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Block diagram of a typical impedance plethysmograph system. Constant amplitude sinusoidal current is passed through the body segment with the help of current electrodes I1 and I2. Voltage sensing electrodes V1 and V2 are applied at desired location on the body segment along the current path. The amplitude of the sensed voltage is directly proportional to the instantaneous impedance Z of the body segment between the voltage electrodes. Z is processed electronically to yield basal impedance Zo, ?Z (t) and dZ/dt waveform.

Block diagram of a typical impedance plethysmograph system. Constant amplitude sinusoidal current is passed through the body segment with the help of current electrodes I1 and I2. Voltage sensing electrodes V1 and V2 are applied at desired location on the body segment along the current path. The amplitude of the sensed voltage is directly proportional to the instantaneous impedance Z of the body segment between the voltage electrodes. Z is processed electronically to yield basal impedance Zo, ?Z (t) and dZ/dt waveform.