Study On Impedance Blood Flow Measurement System Based On Miniature Electrodes

Impedance rheogram is also named as electrical impedance plethysmography. Commonly a constant current is passed between two of the electrodes which are located at either of the body segment of object. The voltage drop across this same area is then measured using the other pair of voltage electrodes. Simultaneously electrocardiogram and heart beat are recorded. Thus we can get changes information of blood dynamics about heart,lung,liver,brain,trunk and kidney. Its greatest advantage is that we can evaluate tissue and organs of body function applying the rich information of bio-impedance. It has advantages in accurate and reliable measurement ,simple operation and continuous measurement in vivo and it can be easily accepted by doctors and patients. Now it is used in a variety of applications. But Present impedance rheogram plays too much emphasis on pulsant component of impedance blood flow and ignors the direct current component which includes body fluid change and unpulsant blood volume of other tissues such as muscle and microvessels and so on. Under the condition of exercise load, artery vessel pulsant component of local segments will be induced to change, so does the change of body fluid and unpulsant blood volume of muscle and microvessels. The later displays the change of direct current component. Study has shown that blood flow parameters of most people displays abnormal performance under the condition of exercise load although they are normal at rest. In 1976, Balasubrsmanian et al used direct current component as the distinction between real and pseudo cardiac muscle ischematic. At the same time, comparing to cardiac signal and breath wave, impedance blood flow is too small to be processed. In order to improve signal to noise ratio and detect effective signal, usually a large zone is measured and thus measured parts are limited. For the purpose of minimizing the defects narrated above, we designed a small and integrative electrode transducer which can be used in different parts measurement such as wrist,neck,brain and so on. Experiments conformed that the electrode transducer had the characteristics of high sensitivity,low noise,strong resistance of anti-jamming and good dynamics. Combining with impedance blood flow measurement system, the pulsant blood supply and nonpulsatile component which includes body fluid and other tissues such as muscle and microvessels were measured to evaluate the local blood circulation. In addition, it is promising to be used under the condition of exercise load. Our impedance blood flow measurement system based on integrative and miniature electrodes can be adapted to measure impedance blood flow located at different parts of body because of improving the design of electrodes and applying phase sensitive demodulator(PSD) technique. Impedance blood flow located at radial artery of wrist ,carotid and forehead of several objects were measured and local pulsatile component of artery and nonpulsatile component which includes body fluid change and blood volume of other tissues such as muscle and microvessels. The results proved that the measurement system can acquires the impedance blood flow located at different parts of body. Blood flow was decreased greatly, thus ascending time and descending time increased obviously when the brachial artery of upper arm was blocked. Change of nonpulsatile component magnitude was about 100mv(7.3%). When the artery is blocked, blood circulation is interrupted and local blood flow decreasing greatly. Simultaneously resistance of microvessels increase. All of these changes leads to decrease of pulsatile blood supply and increase of direct current component. By analyzing the blood flow wave, we can get the information of local pulsatile blood supply and nonpulsatile component which includes body fluid change and blood volume of other tissues such as muscle and microvessels. According to the results, we can judge whether local blood supply is normal. At the same time, we measured cerebral impedance blood flow under different conditions and made spectral analysis. The results were consistent with the reports of other researchers. So the measurement system is reliable and can be used to measure impedance blood flow of local tissue under the condition of exercise load and evaluate physiological state of body more accurately.