show the relationship between pulmonary pulse wave transit time (pPTT), pulmonary artery stiffness (PAS), and aortic stiffness parameters measured by non-invasive methods, HFpEF patients, and HFpEF scores (H2 FPEF, HFA-PEFF). A total of 101 patients were included in our study, 52 of whom were HFpEF patients and 49 were control groups without heart failure. Echocardiographic parameters for PAS and pPTT were calculated, along with diastolic parameters that support the diagnosis of HFpEF. Aortic stiffness was assessed using a PWA monitor. Demographic features, laboratory findings, aortic stiffness parameters, and echocardiographic findings including pulmonary artery parameters were compared with the control group. PAS, pPTT, PWV were significantly higher in the HFpEF group than in the control group (p < 0.001). PAS and pPTT correlated positively with HFpEF scores. In linear regression analysis for PAS, a directly positive correlation was found between E/e' and PAS, independent of aortic stiffness. These parameters can be used as a predictive value in the diagnosis process of patients with suspected HFpEF. A significant relationship between PAS and ventricular stiffness (E/e') was shown independently of aortic stiffness.

Geomechanical Properties of Clay Stabilised with Fly Ash-Based Geopolymer Subjected to Long-Term Sulfate Attack

Fly ash-based geopolymers have emerged as an eco-friendly alternative binder compared to conventional Portland cement for soil stabilisation. However, the gap in the current literature is the lack of a comprehensive study regarding the geomechanical behaviour of fly ash geopolymer-treated clay subjected to long-term sulfate attack, particularly in terms of potential ettringite formation and the corresponding impact on cementitious soil structure. The goal of this paper is to address this knowledge gap and provide a comprehensive study to fulfil it. In this work, sulfate attack was simulated by submerging geopolymer-treated clay specimens in two distinct sulfate-based solutions (i.e., sodium and magnesium), for one year. Subsequently, comparative analyses of the geomechanical and microstructural changes in geopolymer-treated clay under various curing conditions were conducted through unconfined compressive strength, direct shear, volume change and microscopic tests. The findings indicate that the addition of geopolymer for the stabilisation of clay soil significantly improves soil strength without affecting the soil volumetric response. Although the clay used exhibited similar qualitative stress–strain behaviour across all simulated attacks, notable quantitative differences emerged in the peak strength, stiffness and shear strength parameters. Such discrepancies can primarily be attributed to the varying buffering capacities (i.e., pH changes associated with acidification) of the sulfate solutions and the subsequent residual pH, cementitious product formation and strength enhancement within the treated clay.

Biomechanical comparison of fixation methods on third-generation femoral composite bone models in Pauwels type 3 femoral neck fractures: Contribution of the medial buttress plate to fixation.

To compare the use of cannulated screws in an inverted triangular configuration, medial buttress plates, and the combination of these 2 fixation methods in the treatment of Pauwels type 3 femoral neck fractures. Twenty-eight anatomical composite third-generation femoral bone models were divided into 4 groups. The control group (group 1) was formed with 7 third-generation intact bone models. The fracture model was created with a 70° cutting block to fit 21 Pauwels type 3 fracture configurations. Seven models were fixed with an isolated 3.5 mm one-third semi-tubular medial buttress plate (group 2), 7 were fixed in an inverted triangular configuration with 6.5 mm cannulated screws (group 3), and 7 were fixed using a combination of 6.5 mm cannulated screws and a medial buttress plate (group 4). Cyclic loading was applied using axial forces ranging from 60 N to 600 N and moments ranging from 0.7 Nm to 7.0 Nm for 500 cycles. Once the cyclic loading stage was completed, the loads were removed from the system, and the quasi-static loading stage was employed to determine the stiffness and failure forces of the system under both axial and torsional forces. Quasi-static tests were performed with an axial speed of 1.8 mm/min and a torsional speed of 4.5°/min. The biomechanical properties of all groups were examined in terms of axial stiffness, torsional stiffness, and maximum axial force parameters. The stiffness values of groups 1, 2, 3, and 4 were 303 ± 35.8 N/mm, 159.6 ± 25 N/mm, 232 ± 35.9 N/mm, and 366.9 ± 58 N/mm, respectively, under axial forces (P < .01); 2172.7 ± 252.1 Nmm/°, 1225.3 ± 238.6 Nmm/°, 2123 ± 359.4 Nmm/°, and 2721.85 ± 304 Nmm/°, respectively, under torsional moments (P < .01); and 2072.1 ± 256.1 N, 1379.9 ± 290.6 N, 2099.1 ± 454.2 N, and 2648.4 ± 364.6 N, respectively, under the maximum force (P < .01). This study showed that in the fixation of Pauwels type 3 fractures formed on third-generation bone models, the utilization of half-thread cannulated screws in an inverted triangle configuration, along with a medial buttress plate, provided stronger fixation compared to the remaining implant groups and the control group. According to the evaluation of the parameters, the isolated application of a medial buttress plate had poorer biomechanical properties than other fixation methods.

Research on Bowden Cable–Fabric Force Transfer System Based on Force/Displacement Compensation and Impedance Control

Bowden cable–fabric is a key force transfer device for flexible exoskeletons, and its precise control of force/displacement is a significant factor in the human–machine interaction of flexible exoskeletons. In this paper, a force/displacement control method based on friction compensation and impedance control was proposed based on a flexible Bowden cable–fabric force transfer testbed system. First, a set of in vitro experimental platforms simulating Bowden cable–fabric force transfer was built according to a typical flexible exoskeleton force transfer system, and following the walking gait of lower limbs, the expected force and knee joint motion were set. Secondly, the Bowden cable–fabric force transfer friction model was constructed as the basis of the system’s force transfer compensation. In addition, the stiffness model of Bowden cable–fabric and the lower leg movement model were established and combined with impedance control to realize the precise control of system displacement. Finally, the damping and stiffness parameters suitable for the system were obtained through the impedance control simulation. In terms of the experiment, an in vitro Bowden cable–fabric force transfer experimental platform was built, and the expected force with the input peak value of 40 N, 50 N, and 60 N was set. Through the friction and position compensation model of Bowden cable–fabric force transfer and impedance control, the relative root-mean-square errors of the output force and expected force were obtained as 2.53%, 2.16%, and 2.07%, respectively. Therefore, the effectiveness of the proposed method is verified, which provides a foundation for the engineering application of flexible exoskeletons.

Estimation of Multiple Unknown Parameters Using Adaptive Observers for Lipschitz Nonlinear Systems

This work presents the design of an adaptive observer for a class of Lipschitz nonlinear systems, where the observer is able to estimate more than one unknown parameter. Thanks to this, it is possible to estimate the system states, which facilitates the monitoring of nonlinear Lipschitz systems. The proposed observer is tested for monitoring a semiactive suspension, in order to know the stiffness parameters of the tire and chassis, allowing the detection of possible anomalies in the system. To ensure observer stability, the gains are calculated by LMI obtained by Lyapunov analysis. The proposed observer is evaluated by estimating the unknown states and parameters of a mechanical system allowing monitoring of its performances.

Evaluation of Arterial Stiffness in Depression Patients.

It has been known that there is a significant correlation between depression and cardiovascular diseases. However, the reasons behind this correlation that could affect mortality and morbidity were not fully identified. The present study aimed to analyze arterial stiffness diagnosed with ultrasonography, which could be associated with cardiovascular disease risks in depression patients, and to compare the findings with those of healthy controls. The study was conducted with 35 depression patients and 35 healthy individuals. Routine complete blood and biochemistry tests were requested for all patients, and their weight and height, waist circumference, and diastolic and systolic arterial blood pressure were measured. Femoral and carotid artery intima-media thickness and other arterial stiffness parameters were determined with Doppler ultrasonography. It was determined that the systolic pressure (P = .028) was higher in the patient group (P = .028). Also, the carotid elastic modulus (P = .048) was significantly higher in the patient group. A negative and significant correlation was determined between femoral compliance and chlorpromazine equivalent dose (P = .021, r = -0.389). It was determined that the systolic blood pressure and carotid elastic modulus arterial stiffness parameters were significantly higher in depression patients. Measurable arterial stiffness parameters should be investigated in depression patients as cardiovascular risk markers. Furthermore, the determination of the effects of psychotropic drugs employed in arterial stiffness treatment could play an important role in the determination of cardiovascular disease risk in these patients.

Effect of corneal flap thickness on opaque bubble layer formation in Visumax FS-LASIK using GEE analysis

IntroductionThis study aimed to investigate two types of corneal flap thickness on opaque bubble layer (OBL) formation in Visumax femtosecond laser-assisted stromal for situ keratomileusis (FS-LASIK). MethodsThis retrospective study analyzed 203 eyes of 103 patients (32 men and 71 women) who underwent Visumax FS-LASIK between January 2020 and June 2020, and according to corneal flap thickness, they were divided into the 100-μm group (64 eyes) and the 110-μm group (139 eyes). Anterior-segment examination revealed no abnormal findings. Preoperatively, intraocular pressure (IOP), central corneal thickness (CCT), residual stromal thickness (RST), spherical power, cylindrical power, flat keratometry (K1), steep keratometry (K2), and biomechanical parameters including deformation amplitude (DA) ratio, Integrated Radius, stiffness parameter at first applanation (SP-A1), and Ambrosio relational thickness to the horizontal profile (ARTh) were evaluated. Primary outcomes were the incidence of OBL formation in the two groups compared by the Chi-square test and the correlation between the incidence of OBL and the above preoperative data by Spearman's Rho test. Secondary outcomes were the comparisons corrected by the generalized estimating equation (GEE) model. ResultsThe incidence of OBL formation in the 100-μm group was 59.4 %, which was higher than that in the 110-μm group (23.0 %) with a significant difference (χ2 = 25.635, P < 0.001). The thinner corneal flap thickness (r = −0.355, P < 0.001) and higher spherical power (r = −0.142, P < 0.05) correlated with OBL formation. Higher K1 (r = 0.217, P < 0.01) and K2 (r = 0.198, P < 0.01) also correlated with OBL formation. The results of the GEE correction analysis showed higher rates of OBL formation in the 100-μm group (odds ratio [OR] = 4.704, 95 % CI 1.681–13.161, P < 0.01). ConclusionsOBL was more likely to occur with the 100-μm corneal flap than with the 110-μm corneal flap in Visumax FS-LASIK. The risk of OBL formation in the 100-μm group was 4.704 times higher than that in the 110-μm group.

Jacobian-free implicit MDRK methods for stiff systems of ODEs

In this work, an approximate family of implicit multiderivative Runge-Kutta (MDRK) time integrators for stiff initial value problems is presented. The approximation procedure is based on the recent Approximate Implicit Taylor method (Baeza et al., 2020 [7]). As a Taylor method can be written in MDRK format, the novel family constitutes a multistage generalization. Two different alternatives are investigated for the computation of the higher order derivatives: either directly as part of the stage equation, or either as a separate formula for each derivative added on top of the stage equation itself. From linearizing through Newton's method, it turns out that the conditioning of the Newton matrix behaves significantly different for both cases. We show that direct computation results in a matrix with a conditioning that is highly dependent on the stiffness, increasing exponentially in the stiffness parameter with the amount of derivatives. Adding separate formulas has a more favorable behavior, the matrix conditioning being linearly dependent on the stiffness, regardless of the amount of derivatives. Despite increasing the Newton system significantly in size, through several numerical results it is demonstrated that doing so can be considerably beneficial.

Effect of tone normalizing massage on stiffness of accessory inspiratory muscles in patients with COPD

The aim of this study was to evaluate the effect of medical massage on inspiratory accessory muscle function and sensory sensitivity in patients with chronic obstructive pulmonary disease. The participants were divided into two groups: group II (22 patients with COPD in the stable period), and group II (II: 17 participants with no respiratory disorders). Each group was subjected to a series of five massages. The treatment was performed for the sternocleidomastoid, levator scapulae, and the descending part of the trapezius muscle. The parameters of muscle frequency and stiffness were measured using a Myoton Pro Digital device. The compression sensitivity was measured using a Force algometer. The results obtained showed significant differences in the stiffness parameters of the muscles studied between the groups, which indicates a positive effect of massage on muscle function in patients with COPD. The greatest significant differences were found in the patient’s sensitivity parameters. The application of the massage series significantly improved the parameters of frequency and decreased stiffness of inspiratory accessory muscles in patients with COPD compared to the group of healthy participants. This massage is an effective method to normalize muscle tone and thus improve the functional status of patients with COPD.