Reference-Assisted FBG Sensing for Simultaneous Carotid–Radial Pulse-Wave Measurement and PWV Estimation

Simultaneous pulse-wave sensing at the carotid and radial arteries is challenging because the two sites require different mechanical coupling conditions and manually held carotid probes are susceptible to contact pressure and motion disturbances. This study presents a reference-assisted fiber Bragg grating (FBG) system comprising a wristband-type radial unit and a stamp-type carotid unit containing mechanically decoupled measurement and reference FBGs. Reference FBG regression (RFR) was used to suppress components shared by the carotid channels. In a 41.8 s recording from one male participant in his twenties, the reference and carotid measurement channels were essentially uncorrelated within the pulse-wave band (r = −0.05). After signal mean removal, RFR reduced power below 1 Hz by 74.3% without attenuating the pulse-band power (+11.4%), increasing the relative-power signal quality index from 0.174 to 0.458. Pulse transit time (PTT) was estimated by foot-centered windowed correlation. Analysis of 54 cardiac cycles yielded a representative PTT of 0.055 s. With an effective path length of 0.48 m, the corresponding pulse-wave velocity (PWV) was 8.7 m/s, with a within-record bootstrap 95% interval of 7.7–9.9 m/s. Estimates from eight non-overlapping 5 s segments were 9.1 ± 1.8 m/s. RFR produced lower segment-to-segment PTT variability than the baseline processing methods (coefficient of variation, 20.3% versus 34.6–46.7%). These results demonstrate the technical feasibility of reference-assisted FBG sensing for simultaneous carotid–radial pulse-wave acquisition and preliminary PWV estimation. Further validation requires higher-rate acquisition, repeated measurements, a larger cohort, and comparison with a reference PWV device.