Wearable Hyperspectral Photoplethysmography Allows Continuous Monitoring of Exercise-Induced Hypertension

Continuous blood pressure (BP) monitoring is essential for cardiovascular health, yet current BP sensors face cuff-dependent limitations. Cuff-free alternatives still suffer from discomfort and discontinuous measurement. Here a wearable hyperspectral photoplethysmography (HS-PPG) is reported for continuous and nonconscious BP monitoring. The HS-PPG module integrates an ultrathin and high-resolution double-folded solid immersion grating microspectrometer (DFSIG-µSPEC) with a white light LED. DFSIG-µSPEC shows an average spectral resolution of 3.4 nm for 550-800 nm in the operational range. The HS-PPG module has a compact physical dimension of 8 mm × 16 mm × 24 mm, suitable for wrist-wearable configuration. The PPG waveforms contain 50 spectral bands, achieving precise measurement of arteriolar pulse transit time (aPTT). The diastolic and systolic BPs are precisely estimated with R-values of 0.92 and 0.96, and mean absolute differences (MAD) of 1.20 and 0.40 mmHg with the 2-element Windkessel model, respectively. Further, the BP is continuously measured with heart rate (HR) and respiratory exchange ratio (RER) with exercise-induced hypertension. Continuous monitoring of systolic blood pressure (SBP) exhibits immediate responses during hemodynamic changes, with the physiological parameters of SBP, HR, and RER during exercise and recovery. The wearable HS-PPG clearly supports the strong potential for high-fidelity continuous BP monitoring.