Figure 3. Arterial-pulse measurement with nanofiber-based pressure-sensor unit (NFPSU): a) Photograph of NFPSU on tester’s wrist. b, c) Measured arterial-pulse waveforms of a male and a female tester before and after exercise. d) Schematic of nine-point grid with an area of 1×1 cm2 on a tester’s wrist. e) Measured arterial-pulse waveform at different locations (red dots) in the grid. f) Typical pulse waveform showing P, T, and D waves.
To characterize its response to tiny mechanical stimuli, the NFPSU was used to monitor wrist pulses in real time (Figure 3a ). Owing to its high sensitivity, it could readily obtain wrist-pulse waveforms with high resolution; the two distinguishable peaks and late systolic augmentation shoulder agree very well with the expected shape of a noninvasive radial-artery pressure wave.[36] The trace shows clearly that the pulse frequency before the exercise was ~ 70 beats/min and the pulse shape was regular and repeatable. After exercise, the pulse frequency increased to ~ 90 beats/ min, and the shape and intensity were irregular (Figure 3, b and c ).
To prove that the NFPSU response was position independent, we drew a nine-point grid with an area of 1×1 cm2 on the wrist skin, centered on the wrist artery (Figure 3d) . The NFPSU was positioned point-by-point on the grid to obtain pulse signals.Figure 3e presents the measured arterial-pulse signals recorded by the NFPSU at various positions in the grid (indicated by red dots in the figure). Each of the nine pulse waveforms in Figure 3eresembles a typical pulse waveform (Figure 3f ) consisting of a percussion wave (P-wave), a tidal wave (T-wave), and a diastolic wave (D-wave). Thus, we believe that high-fidelity pulse signals can be successfully obtained anywhere within a maximum distance of √(52+52)≈7.07 mm from the arterial pulse. Such position-independent sensing ability of the NFPSU is crucial when the GRW is worn for a long time.