Plethysmography measurements using short current pulses with low-duty cycle

Pulse plethysmography with very low-duty cycle offers much lower current load of examined bio-tissue in comparison to sine-wave impedance plethysmography. This enables application of strong current pulses with the same bio-tissue loading effect as for impedance plethysmography, resulting in larger signal and better signal to noise ratio. Determination of an equivalent electrical circuit of electrodes connected with bio-tissue is possible by fitting the measured waveshape with a resistor and capacitor connected in series, or better with three or four elements. A simplified block diagram of the pulse plethysmograph is given as well. Blood pressure wave-shape obtained on arteries and volume changes during respiration are measured and shown.