Microprocessor-based system for measurement of electrical impedances during haemodialysis and in postoperative care

Monitoring relative fluid balance alterations in haemodialysis of diabetic patients by electrical impedance

“…Electrical bioimpedance spectroscopy is based on established principles of measurement (Tedner 1983, Goovaerts et al 1988, Webster 1990, Ackman 1993, Boone and Holder 1996. High-frequency current with stabilized amplitude and frequency is passed through the body 0967-3334/98/010035+18$19.50 c 1998 IOP Publishing Ltd range is 20 to 1000 , using a current of 2 mA p−p (about 0.7 mA eff ) with a compliance voltage of 20 V p−p .…”

Electrical impedance tomography

“…0.7 V in the use of a diode, is much higher than the signals and also it cannot provide the phase information. Phase-sensitive demodulators (PSDs) in both analogue and digital forms, such as switching demodulators, multipliers and digital matched filters, are widely used in EIT DASs Cook, Saulnier, & Goble, 1991;Goovaerts et al, 1988;Smith, Freeston, Brown, & Sinton, 1992;Webster, 1978). The simplest PSD is illustrated in Figure 2.14, which includes a positive buffer, a negative buffer, a switch and a low-pass filter.…”

On the zero- and first-order interpolation in synthesized sine waves for testing purposes

“…The relative performance of each interpolator with respect to harmonic generation can be evaluated by comparing (4) and (6). From these equations, it is obvious that total hlu"c ' distortion (THD) is considerably smaUer in the case of linear inteplation than in the staircase waveform.…”

“…Some examples are: measurement of audio frequency amplifiers [ 11, calibration and testing of wattmeters with well-known distorted waveforms [ 2 ] , searching for nonlinearities in passive electrical components [3], and invivo characterization of biological tissues [4], [5] by measuring the frequency dependence of their impedance. Some of the requirements of sine wave generators intended for these applications are: provision for easy change of frequency; capability of generating complex waveforms, for example, the sum of two or more sine waves; in some applications such as body fluid shift monitoring, the desired information relies on the ratio of body impedance at low and high frequency, rather than on the absolute value of the impedance [6]; simultaneous generation of control signals to drive a coherent (synchronous) detector to detect both inphase and quadrature components of the tested system output signal; the possibility of phase-shift adjustment in control signals in order to compensate for phase shifts introduced by electronic circuitry, which can be even larger than the one intended to be measured; the generation of a waveform with low distortion.…”