James D. Sweeney

A cytokine immunosensor for Multiple Sclerosis detection based upon label-free electrochemical impedance spectroscopy using electroplated printed circuit board electrodes.

A biosensor for the serum cytokine, Interleukin-12 (IL-12), based upon a label-free electrochemical impedance spectroscopy (EIS) monitoring approach is described. Overexpression of IL-12 has been correlated to the diagnosis of Multiple Sclerosis (MS). An immunosensor has been fabricated by electroplating gold onto a disposable printed circuit board (PCB) electrode and immobilizing anti-IL-12 monoclonal antibodies (MAb) onto the surface of the electrode. This approach yields a robust sensor that facilitates reproducible mass fabrication and easy alteration of the electrode shape. Results indicate that this novel PCB sensor can detect IL-12 at physiological levels, <100 fM with f-values of 0.05 (typically <0.0001) in a label-free and rapid manner. A linear (with respect to log concentration) detectable range was achieved. Detection in a complex biological solution is also explored; however, significant loss of dynamic range is noted in the 100% complex solution. The cost effective approach described here can be used potentially for diagnosis of diseases (like MS) with known biomarkers in body fluids and for monitoring physiological levels of biomolecules with healthcare, food, and environmental relevance.

Finite Element Modeling of Electric Field Effects of TASER Devices on Nerve and Muscle

TASERs deliver electrical pulses that can temporarily incapacitate subjects. The goal of this paper is to analyze the distribution of currents in muscle layers and understand the electro-muscular incapacitation safety and efficacy of TASERs. The analyses describe skeletal muscle and motor nerve activation, cell electroporation and current and electric field distributions through skin, fat and muscle layers, under worst-case assumptions for TASER electrode penetration and separation. For the muscle layer, the analysis predicts worst-case current-density and field-strength values of 94 mA/cm2 and 47 V/cm. Both values are higher than thresholds required for neuromuscular activation but significantly lower than levels needed for permanent cellular electroporation or tissue damage. The results indicate that TASERs are safe and effective in producing temporary subject incapacitation

Theoretical comparisons of nerve and muscle activation by neuromuscular incapacitation devices

In this study important aspects of the TASER® M26™ and X26™ neuromuscular incapacitation device waveforms are simulated, analyzed and contrasted against electrical stimulation with rectangular waveforms (commonly used in therapeutic stimulation devices). Expected skeletal muscle forces evoked by M26™ and X26™ stimulation are simulated also and compared against forces expected with higher or lower frequency trains. The first half-cycle of the M26™ damped 50 kHz sinusoidal wave is the main contributor to stimulation threshold with this device. The pseudo-monophasic component of the X26™ waveform primarily determines threshold for this system, with the leading damped 100 kHz component contributing little in this regard. Simulated isometric forces evoked at 19 Hz with either device are moderately intense (about 46% of maximal). Lower frequencies would likely not provide sufficient levels of contraction to override volitional motor control.

Programmable arbitrary waveform generator for internal defibrillation research

A programmable arbitrary waveform generator for creation of experimental defibrillation shocks is described. The system is capable of delivering shocks for internal defibrillation via 10 channels at 1000 Volts and 30 Amps. A microcontroller driven system that can receive waveform commands from a laptop was designed to be able to deliver shocks to any combination of electrodes. Waveforms are controllable down to 100 microsecond intervals and each channel is capable of serving as anode or cathode. This system can be used to verify predictions for defibrillation waveform efficacy as predicted by modeling efforts or to test new experimental waveforms tuned to parameters from an individual subject.

Segmentation of 4D Cardiac Images: Investigation on Statistical Shape Models

The purpose of this research was two-fold: (1) to investigate the properties of statistical shape models constructed from manually segmented cardiac ventricular chambers to confirm the validity of an automatic 4-dimensional (4D) segmentation model that uses gradient vector flow (GVF) images of the original data and (2) to develop software to further automate the steps necessary in active shape model (ASM) training. These goals were achieved by first constructing ASMs from manually segmented ventricular models by allowing the user to cite entire datasets for processing using a GVF-based landmarking procedure and principal component analysis (PCA) to construct the statistical shape model. The statistical shape model of one dataset was used to regulate the segmentation of another dataset according to its GVF, and these results were then analyzed and found to accurately represent the original cardiac data when compared to the manual segmentation results as the golden standard

Rapid switching between transverse electrode pairs within a biphasic shock lowers implantable defibrillator thresholds

In order to minimize energy requirements and prolong the lifetime of implantable cardioverter-defibrillators (ICDs), it is necessary to optimize the delivered waveform without compromising defibrillation efficacy. Four electrodes were implanted on, in, and near the heart of nine pigs, Results indicate that by rapidly switching between sequential electrode pairs within each phase of a single biphasic shock 2, 4, or 8 times, significantly lower energies are needed for defibrillation.

Progressive pressure expansion in skeletal muscle ventricle conditioning.

Skeletal muscle ventricle (SMV) conditioning typically results in reduced muscle performance. This study investigated the effects of progressive SMV resting pressure expansion and dynamic muscle training on SMV pumping capability. SMVs were formed from latissimus dorsi muscle in five goats. Three experimental SMVs were conditioned against a compliant pneumatic implant system. SMV resting pressure was progressively increased as the SMV adapted to each increment. Resting pressure rose from 40 to 100-120 mmHg over an 8 week period of time. Two control SMVs were conditioned against a non expanded incompressible implant. Both experimental and control SMVs were electrically burst stimulated for at least 6 weeks after an initial 2 week vascular delay interval. Results demonstrate that 1) experimental SMVs increased in volume; 2) SMV passive and active (evoked isovolumetric pressure) pressure-volume curves adapted to the increasing or static resting volume; and 3) two of three experimental SMVs generated greater stroke volumes than control SMVs across a range of counterpulsation pressures and electrical stimulation parameters. Progressive pressure expansion using a compliant implant system improved final SMV pumping performance and merits further investigation.

Extended charge banking model of dual path shocks for implantable cardioverter defibrillators

BackgroundSingle path defibrillation shock methods have been improved through the use of the Charge Banking Model of defibrillation, which predicts the response of the heart to shocks as a simple resistor-capacitor (RC) circuit. While dual path defibrillation configurations have significantly reduced defibrillation thresholds, improvements to dual path defibrillation techniques have been limited to experimental observations without a practical model to aid in improving dual path defibrillation techniques.MethodsThe Charge Banking Model has been extended into a new Extended Charge Banking Model of defibrillation that represents small sections of the heart as separate RC circuits, uses a weighting factor based on published defibrillation shock field gradient measures, and implements a critical mass criteria to predict the relative efficacy of single and dual path defibrillation shocks.ResultsThe new model reproduced the results from several published experimental protocols that demonstrated the relative efficacy of dual path defibrillation shocks. The model predicts that time between phases or pulses of dual path defibrillation shock configurations should be minimized to maximize shock efficacy.DiscussionThrough this approach the Extended Charge Banking Model predictions may be used to improve dual path and multi-pulse defibrillation techniques, which have been shown experimentally to lower defibrillation thresholds substantially. The new model may be a useful tool to help in further improving dual path and multiple pulse defibrillation techniques by predicting optimal pulse durations and shock timing parameters.

Computer controlled circuitry for rapid switching between implanted electrodes during a biphasic defibrillation shock

Presents design and benchtop testing results for computer controlled circuitry that the authors have developed for rapid switching between ICD electrode pairs within a single biphasic shock-potentially yielding enhanced temporal and spatial summation of shock effects.

Circumferential switching between multiple electrode pairs within a biphasic shock lowers implantable defibrillator thresholds

In order to maximize the efficiency of implantable cardioverter-defibrillators (ICDs) it is important to optimize the waveform and electrode placement so as to minimize the energy necessary for successful defibrillation. We placed six electrodes in, near, and on pig hearts in order to explore the efficacy of dividing a biphasic waveform into a series of pulses delivered to four quadrants of the heart so as to more evenly distribute current. Each phase of the waveform was split into four or eight pulses. It was found that dividing the shock into pulses and distributing current around the heart reduced the average voltage and energy required for defibrillation.