Feasibility of Watch-Based Blood Pressure Monitoring in Real-World Settings: A Retrospective Analysis of Multiyear Observational Data (Preprint)

Defines calibration difference = |mean cuffless SBP in the 1-week window before a recalibration − mean in the 1-week window after|, a reference-free index usable without paired cuff readings. Compares observed distributions with reference ranges derived from published day-to-day SBP variability; regression + ML interpretation of age, average SBP, hypertension status and measurement frequency.

• Form factor: wrist

BACKGROUND

Cuffless blood pressure (BP) monitoring using wearable devices enables frequent measurement in everyday settings, yet its real-world reliability remains difficult to assess because of calibration dependency and the absence of paired reference BP measurements in uncontrolled settings.

OBJECTIVE

This study aimed to characterize measurement stability in watch-based BP monitoring using calibration difference as a reference-free analytical index and to examine how calibration stability varies according to user characteristics and measurement frequency.

METHODS

Calibration difference was defined as the absolute difference between the average cuffless systolic BP (SBP) values measured during the 1-week periods before and after calibration. We analyzed large-scale real-world data from 3 nationwide campaigns conducted between 2021 and 2023, comprising 1714 participants and 5728 calibration-difference instances obtained from Samsung Galaxy Watch measurements. Observed calibration-difference distributions were compared with theoretically derived reference ranges based on day-to-day SBP variability reported across multiple independent cohorts. Statistical analyses and machine learning–based interpretation were used to examine nonlinear and interaction effects associated with age, average SBP, hypertension status, and measurement frequency.

RESULTS

Among 5728 calibration-difference instances, the mean calibration difference was 5.95 (SD 4.73) mm Hg. Under the primary analytical assumption of 3 measurements per averaging period, calibration differences in the overall population and in younger or lower-SBP groups were broadly comparable to the theoretically derived reference ranges, whereas older individuals and those with higher average SBP consistently exhibited larger deviations. Age, average SBP, and the minimum number of measurements were independently associated with calibration difference in multivariable regression (all P CONCLUSIONS

Calibration stability varied substantially across user groups, suggesting that uniform usage protocols may not be sufficient for watch-based BP monitoring in real-world settings. In settings where paired reference BP measurements are unavailable, calibration difference may serve as a scalable analytical index for examining measurement stability, rather than as a substitute for regulatory accuracy assessment. These findings provide a practical framework for evaluating real-world stability and optimizing measurement strategies for cuffless BP monitoring systems.

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