Figure 1: Circuit Diagram for the PW Sensor and BP Estimation System

(A) The light-emitting diode (LED) emits light with a wavelength of 940 nm. The light penetrates the finger and arrives at the photo detector (PD). The PD detects blood flow changes, which correspond to the natural pulsation of the blood flow. Baseline fluctuation is removed by a high-pass filter (HPF) with a cutoff frequency of 0.3 Hz, and noise is removed by a low-pass filter (LPF) with a cutoff frequency of 30 Hz. The output signal is digitized at a sampling frequency of 200 Hz and a resolution of 12 bits. (B to E) Schematic diagram (B and D) and illustration (C and E) used to develop the BP estimation algorithm. ∗Leg clamp (E). ∗∗Arithmetic calculation. A total of 887 participants were enrolled (a histogram of participant age and gender is displayed in Supplemental Figure 1A). The obtained pulse waves were analyzed, and feature parameters were extracted and collected. A database of feature parameters was analyzed to generate a BP estimation algorithm. (D) Validation protocol based on Institute of Electrical and Electronics Engineers (IEEE) standard 1708-2014. BP data were obtained by using cuff-less BP estimation (CLB) with simultaneous recording by a cuff-type sphygmomanometer (CB) as a reference conducted at the time point indicated by the closed circle. Calibration was performed at the beginning of each measurement using a cuff-type sphygmomanometer to take 3 measurements at 60-s intervals. After calibration, simultaneous BP monitoring was performed by using CLB and CB under (C) static conditions followed by dynamic measurements using (E) leg stretching and a clamp. ADC = analog to digital converter; Amp = amplifier; PC = personal computer.