Showing papers by "Nigel H. Lovell published in 2013"

Performance of conducting polymer electrodes for stimulating neuroprosthetics.

Abstract: Objective. Recent interest in the use of conducting polymers (CPs) for neural stimulation electrodes has been growing; however, concerns remain regarding the stability of coatings under stimulation conditions. These studies examine the factors of the CP and implant environment that affect coating stability. The CP poly(ethylene dioxythiophene) (PEDOT) is examined in comparison to platinum (Pt), to demonstrate the potential performance of these coatings in neuroprosthetic applications. Approach. PEDOT is coated on Pt microelectrode arrays and assessed in vitro for charge injection limit and long-term stability under stimulation in biologically relevant electrolytes. Physical and electrical stability of coatings following ethylene oxide (ETO) sterilization is established and efficacy of PEDOT as a visual prosthesis bioelectrode is assessed in the feline model. Main results. It was demonstrated that PEDOT reduced the potential excursion at a Pt electrode interface by 72% in biologically relevant solutions. The charge injection limit of PEDOT for material stability was found to be on average 30× larger than Pt when tested in physiological saline and 20× larger than Pt when tested in protein supplemented media. Additionally stability of the coating was confirmed electrically and morphologically following ETO processing. It was demonstrated that PEDOT-coated electrodes had lower potential excursions in vivo and electrically evoked potentials (EEPs) could be detected within the visual cortex. Significance. These studies demonstrate that PEDOT can be produced as a stable electrode coating which can be sterilized and perform effectively and safely in neuroprosthetic applications. Furthermore these findings address the necessity for characterizing in vitro properties of electrodes in biologically relevant milieu which mimic the in vivo environment more closely.

Developments in control systems for rotary left ventricular assist devices for heart failure patients: a review.

Abstract: From the moment of creation to the moment of death, the heart works tirelessly to circulate blood, being a critical organ to sustain life. As a non-stopping pumping machine, it operates continuously to pump blood through our bodies to supply all cells with oxygen and necessary nutrients. When the heart fails, the supplement of blood to the body's organs to meet metabolic demands will deteriorate. The treatment of the participating causes is the ideal approach to treat heart failure (HF). As this often cannot be done effectively, the medical management of HF is a difficult challenge. Implantable rotary blood pumps (IRBPs) have the potential to become a viable long-term treatment option for bridging to heart transplantation or destination therapy. This increases the potential for the patients to leave the hospital and resume normal lives. Control of IRBPs is one of the most important design goals in providing long-term alternative treatment for HF patients. Over the years, many control algorithms including invasive and non-invasive techniques have been developed in the hope of physiologically and adaptively controlling left ventricular assist devices and thus avoiding such undesired pumping states as left ventricular collapse caused by suction. In this paper, we aim to provide a comprehensive review of the developments of control systems and techniques that have been applied to control IRBPs.

Erratum to “Optimisation of a Generic Ionic Model of Cardiac Myocyte Electrical Activity”

Abstract: A generic cardiomyocyte ionic model, whose complexity lies between a simple phenomenological formulation and a biophysically detailed ionic membrane current description, is presented.Themodel provides a user-defined number of ionic currents, employing two-gate Hodgkin-Huxley type kinetics. Its generic nature allows accurate reconstruction of action potential waveforms recorded experimentally from a range of cardiac myocytes. Using a multiobjective optimisation approach, the generic ionic model was optimised to accurately reproduce multiple action potential waveforms recorded from central and peripheral sinoatrial nodes and right atrial and left atrial myocytes from rabbit cardiac tissue preparations, under different electrical stimulus protocols and pharmacological conditions. When fitted simultaneously to multiple datasets, the time course of several physiologically realistic ionic currents could be reconstructed. Model behaviours tend to be well identified when extra experimental information is incorporated into the optimisation.

Current steering in retinal stimulation via a quasimonopolar stimulation paradigm.

Abstract: PURPOSE Research to restore some degree of vision to patients suffering from retinal degeneration is becoming increasingly more promising. Several groups have chosen electrical stimulation of the remaining network of a degenerate retina as a means to generate discrete light percepts (phosphenes). Approaches vary significantly, with the greatest difference being the location of the stimulating electrode itself. METHODS Suprachoroidal positioning offers excellent mechanical stability and surgical simplicity; however, at the cost of activation thresholds and focused stimulation due to the distance from the electrodes to the target neurons. Past studies proposed a hexapolar electrode configuration to focus the cortical activation and minimize cross-talk between electrodes during concurrent stimulation. The high impedance nature of the choroid and pigment epithelium, however, cause current to shunt between the stimulating and return electrodes, resulting in even higher activation thresholds. In our study, we analyzed the effect of stimulating the feline retina using a quasimonopolar stimulation by simultaneously stimulating a hexapolar and distant monopolar return configurations. RESULTS Results of in vivo studies showed that quasimonopolar stimulation can be used to maintain the activation containment properties of hexapolar stimulation, while lowering the activation threshold to values almost equivalent to those of monopolar stimulation. CONCLUSIONS The optimal stimulus was found to be composed of a subthreshold monopolar stimulus combined with a suprathreshold hexapolar stimulation. This resulted in a decrease of activation threshold of 60% with respect to hexapolar alone, but with no discernible deleterious effect on the charge containment of a pure hexapolar stimulation.

Attaining higher resolution visual prosthetics: a review of the factors and limitations.

Abstract: Visual prosthetics is an expanding subfield of functional electrical stimulation which has gained increased interest recently in light of new advances in treatments and technology. These treatments and technology represent a major improvement over prior art, but are still subject to a host of limitations which are dependent on the manner in which one approaches the topic of visual prosthetics. These limitations pose new research challenges whose solutions are directly applicable to the well-being of blind individuals everywhere. In this review, we will outline and critically compare major current approaches to visual prosthetics, and in particular retinal prosthetics. Then, we will engage in an in-depth discussion of the limitations imposed by current technology, physics, and the underlying biology of the retina to highlight several of the challenges currently facing researchers.

A Simplified 3D Model of Whole Heart Electrical Activity and 12-Lead ECG Generation

Abstract: We present a computationally efficient three-dimensional bidomain model of torso-embedded whole heart electrical activity, with spontaneous initiation of activation in the sinoatrial node, incorporating a specialized conduction system with heterogeneous action potential morphologies throughout the heart. The simplified geometry incorporates the whole heart as a volume source, with heart cavities, lungs, and torso as passive volume conductors. We placed four surface electrodes at the limbs of the torso: V R , V L , V F and V GND and six electrodes on the chest to simulate the Einthoven, Goldberger-augmented and precordial leads of a standard 12-lead system. By placing additional seven electrodes at the appropriate torso positions, we were also able to calculate the vectorcardiogram of the Frank lead system. Themodel was able to simulate realistic electrocardiogram (ECG) morphologies for the 12 standard leads, orthogonal X, Y, and Z leads, as well as the vectorcardiogram under normal and pathological heart states. Thus, simplified and easy replicable 3D cardiac bidomain model offers a compromise between computational load and model complexity and can be used as an investigative tool to adjust cell, tissue, and whole heart properties, such as setting ischemic lesions or regions of myocardial infarction, to readily investigate their effects on whole ECG morphology.

Exercise studies in patients with rotary blood pumps: cause, effects, and implications for starling-like control of changes in pump flow

Abstract: This multicenter study examines in detail the spontaneous increase in pump flow at fixed speed that occurs in exercise. Eight patients implanted with the VentrAssist rotary blood pump were subjected to maximal and submaximal cycle ergometry studies, the latter being completed with patients supine and monitored with right heart catheter and echocardiography. Maximal exercise studies conducted in each patient at three different pump speeds on separate days established initially the magnitude and consistency of increases in pump flow that correlated well with changes in heart rate. However, there was considerable variation, coefficients of variation for mean heart rate and pump flow being 47.9 and 49.3%, respectively. Secondly, these studies indicated that increasing pump flows caused significant improvements in maximal exercise capacity. An increase of 2.1 L/min (35%) in maximum blood flow caused 12 W (16%) further increase in achievable work, 1.26 (9.3%) mL/kg/min in maximal oxygen uptake, and 2.3 (23%) mL/kg/min in anaerobic threshold. Mean increases in lactate were 0.85mm (24%), but mean B-type natiuretic peptide fell by 126mm, (-78%). From submaximal supine exercise studies, multiple linear regression of pump flow on factors thought to underlie the spontaneous increase in pump flow indicated that it was associated with increases in heart rate (P=0.039), pressure gradient across the left ventricle (P=0.032), and right atrial pressure (P=0.003). These changes have implications for the recently reported Starling-like controller for pump flow based on pump pulsatility values, which emulates the Starling curve relating pump output to left ventricular preload. Unmodified, the controller would not permit the full benefits of this effect to be afforded to patients implanted with rotary blood pumps. A modification to the pump control algorithm is proposed to eliminate this problem

A cardiovascular mathematical model of graded head-up tilt.

Abstract: A lumped parameter model of the cardiovascular system has been developed and optimized using experimental data obtained from 13 healthy subjects during graded head-up tilt (HUT) from the supine position to [Formula: see text]. The model includes descriptions of the left and right heart, direct ventricular interaction through the septum and pericardium, the systemic and pulmonary circulations, nonlinear pressure volume relationship of the lower body compartment, arterial and cardiopulmonary baroreceptors, as well as autoregulatory mechanisms. A number of important features, including the separate effects of arterial and cardiopulmonary baroreflexes, and autoregulation in the lower body, as well as diastolic ventricular interaction through the pericardium have been included and tested for their significance. Furthermore, the individual effect of parameter associated with heart failure, including LV and RV contractility, baseline systemic vascular resistance, pulmonary vascular resistance, total blood volume, LV diastolic stiffness and reflex gain on HUT response have also been investigated. Our fitted model compares favorably with our experimental measurements and published literature at a range of tilt angles, in terms of both global and regional hemodynamic variables. Compared to the normal condition, a simulated congestive heart failure condition produced a blunted response to HUT with regards to the percentage changes in cardiac output, stroke volume, end diastolic volume and effector response (i.e., heart contractility, venous unstressed volume, systemic vascular resistance and heart rate) with progressive tilting.

Spatially restricted electrical activation of retinal ganglion cells in the rabbit retina by hexapolar electrode return configuration

Abstract: Objective. Visual prostheses currently in development aim to restore some form of vision to patients suffering from diseases such as age-related macular degeneration and retinitis pigmentosa. Most rely on electrically stimulating inner retinal cells via electrodes implanted on or near the retina, resulting in percepts of light termed ?phosphenes?. Activation of spatially distinct populations of cells in the retina is key for pattern vision to be produced. To achieve this, the electrical stimulation must be localized, activating cells only in the direct vicinity of the stimulating electrode(s). With this goal in mind, a hexagonal return (hexapolar) configuration has been proposed as an alternative to the traditional monopolar or bipolar return configurations for electrically stimulating the retina. This study investigated the efficacy of the hexapolar configuration in localizing the activation of retinal ganglion cells (RGCs), compared to a monopolar configuration. Approach. Patch-clamp electrophysiology was used to measure the activation thresholds of RGCs in whole-mount rabbit retina to monopolar and hexapolar electrical stimulation, applied subretinally. Main results. Hexapolar activation thresholds for RGCs located outside the hex guard were found to be significantly (>2 fold) higher than those located inside the area of tissue bounded by the hex guard. The hexapolar configuration localized the activation of RGCs more effectively than its monopolar counterpart. Furthermore, no difference in hexapolar thresholds or localization was observed when using cathodic-first versus anodic-first stimulation. Significance. The hexapolar configuration may provide an improved method for electrically stimulating spatially distinct populations of cells in retinal tissue.

Living electrodes: Tissue engineering the neural interface

Abstract: Soft, cell integrated electrode coatings are proposed to address the problem of scar tissue encapsulation of stimulating neuroprosthetics. The aim of these studies was to prove the concept and feasibility of integrating a cell loaded hydrogel with existing electrode coating technologies. Layered conductive hydrogel constructs are embedded with neural cells and shown to both support cell growth and maintain electro activity. The safe charge injection limit of these electrodes was 8 times higher than conventional platinum (Pt) electrodes and the stiffness was four orders of magnitude lower than Pt. Future studies will determine the biological cues required to support stem cell differentiation from the electrode surface.

Numerical investigation of the effect of cannula placement on thrombosis.

Abstract: Despite the rapid advancement of left ventricular assist devices (LVADs), adverse events leading to deaths have been frequently reported in patients implanted with LVADs, including bleeding, infection, thromboembolism, neurological dysfunction and hemolysis. Cannulation forms an important component with regards to thrombus formation in assisted patients by varying the intraventricular flow distribution in the left ventricle (LV). To investigate the correlation between LVAD cannula placement and potential for thrombus formation, detailed analysis of the intraventricular flow field was carried out in the present study using a two way fluid structure interaction (FSI), axisymmetric model of a passive LV incorporating an inflow cannula. Three different cannula placements were simulated, with device insertion near the LV apex, penetrating one-fourth and mid-way into the LV long axis. The risk of thrombus formation is assessed by analyzing the intraventricular vorticity distribution and its associated vortex intensity, amount of stagnation flow in the ventricle as well as the level of wall shear stress. Our results show that the one-fourth placement of the cannula into the LV achieves the best performance in reducing the risk of thrombus formation. Compared to cannula placement near the apex, higher vortex intensity is achieved at the one-fourth placement, thus increasing wash out of platelets at the ventricular wall. One-fourth LV penetration produced negligible stagnation flow region near the apical wall region, helping to reduce platelet deposition on the surface of the cannula and the ventricular wall.

Development of nanoparticle film-based multi-axial tactile sensors for biomedical applications

Abstract: Tactile feedback in biomedical applications, e.g. prosthetic artificial skin and minimally invasive surgery, requires multi-axial detection capabilities, with high sensitivity and reliability. This paper presents the fabrication, modeling and experimental characterization of a novel nanoparticle resistive-based multi-axial sensor over the range of 0–300 mN for use in tactile feedback. The fabrication uses inkjet printing, and micro-molding techniques scalable to sub millimeter dimensions. Sensitivities of 0.037%/mN in the normal, 0.036%/mN in the shear x and 0.048%/mN shear y directions respectively were achieved. Dynamic characteristics indicated minimal change in hysteresis (standard deviation – 1.2%) and response (standard deviation – 0.4%) compared with the applied load for increasing strain-rates.

Estimation of cardiac output and systemic vascular resistance using a multivariate regression model with features selected from the finger photoplethysmogram and routine cardiovascular measurements.

Abstract: Cardiac output (CO) and systemic vascular resistance (SVR) are two important parameters of the cardiovascular system The ability to measure these parameters continuously and noninvasively may assist in diagnosing and monitoring patients with suspected cardiovascular diseases, or other critical illnesses In this study, a method is proposed to estimate both the CO and SVR of a heterogeneous cohort of intensive care unit patients (N=48) Spectral and morphological features were extracted from the finger photoplethysmogram, and added to heart rate and mean arterial pressure as input features to a multivariate regression model to estimate CO and SVR A stepwise feature search algorithm was employed to select statistically significant features Leave-one-out cross validation was used to assess the generalized model performance The degree of agreement between the estimation method and the gold standard was assessed using Bland-Altman analysis The Bland-Altman bias ±precision (196 times standard deviation) for CO was -001 ±270 L min-1 when only photoplethysmogram (PPG) features were used, and for SVR was -087 ±412 dynscm-5 when only one PPG variability feature was used These promising results indicate the feasibility of using the method described as a non-invasive preliminary diagnostic tool in supervised or unsupervised clinical settings

Electrical Stimulation of Inner Retinal Neurons in Wild-Type and Retinally Degenerate (rd/rd) Mice

Abstract: Electrical stimulation of the retina following photoreceptor degeneration in diseases such as retinitis pigmentosa and age-related macular degeneration has become a promising therapeutic strategy for the restoration of vision. Many retinal neurons remain functional following photoreceptor degeneration; however, the responses of the different classes of cells to electrical stimuli have not been fully investigated. Using whole-cell patch clamp electrophysiology in retinal slices we investigated the response to electrical stimulation of cells of the inner nuclear layer (INL), pre-synaptic to retinal ganglion cells, in wild-type and retinally degenerate (rd/rd) mice. The responses of these cells to electrical stimulation were extremely varied, with both extrinsic and intrinsic evoked responses observed. Further examination of the intrinsically evoked responses revealed direct activation of both voltage-gated Na+ channels and K+ channels. The expression of these channels, which is particularly varied between INL cells, and the stimulus intensity, appears to dictate the polarity of the eventual response. Retinally degenerate animals showed similar responses to electrical stimulation of the retina to those of the wild-type, but the relative representation of each response type differed. The most striking difference between genotypes was the existence of a large amplitude oscillation in the majority of INL cells in rd/rd mice (as previously reported) that impacted on the signal to noise ratio following electrical stimulation. This confounding oscillation may significantly reduce the efficacy of electrical stimulation of the degenerate retina, and a greater understanding of its origin will potentially enable it to be dampened or eliminated.

Polymer micro-fiber Bragg grating.

Abstract: Polymer micro-fibers with inscribed Bragg gratings are reported in this Letter. Starting with a single-mode polymer optical fiber and implementing a two-stage tapering process, a 16 μm diameter micro-fiber is fabricated and a Bragg grating is inscribed in it that exhibits a peak reflected wavelength circa 1530 nm. The growth dynamics of the polymer micro-fiber Bragg grating are also observed and analyzed. A maximum reflectivity of 5% is obtained after an exposure time of 3 min to a 50 mW power He-Cd laser of 325 nm wavelength. The temperature and strain characterization results of the micro-fiber Bragg grating with different diameters are also presented. Such polymer micro-fiber Bragg gratings can be used as sensors for high-sensitivity measurements in a number of application areas.

Simulation of a smart home environment

Abstract: This research will focus on options to reduce the complexity and cost of designing and evaluating smart homes by developing a residential environment and ambient sensor simulator that can respond to different movements of people. The map editor is used to create and save different types of floor plans, including existing furniture or appliances and to add ambient sensors in a 2-dimensional (2D) model. The WSN simulator provides the ability to simulate the resident's movement through the residential environment, as defined by the 2D model, and monitor how ambient sensors respond in a binary (on/off) manner to the resident's movement.

Design of Safe Two-Wire Interface-Driven Chip-Scale Neurostimulator for Visual Prosthesis

Abstract: Visual prostheses with a high number of electrodes are now of great research interest driven by the successful recent clinical trials. High channel devices are confronted with numerous challenges many of which can be addressed by adopting a multi-implant architecture. However now the difficulties lie in ensuring safety of the inter-implant interface by addressing the associated risks, often neglected in the past. This paper presents a multi-implant architecture-based 98-channel neurostimulator with an inter-implant interface consisting only of two wires, carrying both power and semi-duplex data. The interface is ac-coupled both to prevent high levels of dc current in the presence of insulation failures and to maintain a charge-balanced interface. The interface is also monitored within the stimulator itself for added means of safety. The stimulator is fabricated using a 0.35-μm HVCMOS technology and occupies 4.9 × 4.9 mm2 without any external discrete components, making it suitable for a chip-scale packaging.

Optimisation of a Generic Ionic Model of Cardiac Myocyte Electrical Activity

Abstract: A generic cardiomyocyte ionic model, whose complexity lies between a simple phenomenological formulation and a biophysically detailed ionic membrane current description, is presented. The model provides a user-defined number of ionic currents, employing two-gate Hodgkin-Huxley type kinetics. Its generic nature allows accurate reconstruction of action potential waveforms recorded experimentally from a range of cardiac myocytes. Using a multiobjective optimisation approach, the generic ionic model was optimised to accurately reproduce multiple action potential waveforms recorded from central and peripheral sinoatrial nodes and right atrial and left atrial myocytes from rabbit cardiac tissue preparations, under different electrical stimulus protocols and pharmacological conditions. When fitted simultaneously to multiple datasets, the time course of several physiologically realistic ionic currents could be reconstructed. Model behaviours tend to be well identified when extra experimental information is incorporated into the optimisation.

Cell-specific modeling of retinal ganglion cell electrical activity

Abstract: Variations in ionic channel expression and anatomical properties can influence how different retinal ganglion cell (RGC) types process synaptic information. Computational modeling approaches allow us to precisely control these biophysical and physical properties and isolate their effects in shaping RGC firing patterns. In this study, three models based on realistic representations of RGC morphologies were used to simulate the contribution of spatial structure of neurons and membrane ion channel properties to RGC electrical activity. In all simulations, the RGC models shared common ionic channel kinetics, differing only in their regional ionic channel distributions and cell morphology.

Optimisation of Ionic Models to Fit Tissue Action Potentials: Application to 3D Atrial Modelling

Abstract: A 3D model of atrial electrical activity has been developed with spatially heterogeneous electrophysiological properties. The atrial geometry, reconstructed from the male Visible Human dataset, included gross anatomical features such as the central and peripheral sinoatrial node (SAN), intra-atrial connections, pulmonary veins, inferior and superior vena cava, and the coronary sinus. Membrane potentials of myocytes from spontaneously active or electrically paced in vitro rabbit cardiac tissue preparations were recorded using intracellular glass microelectrodes. Action potentials of central and peripheral SAN, right and left atrial, and pulmonary vein myocytes were each fitted using a generic ionic model having three phenomenological ionic current components: one time-dependent inward, one time-dependent outward, and one leakage current. To bridge the gap between the single-cell ionic models and the gross electrical behaviour of the 3D whole-atrial model, a simplified 2D tissue disc with heterogeneous regions was optimised to arrive at parameters for each cell type under electrotonic load. Parameters were then incorporated into the 3D atrial model, which as a result exhibited a spontaneously active SAN able to rhythmically excite the atria. The tissue-based optimisation of ionic models and the modelling process outlined are generic and applicable to image-based computer reconstruction and simulation of excitable tissue.

Quasi-monopolar stimulation: a novel electrode design configuration for performance optimization of a retinal neuroprosthesis.

Abstract: In retinal neuroprostheses, spatial interaction between electric fields from various electrodes – electric crosstalk – may occur in multielectrode arrays during simultaneous stimulation of the retina. Depending on the electrode design and placement, this crosstalk can either enhance or degrade the functional characteristics of a visual prosthesis. To optimize the device performance, a balance must be satisfied between the constructive interference of crosstalk on dynamic range and power consumption and its negative effect on artificial visual acuity. In the present computational modeling study, we have examined the trade-off in these positive and negative effects using a range of currently available electrode array configurations, compared to a recently proposed stimulation strategy – the quasi monopolar (QMP) configuration – in which the return current is shared between local bipolar guards and a distant monopolar electrode. We evaluate the performance of the QMP configuration with respect to the implantation site and electrode geometry parameters. Our simulation results demonstrate that the beneficial effects of QMP are only significant at electrode-to-cell distances greater than the electrode dimensions. Possessing a relatively lower activation threshold, QMP was found to be superior to the bipolar configuration in terms of providing a relatively higher visual acuity. However, the threshold for QMP was more sensitive to the topological location of the electrode in the array, which may need to be considered when programming the manner in which electrode are simultaneously activated. This drawback can be offset with a wider dynamic range and lower power consumption of QMP. Furthermore, the ratio of monopolar return current to total return can be used to adjust the functional performance of QMP for a given implantation site and electrode parameters. We conclude that the QMP configuration can be used to improve visual information-to-stimulation mapping in a visual prosthesis, while maintaining low power consumption.

Sensitivity analysis of left ventricle with dilated cardiomyopathy in fluid structure simulation.

Abstract: Dilated cardiomyopathy (DCM) is the most common myocardial disease. It not only leads to systolic dysfunction but also diastolic deficiency. We sought to investigate the effect of idiopathic and ischemic DCM on the intraventricular fluid dynamics and myocardial wall mechanics using a 2D axisymmetrical fluid structure interaction model. In addition, we also studied the individual effect of parameters related to DCM, i.e. peak E-wave velocity, end systolic volume, wall compliance and sphericity index on several important fluid dynamics and myocardial wall mechanics variables during ventricular filling. Intraventricular fluid dynamics and myocardial wall deformation are significantly impaired under DCM conditions, being demonstrated by low vortex intensity, low flow propagation velocity, low intraventricular pressure difference (IVPD) and strain rates, and high-end diastolic pressure and wall stress. Our sensitivity analysis results showed that flow propagation velocity substantially decreases with an increase in wall stiffness, and is relatively independent of preload at low-peak E-wave velocity. Early IVPD is mainly affected by the rate of change of the early filling velocity and end systolic volume which changes the ventriculo:annular ratio. Regional strain rate, on the other hand, is significantly correlated with regional stiffness, and therefore forms a useful indicator for myocardial regional ischemia. The sensitivity analysis results enhance our understanding of the mechanisms leading to clinically observable changes in patients with DCM.

Detrended fluctuation analysis of blood pressure in preterm infants with intraventricular hemorrhage.

Abstract: Very preterm infants are at high risk of death and serious permanent brain damage, as occurs with intraventricular hemorrhage (IVH). Detrended fluctuation analysis (DFA) that quantifies the fractal correlation properties of physiological signals has been proposed as a potential method for clinical risk assessment. This study examined whether DFA of the arterial blood pressure (ABP) signal could derive markers for the identification of preterm infants who developed IVH. ABP data were recorded from a prospective cohort of 30 critically ill preterm infants in the first 1–3 h of life, 10 of which developed IVH. DFA was performed on the beat-to-beat sequences of mean arterial pressure (MAP), systolic blood pressure (SBP) and pulse interval, with short-term exponent (α 1, for timescale of 4–15 beats) and long-term exponent (α 2, for timescale of 15–50 beats) computed accordingly. The IVH infants were found to have higher short-term scaling exponents of both MAP and SBP (α 1 = 1.06 ± 0.18 and 0.98 ± 0.20) compared to the non-IVH infants (α 1 = 0.84 ± 0.25 and 0.78 ± 0.25, P = 0.017 and 0.038, respectively). The results have demonstrated that fractal dynamics embedded in the arterial pressure waveform could provide useful information that facilitates early identification of IVH in preterm infants.

Bidomain Modeling of Neural Tissue

Abstract: Computational models of excitable neural tissue provide a quantitative perspective in neurophysiology and neural engineering by coupling experimental observations with mathematical formulations. The reduction of complex neural systems into simplified mathematical descriptions provides a powerful tool to explore nature in which activation arises in neurons from extracellular stimulation. This quantitative approach is driven in part by therapeutic technologies which employ electrical stimulation to restore or improve function of damaged tissue, such as functional electrical stimulation. More recently in the area of neuroprostheses, implanted devices employing electrical stimulation have been used to restore varying degrees of sensory perception in deaf and blind patients [1–1]. In all these areas, an understanding of the mechanisms of excitation and propagation of neural activation is highly desirable. Mathematical models of electrical stimulation can help predict localized activation in desirable regions of tissue, and conversely regions where undesirable activation may occur.

Evaluation of suction detection during different pumping states in an implantable rotary blood pump.

Abstract: In recent times, the problem of noninvasive suction detection for implantable rotary blood pumps has attracted substantial research interest. Here, we compare the performance of various suction indices for different types of suction and non-suction events based on pump speed irregularity. A total of 171 different indices that consist of previously proposed as well as newly introduced suction indices are tested using regularized logistic regression. These indices can be classified as amplitude based (derived from the mean, maximum, and minimum values of a cycle), duration based (derived from the duration of a cycle), gradient based (derived from the first order as well as higher order differences) and frequency based (derived from the power spectral density). The non-suction event data consists of ventricular ejection with or without arrhythmia and intermittent and continuous non-opening of the aortic valve. The suction event data consists of partial ventricular collapse that occurs intermittently as well as continuously with or without arrhythmia. In addition, we also attempted to minimize the usage of multiple indices by applying the sequential forward floating selection method to find which combination of indices gives the best performance. In general, the amplitude-based and gradient-based indices performed quite well while the duration-based and frequency-based indices performed poorly. By having only two indices ([i] the maximum gradient change in positive slope; and [ii] the standard deviation of the maximum value in a cycle), we were able to achieve a sensitivity of 98.9% and a specificity of 99.7%.

Design of an unobtrusive system for fall detection in multiple occupancy residences

Abstract: A small trial was conducted to examine the feasibility of detecting falls using a combination of ambient passive infrared (PIR) and pressure mat (PM) sensors in a home with multiple occupants. The key tracking method made use of graph theoretical concepts to track each individual in the residence and to monitor them independently for falls. The proposed algorithm attempts to recognize falls where the subject experiences a hard fall on an indoor surface that leads to loss of consciousness or an inability to get up from the floor without assistance, due to severe injuries. The sensitivity, specificity and accuracy of the algorithm in detecting falls are 85.00%, 80.00% and 82.86%, respectively.

Physiological control of implantable rotary blood pumps for heart failure patients

Abstract: In general, patient variability and diverse environmental operation makes physiological control of a left ventricular assist device (LVAD) a complex and complicated problem. In this work, we implement a Starling-like controller which adjusts mean pump flow using pump flow pulsatility as the feedback parameter. The linear relationship between mean pump flow and pump flow pulsatility forms the desired flow of the Starling-like controller. A tracking control algorithm based on sliding mode control (SMC) has been implemented. The controller regulates the estimated mean pulsatile flow (Qp) and flow pulsatility (PIQp) generated from a model of the assist device. A lumped parameter model of the cardiovascular system (CVS) was used to test the control strategy. The immediate response of the controller was evaluated by inducing a fall in left ventricle (LV) preload following a reduction in circulating blood volume. The simulation supports the speed and robustness of the proposed strategy.

Design of a Decision Support System for a Home Telehealth Application

Abstract: A decision support system (DSS) that has been designed to manage patients using a home telehealth system is presented. The DSS has been developed to assist home telehealth clinical support staff with their workload, and to provide more effective communication between multiple home telehealth users. The three-tier system architecture that consists of a data layer; a business logic layer; and a front-end layer employs business processes and uses a rule engine for its logic and knowledge base. This paper discusses the design considerations involved in the construction of a DSS for the purpose of home telehealth, and illustrates how it may be developed using entirely open source software.