فصلنامه مهندسی پزشکی زیستی
سال نهم شماره 3 (پاییز 1394)

One of the most important newborn EEG abnormalities is the synchrony between different channels which, according to the clinical studies, can lead to neurological and neurodevelopmental outcomes in adulthood. This paper introduces a new method for automated detection of phase synchrony in multivariate signals with applications to newborn EEG signals. In this method, first the instantaneous phase of each channel of the signal is estimated using Hilbert transform. In the case of EEG signals, due to their multicomponent nature, components of the signal are needed to be extracted using a bank of band-pass filters. The synchronization between different channels of the signal is then quantitatively measured using a criterion based on the mutual information between instantaneous phases of the components of the signal. The proposed method in this paper is then used to analyze, from synchronization point of view, multichannel EEG signals acquired from 5 newborns which include seizure-nonseizure periods and burst-suppression (B-S) patterns. Reciever operating curves (ROCs) are used to illustrate the performance of the method. The performance of the proposed method is also compared with that of the existing one based on the cointegration concept. Experimental results prove that the proposed method outperforms the existing one in measuring the generalized phase synchrony in multichannel newborn EEG signals. Also, results of analyzing seizure and nonseizure segments show that for all segmants there is a phase synchronization among EEG channels which is due to the connections between brain hemispheres in both cases. The results also show that seizure periods are more synchronous than nonseizure periods. The phase synchrony assessment of B-S patterns indicates that burst patterns are more synchronous than suppression patterns and there is a phase synchrony in both cases.

Every organ has its own metabolic and functional requirements and needs a variable amount of blood; hence, autoregulation is an important phenomenon. Shear stress induced autoregulation is defined as the innate ability of an organ to keep its hemodynamic conditions stable against changes in heart rate and perfusion pressure. For example, when heart rate changes arterial vessels undergo vasodilation or vasoconstriction in order to stabilize the hemodynamic forces and stresses with respect to the flow needed. The current study examines the local mechanisms employed in automatic control. Local regulatory mechanisms function independently of external control mechanisms, such as sympathetic nerves and endocrine hormones. Therefore, they can be considered isolated mechanisms.The application of boundary conditions in numerical modeling is of utmost importance, hence, using arterial tree modeling to achieve appropriate boundary conditions seems necessary. Thus, we have presented a zero-dimensional (lumped parameter) extensive model first. Then, we used this model to achieve boundary conditions for the common carotid artery. As one of the most important hemodynamic parameters, shear stress regulation will then be modeled in an axisymmetric model of this artery.

Evaluation and measurement of parameters associated with methamphetamine craving can be a valuable tool in the management and intervention programs related to methamphetamine use and dependence. We believe that quantitative electroencephalography (EEG) have brought about a revolution in identification the neurologic infrastructure of craving processing. This study has been conducted aimed to design and develop a new method to measure baseline craving in methamphetamine-dependent patients using EEG signals in neurofeedback therapy for separation of the three modes of low, medium, and high craving. For this purpose, 10 methamphetamine abusers were selected by available method in terms of age, sex and IQ. All patients received 10 sessions of neurofeedback therapy with alpha-theta protocol. During the period of treatment with neurofeedback, before and 60 minutes after each training session, at rest state, on Pz, for 2 minutes and 10 seconds EEG was recorded. To labeling EEG signals we have used Desire for Drug Questionnaire (DDQ). After collecting the required data from signals, time, frequency and nonlinear features were extracted. Then by calculating the linear correlation coefficient of the two variables and variance analysis on three levels optimized and effective features were selected. Finally, using fuzzy classifier, those features were separated into three classes of low, medium and high craving. According to the results, separation accuracy of EEG signals in three classes by K-fold Cross-Validation (KCV) method was 96.67% and test data was 75.15%. This study showed in addition to estimating baseline craving in methamphetamine abusers by quantifying EEG we can optimize the number of training sessions for participants.

The study focuses on the optimal design of a hybrid rotary MR (Magneto Rheological) with waveform boundary T-shaped rotor as prosthesis knee. In the biomechanical prosthesis knee MR fluid to create a variable braking torque depending on the magnetic field is used. By applying a magnetic field, the viscosity of the fluid is actively controlled to achieve the desired braking torque. After a brief description of the configuration of the rotary damper; achievable braking torque formulas is presented. In the following, optimization problem aims to find the optimal geometry in order to maximize the on-state braking torque while off-state torque and weight are within the permitted range. Depending on the application of the referred damper, the maximum braking torque, minimizing torque at off-state, minimizing damper’s weight and have uniform flux density are under consideration. The results of the optimized rotary damper are compared with the reference brake. Then, the performance improvement of the optimized MR brake is discussed.

Time constant is a physical concept that one may deduce the speed of response or reaction of a system from it. Experimental findings confirm the dependency of the speed of opening-closing of ionic channels to the membrane voltage. In this paper with the reasoning of the voltage dependency of ionic channels and gates, a model for time constant of membrane voltage in neurons has been presented. At first, the presented model has been established as a theorem and then the theorem has been proved. According to the presented theorem, one can simulate different morphology and time course of action potential (AP) in neurons by tuning the model parameters. The validation of the presented theorem (model) has been shown by simulation examples of some kinds of neurons and cells APs. Regarding the generality of the presented theorem, our model not only can be applied in biomedical systems but also it may be used in any physical systems.

The cervical multifidus muscle is known as one of the deep neck extensor muscles that its dysfunction have been reported in people with neck pain.With regard to the limits on the evaluation of this muscle activity using electromyography, ultrasound was used to find out its function recently. The aim of this study is evaluation of this muscle dimansions change during six shoulder joint activities in healthy subjects and people with chronic neck pain and providing predictive models. So The relationship between strength of shoulder joint during contraction with the changes of anterior-posterior dimension, lateral dimension, shape ratio and size of the cervical multifidus muscle were assessed using of Response Surface Method in the first step for subjects and activities and then for activities with subject blocking. Finally, data classification in two groups of over 50% and less than 50% of maximum voluntary contraction and predictive models were provided for abduction activity in right side. The anterior-posterior dimension showed a higher correlation with the shoulder joint strength than other factors. R2 values for this dimension in healthy subjects before and after data clustering is 0.552 and 0.66 and in patients is 0.339 and 0.505 respectively. Given the models correlation coefficient and its enhance by data clustering, it seems that evaluation of anterior-posterior dimension of this muscle during isometric abduction activiy of shoulder joint with the sttrength of 0-50% MVC for healthy subjects and 50-100% for patients with neck pain can be provide useful information about its function.

It is accepted that wall shear stress (WSS) and Oscillatory Shear index (OSI) are strong hemodynamic factors to development of atherosclerotic (AS) plaque. Sometimes, OSI has an important effect on AS plaque formation, because WSS doesnt make it happen alone. Most computational fluid dynamic (CFD) simulations were performed on left main coronary bifurcation geometry, and whole left coronary artery tree has not been investigated by now. In this paper, a thorough three-dimensional model of left coronary artery tree was considered, including left main coronary, left anterior descending and its branches, left circumflex artery and its branches. Effects of cardiac motions on vessel wall of left coronary were considered. The governing Navier–Stokes equations for pulsatile flow and incompressible non-Newtonian blood was analyzed with finite element method. The study concentrates on shear stress distribution and OSI distribution on the vessel wall. Comparing the results of this study with previous clinical investigations shows that the regions with low wall shear stress (equal to and less than 1.5[Pa]) along with high OSI value (equal to and more than 0.3) have potential to development of AS plaque. So it can be predicted that the LAD region after D3 and the bifurcation of LCxA-OM have high potential to development of AS, in addition to the bifurcation of LCxA-LMCA which had been specified before.

The statistical studies indicate that diseases, accidents and wares are the principal causes to increase the number of amputees in the world. These studies also show that the most of mutilation disabilities are related to musculoskeletal. Obesity, sedentary, lack of proper exercise as well as the risk of some diseases, cause weaken in knee muscles and other difficulties of this hand. As a consequence, the knee muscles can`t apply a mighty torque to accomplish knee motion. The objective of this study is to propose a proper solution to improve the life quality of those who suffer from weak knees.in this study, by investigating the biomechanical behavior of a healthy foot in a normal gait, the indispensable power which can enforce a 50% weak Knee to achieve the same gait can be calculated. To naturalize the mentioned knee, a new control-active orthosis is designed. The proposed design is specified by an electromechanical actuator and an elastic component articulated in a light weight four-bar mechanism. Its mechanical behavior is tested in a simulated walking gait and the optimum value of elastic coefficient is estimated as 7KN/m. In this case, the maximum torque applicable to knee joint has increased by 34 per cent.