Multi-Wavelength Photoplethysmography Enabling Continuous Blood Pressure Measurement With Compact Wearable Electronics

• Published in: IEEE transactions on biomedical engineering Vol. 66; no. 6; pp. 1514 - 1525
• Main Authors: Liu, Jing, Yan, Bryan P., Zhang, Yuan-Ting, Ding, Xiao-Rong, Su, Peng, Zhao, Ni
• Format: Journal Article
• Language: English
• Published: United States IEEE 01.06.2019; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Arteries; Arterioles; Biomedical monitoring; Blood; Blood pressure; Blood Pressure - physiology; Blood Pressure Determination - instrumentation; Blood Pressure Determination - methods; Blood vessels; Cuffless blood pressure; Electrical resistance measurement; Electronics; Fingers - blood supply; Fingers - physiology; Human performance; Humans; Hypertension; Light penetration; Maneuvers; Monitoring; multi-wavelength photoplethysmography; Occlusion; Penetration depth; Penetration resistance; Photoplethysmography - instrumentation; Photoplethysmography - methods; Pressure measurement; Skin; Smartwatches; systemic vascular resistance; Transit time; Vascular Resistance - physiology; Wavelength; Wavelength measurement; wearable device; Wearable Electronic Devices; Wearable technology
• ISSN: 0018-9294; 1558-2531; 1558-2531
• DOI: 10.1109/TBME.2018.2874957

Objective: To fight the "silent killer" hypertension, continuous blood pressure (BP) monitoring has been one of the most desired functions in wearable electronics. However, current BP measuring principles and protocols either involve a vessel occlusion process with a cuff or require multiple sensing nodes on the body, which makes it difficult to implement them in compact wearable electronics like smartwatches and wristbands with long-term wearability. Methods: In this work, we proposed a highly compact multi-wavelength photoplethysmography (MWPPG) module and a depth-resolved MWPPG approach for continuous monitoring of BP and systemic vascular resistance (SVR). By associating the wavelength-dependent light penetration depth in the skin with skin vasculatures, our method exploited the pulse transit time (PTT) on skin arterioles for tracking SVR (n = 20). Then, we developed an arteriolar PTT-based method for beat-to-beat BP measurement. The BP estimation accuracy of the proposed arteriolar PTT method was validated against Finometer (n = 20) and the arterial line (n = 4). Results: The correlation between arteriolar PTT and SVR was theoretically deduced and experimentally validated on 20 human subjects performing various maneuvers. The proposed arteriolar PTT-based method outperformed the traditional arterial PTT-based method with better BP estimation accuracy and simpler measurement setup, i.e., with a single sensing node. Conclusion: The proposed depth-resolved MWPPG method can provide accurate measurements of SVR and BP, which are traditionally difficult to measure in a noninvasive or continuous fashion. Significance: This MWPPG work provides the wearable healthcare electronics of compact size with a low-cost and physiology-based solution for continuous measurement of BP and SVR.