Time and Spatial Invariance of Impedance Signals in Limbs of Healthy Subjects by Time–Frequency Analysis

Abstract

The bioelectric impedance technique is a non-invasive method that provides the analysis of blood volume changes in the arteries. This is made possible by an interpretation of the impedance signal variations. In this paper, time and spatial variations of such impedance signals are studied on recordings made on limbs of 15 healthy subjects at rest. For that purpose, the scalogram of each signal has been computed and quantitative measures based on energies were determined. The results show that the signals are statistically time invariant on three anatomical segments of the limbs: pelvis, thigh and calf. p Value varies between 0.20 and 0.52 for the absolute energies computed on scalograms of signals recorded at 5 min intervals. Moreover, the analysis made on the two legs of each subject shows that the signals are spatial invariant on the three anatomical segments. p Value varies between 0.0785 and 1.000 for the absolute energies computed on the scalograms of signals recorded simultaneously on the two legs. These conclusions will therefore help the clinicians in studying the temporal variations of physiological parameters on limbs with the impedance technique. Moreover, the results on the spatial invariance make possible the comparisons of these parameters with those given by other acquisition techniques.

Assessment of aortic stiffness by local and regional methods

“…The electrodes were positioned along the main axis of the femoral artery to increase the signal-to-noise ratio 17 (see Figure 2). After appropriate signal filtering, IWV (in m s À1 ) between the ascending aorta and the femoral artery was derived from the following formula:…”

“…The local AoStiff index can also be assessed from recordings performed at the level of chest. 17,18 We performed the present study to compare the local AoStiff estimated by the BI technique with the regional methods, PWV and IWV.…”

Measurement of the local aortic stiffness by a non-invasive bioelectrical impedance technique

“…The BI signals were recorded in the chest by means of two pairs of surface ECG electrodes using a four-electrode impedance device (PhysioFlow PF-05 lab1, Manatec laboratories, France) [7]. Herein, a very low electrical current at high frequency (3.8 mA, 75 kHz) was administered through a first pair of electrodes (1 and 4) and the differential electrical potential was recorded by a second pair (3 and 4) (Fig.…”

“…Recently, a novel and simple method for the evaluation of the local aortic stiffness has been proposed [7,9]. This new method can be considered as a complementary technique to assess the elastic properties of the large arteries (i.e.…”

Modeling and interpretation of the bioelectrical impedance signal for the determination of the local arterial stiffness

“…The BI technique is a well-known technique for the measure-ment of the cardiac output. 17,18 The cardiac output measurement is based on the Kubicek's equation, which relates the derivative of the BI signal to the variation in the blood volume inside the aorta. 19,20 Another application of the BI technique in medical research is the noninvasive imaging used to determine the impedance distribution of the biological tissues.…”