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Aim: Continuous physical activity is required after coronary artery bypass graft (CABG) surgery to prevent recurrence of the disease; however, its amount is not suitable in many patients. The present study aimed to investigate the stages of physical activity in patients after CABG using the Trans-Theoretical Model (TTM).
Methods: In this cross-sectional research, 120 cardiac patients participated; they had CABG surgery and referred to Ekbatan Hospital of Hamadan. Sampling was conducted using a purpose-based approach. Data were collected using a researcher-made questionnaire based on the TTM and analyzed using the SPSS18 software. Descriptive statistics and statistical processes of one-way ANOVA, Tukey's post-hoc, and Chi-square tests were also conducted at a significant level of p<0.05.
Findings: The mean age of the participants was 57.87±9.89 years. From the 120 patients under study, 4.2% were in the pre-contemplation phase, 14.2% in the contemplation stage, 58.3% in the preparation stage, 10.8% in the action stage, and 12.5% in the maintenance phase of the physical activity. The results of ANOVA test showed a significant difference between the stages of change in behavior with perceived advantages, perceived disadvantages, perceived self-efficacy, and processes of change (p <0.001).
Conclusion: The results showed that many patients did not have regular physical activity after surgery. This makes clear the need for educational interventions based on theoretical models by health educators.

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Recently, the use of coronary stents in interventional procedures has rapidly increased and different stent models, with different geometries and materials, have been introduced in the market. In order to select the most appropriate stent model, it is necessary to analyze and compare the mechanical behavior of different types of stent. In this paper, finite element method is used for investigating the effect of stent geometry and material properties on its behavior. Two commercially available stent designs with different geometries (the Palmaz–Schatz and NIR stents) and two different stent materials (stainless steel 304 and Cobalt alloy MP35N) are modeled and their behavior during the deployment is compared in terms of stress distribution in the stent and vessel, and outer diameter changes. Moreover, the effect of stent geometry and material properties on the restenosis after coronary stent placement is investigated by comparing the stress distribution in the arteries. According to the findings, the possibility of restenosis after coronary stenting is lower for NIR stent in comparison with Palmaz–Schatz stent. Moreover, stainless steel 304 is more suitable material for manufacturing stents, in comparison with the other one.

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Lipid solutes in blood such as Low-Density Lipoproteins (LDLs) are the major cause of most cardiovascular diseases. Increase of fatty materials in the blood flow endanger personal healthiness and enhance possibility of cardio and cerebrovascular infarctions. In order to provide nutritional blood for different tissues, heart sends pulsatile flow with high pressure to the circulatory system such that LDL particles spread over the entire body. Contraction and expansion of the heart create pulsatile flow that affect blood hemodynamics and LDL mass transfer in vessels. In this paper, effects of the pulsatile flow on LDL mass transport in a multilayered artery with atherosclerotic plaques are investigated numerically. In order to apply pulsatile flow in the artery, a set of specific-person flow and pressure pulses, which are resulted from the ultrasound method, are employed directly. Results indicate that pulsatile flow increases LDL concentration both on the luminal surface and across arterial layers and produces interesting periodic concentration patterns in these regions. Moreover, pulsatile effect intensifies remarkable reversal flow right at post-stenotic regions of plaques locations, where the flow is recirculated naturally, and lowers LDL accumulation.

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Mechanical behavior of live cells and tissues is non-linear and their deformations are large. Using a suitable mechanical model that could predicts this behavior, is an important step in the prevention and treatment of various diseases and the production of artificial tissues. In this paper, using the non-linear elasticity theory and non-linear Mooney-Rivlin model, mechanical analysis of human arteries has been studied under internal pressure and axial tension. In the first By using the experimental study was conducted of biaxial test, the elastic constants of the arteries are calculated. For modeling, the arteries are considered as long homogeneous and isotropic cylinders. Radial and circumferential stress distribution on the minimum and maximum blood pressure is calculated. Variation of artery radius due to internal pressure is calculated and compared with the reported experimental data, and a good agreement is seen. The stress distribution curves versus radius are plotted which show that the inner layers of the arteries have much greater role in stress distribution than the outer layers. The elastic constants which are calculated for different ages show that the arteries of older people become stiffer and their flexibility decrease.

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Recent observations have shown that artery stenosis occurs as multiple-stenosis in 70% of patients with atherosclerosis plaques. Accordingly, the frequent occurrence of double-stenosis in blood arteries has inspired this paper to investigate and compare the plaque rupture risk in different arrangements of common plaque shapes in a double-stenosis. The plaque von-Mises stress in plaque fibrous cap is calculated by finite element modeling of the fluid-structure interaction (FSI) between the blood flow, artery and plaque components. Arbitrary Lagrangian-Eulerian approach is employed for FSI simulations and a benchmark problem dealing with wave propagation in a fluid-filled elastic tube is used for model verification. Transient velocity and pressure conditions of actual pulsatile blood flow through coronary artery are prescribed. The blood is assumed to be a Newtonian fluid and hyper-elastic material model is employed for describing nonlinear behavior of the human tissue composed of the arterial wall, lipid core and fibrous cap. It was observed that the arrangement composed of two diffused plaques is subjected to the maximum von-Mises stress, while the arrangement of ascending-descending plaques experiences the minimum von-Mises stress. The effect of different parameters such as the stenosis degree, the space length between the plaques, and the plaque length is studied and discussed.

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Vertebrobasilar system stenosis is one of the risk factor for deaths caused by stroke, the risk of stenosis in these arteries are highly depend on the people’s age. In the present study, atherosclerosis susceptible sites in vertebrobasilar system at different ages 20, 50 and 70 have been investigated. Numerical method (Fluent software) is employed to solve the equations. Blood flow is simulated in these arteries to investigate probable risky sites (prone to stenosis). To find these locations, critical values of the averaged wall shear stress (AWSS) and oscillatory shear index (OSI) have been studied. By considering the AWSS and OSI criteria in 20 years old person it becomes clear that the risk of stenosis is not considerable at this age, somehow ageing increases OSI figures in the right vertebral artery and in its junction reaching to the critical values, besides at this age, the area of the sites with lower amount of AWSS are stretched significantly. At the age of 70, risky sites are expanded toward right vertebral artery. Furthermore the risk of stenosis in all determined risky sites of age 50 increased at the age of 70.

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Stenting is considered to be the favoured tool for therapy of coronary stenosis disease. However, despite the many advantages of this treatment strategy, its outcome may be undermined by the restenosis occurrence in the stent deployment site. Observations have shown that stent deployment in the artery alters the hemodynamic parameters such as wall shear stress and vortices size and prepares the conditions for in-stent restenosis development. Considering this fact, in this paper, the effect of some geometrical parameters such as the shape and the size of the stent strut on the wall shear stress distribution and vortices size is investigated. Furthermore, employment of a stent with partial flexible strut is suggested to decrease the restenosis risk, and the effect of the flexible part stiffness is explored. For this purpose, the interaction between the blood flow and the flexible part is simulated by arbitrary Lagrangian-Eulerian approach in the framework of the finite element method. The results indicate that in stents with circular strut, the partial flexibility of the cross-section can be effective in reducing the restenosis risk by lowering the maximum value of the wall shear stress and considerably decreasing the vortices size. On the other hand, in stents with rectangular struts, it not only does not decrease the shear stress maximum value but also significantly increases the vortices size and may lead to increase of the restenosis risk.

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Injection drug micro particles into arteries is one of the stenosis treatments. Micro particles scattered in blood flow collide with plaques, drug is absorbed to treat stenosis. Since the collision of drug particles with artery wall depends on blood flow pattern, the efficiency of this method relies on guiding drug particles to stenosed site, otherwise the patient must take much higher drug dosage which has various side effects. Applying magnetic field and guiding drug particles to the target area extensively increases efficiency of the treatment and cuts side effects. In the present study, efficiency of using drug particles in vertebrobasilar system to treat atherosclerosis with and without applying magnetic field has been investigated. Ansys-Fluent commercial software has been used for numerical simulation. Results indicate applying magnetic field plays an important role in drug particles circulation as drug captivation surges almost 16 times. Injecting location and the particle diameters also have been examined and found to be important in the treatment effectiveness.

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Stenosis in coronary artery and the other cardiac diseases such as Atherosclerosis is major cause of death in the world. Numerical simulation of blood flow can help medical evaluation to curve arteries have been stenosis. The purpose of this paper is to find the effect of arteries stenosis on the hemodynamic parameters by simulation of blood flow in LAD branch of coronary artery. The computational domain has been determined from CT images of human heart. In this study, blood is assumed to be homogeneous, Newtonian and the blood flow assumed to be pulsatile. In order to more realistic modeling of flow and pressure, Seven–element lumped model has been used in coronary artery outlet, in order words the 0D and 3D models are coupled together. The results indicate that the calculated flow wave is the minimum in systolic phase and maximum in diastolic phase in coronary artery, in contrast with Aorta. On the other hand, by increasing the stenosis percent from 30 to 60 percent, no significant drop of flow has been observed in the state of rest, and it has been validated with experimental results. The results indicate that with increasing stenosis, time average wall shear stress in the stenosis region increases, while it decreases before and after the stenosis, also the investigation of oscillating shear index indicates that in the state of 60% of stenosis and in the main downstream branch, it has the maximum value, that is indicative of the presence of turbulent flow in this region.

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In the present study, a finite element model has been presented using both the in-vivo geometry of a healthy man carotid artery, which was extracted from consecutive transverse ultrasound images and the pulse pressure waveform and Kelvin viscoelastic model parameters that were obtained from processing the consecutive longitudinal ultrasound images. Extracting the internal diameter waveform from longitudinal ultrasonic image processing and calibrating it via an exponential equation, blood pressure waveform of the carotid artery was extracted. A Gaussian function was fitted to the blood pressure waveform. Differentiating the fitted Gaussian equation resulted in the pressure differentiation of the carotid artery over the cardiac cycle. Kelvin viscoelastic parameters were estimated using an optimization method. Finite element model of the carotid artery was reconstructed in ADINA software and implemented by loading over three cardiac cycles. To validate the model, radial displacement waveform resulted from finite element model and that resulted from image processing were compares in nearly the same spatial position. Percentage of the mean proportional differences between the radial displacement resulted from finite element model and that from consecutive ultrasound images was 9.3. Since the appropriate mechanical models can calculate true stress/strain distribution of the carotid artry wall and plaque and distinguish the location of the plaque areas prone to vulnireability; and because of the capability of the ultrasonic model proposed in this study for describing the pulsatile behavior of artery wall accurately, it is expected that the introduced dynamic model to be applied for accurate evaluation of the arterial disease.

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Biologic tissues modeling play an important role in understanding the tissue behavior and development of synthetic materials for medical applications. It is also a vital action to develop the predictive models for a wide range of uses including medical and tissue engineering. Various strain energy functions have been introduced to model arteries to date. The newest introduced strain energy function is the Nolan strain energy function. Two-layer arterial modeling using this strain energy function has not been performed so far. In this paper, modeling the arteries was carried out in the form of double layers including media and adventitia and hyperelastic material assumption. At first, governing equations were driven based on continuum mechanics. Boundary conditions including inner pressure of artery, axial load and torque as well as static equilibrium were applied. Moreover, Cauchy stress components were gotten by using the continuum mechanics relations. Then, the equilibrium equations in cylindrical coordinate were obtained by using the Cauchy stress. Stress distribution through the artery wall was specified by solving the resulting nonlinear partial differential equations based on generalized differential quadrature method. In the beginning, the artery modeling was conducted in the form of monolayer including the media layer and the results were compared with experimental ones, comparison between stresses in the artery wall and experimental data showed that the volcanic energy function of Nolan is suitable for modeling. After that, the stress distribution was obtained by artery modeling in the form of double layers including the media and adventitia layers.

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