Posture-Dependent Variability in Wrist Ballistocardiogram-Photoplethysmogram Pulse Transit Time: Implication to Cuff-Less Blood Pressure Tracking

• Published in: IEEE transactions on biomedical engineering Vol. 69; no. 1; pp. 347 - 355
• Main Authors: Shin, Sungtae, Mousavi, Azin, Lyle, Sophia, Jang, Elisabeth, Yousefian, Peyman, Mukkamala, Ramakrishna, Jang, Dae-Geun, Kwon, Ui Kun, Kim, Youn Ho, Hahn, Jin-Oh
• Format: Journal Article
• Language: English
• Published: United States IEEE 01.01.2022; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Arm; Ballistocardiograms; Ballistocardiography; Biomedical measurement; Blood Pressure; Blood Pressure Determination; Electrocardiography; Feet; Foot; Heart rate; Humans; Photoplethysmography; Posture; pulse transit time; Pulse Wave Analysis; Time measurement; Timing; Tracking; Transit time; Variability; Waveforms; Wrist
• ISSN: 0018-9294; 1558-2531; 1558-2531
• DOI: 10.1109/TBME.2021.3094200

Objective: Toward the ultimate goal of robust cuff-less blood pressure (BP) tracking with wrist wearables against postural changes, the goal of this work was to investigate posture-dependent variability in pulse transit time (PTT) measured with ballistocardiogram (BCG) and photoplethysmogram (PPG) signal pair at the wrist. Methods: BCG and PPG signals were acquired from 25 subjects under the combination of 3 body (standing, sitting, and supine) and 3 arm (vertical in head-to-foot direction, placed on the chest, and holding a shoulder) postures. PTT was computed as the time interval between the BCG J wave and the PPG foot, and the impact of the 9 postures on PTT was analyzed by invoking an array of possible physical mechanisms. Results: Our work suggests that (i) wrist BCG-PPG PTT is consistent under standing and sitting postures with vertically held arms; and (ii) changes in wrist orientation and height as well as restrictions in body and arm movement may alter wrist BCG-PPG PTT via distortions in the wrist BCG and PPG waveforms. The results indicate that wrist BCG-PPG PTT varies with respect to postures even when BP remains constant. Conclusion: The potential of cuff-less BP tracking via wrist BCG-PPG PTT demonstrated under standing posture with arms vertically down in the head-to-foot direction may not generalize to other body and arm postures. Significance: Understanding the physical mechanisms responsible for posture-induced BCG-PPG PTT variability may increase the versatility of the wrist BCG for cuff-less BP tracking.