An approach to improve impedance plethysmography on the wrist by using adaptive feedback control

The growing market of wearable devices made ambulant vital sign monitoring popular in recent years. Impedance plethysmography (IPG) provides a promising low power solution for detecting pulse waves and respiration by measuring the impedance of blood vessels at the wrist. However, the measurement principle makes high demands on the analog front end, due to low signal-to-noise ratio (SNR) and unknown measurement conditions. In this paper an approach to apply impedance plethysmography is presented. The proposed circuit is based on the impedance measurement IC AD5933 and an adaptive feedback control to regulate current injection and measuring amplification in order to adjust the optimal operating point. Experimental studies demonstrate the potential of the system as promising technology for continuous vital sign monitoring on the wrist.