Prescribed-time distributed optimization problem with constraints.

In recent years, distributed optimization problem have a wide range of applications in various fields. This paper considers the prescribed-time distributed optimization problem with/without constraints. Firstly, we assume the state of each agent is constrained, and the prescribed-time distributed optimization algorithm with constraints is designed on the basis of gradient projection algorithm and consensus algorithm. Secondly, the constrained distributed optimization problem is transformed into the unconstrained distributed optimization problem, and according to the gradient descent algorithm and consensus algorithm, we also propose the prescribed-time distributed optimization algorithm without constraints. By designing the appropriate objective functions, we prove the multi-agent system can converge to the optimal solution within any prescribed-time, and the convergence time is fully independent of the initial conditions and system parameters. Finally, three simulation examples are provided to verify the validity of the designed algorithms.

Mechanical difference of left ventricle between rabbits of myocardial infarction and hypertrophy.

The analysis of cardiac wall stress is of importance to understand the development of heart failure (HF). The aim of the study is to carry out the cardiac mechanics analysis to show the changes of left ventricular (LV) wall stresses after LV hypertrophy (LVH) and myocardial infarction (MI). Here, LVH and MI were generated in rabbit hearts through the transverse aortic constriction (TAC) and the distal left circumflex (LCx) artery ligation operations, respectively. Physiological and CT measurements were carried out at postoperative 2 and 4 weeks, based on which a finite element (FE) model was developed to perform the mechanics computation. We found a gradual increase of end-diastolic myofiber stress in free wall and interventricular septum of LVH and MI (higher stress in the free wall than the septum). In the interventricular septum, the 4-weeks LVH group has the highest ED myofiber stresses (11.378 ± 3.022 kPa), while the 4-weeks MI group has the highest ED myofiber stresses (13.494 ± 2.835 kPa) in the free wall. LVH increased myocardial volume (3.49 ± 0.07 and 4.52 ± 0.26 ml at postoperative 2 and 4 weeks) while MI increased LV volume (from 2.75 ± 0.29 to 4.19 ± 0.27 ml). LVH and MI had different distributions of local myofiber stress.

Speckle tracking echocardiography could detect the difference of pressure overload-induced myocardial remodelling between young and adult rats.

The assessment by speckle tracking echocardiography (STE) provides useful information on regional and global left ventricular (LV) functions. The aim of the study is to investigate if STE-based strain analysis could detect the difference of pressure overload-induced myocardial remodelling between young and adult rats. Physiological, haemodynamic, histological measurements were performed post-operatively in young and adult rats with transverse aortic constriction (TAC) as well as the age-matched shams. Two-way ANOVA was used to detect the statistical difference of various measured parameters. Pressure overload decreased the ejection fraction, fractional shortening, dp/dtmax and |dp/dtmin|, but increased the LV end-diastolic (ED) pressure in adult rat hearts for nine weeks after TAC operation than those in young rat hearts. Pressure overload also resulted in different changes of peak strain and strain rate in the free wall, but similar changes in the interventricular septum of young and adult rat hearts. The changes in myocardial remodelling were confirmed by the histological analysis including the increased apoptosis rate of myocytes and collagen area ratio in the free wall of adult rat hearts of LV hypertrophy when compared with the young. Pressure overload alters myocardial components in different degrees between young and adult animals. STE-based strain analysis could detect the subtle difference of pressure overload-induced myocardial remodelling between young and adult rats.

Cardiac wall mechanics analysis in hypertension-induced heart failure rats with preserved ejection fraction.

Although cardiac wall mechanics is of importance for understanding heart failure with preserved ejection fraction (HFpEF), there is a lack of relevant mechanics studies. The aim of this study was to analyze the changes in stress and strain in the left ventricle (LV) in hypertension-induced HFpEF rats. Based on experimental measurements in DSS rats fed with high-salt (HS) and low-salt (LS) diets, LV stress and strain were computed throughout the cardiac cycle using Continuity software. HS-feeding increased myofiber stress and strain along both the transmural and longitudinal directions at the end-diastolic state but resulted in a lower absolute value of strain and relatively unchanged stress at the end-systolic state. Moreover, the end-diastolic stress and strain decreased with increasing radial position from the endocardial towards the epicardial walls despite negligible changes along the longitudinal direction. The changes in LV wall mechanics characterized the elevated diastolic LV stiffness and slow LV relaxation in HS-fed rats of HFpEF. These findings denote that a vicious cycle of increased stress and strain and diastolic dysfunction can prompt the development of HFpEF.

[Application of cardiac assist device and its biomechanics research for heart failure].

As an important means of treating heart failure (HF), cardiac assist device has been widely used in clinic. This paper reviews the application status, existing problems and future development trend of cardiac assist devices, including the classification of cardiac assist devices, representative research achievements and indications of the assist devices. It also summarizes the biomechanical indexes of the heart and the new approaches and methods for treating heart failure, as well as the hemodynamic studies of cardiac assist devices in recent years. The research findings provide references for further optimization of cardiac assist device structure and clinical application of the device.

A comparison of postoperative morphometric and hemodynamic changes between saphenous vein and left internal mammary artery grafts.

There is higher long-term failure of the saphenous vein graft (SVG) compared with the left internal mammary artery (LIMA) graft, which is affected by the hemodynamic environment. A comprehensive analysis of postoperative structure-function changes is important to study the atherogenesis in the SVG A comparison of morphometric and hemodynamic parameters was carried out between LIMA grafts and SVGs and between different time points postoperatively. Various parameters were obtained from the image reconstruction and flow simulation in patients, who underwent CT exams for ~1 year, 5 and 10 years after revascularization. Morphometric data showed a decrease in lumen size in the entire SVG and anastomosis of different patients in a sequence of ~1 year, 5 and 10 years postoperatively despite negligible changes of LIMA size. Computational results indicated the fourfold increased surface area ratio (SAR) of low time-averaged wall shear stress (TAWSS) in the SVG and anastomosis at postoperative 10 years than that at postoperative ~1 year. The SAR of high TAWSS gradient (TAWSSG) at the distal anastomosis between SVG and coronary arteries was significantly higher (14 ± 9% vs. 6 ± 8%) than that in the LIMA group at postoperative ~1 year. There were strong correlations between morphometric and hemodynamic parameters in the SVG and distal anastomosis at various time points postoperatively, which showed deterioration relevant to persistent diffuse diseases at postoperative ~10 years.