Challenges in using seismocardiography for blood pressure monitoring

The capability of continuously and non-invasive blood pressure (BP) monitoring is valuable in the clinical setting. Pulse transit time (PTT) has shown the promise to track changes in the arterial BP. This study examines the efficacy of seismocardiogram (SCG) and photoplethysmogram (PPG) combination for timing the proximal and distal pulse respectively of a pulse wave. The PTT is defined as a difference between the proximal and distal timing of a pulse wave. Methods: A total of 18 subjects participated in the study. Subjects were subjected to a lower-body negative pressure (LBNP) protocol to -60 mmHg. Electrocardiogram (ECG), SCG, PPG and BP was recorded simultaneously during the LNBP protocol. Subjects that endured negative pressure to -40mmHg, had SCG signals with distinct AO points and for whom the average BP was lower in the final stage of LBNP compared to supine baseline were included in data analysis. A simple logarithmic model was used to estimate BP based on PTT. Estimated BP was then correlated with PTT. Results: A total of 7 subjects were included in the final data analysis. On an average the subjects systolic BP dropped during the LBNP protocol and PTT was shortened. None of these changes were significant. For 3 subjects the correlation between PTT and estimated systolic blood pressure was significant. Conclusion: The current study showed a trend toward shorter PTT as blood pressure lowers, but the trend was weak and not consistent.