Thermo-optic control of the longitudinal radiation angle in a silicon-based optical phased array.

We demonstrate longitudinal beam-steering with a 1×16 silicon optical phased array (OPA) using a monochromatic light source and thermo-optic control of the refractive index in the grating radiator region. The refractive index is controlled by forming a series of n-i-n heaters, placing i-regions in each radiator of the OPA. When the biased voltage in the heaters is increased, the refractive index of the radiator region is increased by the thermo-optic effect, and the longitudinal radiation angle is changed according to the Bragg condition. The transversal beam-steering is accomplished by phase control with the phase shifters, which are devised with a p-i-n diode using the electro-optic effect. With these electro-optic p-i-n phase shifters and n-i-n thermo-optic radiators, we achieve a relatively wide 2D beam-steering in a range of 10.0°/45.4° in the longitudinal/transversal directions with a 1.55 µm light source. The tuning efficiency is 0.016°/mW in the longitudinal beam-steering.

An integrative model of the cardiovascular system coupling heart cellular mechanics with arterial network hemodynamics.

The current study proposes a model of the cardiovascular system that couples heart cell mechanics with arterial hemodynamics to examine the physiological role of arterial blood pressure (BP) in left ventricular hypertrophy (LVH). We developed a comprehensive multiphysics and multiscale cardiovascular model of the cardiovascular system that simulates physiological events, from membrane excitation and the contraction of a cardiac cell to heart mechanics and arterial blood hemodynamics. Using this model, we delineated the relationship between arterial BP or pulse wave velocity and LVH. Computed results were compared with existing clinical and experimental observations. To investigate the relationship between arterial hemodynamics and LVH, we performed a parametric study based on arterial wall stiffness, which was obtained in the model. Peak cellular stress of the left ventricle and systolic blood pressure (SBP) in the brachial and central arteries also increased; however, further increases were limited for higher arterial stiffness values. Interestingly, when we doubled the value of arterial stiffness from the baseline value, the percentage increase of SBP in the central artery was about 6.7% whereas that of the brachial artery was about 3.4%. It is suggested that SBP in the central artery is more critical for predicting LVH as compared with other blood pressure measurements.

Theoretical estimation of cannulation methods for left ventricular assist device support as a bridge to recovery.

Left ventricular assist device (LVAD) support under cannulation connected from the left atrium to the aorta (LA-AA) is used as a bridge to recovery in heart failure patients because it is non-invasive to ventricular muscle. However, it has serious problems, such as valve stenosis and blood thrombosis due to the low ejection fraction of the ventricle. We theoretically estimated the effect of the in-series cannulation, connected from ascending aorta to descending aorta (AA-DA), on ventricular unloading as an alternative to the LA-AA method. We developed a theoretical model of a LVAD-implanted cardiovascular system that included coronary circulation. Using this model, we compared hemodynamic responses according to various cannulation methods such as LA-AA, AA-DA, and a cannulation connected from the left ventricle to ascending aorta (LV-AA), under continuous and pulsatile LVAD supports. The AA-DA method provided 14% and 18% less left ventricular peak pressure than the LA-AA method under continuous and pulsatile LVAD conditions, respectively. The LA-AA method demonstrated higher coronary flow than AA-DA method. Therefore, the LA-AA method is more advantageous in increasing ventricular unloading whereas the AA-DA method is a better choice to increase coronary perfusion.

Theoretical analysis of the magnetocardiographic pattern for reentry wave propagation in a three-dimensional human heart model.

We present a computational study of reentry wave propagation using electrophysiological models of human cardiac cells and the associated magnetic field map of a human heart. We examined the details of magnetic field variation and related physiological parameters for reentry waves in two-dimensional (2-D) human atrial tissue and a three-dimensional (3-D) human ventricle model. A 3-D mesh system representing the human ventricle was reconstructed from the surface geometry of a human heart. We used existing human cardiac cell models to simulate action potential (AP) propagation in atrial tissue and 3-D ventricular geometry, and a finite element method and the Galerkin approximation to discretize the 3-D domain spatially. The reentry wave was generated using an S1-S2 protocol. The calculations of the magnetic field pattern assumed a horizontally layered conductor for reentry wave propagation in the 3-D ventricle. We also compared the AP and magnetocardiograph (MCG) magnitudes during reentry wave propagation to those during normal wave propagation. The temporal changes in the reentry wave motion and magnetic field map patterns were also analyzed using two well-known MCG parameters: the current dipole direction and strength. The current vector in a reentry wave forms a rotating spiral. We delineated the magnetic field using the changes in the vector angle during a reentry wave, demonstrating that the MCG pattern can be helpful for theoretical analysis of reentry waves.

Mathematical modeling of cardiovascular system dynamics using a lumped parameter method.

This work reviews the main aspects of cardiovascular system dynamics with an emphasis on modeling hemodynamic characteristics by the use of a lumped parameter approach. The methodological and physiological aspects of the circulation dynamics are summarized with the help of existing mathematical models. The main characteristics of the hemodynamic elements, such as the heart and arterial and venous systems, are first described. Distributed models of an arterial network are introduced, and their characteristics are compared with those of lumped parameter models. We also discuss the nonlinear characteristics of the pressure-volume relationship in veins. Then the control pathways that participate in feedback mechanisms (baroreceptors and cardiopulmonary receptors) are described to explain the interaction between hemodynamics and autonomic nerve control in the circulation. Based on a set-point model, the computational aspects of reflex control are explained.

A collaborative computing framework of cloud network and WBSN applied to fall detection and 3-D motion reconstruction.

As cloud computing and wireless body sensor network technologies become gradually developed, ubiquitous healthcare services prevent accidents instantly and effectively, as well as provides relevant information to reduce related processing time and cost. This study proposes a co-processing intermediary framework integrated cloud and wireless body sensor networks, which is mainly applied to fall detection and 3-D motion reconstruction. In this study, the main focuses includes distributed computing and resource allocation of processing sensing data over the computing architecture, network conditions and performance evaluation. Through this framework, the transmissions and computing time of sensing data are reduced to enhance overall performance for the services of fall events detection and 3-D motion reconstruction.

A novel model for metabolic syndrome risk quantification based on areal similarity degree.

Metabolic syndrome (MS) refers to a clustering of specific cardiovascular disease (CVD) risk factors whose underlying pathology is thought to be related to insulin resistance. The risk factors include insulin resistance, obesity, dyslipidemia, and hypertension and it is known to increase the risk for CVD and type II diabetes. Since MS helps to identify individuals at high risk for both CVD and type II diabetes, it has become a major public healthcare issue in many countries. There has been much effort to establish diagnostic criteria for MS, but the current diagnostic criteria of MS have weaknesses, such as binary decision based on diagnostic criteria, equal weight among risk factors, and difficulty in estimating the temporal progress of the risk factors. To resolve these problems, this paper proposes a risk quantification model for MS, which is based on areal similarity degree analysis between weighted radar charts comprising MS diagnostic criteria and examination results of risk factors. The clinical effectiveness of the proposed model is extensively evaluated by using data of a large number of subjects obtained from the third Korea National Health and Nutrition Examination Survey. The evaluation results show that the proposed model can quantify the risk of MS and effectively identify a group of subjects who might be classified into a potential risk group for having MS in the future.

An integrated healthcare system for personalized chronic disease care in home-hospital environments.

Facing the increasing demands and challenges in the area of chronic disease care, various studies on the healthcare system which can, whenever and wherever, extract and process patient data have been conducted. Chronic diseases are the long-term diseases and require the processes of the real-time monitoring, multidimensional quantitative analysis, and the classification of patients' diagnostic information. A healthcare system for chronic diseases is characterized as an at-hospital and at-home service according to a targeted environment. Both services basically aim to provide patients with accurate diagnoses of disease by monitoring a variety of physical states with a number of monitoring methods, but there are differences between home and hospital environments, and the different characteristics should be considered in order to provide more accurate diagnoses for patients, especially, patients having chronic diseases. In this paper, we propose a patient status classification method for effectively identifying and classifying chronic diseases and show the validity of the proposed method. Furthermore, we present a new healthcare system architecture that integrates the at-home and at-hospital environment and discuss the applicability of the architecture using practical target services.

A cooperative metabolic syndrome estimation with high precision sensing unit.

In this letter, we discuss a sensor-integrated system model for metabolic syndrome prediction with workflow system. This model measures not only a cell temperature variation using invasive method but also controlling simulation for metabolic syndrome prediction. To identify the system realization, we discuss the schemes for predicting metabolic syndrome from measurement of mitochondrial activity by using high precision sensors and integrated simulation model of human energetic under high performance workflow computing environment. To predict metabolic syndrome, we built a sensor-integrated chamber that had network interface to deliver analysis results of human cells, annotation data from public hospital, and metabolic data. Using the proposed system, we showed the possibility to evaluate the functionality of human mitochondria and analyze energy metabolism.

Detection of atrial fibrillation episodes using multiple heart rate variability features in different time periods.

Circadian variations of cardiac diseases have been well known. For example, atrial fibrillation (AF) episodes show nocturnal predominance. In this study, we have developed multiple formulas that detect AF episodes in different times of the day. Heart rate variability features were calculated from randomly sampled three min ECG data. Logistic regression analyses were performed to generate three formulas for the entire day, daytime, and evening time. Compared to the first formula that disregarded the time of the day, the second formula for the daytime detection detected AF episodes more accurately (95.2% vs. 99.3%), whereas third formula for the evening time detection did less accurately (93.8%). These results suggest the detection of AF episodes might become more accurate by considering the time-dependent changes of HRV features. In addition, the detection method for the evening time requires further investigation.

Association of heart rates with stress response inventory scores in different age groups.

Many studies reported heart rate changes were associated with mental stress. Recently, a Stress Response Inventory (SRI) questionnaire has been devised to score physical, mental, and emotional symptoms related to mental stress occurred during the past two weeks. However, SRI has too many items to be asked routinely in a mobile device such as a cellular phone. Furthermore, its individual scores may not contribute equally to estimating stress levels in different age groups. Therefore, we sought to identify mental stress factors in the SRI that were associated with heart rate changes in different age groups. Subjects aged from 20 to 69 (n=369) scored a simplified SRI and then heart rates were measured. Multiple linear regression analysis was performed to detect subsets of SRI items that showed significant relationships with heart rates (p-value<0.1). We expect that these age dependent models could be used in identifying the cause of heart rate changes in a mobile application.

Computational analysis of the three-dimensional hemodynamics of the blood sac in the twin-pulse life-support system.

Blood flow in the twin-pulse life-support system (T-PLS) pulsatile blood pump was simulated using a three-dimensional rigid body-fluid-solid interaction model. This model can delineate the blood flow in the T-PLS resulting from operation of a moving actuator. The numerical method used in this study was a commercial finite element package called ADINA. We used a contact and fluid-solid interaction model to compute the blood hemodynamics in the sac. Blood flow is generated by the motion of the actuator, which strongly interacts with the solid material surrounding the blood. To obtain basic bioengineering data on the optimum operation of the T-PLS, we simulated four models in which the actuator moved at different speeds and investigated both the flow pattern and the distribution of shear stress. During the contraction phase, a strong axial flow is observed around the outlet, whereas there is stagnant flow around the inlet. The maximum shear stress in each model depends on the operation mode; however, all four models have similar flow rates. The sinusoidal mode exhibited the lowest maximum shear stress and is thus considered the most efficient of the four operating modes.

Numerical analysis of the three-dimensional blood flow in the korean artificial heart.

Flow in the blood sac of the Korean artificial heart is numerically simulated by finite element method. Fluid-structure interaction algorithm is employed to compute the three-dimensional blood flow interacting with the sac material. For verification of the numerical method of fluid-structure interaction, two-dimensional flow in a collapsible channel with initial tension is simulated and the results are compared with numerical solutions from the literature. Incompressible viscous flow and linear elastic solid are assumed for the blood and the sac material in the device, respectively. The motion of the actuator is simplified by a time-varying pressure boundary condition imposed on the outer surface of the sac. Numerical solutions on the unsteady three-dimensional blood flow in the sac are provided for the cactus-type model in this study. During systole, the inlet is closed and the blood sac is squeezed by the action of the prescribed pressure on the surface. During diastole, the sac is filled with the blood coming from the inlet while the outlet is closed. A strong flow to the outlet and a stagnated flow near the inlet are observed during systole. Shear stress distribution is also delineated to assess the possibility of thrombus formation. We also simulate numerically the hemodynamics of "the reversed model" where the inlet and outlet are reversed for surgical convenience. It is observed that a recirculating flow was generated near the inner corner of the sac in the reversed model. To assess the material strength of the sac, the shear stress distribution in the solid material is also presented.