Tomografía de impedancia eléctrica: fundamentos de hardware y aplicaciones médicas

Introduction: The following article shows a systematic review of publications on hardware topologies used to capture and process electrical signals used in Electrical Impedance Tomography (EIT) in medical applications, as well topicality of the EIT in the field of biomedicine. This work is the product of the research project “Electrical impedance tomography based on mixed signal devices”, which took place at the University of Cauca during the period 2017-2019. Objective: This review describes the operation, topicality and clinical use of Electrical Impedance Tomography systems. Methodology: A systematic review was carried out in the IEEE-Xplore, ScienceDirect and Scopus databases. After the classification, 106 relevant articles were obtained on scientific studies of EIT systems; applications dedicated to the analysis of medical images. Conclusions: Impedance-based methods have a variety of medical applications as they allow for the reconstruction of a body region, by estimating the conductivity distribution inside the human body; this is without exposing the patient to the damaging effects of radiation and contrast elements. Impedance-based methods are therefore a very useful and versatile tool in the treatment of diseases such as: monitoring blood pressure, detection of atherosclerosis, localization of intracranial hemorrhages, determining bone density, among others. Originality: It describes the necessary components to design an EIT system, as well as the design characteristics depending on the pathology to be visualized.  Introducción: En el siguiente artículo se muestra una revisión sistemática de publicaciones sobre topologías hardware utilizadas para capturar y procesar señales eléctricas utilizadas en tomografía por impedancia eléctrica (TIE) en aplicaciones médicas, así como la actualidad del TIE en el campo de la biomedicina. Este trabajo es producto del proyecto de investigación “Tomografía de impedancia eléctrica basada en dispositivo de señal mixta”, que tiene lugar en la Universidad del Cauca durante el período 2017-2019.   Objetivo: Esta revisión describe la estructura hardware de los sistemas de TIE, además de sus características, como frecuencia y magnitud de señales de corriente, patrones de inyección y medición de señales y número de electrodos orientado a, uso clínico.   Metodología: Se realizó una revisión sistemática, en las bases de datos IEEE-Xplore, ScienceDirect y Scopus. Tras la clasificación se obtuvo 106 artículos relevantes sobre estudios científicos de sistemas, aplicaciones dedicadas al análisis de imágenes médicas.   Conclusión: Los métodos basados en impedancia, tienen una variedad de aplicaciones médicas, puesto que permite la reconstrucción de una región corporal, mediante la estimación de la distribución de conductividad al interior del cuerpo humano, sin radiación y elementos de contraste, tan perjudiciales para la salud de los pacientes; convirtiéndola en una herramienta muy útil y versátil en el tratamiento de enfermedades como: monitorear la presión arterial, detección de arterosclerosis, localización de hemorragias intracraneales, determinar la densidad ósea, entre otras.     &nbsp

Interventional Pulmonology and Pulmonary Hypertension

This book, published by IntechOpen, focuses on interesting aspects of pulmonary medicine. The first section of the book is dedicated to interventional pulmonology, and includes updates on bronchial thermoplasty, virtual bronchoscopy, and endobronchial ultrasound. The second section highlights special aspects of pulmonary circulation and pulmonary hypertension. Throughout the book, the authors offer us not only a "vigorous" review of the current literature but also a research path to further advancement

Anterior-posterior impedance cardiography: a new approach to accurate, non-invasive monitoring of cardiac function

The conventional impedance cardiogram is a record of pulsatile changes in the electrical impedance of the chest with each heartbeat. The signal seems intuitively related to cardiac stroke volume. However doubts persist about the validity of stroke volume measurements based on electrical impedance. This paper presents a new electrical axis for impedance cardiography that is perpendicular to the conventional head-to-foot axis in an anterior-posterior direction. Dual chest and back electrodes are concentric, permitting tetrapolar technique. A relatively simple analytical model is developed, and this model is validated in a three-dimensional finite element model of current flow through the human chest. Three-dimensional simulations show predictable relationships between the fractional increase in anterior-posterior chest impedance and the ventricular ejection fraction (cardiac stroke volume / ventricular end-diastolic volume). Ejection fraction can be computed accurately with a roughly 30-fold increase in signal level compared to the conventional impedance cardiogram. Breathing causes only modest changes in the signal. When the axis of current flow is optimized, one can interpret the impedance changes during the cardiac cycle with greater confidence as a painless, noninvasive, beat-by-beat indicators of ventricular ejection fraction in a wide variety of clinical settings

Understanding cardiopulmonary interactions through esophageal pressure monitoring

Esophageal pressure is the closest estimate of pleural pressure. Changes in esophageal pressure reflect changes in intrathoracic pressure and affect transpulmonary pressure, both of which have multiple effects on right and left ventricular performance. During passive breathing, increasing esophageal pressure is associated with lower venous return and higher right ventricular afterload and lower left ventricular afterload and oxygen consumption. In spontaneously breathing patients, negative pleural pressure swings increase venous return, while right heart afterload increases as in passive conditions; for the left ventricle, end-diastolic pressure is increased potentially favoring lung edema. Esophageal pressure monitoring represents a simple bedside method to estimate changes in pleural pressure and can advance our understanding of the cardiovascular performance of critically ill patients undergoing passive or assisted ventilation and guide physiologically personalized treatments

What can computed tomography and magnetic resonance imaging tell us about ventilation?

This review provides a summary of pulmonary functional imaging approaches for determining pulmonary ventilation, with a specific focus on multi-detector x-ray computed tomography and magnetic resonance imaging (MRI). We provide the important functional definitions of pulmonary ventilation typically used in medicine and physiology and discuss the fact that some of the imaging literature describes gas distribution abnormalities in pulmonary disease that may or may not be related to the physiological definition or clinical interpretation of ventilation. We also review the current state-of-the-field in terms of the key physiological questions yet unanswered related to ventilation and gas distribution in lung disease. Current and emerging imaging research methods are described, including their strengths and the challenges that remain to translate these methods to more wide-spread research and clinical use. We also examine how computed tomography and MRI might be used in the future to gain more insight into gas distribution and ventilation abnormalities in pulmonary disease

Hyperpolarized Carbon-13 Magnetic Resonance Imaging As A Tool For Assessing Lung Transplantation Outcomes

Lung transplantation is the established treatment for patients with chronic, end-stage lung diseases such as chronic obstructive pulmonary disease (COPD), idiopathic pulmonary fibrosis (IPF) and cystic fibrosis (CF). However, its utility remains limited by the chronic shortage of donor lungs, limited lung preservation strategies and post-transplant complications leading to graft failure. Although efforts have been made to expand the limited pool of viable donor lungs via novel preservation strategies such as ex vivo lung perfusion (EVLP), our limited understanding of the mechanism and progression of donor lung injury continues to inhibit our ability to fully exploit these advances to improve lung transplant outcomes. Furthermore, the clinical standard for post-transplant assessment is limited to whole lung measurement such as pulmonary functional tests (PFTs) and structural imaging via radiography or HRCT, both of which lack the necessary sensitivity to detect lung rejection early. Given these limitations of currently available pre- and post-transplant lung assessment tools, a novel metabolic biomarker may provide higher sensitivity for determining the viability of donated lungs, as well as for assessing the onset of rejection before permanent structural changes in the lungs become apparent. We proposed that hyperpolarized (HP) [1-13C]pyruvate magnetic resonance imaging (MRI)—which provides real-time metabolic assessment of tissue based on the conversion of [1-13C] pyruvate to [1-13C]lactate via glycolysis, or to 13C bicarbonate via oxidative phosphorylation—may be an effective tool for assessing the health of donated lungs and may also serve as an early biomarker for detecting pulmonary graft dysfunction (PGD)-associated inflammation or acute lung rejection. In a rat model, we demonstrated the feasibility of using HP [1-13C]pyruvate nuclear magnetic resonance (NMR) spectroscopy to assess the viability of ex vivo perfused lungs. We further showed that our technique can be used to measure the improved viability of those lungs after treatment with ascorbic acid. Finally, translating our previously developed technique to in vivo HP [1-13C]pyruvate imaging of an inflamed rat lung, we not only demonstrated its utility for detecting lung transplantation rejection, but found that the HP lactate-to-pyruvate ratio is a better predictor of acute lung rejection in a rat model than computed tomography