Wrist Photo-Plethysmography and Bio-Impedance Sensor for Cuff-Less Blood Pressure Monitoring

A multimodal wrist sensor system is proposed in this paper for a wearable reflectance photo-plethysmography (PPG) and impedance-plethysmography (IPG) biomedical data sensing. A near Infrared (NIR) optical wavelength has been used to extract PPG signal from subject's wrist, while tetra-polar configuration based IPG sensor using two pairs of electrodes for current injection and voltage detection are used to acquire IPG signal. Furthermore, the signal arrival time delay between the IPG and PPG signal in two different but closed arterial sites (wrist area) known as pulse transit time (PTT) is used to estimate subject's blood pressure cufflessly. As an initial study, two clinical points have been extracted from both IPG and PPG signal, such as B-point, and Maximum of 2nd derivative of the signal, respectively. Therefore, a predicted systolic blood pressure (SBP) and diastolic blood pressure (DBP) achieved a mean absolute deviation of 4.16 $\pmb{\pm 5.23}$ and 2.44 $\pmb{\pm 3.12}$ , respectively.