RESUMEN
The forced oscillation technique (FOT) is a non-invasive method to measure the respiratory impedance Z, defined as the complex ratio of transrespiratory pressure P to the airflow at the airway opening Q as a function of frequency. FOT determines Z by superimposing small amplitude pressure oscillations on the normal breathing and measuring the resulting air flow. In this work a new approach for the analysis of the respiratory impedance Z at low frequencies (0.1-5 Hz) during spontaneous breathing is presented. When the respiratory impedance is measured in frequency ranges that overlap with the frequency of spontaneous breathing (0.1-1 Hz), the measured air flow will contain both the breathing of the patient and the response of the respiratory impedance to the pressure oscillations. A nonlinear estimator is developed which is able to separate the breathing signal from the respiratory response in order to obtain the respiratory impedance. The estimated results are used to obtain accurate estimates of airway and tissue components of a constant phase model.
Asunto(s)
Fisiología/métodos , Respiración , Algoritmos , Simulación por Computador , Impedancia Eléctrica , Humanos , Pulmón/fisiologíaRESUMEN
The goal of this manuscript is to present a new methodology for real time analysis of time-varying electrical bioimpedance data. The approach assumes that the Fricke-Morse model of living tissues is meaningful and valid within the measured frequency range (10 kHz to 1 MHz). The parameters of this model are estimated in the whole frequency range with the presented method based on differential impedance analysis (DIA). The numerical accuracy of the developed approach has been validated and compared to complex nonlinear least square (CNLS) approach through simulations and also with experimental data from in vivo time-varying human lung tissue bioimpedance. The new developed method has demonstrated a promising performance for fast and easily interpretable information in real time.
Asunto(s)
Espectroscopía Dieléctrica/métodos , Impedancia Eléctrica , Humanos , Análisis de los Mínimos Cuadrados , Pulmón/citología , Factores de Tiempo , Supervivencia TisularRESUMEN
Lung biopsies form the basis for the diagnosis of lung cancer. However, in a significant number of cases bronchoscopic lung biopsies fail to provide useful information, especially in diffuse lung disease, so more aggressive procedures are required. Success could be improved using a guided electronic biopsy based on multisine electrical impedance spectroscopy (EIS), a technique which is evaluated in this paper. The theoretical basis of the measurement method and the instrument developed are described, characterized and calibrated while the performance of the instrument is assessed by experiments to evaluate the noise and nonlinear source of errors from measurements on phantoms. Additional preliminary results are included to demonstrate that it is both feasible and safe to monitor in vivo human lung tissue electrical bioimpedance (EBI) during the bronchoscopy procedure. The time required for performing bronchoscopy is not extended because the bioimpedance measurements, present no complications, tolerance problems or side effects among any of the patients measured.
Asunto(s)
Broncoscopía , Espectroscopía Dieléctrica , Pulmón/citología , Anciano , Calibración , Impedancia Eléctrica , Estudios de Factibilidad , Femenino , Humanos , Pulmón/patología , Masculino , Persona de Mediana Edad , Factores de TiempoRESUMEN
Classical measurements of myocardium tissue electrical impedance for characterizing the morphology of myocardium cells, as well as cell membranes integrity and intra/extra cellular spaces, are based on the frequency-sweep electrical impedance spectroscopy (EIS) technique. In contrast to the frequency-sweep EIS approach, measuring with broadband signals, i.e., multisine excitations, enables to collect, simultaneously, multiple myocardium tissue impedance data in a short measuring time. However, reducing the measuring time makes the measurements to be prone to the influence of the transients introduced by noise and the dynamic time-varying properties of tissue. This paper presents a novel approach for the impedance-frequency-response estimation based on the local polynomial method (LPM). The fast LPM version presented rejects the leakage error's influence on the impedance frequency response when measuring electrical bioimpedance in a short time. The theory is supported by a set of validation measurements. Novel preliminary experimental results obtained from real-time in vivo healthy myocardium tissue impedance characterization within the cardiac cycle using multisine excitation are reported.
Asunto(s)
Espectroscopía Dieléctrica/métodos , Corazón/fisiología , Procesamiento de Señales Asistido por Computador , Animales , Femenino , Modelos Cardiovasculares , Análisis de Regresión , Reproducibilidad de los Resultados , Relación Señal-Ruido , PorcinosRESUMEN
Measurements of myocardium tissue impedance during the cardiac cycle have information about the morphology of myocardium cells as well as cell membranes and intra/extra cellular spaces. Although the variation with time of the impedance cardiac signal has information about the myocardium tissue activity during the cardiac cycle, this information has been usually underestimated in the studies based on frequency-sweep Electrical Impedance Spectroscopy (EIS) technique. In these cases, the dynamic behavior was removed from the impedance by means of averaging. The originality of this research is to show the time evolution of in-vivo healthy myocardium tissue impedance during the cardiac cycle, being measured with a multisine excitation at 26 frequencies (1 kHz-1 MHz). The obtained parameters from fitting data to a Cole model are valid indicators to explain the time relation of the systolic and diastolic function with respect to the myocardium impedance time variation. This paper presents a successful application of broadband Impedance Spectroscopy for time-varying impedance monitoring. Furthermore, it can be extended to understand various unsolved problems in a wide range of biomedical and electrochemical applications, where the system dynamics are intended to be studied.
Asunto(s)
Espectroscopía Dieléctrica/métodos , Impedancia Eléctrica , Corazón/fisiología , HumanosRESUMEN
Electrical Impedance Spectroscopy (EIS) is a powerful tool to collect data from many biological materials in a wide variety of applications. Body composition fluid or tissue and organ state monitoring are just some examples of these applications. While the classical EIS is based on frequency sweep, the EIS technique using broadband excitations allows to acquire simultaneous impedance spectrum data. The strength and weakness of broadband EIS relies on the fact that it enables multiple Electrical Bio-Impedance (EBI) data collection in a short measuring time but at the cost of losing impedance spectrum accuracy. In general, there is a relationship between the broadband excitation time/frequency properties and the final EBI's accuracy obtained. This paper studies the influence of the multisine broadband excitation amplitude's design over the EBI accuracy by means of the resultant Noise-to-Signal Ratio (NSR) obtained when measuring with a custom impedance analyzer. Theory has been supported by a set of validation experiments.