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The cardiovascular system consists of the heart, a network of vessels and blood. Blood vessels are the tubular structure carrying blood through the tissues and organs. Disorders in this vast network can cause a range of health problems which can be severe or fatal. Blood pooling method has been used to measure the change in blood volume of the thigh, abdomen, limbs, etc. with the pressure change. This method occludes the vessel to prevent blood flowing out of the segment being investigated. In recent years, bioimpedance analysis (BIA) has become a popular modality in detecting various body diseases since it is a non-invasive, low-cost and simple for usage. In this paper, a novel scheme is proposed to extract the properties of a blood vessel (e.g. compliance) from which vascular diseases can be detected by analyzing the difference in bioimpedance measurements calculated before and after blood pooling. The paper presents a simple mathematical model to describe vessel compliance and its influence on bioimpedance measurements. Furthermore, the finite element model of human forearm is constructed, in which various vascular disorders are simulated and the impedances are measured before and after blood pooling. The simulation results clarify the ability of BIA in estimating vascular abnormalities, depending on the changes caused by diseases in vessel compliance, which are reflected on bioimpedance measurements using blood pooling method. [ABSTRACT FROM AUTHOR]

Lumped-parameter models are widely used by cardiovascular researchers in the analysis of the circulatory dynamics. However, portability and model exchange have always been a problem, with different researchers implement the model differently. To improve the situation, in this study, a group of lumped-parameter cardiovascular system models with different levels of complexity have been implemented using the CellML mark-up language. The models have been curated and made publicly available in the CellML model repository, and the purpose of this paper is to provide further technical details to support the usage of these models by the research community. The developed models are validated and tested under the OpenCell environment as part of the curation process. Simulation results agree well with typical published data on cardiovascular system response. [ABSTRACT FROM AUTHOR]

One method of removing malignant tissues from human organs is radiofrequency ablation. Thermal radiofrequency is a common technique of liver tumour therapy, which depends mainly on heating the infected region. This work proposes to investigate the thermal issue, which - in instance of excessive current - leads to extra lesion in liver tissues. However, the thermal lesions and the mistakes occurred in positioning the trocar instrument in the correct and accurate place arise the need to simulate and prediction of the thermal and electrical behaviour of the ablation operation. By using COMSOL multiphysics package, the process of hepatic tumour ablation has been simulated. Results show that by virtue of higher blood electrical conductivity, the nearby liver tissue around the electrode can be heated by rising its temperature due to electrical current from the radiofrequency probe according to the Joule law. Also, in this paper, different values of blood perfusion rate have been applied in the simulation process to investigate its effect on the ablation process. It is found that the increasing of mass flow rate of blood flow tends to bring down the fraction of necrotic tissue, which is contraindicated to the tumour ablation process. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to provide a scientific basis for a unified standard of the reference value of young people's erythrocyte sedimentation rate (ESR) in China. The reference values of healthy young people's ESR were collected according to the Wintrobe method, and the relationship between the reference value of young people's ESR and altitude was tested in this paper. It was found that the reference value of young people's ESR decreases when the altitude gradually increases, and the relationship is significant. The method of mathematical univariate regression analysis was used to deduce two regression equations: Y(1) = 10.92-0.00183X +/-2.59 and Y(2) = 18.58-0.00319X +/-4.37. If the altitude value of a particular area of China is known, the reference value of young people's ESR can be calculated by means of the regression equations. Furthermore, depending on the altitude, China can be divided into three districts: Qingzang, Central and Eastern districts. [ABSTRACT FROM AUTHOR]

In this paper, the effects of geometric parameters on the development of stress in custom cementless hip implant have been studied. Taguchi methods and analysis of variance (ANOVA) were used to find out which geometric parameters are statistically significant for the maximum von Mises stresses in the hip implant. The multiple regression analysis was also performed, to replace the FE solver and accurately and quickly predict the stress values for new patients. Three parameters horizontal offset (HO), vertical offset and neck shaft angle (NSA), with three levels have been selected. Based on L9 orthogonal array, nine hip implant shapes with three different geometric parameters were modelled. Stress analysis was carried out by using finite element analysis. ANOVA results showed that HO has the maximum impact on von Mises stresses followed by the NSA. It is shown that as the HO increases, the stress at the given region increases, however, as the neck shaft (NSA) increases the stress at the given region decreases. Good agreement is found between von Mises stresses, calculated from multiple regression analysis and obtained from FE analysis. To redesign customised hip implant for the minimum stresses, the results of this work will be important. [ABSTRACT FROM AUTHOR]

Fluid-solid interaction is a primary feature of cardiovascular flows. There is increasing interest in the numerical solution of these systems as the extensive computational resource required for such studies becomes available. One form of coupling is an external weak coupling of separate solid and fluid mechanics codes. Information about the stress tensor and displacement vector at the wetted boundary is passed between the codes, and an iterative scheme is employed to move towards convergence of these parameters at each time step. This approach has the attraction that separate codes with the most extensive functionality for each of the separate phases can be selected, which might be important in the context of the complex rheology and contact mechanics that often feature in cardiovascular systems. Penrose and Staples describe a weak coupling of CFX for computational fluid mechanics to ANSYS for solid mechanics, based on a simple Jacobi iteration scheme. It is important to validate the coupled numerical solutions. An extensive analytical study of flow in elastic-walled tubes was carried out by Womersley in the late 1950s. This paper describes the performance of the coupling software for the straight elastic-walled tube, and compares the results with Womersley's analytical solutions. It also presents preliminary results demonstrating the application of the coupled software in the context of a stented vessel. [ABSTRACT FROM AUTHOR]

This paper presents a robust finite element model (FEM) with multiple-layers of varying properties for investigation of burn effects on human skin during a burning process resulting from exposure of skin surface to a contact heat source and a hot moving fluid. Henriques' theory of skin burns is used in conjunction with two-dimensional Pennes bioheat transfer equation for determining the spatial and temporal extent of burn injury. The model developed is a two-dimensional axisymmetric model in cylindrical coordinates. The various tissue layers account for changing thermal properties with respect to skin anatomy. A finite element scheme that uses the backward Euler method is used to solve the problem. The injury processes of skin subsequent to the removal of the heat source (post-burn) will also be inspected. The mesh employed in this model consists of a high density of nodes and elements in which a thorough mesh convergence study was done. A comparison of the transient temperature field computed by this model against Diller's results using the FE technique with a comparatively coarse mesh of 125 elements and experimental data by Orgill et al. has been done in the present study. It concluded that improved accurate solutions have been performed using the robust model developed due to the achievement of a mesh-independent solution. [ABSTRACT FROM AUTHOR]

Currently the best indicator for surgical treatment of arterio-sclerosis is the degree of stenosis. Although X-ray angiography is currently the standard, cost and morbidity are distinct disadvantages. By modelling stenosis and studying its biofluid mechanics, one can apply its results in the field of arterial disease research. This formed the motivation for this work. A non-Newtonian (power law) incompressible Navier-Stokes (N-S) solver was developed using the method of operator splitting and artificial compressibility. The vehicle used is the computational fluid dynamics (CFD) numerical library FASTFLO. The power-law model developed is then used to do a parametric study of the effect of 'n' on blood flow mechanics where 'n' is the power index that determines the haematocrit of blood. A pulsatile pressure wave over a cardiac cycle of a second was used to simulate transient flow over a hypothetical two-dimensional stenotic geometry. By comparing the different velocity pressure, wall shear stress and viscosity profiles, it has been found when 'n' increases, the vortex formation and peak wall shear stress decreases (magnitudes of < 1.5 Pa). Since the formation of vortices and low oscillatory wall shear stress on the stenotic wall is detrimental to the well-being of the arterial tract, it can therefore be inferred that there might be a relationship between the diseased state of blood (power law) and early genesis of atherosclerosis. However, the conclusion of this paper marks the advent of new research directions in this field of study. [ABSTRACT FROM AUTHOR]

Mobile devices are extensively used to store more private and often sensitive information. Therefore, it is important to protect them against unauthorised access. Authentication ensures that authorised users can use mobile devices. However, traditional authentication methods, such as numerical or graphic passwords, are vulnerable to passive attacks. For example, an adversary can steal the password by snooping from a shorter distance. To avoid these problems, this study presents a biometric approach that uses cloud models of heartbeats as the entity identifier to secure mobile devices. Here, it is identified that these concepts including cloud model or cloud have nothing to do with cloud computing. The cloud model appearing in the study is the cognitive model. In the proposed method, heartbeats are collected by two ECG electrodes that are connected to one mobile device. The backward normal cloud generator is used to generate ECG standard cloud models characterising the heartbeat template. When a user tries to have access to their mobile device, cloud models regenerated by fresh heartbeats will be compared with ECG standard cloud models to determine if the current user can use this mobile device. This authentication method was evaluated from three aspects including accuracy, authentication time and energy consumption. The proposed method gives 86.04% of true acceptance rate with 2.73% of false acceptance rate. One authentication can be done in 6s, and this processing consumes about 2000 mW of power. [ABSTRACT FROM PUBLISHER]

A three-dimensional hip model was created from the MRI scans of one human subject based on constructing the entire pelvis and femur. The ball and socket joint was modelled between the hip's acetabulum and the femoral head to analyse the multiaxial loads applied in the hip joint. The three key ligaments that reinforce the external surface of the hip to help to stabilise the joint were also modelled which are the iliofemoral, the pubofemoral and ischiofemoral ligaments. Each of these ligaments wraps around the joint connection to form a seal over the synovial membrane, a line of attachment around the head of the femur. This model was tested for different loading and boundary conditions to analyse their sensitivities on the cortical and cancellous tissues of the human hip bones. The outcomes of a one-legged stance finite element analysis revealed that the maximum of 0.056 mm displacement occurred. The stress distribution varied across the model which the majority occurring in the cortical femur and dissipating through the cartilage. The maximum stress value occurring in the joint was 110.1 MPa, which appeared at the free end of the proximal femur. This developed finite element model was validated against the literature data to be used as an asset for further research in investigating new methods of total hip arthroplasty, to minimise the recurrence of dislocations and discomfort in the hip joint, as well as increasing the range of movement available to a patient after surgery. [ABSTRACT FROM AUTHOR]

The varus knee has been defined as a Hip-Knee-Ankle alignment of less than 180 degrees. Varus knee alignment increases the load on the medial knee and also the risk of osteoarthritis. High tibial osteotomy has been designed to modify the malalignment of varus knee. The aim of this study was to investigate the osteotomy effects on knee adduction moment (KAM) and contact forces using a musculoskeletal and subject-specific knee model. A patient with varus knee and no symptoms of any other disease or disability participated in this study. The geometry of the multibody knee model has been modified using MR images. The solutions of its finite element model have been used to determine the parameters of the multibody model. The motion data, ground reaction force and kinetic data have been applied to run the subject-specific musculoskeletal model during the stance phase of gait. After osteotomy, the adduction moment decreased, where the maximum values are comparable to other studies. The pattern of KAM did not witness any significant changes. The total and medial contact forces reduced considerably after surgery, but the lateral contact force did not significantly change. The changes in total and medial contact forces and lack of change in lateral contact force could be explained by modification of the gait pattern after surgery. [ABSTRACT FROM AUTHOR]

Donation after cardiac death has been adopted to address the critical shortage of donor organs for transplant. Recovery of these organs is hindered by low blood flow that leads to permanent organ injury. We propose a novel approach to isolate the perfusion of the abdominal organs from the systemic malperfusion of the dying donor. We reasoned that this design could improve blood flow to organs without open surgery, while respecting the ethical principle that cardiac stress not be increased during organ recovery. Conditions within the stent were analysed using a computational fluid dynamics (CFD) method and validated on two prototypesin vitro. The hydrodynamic pressure drop across the stent was measured as 0.14–0.22 mmHg, which is a negligible influence. Device placement studies were also conducted on swine model fluoroscopically. All these results demonstrated the feasibility of rapidly isolating the perfusion to abdominal organs using a compartmentalised stent graft design. [ABSTRACT FROM PUBLISHER]

Overlying soft tissues attenuate ultrasound backscattered from bone, complicating diagnostics of osteoporosis at the most important fracture sites. Dual-frequency ultrasound technique (DFUS) has been proposed to solve this problem through determination of thickness and composition of overlying soft tissue. This study applies DFUS technique for the first time with a phased-array transducer to investigate if the thickness of two interfering layers (oil and water) can be accurately determined in a variety of configurations. Results indicate that DFUS may be used with phased-array ultrasound systems, making them a suitable combination to consider in future development of clinical in vivo ultrasound methodologies. [ABSTRACT FROM AUTHOR]

The aim of this study was evaluate the biomechanical behaviour of prostheses screwed into conventional (0° angulation) and pre-angled experimental (8, 12 and 20°) external hexagon implants (13 × 4 mm) by photoelastic analysis. Eight casts were made in photoelastic resin. Casts were divided into groups of single crowns or three combined elements. Each unit was positioned in a circular polariscope. By using a universal testing machine, 100 N loads were applied in the axial and oblique (45°) directions to fixed points on the occlusal surfaces of the crowns. Generated stresses were recorded photographically and analysed qualitatively in a graphics program. In single-element prostheses, the number of high-stress fringes increased with increasing implant angle. However, in three-element prostheses, there was no difference in the stress distribution with implant angle, except for the 12° implant that had a higher degree of stress. For the other groups pre-angulation of the implant increases the concentration and intensity of stresses for single prosthesis and has similar stress distribution in three-element fixed prostheses. [ABSTRACT FROM PUBLISHER]

A dynamic model of the inverted pendulum characteristics of the head and cervical spine is presented. Using simple approximations and a single rotational-degree-of-freedom approach, the model is shown to conform to the classical mathematical description of an inverted pendulum motion. It also exhibits the well-known point of unstable equilibrium which is a standard property of such systems. Specific predictions of this theoretical description are compared against other values for the tilt, angular velocity and acceleration of the head during acceleration-sled testing, and with the Kapitza relation for mechanical-dither stabilization of an inverted pendulum. Numerical evaluations of the dynamic variables, resonant frequencies and time constants important to the problem are provided, and suggestions are made about how further results might be derived from extended versions of the model. This approach can now be refined to serve as a testing ground for analysing the biomechanics of traumatic neck injuries and for interpreting the possible roles that mandibular dysfunctions and dental malocclusion may play in disorders of the cervical spine. (Some background needed for exploring the latter possibility is presented.) [ABSTRACT FROM AUTHOR]

We applied nonlinear dynamics theory to EEG analysis of schizophrenic patients and estimated the correlation dimension with both temporal embedding and spatial embedding. A higher D2 was found when using a time-delay embedding method. Especially at F7 and Fp1, a significant increase showed. We concluded that more complex activity occurred in certain lobes of schizophrenic patients. Using the spatial embedding method, a relative lower global correlation dimension was obtained. This shows that there might be a diffuse slow wave activity through a schizophrene's global cerebrum. Finally, we discuss the study from three angles of clinical semiology, spectrum analysis and neuropsychology and draw some conclusions about the relationship between the nonlinear analysis of schizophrenia EEG and clinical research. It seems that the theory of a nonlinear dynamics system is a powerful tool for EEG research and may prove useful in complementing visual analysis of EEG accompanied with other study means for brain electrical activity. [ABSTRACT FROM AUTHOR]

Representative double bifurcation airway models with asymmetric branch flow rate ratios, caused by spatially different downstream impedances or a carinal tumour in one branch, have been considered. For steady laminar inhalation of a dilute micron-particle suspension, i.e. 500 < or = Re < or = 2000 and 0.02 < or = St < or = 0.12, air flow fields, aerosol distributions, and wall particle concentrations have been simulated with a user-enhanced finite-volume code and an off-line particle tracking routine. Particle deposition efficiencies are shown for both asymmetric branch flow rate cases, i.e. unobstructed and tumour-induced. [ABSTRACT FROM AUTHOR]

The head and neck constitute an inverted pendulum that is stabilized during consciousness by neuromuscular restoring forces. An analysis of the dynamics of this inverted pendulum suggests that the mechanics of the mandible and temporomandibular joint might couple into those of the pendulum's stabilization process. In this article, physical principles of the inverted pendulum model as these apply to the head and neck are explored, and the authors describe implications of mandibular mechanics for the forces acting on the head and neck at equilibrium. This novel application of the inverted pendulum model predicts that alteration or pathology of temporomandibular mechanics would lead to perturbations of the normal forces acting in the head and neck. Under certain circumstances, these perturbations could be expected to contribute to symptoms and result in additional or accelerated degenerative effects. [ABSTRACT FROM AUTHOR]