Research On Impedance Plethysmography Measurement Technique For Cerebral Blood Flow Excited By Current Pulses

It was well known that the brain requires about 20% of the circulation of blood in the body. Interruption of the blood supply of brain may cause serious consequences, such as stroke, which is a lethal disease for human beings. In addition, the blood flow to the brain of pilots will reduce under acceleration stress. And this reduction may cause G-induced loss of consciousness (G-LOC) and transient blindness of pilots, which threaten their safety greatly. Therefore, it is necessary and significant to develop a technique to monitor the blood flow of brain, and give an indication for preventing neurological complications.This project studied the mechanism of noninvasive monitoring to the cerebral blood flow(CBF)by impedance plethysmography. And an exciting source of current pulses with very low duty cycle was introduced. As a result, an experimental impedance plethysmography system was designed and implemented. In the hardware, circular gold-filled electrodes were adopted. The novel exciting source of short current pulses was implemented by timer, high speed analog switch, monostable multivibrators (M.M.) and constant current diode. The resulting impedance signals were demodulated by high speed sample-and-hold amplifier (SHA) , amplified and filtered by precision operational amplifier, and acquired by A/D board to computer. In the software, acquisition of signals was controlled, the wave of blood flow was displayed, and the algorithm of cross correlation templatewas provided to get the characters of blood flow.Based on the experimental system mentioned above, the measurement results of the head of human beings under different electrodes and configurations were discussed. These results were also compared with those detected by a traditional impedance plethysmography system. In addition, a transcranial impedance animal model was built to validate the penetrability to skull of the system.The results from the experiments elucidated the impedance measurement system excited by current pulses with very low duty cycle can detect the blood flow of brain. Compared with the traditional exciting source of sine wave, the short current pulses exciting mode can penetrate bio-tissues easily and safely.