Cardiac-related changes in lung resistivity as a function of frequency and location obtained from EITS images

Novel approach of processing electrical bioimpedance data using differential impedance analysis

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.

Determination of radial artery compliance can increase the diagnostic power of pulse wave velocity measurement

Pulse wave velocity (PWV) is an indicator associated with the arterial stiffness. Although this technique has been used in the diagnosis of systemic arterial hypertension (SAH), it cannot supply alone enough information about the pathogenesis of this disturbance. This paper aims to determine the compliance of brachial-radial arterial segment by applying a three-element windkessel model, and by using the same pressure waveforms acquired to calculate the PWV. The proposed method to determine the arterial compliance was evaluated with a physical simulation of the arterial system, where parameters were known, resulting in an estimation error of 0.73 x 10(-7) cm5 dyne(-1). In a clinical study the estimated compliance was statistically different (p < 0.01) in a controlled group ((3.12 +/- 3.53) x 10(-7) cm5 dyne(-1)) and in an SAH group ((1.04 +/- 0.74) x 10(-7) cm5 dyne(-1)). It was observed that the PWV value calculated using the maximum of the first derivative of the pressure waveform upstroke as characteristic points was the best correlated (r = -0.71) with the determined compliance. Because SAH normally results, among other causes. from a decreased arterial compliance the results suggest that the determined compliance could be used concomitantly with PWV to supply more diagnostic information about the pathogenesis of SAH.

Model for the dielectric properties of human lung tissue against frequency and air content

Electrical impedance tomographic spectroscopy measurements of the lungs are taken from nine normal subjects, in the frequency range 9.6 kHz-1.2 MHz. The results show that resistivity rho'FRC relative to functional residual capacity increases almost linearly with inspiration volume V, with the slope of the curve increasing with frequency f. Resistivity rho'9.6 kHz relative to 9.6 kHz decreases with f. rho'9.6 kHz increases with V, at any given frequency. Curves for rho'9.6 kHz show a roughly linear trend with log10(f). Based on a discussion of the measurement results, a mathematical lung tissue model is designed that involves extra-capillary blood vessels and alveoli, the walls of which consist of blood-filled capillaries, epithelial cells and intercellular liquid. Using this model, the increase in rho'FRC with V is explained by the thinning of alveolar walls with increasing air content. The almost linear shape of curves for rho'9.6 kHz is attributed to four partly overlapping main dispersions caused by extra-capillary blood vessels, epithelial cells, blood and the capillary network.

Modelling of cardiac-related changes in lung resistivity measured with EITS

Resistivity data from 9.6 kHZ to 1.2 MHz were recorded from eight normal subjects using an electrical impedance tomographic spectroscopy (EITS) system and then averaged to a mean cardiac cycle using the ECG gating technique. The Cole-Cole model, that is, extracellular resistance R connected in parallel with intracellular resistance S and membrane capacitance C in series, with a distribution parameter a, was applied to model the frequency characteristics and to produce parametric images. During systole, SC and RC were found to decrease and FR increase. The changes in R/S were not consistent among the subjects. We estimated the peak changes in R, S and C to be -2.5%, -3.3% and -7.6% respectively. The results can be explained by considering the blood vessels as spheres of different sizes with blood inside them. The decrease in R during systole might be caused by the increased blood content in relatively large vessels, whereas that in S by the increased blood volume in relatively small vessels. The capacitance of blood is normally smaller than that of lung tissue, whereas FR blood is higher than that of lung tissue. Hence, as blood content increases, C should decrease and FR increase.