Physiologic Impedance Components

Data acquired from the various possible electrode vectors typically contain three major physiologic components that may provide useful information for diagnostics or implantable device control  

More specifically, change in impedance waveform morphologies may be an indicator of change in blood volume, interstitial volume, or tissue integrity. Deviations in the impedance waveform morphologies such as in the positive or negative slope, time duration 

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The frequency response of the system is a high-pass filter, since, for tor 1, Vo(ift))/X] (io)) = E/xo, which is a constant. However, the response drops off for low frequencies, and it is zero when at = 0. This frequency response is sufficient for a microphone that does not measure sound pressures at frequencies below 20 Hz. The input impedance of the read-out device must be high (10 MS2 or higher) in order to achieve a required low-frequency bandwidth. Capacitance sensors are not suitable for measuring most physiological signals because the frequency spectra of these signals have dominant low-frequency components. 

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