Feasibility, credence, and usefulness of out-of-office cuffless blood pressure monitoring using smartwatch: a population survey

The event "Daily BP measurement with your Galaxy Watch" was organized by the KSH from May 25 to June 8, 2022, to raise awareness of the public about the usefulness of cuffless BP monitoring using a smartwatch. Interested participants voluntarily signed up on the KSH website (http://​www.​koreanhypertensi​on.​co.​kr), and only adults (22 years or older) were eligible to participate since the Samsung Health Monitor App is only available for adults. Before participating in the event, the participants were asked to sign an informed consent form available on the KSH website. The research protocol for this event was approved by the institutional review board of Seoul National University Hospital (H-2207–026-1337).

To promote the event, the KSH used various social media platforms such as Naver blog, Facebook, Instagram, and Kakao Talk channel. Participants were incentivized to participate through giveaways, which were provided by lottery among those who correctly performed the BP calibration, BP measurement, and transmitting procedure as per the provided instructions during the event period. The manufacturer of the device was not involved in the study, including study design, conduction, and data interpretation.

During the event, participants of the event were requested to share their BP measurement experience using a smartwatch App through online survey. The questionnaires are divided into three areas. First part was the questions about participants` characteristics, including age, underlying medical condition, and the length of the smartwatch use. Second part was the question about the status of smartwatch utilization, including the question about health-related functions of the smartwatch, frequency of exercise with wearing the smartwatch, users` perception about accuracy and reliability of BP monitoring function, and willingness to use the BP monitoring function in the future. The third area was the question about the BP calibration process, including feasibility and the way of the calibration process. Questions included in the questionnaire are translated and listed in Table 1. There were no additional exclusion criteria. All responses sent by event participants were included.

During the campaign, participants were asked to calibrate the smartwatch using an automated upper-arm cuff-based BP monitor approved by the Ministry of Food and Drug Safety. Step-by-step instruction for BP calibration was as follows according to the position statement of the KSH [15]: (i) avoid alcohol, caffeine, and nicotine intake, exercise, and bathing 30 min before correction; (ii) sit comfortably with your back in a chair; (iii) wear your smartwatch on the wrist, without overtightening; (iv) position the cuff around the middle of the upper arm on the same side wearing smartwatch; (v) tap ‘start calibration’ button on the smartphone connected to the smartwatch; (vi) take a reference BP value by the cuff-based BP monitoring device; (vii) put the BP value appeared on the cuff-based BP monitoring device in the smartwatch application; (viii) repeat these for two more times. After the first calibration, participants were instructed to measure their BP twice daily, morning and evening. After a total of 14 measurements over a week, they were instructed to recalibrate their smartwatch. After the second calibration, they were asked to measure their BP twice a day again for one more week, just as they had done before. After every measurement was made, participants were instructed to extract their BP reading data from the Samsung Health Monitor App and send their BP measurement results to the Kakao Talk channel or e-mail address of the KSH in the form of a PDF file. It is recommended to select the last three months from last week, last month, last three months, and last year as the extraction period option so that data for the entire period of the event can be extracted without loss. All personally identifiable information transferred was used for research and analysis in a form in which individuals cannot be identified.

No specific statistical method or statistics program was used to analyze the survey results, and survey data were analyzed mainly with percentage (%) values.

A total of 13,539 people applied for the event "Daily BP measurement with your Galaxy Watch." Among the participants who applied and received the questionnaire, 1,071 people responded to the survey. The largest age group was 50–59 years old (33.3%), followed by 40–49 years old (29.9%) and 30–39 years old (16.7%). The population group of 20–29 years old accounted for 6.6% of the total, and only 2.0% were over 70 (Fig. 1A). Regarding the length of smartwatch usage, 86.2% of participants had been using a smartwatch for more than a year, with 45.9% using it for more than 2–3 years, 22.1% for more than 3–4 years, and 11.7% for more than five years. Only 12% of participants were first-time smartwatch users at this event (Fig. 1B). Regarding underlying medical conditions, nearly half (47.5%) of the participants responded that they had no history of chronic disease, while 40.1% reported having hypertension, followed by diabetes mellitus (9.6%), hyperlipidemia (3.6%), angina pectoris/myocardial infarction (3.5%), stroke (1.4%), and other conditions (1.7%) (Fig. 1C). Detailed information about participants’ age distribution, duration of smartwatch usage, and underlying medical conditions is shown in Fig. 1.

Among the health-related apps built into the smartwatch, BP monitoring (95.8%) was the most commonly utilized app, followed by heart rate measurement (87.1%), electrocardiogram (64.2%), stress evaluation (62.9%), body fat examination (57.8%), oxygen saturation measurement (53.4%), and snoring detection (35.3%) (see Fig. 2A). With regards to the frequency of exercise using a smartwatch, 66.8% of users exercised while wearing a smartwatch at least three times a week. 21.1% exercised 1-2 times a week with a smartwatch, while 3.5% exercised 2-3 times a month with a smartwatch. 5.5% had never exercised while wearing a smartwatch (see Fig. 2B). The most frequently used smartwatch model was the Galaxy Watch 4 (44.7%), followed by the Samsung Galaxy Watch 3 (26.7%), Samsung Galaxy Watch Active 2 (19.9%), Samsung Galaxy Watch 4 Classic (19%), Samsung Galaxy Watch (17%), and Samsung Galaxy Watch 2 (11.3%). The Apple Watch 1–6, Galaxy Fit, and Mi Band were used by 1–2% of participants for each model.

In terms of the usefulness and reliability of the BP monitoring app on smartwatches, 31.8% of participants answered that the smartwatch’s BP monitoring was ‘very accurate and helpful’. 44.4% rated it as ‘displaying slightly lower BP levels than their conventional counterpart but still helpful’, and 19.1% think that it ‘displays slightly higher BP levels than their conventional counterpart but still helpful’. Only 1.3% said it was ‘not accurate to be of help to’ (see Fig. 2C). When asked about their intention to use the BP monitoring function in the future, 93% of participants said they would use it at least once a week regularly in the future, with 53.5% saying they would use it daily (see Fig. 2D). Detailed information about the status of smartwatch utilization is shown in Fig. 2.

Regarding the calibration process of a smartwatch for BP measurement, 75.9% of participants used the arm wearing the smartwatch for calibration, while 24.1% used the arm not wearing the smartwatch (Fig. 3A). The reason for including this question is that the BP measurement manual of the Samsung Galaxy Watch and the KSH’s recommendations for BP calibration differ. The manual for the Samsung Galaxy Watch recommends wearing a cuff-type BP monitoring device on the arm not wearing the smartwatch during BP calibration, but the KSH recommends wearing it on the arm wearing the smartwatch.

Most participants (93.9%) were able to calibrate their BP by themselves without needing help from others (Fig. 3B). Regarding the difficulty of the calibration procedure with a cuff-based BP monitoring device, 93.2% of responders rated the process as easy enough for them to do by themselves without assistance. Among them, 50.8% rated the difficulty of the BP calibration process as ‘very easy’. Only 3.7% said they needed family assistance to perform BP calibration, and only 0.4% said they could never calibrate their BP by themselves (Fig. 3C). Detailed information about the feasibility and users’ perception of BP calibration using a smartwatch BP monitoring application is shown in Fig. 3.