A bio-impedance measurement system for portable monitoring of heart rate and pulse wave velocity using small body area

Continuous monitoring of cardiovascular system can prevent death and disabilities due to heart failure. In this paper, a bio-impedance measurement system that operates on a small local area of the forearm is presented for portable and continuous monitoring of the heart rate and pulse wave velocity (PWV). The impedance variation caused by the heart pump is measured by analog circuitries that consist of amplifiers, mixers and filters. The overall gain, CMRR, and input impedance of the implemented system using discrete components are 80dB, 72dB and 477kΩ at 100kHz, respectively, which results in a system sensitivity of 21V/Ω. Experimental results show that the heart rate and PWV can be measured by using only 1.5cm × 7cm area of the body. The measured heart rate is in the range of 65∼110 beats/min, and PWV is in 6.51±2.39 (m/s), which fits well with a reference device and normal physiological range. The optimum location for small electrodes in terms of signal quality is also investigated, and the results show that the location at the lower forearm along the radial artery has the best signal quality.