Feasibility of Watch-Type Cuff-Less Blood Pressure Measurement Device in Daily Blood Pressure Monitoring

Objective: Cuff-less blood pressure (BP) measurement devices integrated into smartwatches have gained prominence for daily monitoring, yet limited studies provide the analysis of real-world BP data collected by such devices. In this study, we evaluated the feasibility of photoplethysmographic BP measuring smartwatch by analyzing data collected in real-world. Design and method: The campaign, “Smartwatch Blood Pressure Monitoring Challenge with Korean Hypertension Society”, was held in June 1-14, 2023 and 896 participants reported 35592 BP values measured by smartwatch (Samsung Galaxy Watch 6, approved in Korean Ministry of Food and Drug Safety). Participants were instructed to measure BP daily, in the morning (5AM-8AM) and evening (6PM-9PM) for two weeks, with initial calibration and re-calibration after the first week. We evaluated 1) BP difference between before and after re-calibration, and 2) difference in morning and evening BP. We also evaluated the determining factors of the BP differences. Results: Morning and evening BP values showed significant difference, higher in the evening by 1.42±5.25 mmHg (p<0.05). However, the diurnal variation was much smaller than reported in other studies using conventional BP monitoring devices. ANOVA identified significant variables for evening-morning differences, including basal metabolic rate, skeletal muscle mass, total body water, average systolic BP (SBP), diastolic BP (DBP), and heart rate in the morning (p < 0.01 in both ITT and PP). Participants who have evening-morning difference higher than the third quartile, where evening SBP was significantly higher than morning SBP, exhibited smaller variable sizes. Turkey’s Honest Significant Difference showed that this relationship is statistically significant between Q1-Q4 and Q2-Q4 in all variables. The calibration stability was assessed by the difference in average BP before and after calibration, resulting in an SBP difference of 4.64±4.73 mmHg and DBP of 3.66±3.62 mmHg, smaller than a 2021 campaign (6.8±5.6mmHg). When the difference of average was measured between same period of time (morning versus morning and evening versus evening), SBP of 5.39±5.22 mmHg and DBP of 4.3±3.99 mmHg. Conclusions: In conclusion, watch-based devices may not detect clinical-level BP variability, but refining calibration protocols offers improvement potential.