On using impedance plethysmography for estimation of blood flow

Electrical impedance method has found utility in many fields of medical research, but the old instrumentation can be expensive to use and complicated to build. Advancements in electronic component design and equipment allow a bioimpedance analysis using a simple medical device. The aim of this work is to design a medical device which estimates the blood flow and calculates some hemodynamic parameters on the plethysmographic wave. We designed an equilibrated bridge designed on a small circuit board with connections for power and bioimpedance electrodes. A programmable function generator and an oscilloscope were connected to a computer and were tasked to drive and receive data from the circuit. The alternating - current generator is the current source; a series resistor limits the amount of current that passes through the subject. The frequency of the delivered current is between 20 kHz and 250 kHz. Because the skin impedance increases at higher frequencies, a small amount of energy will be delivered to the patient, that ensuring the safety of the system. The circuit was validated by testing its current output over a range of frequencies and comparing measured values of impedance across a test circuit to expected values. The software receives data and inserts it into a data sheet for analysis.