Instantaneous measurement of electrical parameters in a palm during electrodermal activity

Abstract

-T h e determination of impedance is performed by means of the frequency domain analysis or the time dom a i n analysis. T h e latter has an advantage of being able to measure instantaneously the whole frequency characteristics of impedance. T h e method is hence powerful t o obtain the biological impedance which changes with time. An instantaneous measuring method by using the time domain analysis has been then developed. Fast Fourier Transformation(FFT) of indicia1 response f o r current to the skin can determine the palm impedance. This method can carry o u t the determination of the parameters of the palm skin impedance during a galvanic skin refEex(GSR), which is impossible by means of the frequency d o m a i n analysis.

Real time impedance plots with arbitrary frequency components

“…The terminology of impedance spectroscopy is used here rather than 'multifrequency impedance analysis', since this usually refers to bioimpedance techniques which sample at a limited number of preset frequencies (Griffiths 1992), or else sweep across a range of frequencies to build a complete spectrum (Gudivaka et al 1996, Palko et al 1995. Teorell (1947) and more recently Yamamoto et al (1996) describe methods using the sinusoidal frequency components of an applied square wave to obtain biological impedance measures for a large number of frequencies. The impedance values are calculated from a single recording of the response to the applied square wave.…”

“…More recently Yamamoto et al (1996) used computers (taking advantage of the FFT) to acquire and process waveforms resulting from square wave current application to palmar skin. The major disadvantage inherent in both of these techniques is that the amplitude of the sinusoidal components in the square wave drops off rapidly (following a 1/n series, as indicated in (2)) at higher harmonics, thus making measurements at higher frequencies less precise.…”

Measurement and Evaluation of the Bioelectrical Impedance of the Human Body by Deconvolution of a Square Wave

“…Then, the deconvolution of V L (s) by V T (s) is performed to obtain the system transfer function H(s) in Eq. (8).…”

“…Methods in one category measure the impedance of skin and body parts using a series of sinusoidal test waveforms with various frequency inputs into the measured human body; the bioelectrical impedance of the human body is then evaluated using the output voltage and current of the measured human body ( [3]- [7]). The methods in the other category input a square waveform into the measured human body to differentiate the transient response of the resulting current in order to estimate bioelectrical impedance ( [8]- [10]). …”

A versatile multichannel direct-synthesized electrical stimulator for FES applications

“…The constant-current sources are more prevalent than the constant-voltage sources in the FES stimulators due to inevitable variations of tissue impedance [10], [11]. The constant-current stimulation provides more predictable responses, but a high voltage ( 100 V) might be induced from the tissue when a large current ( 50 mA) is applied to high impedance tissue ( 2 k ).…”