A 3-Dimensional In Silico Test Bed for Radiofrequency Ablation Catheter Design Evaluation and Optimization

Atrial fibrillation (AF) is the disordered activation of the atrial myocardium, which is a major cause of stroke. Currently, the most effective, minimally traumatic treatment for AF is percutaneous catheter ablation to isolate arrhythmogenic areas from the rest of the atrium. The standard in vitro evaluation of ablation catheters through lesion studies is a resource intensive effort due to tissue variability and visual measurement methods, necessitating large sample sizes and multiple prototype builds. A computational test bed for ablation catheter evaluation was built in SolidWorks® using the morphology and dimensions of the left atrium adjacent structures. From this geometry, the physical model was built in COMSOL Multiphysics®, where a combination of the laminar fluid flow, electrical currents, and bioheat transfer was used to simulate radiofrequency (RF) tissue ablation. Simulations in simplified 3D geometries led to lesions sizes within the reported ranges from an in-vivo ablation study. However, though the ellipsoid lesion morphologies in the full atrial model were consistent with past lesion studies, perpendicularly oriented catheter tips were associated with decreases of -91.3% and -70.0% in lesion depth and maximum diameter. On the other hand, tangentially oriented catheter tips produced lesions that were only off by -28.4% and +7.9% for max depth and max diameter. Preliminary investigation into the causes of the discrepancy were performed for fluid velocities, contact area, and other factors. Finally, suggestions for further investigation are provided to aid in determining the root cause of the discrepancy, such that the test bed may be used for other ablation catheter evaluations

Development of High Resolution Tools for Investigating Cardiac Arrhythmia Dynamics

Every year 300,000 Americans die due to sudden cardiac death. There are many pathologies, acquired and genetic, that can lead to sudden cardiac death. Regardless of the underlying pathology, death is frequently the result of ventricular tachycardia and/or fibrillation (VT/VF). Despite decades of research, the mechanisms of ventricular arrhythmia initiation and maintenance are still incompletely understood. A contributing factor to this lack of understanding is the limitations of the investigative tools used to study VT/VF. Arrhythmias are organ level phenomena that are governed by cellular interactions and as such, near cellular levels of resolution are needed to tease out their intricacies. They are also behaviors that are not limited by region, but dynamically affect the entirety of the heart. For these reasons, high-resolution methodologies capable of measuring electrophysiology of the whole entirety of the ventricles will play an important role in gaining a complete understanding of the principles that govern ventricular arrhythmia dynamics. They will also be essential in the development of novel therapies for arrhythmia management. In this dissertation, I first present the validation and characterization of a novel capacitive electrode design that overcomes the key limitations faced by modern implantable cardiac devices. I then outline the construction, methodologies, and open-source tools of an improved optical panoramic mapping system for small mammalian cardiac electrophysiology studies. I conclude with a small mammal study of the relationship between action potential duration restitution dynamics and the mechanisms of maintenance in ventricular arrhythmias

Abbott Lab Instrumentation Validation

Over the past 40 years, since the initial catheter ablation procedure was completed, cardiac mapping has become an essential part of electrophysiological procedures. Cardiac mapping is an electrophysiological study that allows physicians to analyze the electrical activity of the heart in order to diagnose and treat cardiovascular disease. Institutions like Cal Poly can utilize professional instrumentation systems with an appropriate wet lab to develop new devices and study various phenomena in an in-vitro physiological environment. Cardiac mapping systems used in tandem with catheter ablation procedures are essential to ensuring that the trend of deaths due to cardiovascular disease continues to decline. This project thesis will signify the importance of the development of a wet lab integrated with Abbott’s Ensite Precision Cardiac Mapping System for future product development and in-vitro studies

Atrial substrate characterization based on bipolar voltage electrograms acquired with multipolar, focal and mini-electrode catheters.

BACKGROUND Bipolar voltage (BV) electrograms for left atrial (LA) substrate characterization depend on catheter design and electrode configuration. AIMS The aim of the study was to investigate the relationship between the BV amplitude (BVA) using four catheters with different electrode design and to identify their specific LA cutoffs for scar and healthy tissue. METHODS AND RESULTS Consecutive high-resolution electroanatomic mapping was performed using a multipolar-minielectrode Orion catheter (Orion-map), a duo-decapolar circular mapping catheter (Lasso-map), and an irrigated focal ablation catheter with minielectrodes (Mifi-map). Virtual remapping using the Mifi-map was performed with a 4.5 mm tip-size electrode configuration (Nav-map). BVAs were compared in voxels of 3 × 3 × 3 mm3. The equivalent BVA cutoff for every catheter was calculated for established reference cutoff values of 0.1, 0.2, 0.5, 1.0, and 1.5 mV. We analyzed 25 patients (72% men, age 68 ± 15 years). For scar tissue, a 0.5 mV cutoff using the Nav corresponds to a lower cutoff of 0.35 mV for the Orion and of 0.48 mV for the Lasso. Accordingly, a 0.2 mV cutoff corresponds to a cutoff of 0.09 mV for the Orion and of 0.14 mV for the Lasso. For healthy tissue cutoff at 1.5 mV, a larger BVA cutoff for the small electrodes of the Orion and the Lasso was determined of 1.68 and 2.21 mV, respectively. CONCLUSION When measuring LA BVA, significant differences were seen between focal, multielectrode, and minielectrode catheters. Adapted cutoffs for scar and healthy tissue are required for different catheters

Thoracic Electrical Impedance Tomography—The 2022 Veterinary Consensus Statement

Electrical impedance tomography (EIT) is a non-invasive real-time non-ionising imaging modality that has many applications. Since the first recorded use in 1978, the technology has become more widely used especially in human adult and neonatal critical care monitoring. Recently, there has been an increase in research on thoracic EIT in veterinary medicine. Real-time imaging of the thorax allows evaluation of ventilation distribution in anesthetised and conscious animals. As the technology becomes recognised in the veterinary community there is a need to standardize approaches to data collection, analysis, interpretation and nomenclature, ensuring comparison and repeatability between researchers and studies. A group of nineteen veterinarians and two biomedical engineers experienced in veterinary EIT were consulted and contributed to the preparation of this statement. The aim of this consensus is to provide an introduction to this imaging modality, to highlight clinical relevance and to include recommendations on how to effectively use thoracic EIT in veterinary species. Based on this, the consensus statement aims to address the need for a streamlined approach to veterinary thoracic EIT and includes: an introduction to the use of EIT in veterinary species, the technical background to creation of the functional images, a consensus from all contributing authors on the practical application and use of the technology, descriptions and interpretation of current available variables including appropriate statistical analysis, nomenclature recommended for consistency and future developments in thoracic EIT. The information provided in this consensus statement may benefit researchers and clinicians working within the field of veterinary thoracic EIT. We endeavor to inform future users of the benefits of this imaging modality and provide opportunities to further explore applications of this technology with regards to perfusion imaging and pathology diagnosis

Thoracic Electrical Impedance Tomography—The 2022 Veterinary Consensus Statement

Electrical impedance tomography (EIT) is a non-invasive real-time non-ionising imaging modality that has many applications. Since the first recorded use in 1978, the technology has become more widely used especially in human adult and neonatal critical care monitoring. Recently, there has been an increase in research on thoracic EIT in veterinary medicine. Real-time imaging of the thorax allows evaluation of ventilation distribution in anesthetised and conscious animals. As the technology becomes recognised in the veterinary community there is a need to standardize approaches to data collection, analysis, interpretation and nomenclature, ensuring comparison and repeatability between researchers and studies. A group of nineteen veterinarians and two biomedical engineers experienced in veterinary EIT were consulted and contributed to the preparation of this statement. The aim of this consensus is to provide an introduction to this imaging modality, to highlight clinical relevance and to include recommendations on how to effectively use thoracic EIT in veterinary species. Based on this, the consensus statement aims to address the need for a streamlined approach to veterinary thoracic EIT and includes: an introduction to the use of EIT in veterinary species, the technical background to creation of the functional images, a consensus from all contributing authors on the practical application and use of the technology, descriptions and interpretation of current available variables including appropriate statistical analysis, nomenclature recommended for consistency and future developments in thoracic EIT. The information provided in this consensus statement may benefit researchers and clinicians working within the field of veterinary thoracic EIT. We endeavor to inform future users of the benefits of this imaging modality and provide opportunities to further explore applications of this technology with regards to perfusion imaging and pathology diagnosis

Computational design and optimization of electro-physiological sensors

Electro-physiological sensing devices are becoming increasingly common in diverse applications. However, designing such sensors in compact form factors and for high-quality signal acquisition is a challenging task even for experts, is typically done using heuristics, and requires extensive training. Our work proposes a computational approach for designing multi-modal electro-physiological sensors. By employing an optimization-based approach alongside an integrated predictive model for multiple modalities, compact sensors can be created which offer an optimal trade-off between high signal quality and small device size. The task is assisted by a graphical tool that allows to easily specify design preferences and to visually analyze the generated designs in real-time, enabling designer-in-the-loop optimization. Experimental results show high quantitative agreement between the prediction of the optimizer and experimentally collected physiological data. They demonstrate that generated designs can achieve an optimal balance between the size of the sensor and its signal acquisition capability, outperforming expert generated solutions

From wearable towards epidermal computing : soft wearable devices for rich interaction on the skin

Human skin provides a large, always available, and easy to access real-estate for interaction. Recent advances in new materials, electronics, and human-computer interaction have led to the emergence of electronic devices that reside directly on the user's skin. These conformal devices, referred to as Epidermal Devices, have mechanical properties compatible with human skin: they are very thin, often thinner than human hair; they elastically deform when the body is moving, and stretch with the user's skin. Firstly, this thesis provides a conceptual understanding of Epidermal Devices in the HCI literature. We compare and contrast them with other technical approaches that enable novel on-skin interactions. Then, through a multi-disciplinary analysis of Epidermal Devices, we identify the design goals and challenges that need to be addressed for advancing this emerging research area in HCI. Following this, our fundamental empirical research investigated how epidermal devices of different rigidity levels affect passive and active tactile perception. Generally, a correlation was found between the device rigidity and tactile sensitivity thresholds as well as roughness discrimination ability. Based on these findings, we derive design recommendations for realizing epidermal devices. Secondly, this thesis contributes novel Epidermal Devices that enable rich on-body interaction. SkinMarks contributes to the fabrication and design of novel Epidermal Devices that are highly skin-conformal and enable touch, squeeze, and bend sensing with co-located visual output. These devices can be deployed on highly challenging body locations, enabling novel interaction techniques and expanding the design space of on-body interaction. Multi-Touch Skin enables high-resolution multi-touch input on the body. We present the first non-rectangular and high-resolution multi-touch sensor overlays for use on skin and introduce a design tool that generates such sensors in custom shapes and sizes. Empirical results from two technical evaluations confirm that the sensor achieves a high signal-to-noise ratio on the body under various grounding conditions and has a high spatial accuracy even when subjected to strong deformations. Thirdly, Epidermal Devices are in contact with the skin, they offer opportunities for sensing rich physiological signals from the body. To leverage this unique property, this thesis presents rapid fabrication and computational design techniques for realizing Multi-Modal Epidermal Devices that can measure multiple physiological signals from the human body. Devices fabricated through these techniques can measure ECG (Electrocardiogram), EMG (Electromyogram), and EDA (Electro-Dermal Activity). We also contribute a computational design and optimization method based on underlying human anatomical models to create optimized device designs that provide an optimal trade-off between physiological signal acquisition capability and device size. The graphical tool allows for easily specifying design preferences and to visually analyze the generated designs in real-time, enabling designer-in-the-loop optimization. Experimental results show high quantitative agreement between the prediction of the optimizer and experimentally collected physiological data. Finally, taking a multi-disciplinary perspective, we outline the roadmap for future research in this area by highlighting the next important steps, opportunities, and challenges. Taken together, this thesis contributes towards a holistic understanding of Epidermal Devices}: it provides an empirical and conceptual understanding as well as technical insights through contributions in DIY (Do-It-Yourself), rapid fabrication, and computational design techniques.Die menschliche Haut bietet eine große, stets verfügbare und leicht zugängliche Fläche für Interaktion. Jüngste Fortschritte in den Bereichen Materialwissenschaft, Elektronik und Mensch-Computer-Interaktion (Human-Computer-Interaction, HCI) [so that you can later use the Englisch abbreviation] haben zur Entwicklung elektronischer Geräte geführt, die sich direkt auf der Haut des Benutzers befinden. Diese sogenannten Epidermisgeräte haben mechanische Eigenschaften, die mit der menschlichen Haut kompatibel sind: Sie sind sehr dünn, oft dünner als ein menschliches Haar; sie verformen sich elastisch, wenn sich der Körper bewegt, und dehnen sich mit der Haut des Benutzers. Diese Thesis bietet, erstens, ein konzeptionelles Verständnis von Epidermisgeräten in der HCI-Literatur. Wir vergleichen sie mit anderen technischen Ansätzen, die neuartige Interaktionen auf der Haut ermöglichen. Dann identifizieren wir durch eine multidisziplinäre Analyse von Epidermisgeräten die Designziele und Herausforderungen, die angegangen werden müssen, um diesen aufstrebenden Forschungsbereich voranzubringen. Im Anschluss daran untersuchten wir in unserer empirischen Grundlagenforschung, wie epidermale Geräte unterschiedlicher Steifigkeit die passive und aktive taktile Wahrnehmung beeinflussen. Im Allgemeinen wurde eine Korrelation zwischen der Steifigkeit des Geräts und den taktilen Empfindlichkeitsschwellen sowie der Fähigkeit zur Rauheitsunterscheidung festgestellt. Basierend auf diesen Ergebnissen leiten wir Designempfehlungen für die Realisierung epidermaler Geräte ab. Zweitens trägt diese Thesis zu neuartigen Epidermisgeräten bei, die eine reichhaltige Interaktion am Körper ermöglichen. SkinMarks trägt zur Herstellung und zum Design neuartiger Epidermisgeräte bei, die hochgradig an die Haut angepasst sind und Berührungs-, Quetsch- und Biegesensoren mit gleichzeitiger visueller Ausgabe ermöglichen. Diese Geräte können an sehr schwierigen Körperstellen eingesetzt werden, ermöglichen neuartige Interaktionstechniken und erweitern den Designraum für die Interaktion am Körper. Multi-Touch Skin ermöglicht hochauflösende Multi-Touch-Eingaben am Körper. Wir präsentieren die ersten nicht-rechteckigen und hochauflösenden Multi-Touch-Sensor-Overlays zur Verwendung auf der Haut und stellen ein Design-Tool vor, das solche Sensoren in benutzerdefinierten Formen und Größen erzeugt. Empirische Ergebnisse aus zwei technischen Evaluierungen bestätigen, dass der Sensor auf dem Körper unter verschiedenen Bedingungen ein hohes Signal-Rausch-Verhältnis erreicht und eine hohe räumliche Auflösung aufweist, selbst wenn er starken Verformungen ausgesetzt ist. Drittens, da Epidermisgeräte in Kontakt mit der Haut stehen, bieten sie die Möglichkeit, reichhaltige physiologische Signale des Körpers zu erfassen. Um diese einzigartige Eigenschaft zu nutzen, werden in dieser Arbeit Techniken zur schnellen Herstellung und zum computergestützten Design von multimodalen Epidermisgeräten vorgestellt, die mehrere physiologische Signale des menschlichen Körpers messen können. Die mit diesen Techniken hergestellten Geräte können EKG (Elektrokardiogramm), EMG (Elektromyogramm) und EDA (elektrodermale Aktivität) messen. Darüber hinaus stellen wir eine computergestützte Design- und Optimierungsmethode vor, die auf den zugrunde liegenden anatomischen Modellen des Menschen basiert, um optimierte Gerätedesigns zu erstellen. Diese Designs bieten einen optimalen Kompromiss zwischen der Fähigkeit zur Erfassung physiologischer Signale und der Größe des Geräts. Das grafische Tool ermöglicht die einfache Festlegung von Designpräferenzen und die visuelle Analyse der generierten Designs in Echtzeit, was eine Optimierung durch den Designer im laufenden Betrieb ermöglicht. Experimentelle Ergebnisse zeigen eine hohe quantitative Übereinstimmung zwischen den Vorhersagen des Optimierers und den experimentell erfassten physiologischen Daten. Schließlich skizzieren wir aus einer multidisziplinären Perspektive einen Fahrplan für zukünftige Forschung in diesem Bereich, indem wir die nächsten wichtigen Schritte, Möglichkeiten und Herausforderungen hervorheben. Insgesamt trägt diese Arbeit zu einem ganzheitlichen Verständnis von Epidermisgeräten bei: Sie liefert ein empirisches und konzeptionelles Verständnis sowie technische Einblicke durch Beiträge zu DIY (Do-It-Yourself), schneller Fertigung und computergestützten Entwurfstechniken

The Assessment and Reduction of Motion Artifact in Dry Contact Biopotential Electrodes

The connecting interface between biopotential monitoring systems and the human body is the electrode. Conventional medical electrodes use gel to improve skin-electrode contact and glue to provide secure attachment of the electrode to the skin. However, this type of electrode is neither reusable nor user-friendly when implemented in wearable monitoring systems. For wearable monitoring systems, the best type of electrode to use, as seen from the point of view of user comfort and ease of use of the wearable system, is the un-gelled electrode. The un-gelled electrode foregoes conductive gel and attachment glue and instead uses body moisture and clothing pressure to provide contact and secure attachment. The drawback of un-gelled electrodes is that they are susceptible to the wearer’s movements, namely, to motion artifact.Solving the issue of motion artifact will improve signal quality and reliability for wearable systems and, due to integration and reusability, would reduce costs. These two factors, when combined, would enable the widespread use of wearable monitoring systems in both the medical context and the consumer-user context. One effect of this will be a reduction in load and costs on health care systems due to improved preventive monitoring and better monitoring of patients in the recovery and rehabilitation phase. A second effect, combined with the information exchanging channels between individuals, will be unforeseen developments in health science due to what can be called the crowdsourcing of some aspect of physical and mental health and fitness.This thesis aims to further state-of-the art wearable physiological monitoring by aiding motion artifact research and electrode design. To accomplish this aim, investigations into the programmable and repeatable generation of electrode movement in order to generate motion artifact, the effect of impedance current frequency on the relationship between skin-electrode interface impedance and electrode movement and motion artifact, the effect of using an electrode support structure and how its design affects the motion artifact, and the effects of garment parameters such as tightness are presented in this thesis.A system that generates known and programmable motion of the electrode under controlled circumstances was designed, tested, and after the verification of system functionality, used in subsequent investigations. The presented system generates accurate motion of the electrode and the electrode motion can be observed as both motion artifact and skin-electrode impedance changes.A real time impedance spectroscopy study of 24 impedance current frequencies between 25 Hz and 1 MHz was done on electrodes subject to accurately known motion generated by the designed system in order to find the impedance current frequencies most suited to motion artifact studies.During this research, a hypothesis was formed that states that an electrode with a structural design that restricts epidermis deformation by trapping the epidermis under the electrode area can reduce motion artifact. Different electrode support structures were designed in order to test this hypothesis. The electrodes with support structures were subjected to system-generated motion and the resulting data were analyzed for the verification of support structure functionality and the hypothesis.Electrodes that were supported by a tight garment-mimicking elastic straps were studied under subjectgenerated movement and at various clothing tightness levels. The same study was used to understand the effect of using padding between the garment and the electrode.The motion artifact generation system was seen to be successful in accurately generating electrode motion, thus motion artifact, which was programmable and repeatable. The electrode mounting force monitoring proved to be an important functionality as the mounting force was seen to affect the motion artifact.Skin-electrode impedance was found to correlate well with electrode motion in current frequencies between 17 kHz and 1 MHz. While the correlation between impedance and motion artifact was lower than the correlation between impedance and electrode motion, it was also highest in this frequency band.Electrode support structure design is seen to be an important factor to consider when designing the electrode, and the electrodes that came closest to fulfilling the design criteria of the hypothesis were the best functioning electrodes. The hypothesis is seen to be promising and electrodes that distributed skin deformation over a large area and/or restrict epidermis deformation were found to reduce motion artifact.In the presented studies, the pressures under those electrodes that were found to be the most effective in reducing motion artifact differed between experiments yet stayed in a range between 5 mmHg -36 mmHg (0.66 kPa – 4.80 kPa). A simple guideline is that the electrode should be attached firmly but not so firmly that it becomes uncomfortable. This guideline fitted well with the pressure levels found for each experiment.The presented Motion Artifact Generation and Assessment System can be used for research or commercial purposes, furthering the research on motion artifact and aiding in the successful design of motion artifact resilient electrodes. The issue of which are the best current frequencies to use to measure skin-electrode interface impedance in motion artifact research has been clarified. Possible means of reducing motion artifact at its origin by using structural electrode designs that restrict epidermis deformation is hypothesized and proven worthy of further research. The importance of garment design and guidelines for use are given and tightness recommendations presented. The thesis presents methodology for the furthering of the understanding of motion artifact and electrode design that will eventually make wearable monitoring systems widespread over a large range of applications and a large number of users