Abstract
There is growing evidence of the clinical significance of daytime masked hypertension (MHT) and blood pressure (BP) variability (BPV). Recently, watch‐type wearable devices for self‐BP measurement have become available. Such devices might be promising tools to identify patients with daytime MHT or large BPV in their real‐life conditions. The present study aimed to validate the accuracy of the Omron HEM‐6410T‐ZM and the Omron HEM‐6410T‐ZL, which are automatic watch‐type wearable devices for self‐BP measurement, according to the American National Standards Institute, Inc/Association for the Advancement of Medical Instrumentation/International Organization for Standardization (ANSI/AAMI/ISO) 81060‐2:2013 guideline. Watches were held with the wrist at heart level. The mean differences between reference BPs and HEM‐6410T‐ZM readings were −0.9 ± 7.6/‐1.1 ± 6.1 mm Hg for systolic BP (SBP)/diastolic BP (DBP) for criterion 1, and −0.9 ± 6.8/‐1.1 ± 5.5 mm Hg for SBP/DBP for criterion 2. The mean differences between reference BPs and HEM‐6410T‐ZL readings were 2.4 ± 7.3/0.7 ± 7.0 mm Hg for SBP/DBP for criterion 1, and 2.4 ± 6.5/0.7 ± 6.5 mm Hg for SBP/DBP for criterion 2. The Omron HEM‐6410T‐ZM and the Omron HEM‐6410T‐ZL both fulfilled both validation criteria 1 and 2 of the ANSI/AAMI/ISO 81060‐2:2013 guidelines.
Keywords: blood pressure, self‐measurement, wearable, blood pressure monitor, validation, ANSI, AAMI, ISO81060‐2:2013
1. INTRODUCTION
Home blood pressure (BP) measurement is widely used and recommended for the management of hypertension.1, 2, 3, 4, 5 Several studies have reported that home BP measured by an automatic cuff‐oscillometric device has greater predictive power for cardiovascular (CV) outcomes than clinic BP.6, 7 Moreover, there is a common phenomenon known as masked hypertension (MHT) defined by out‐of‐clinic BP in the hypertensive range among individuals with normal‐range clinic BP.8 According to our recent study conducted by using the same home BP monitor in different Asian countries/regions, the proportion of patients with MHT among 1443 medicated hypertensive patients was 9%.9 MHT patients have an increased risk for CV disease and target organ damage (TOD) compared with patients with sustained normotension defined by both out‐of‐clinic BP and clinic BP in the normotensive range.10, 11 Recently, the clinical significance of daytime MHT defined by hypertensive daytime out‐of‐clinic BP measured by ambulatory BP monitoring (ABPM) and normotensive clinic BP has been highlighted: Namely, compared with individuals without MHT as measured by daytime ABPM or home BP measurement (HBPM), individuals with MHT by these measures have an increased risk for TOD compared to those with MHT only on HBPM.12 Furthermore, there is growing evidence that daytime BP variability (BPV) is an independent predictor of hypertensive TOD and CV events.13, 14 Therefore, measurement of daytime BP is important to stratify CV risk in detail. Historically, ABPM has been used to assess daytime BP. However, as the mental and physical burden in the use of ABPM is heavy, ABPM is not suitable for repeatable daily monitoring to identify daytime hypertension. Hence, a practical alternative to ABPM for evaluating daytime BP has been awaited.
We recently developed a watch‐type wearable BP monitor (Omron HEM‐6410T‐ZM or Omron HEM‐6410T‐ZL) with a cuff‐oscillometric–based automatic BP measurement function. Because of the features of the wearable device, namely its small size (watch‐type) and silent measurement, patients can measure their BPs anytime and anywhere during the daytime. Therefore, this device could be a promising tool to identify patients with not only morning and/or evening MHT but also daytime MHT, and large BPV in their real‐life condition over multiple days. However, it has not been validated that this watch‐type oscillometric device measures BP accurately. Recently, the World Hypertension League, the International Society of Hypertension, and supporting hypertension organizations have recommended that device manufacturers test the accuracy of BP monitors and publish the results in peer‐reviewed scientific journals.15 In the present study, in order to respond to this recommendation, we validated the performance of the Omron HEM‐6410T‐ZM and Omron HEM‐6410T‐ZL with the wrist at heart level according to the American National Standards Institute, Inc/Association for the Advancement of Medical Instrumentation/International Organization for Standardization (ANSI/AAMI/ISO) 81060‐2:2013 guidelines.16
2. METHODS
2.1. Features of the device
The Omron HEM‐6410T‐ZM and Omron HEM‐6410T‐ZL (Omron Healthcare, Kyoto, Japan) (Figure 1) are automatic oscillometric devices for measuring BP at the wrist, with a systolic BP (SBP) range of 60‐230 mm Hg, diastolic BP (DBP) range of 40‐160 mm Hg, and pulse rate (PR) range of 40‐180 beats per min. The device measures SBP, DBP, and PR during the inflation period of the cuff. It analyzes the pulse wave detected during inflation using an algorithm for determining SBP and DBP. The cuff is inflated automatically by an electric pump and then deflated by a mechanical valve. The cuff can be used for wrist circumferences in the range of 16.0‐19.0 cm for HEM‐6410T‐ZM and 18.0‐21.5 cm for HEM‐6410T‐ZL. The features of the Omron HEM‐6410T‐ZM or Omron HEM‐6410T‐ZL are almost the same except for wrist size range.
Figure 1.
Appearance of a watch‐type wearable BP monitor (Omron HEM‐6410T‐ZM or HEM‐6410T‐ZL)
2.2. Participant selection
In each study, the participants were recruited as volunteers. Each study was approved by the institutional review board, and all participants provided their written informed consent to participate. The inclusion criterion was age ≥20 years. The exclusion criteria were arrhythmias, a DBP value with an unclear Korotkoff sound, and a wrist circumference of <16 or >19 cm for the study of HEM‐6410T‐ZM and <18 or >21.5 cm for the study of HEM‐6410T‐ZL.
2.3. Blood pressure measurements
The devices were validated according to the same‐arm, sequential method of the ANSI/AAMI/ISO 81060‐2:2013 guidelines. The participants were seated in a quiet room at a comfortable room temperature, with their back supported, their legs uncrossed, and their measurement arm supported so that the wrist was at heart level. The BP measurements were started after a 5‐minute rest.
The manufacturer provided standard production device models. The validation team consisted of two nurses and one supervisor who were hired by the manufacturer. Nurses were experienced in performing BP measurements and were trained by the British and Irish Hypertension Society online program (http://www.bihsoc.org). The wrist circumference was measured. All measurements using the wearable devices were made on the left wrist. For the BP measurements by a standard mercury sphygmomanometer, two observers simultaneously measured the participant's BP using a Y‐tube and a calibrated mercury sphygmomanometer. Each participant's BP was determined based on the phase I Korotkoff sound. DBP was determined based on the phase V Korotkoff sound, except when the Korotkoff sound was still audible with the cuff deflated, in which case the phase IV sound was used. BP measurements were alternated between the mercury sphygmomanometer and the automatic devices. The time interval between each set of BP measurements was at least 60 seconds. The two observers were blinded to each other's readings, and the third observer served as a supervisor who checked the BP readings by the two observers. BPs measured by the mercury sphygmomanometer were determined as the average value of BPs measured by the two observers.
2.4. Analysis
The first BP measurements taken using the mercury sphygmomanometer and the automatic device were discarded from the analysis. Data were analyzed according to criteria 1 and 2 of the ANSI/AAMI/ISO 81060‐2:2013 guidelines. For criterion 1, we calculated the differences defined as the SBP or DBP value of the automatic test device minus the mean value of the SBP or DBP measured by the mercury sphygmomanometer before and after the BP measurement by the test device. Three difference values were calculated for each participant. The mean value and standard deviation (SD) of these difference values were calculated. For criterion 2, the reference SBP or DBP value was defined as the mean value of SBP or DBP measured by the mercury sphygmomanometer at the current and immediately before measurement sessions. We calculated the differences defined as the mean value of three SBPs or DBPs measured by the test device minus the mean value of three reference SBPs or DBPs. The mean value and SD of these difference values were calculated.
3. RESULTS
3.1. Validation results of the Omron HEM‐6410T‐ZM
In the study of HEM‐6410T‐ZM, 122 participants were screened for the validation studies. All participants were Japanese. We excluded 37 participants for the reasons shown in Table 1, resulting in a final participant group of 47 men (55.3%) and 38 women (44.7%) who underwent the study. The characteristics of these 85 study participants are shown in Table 2. Their average age was 58.8 ± 11.6 years (mean ±SD) (range: 35‐79 years). The mean wrist circumference was 17.4 ± 0.9 cm (range: 16.0‐18.9 cm). Regarding reference SBP, the percentages of high (≥160 mm Hg), medium (≥140 mm Hg), and low SBP (≤100 mm Hg) were 5.5% (5% criterion), 25.1% (20% criterion), and 8.6% (5% criterion), respectively. For reference DBP, the percentages of high (≥100 mm Hg), medium (≥85 mm Hg), and low DBP (≤60 mm Hg) were 5.9% (5% criterion), 31.4% (20% criterion), and 8.2% (5% criterion), respectively (Table 3). The differences of reference BP between the two observers were 0.03 ± 1.5 mm Hg and −0.1 ± 1.6 mm Hg for SBP and DBP, respectively. The mean differences between the reference BPs and HEM‐6410T‐ZM readings were −0.9 ± 7.6 mm Hg and −1.1 ± 6.1 mm Hg for SBP and DBP according to criterion 1. The mean differences between the reference BPs and HEM‐6410T‐ZM readings were −0.9 ± 6.8 mm Hg and −1.1 ± 5.5 mm Hg for SBP and DBP according to criterion 2 (Table 4). These results fulfilled the validation criteria of the ANSI/AAMI/ISO 81060‐2:2013 of ≤5 ± ≤8.0 mm Hg for criterion 1, and SDs <6.88 mm Hg and <6.86 for SBP and DBP for criterion 2.
Table 1.
Recruitment details for each validation study
| Validation for HEM‐6410T‐ZM | Validation for HEM‐6410T‐ZL | |
|---|---|---|
| Total screened, n | 122 | 103 |
| Total excluded, n | 37 | 18 |
| Irregular pulse rate, n | 13 | 9 |
| Poor quality sounds, n | 2 | 0 |
| Body movements, n | 16 | 6 |
| Reference blood pressure variation, n | 5 | 3 |
| Observers’ determination with difference, n | 1 | 0 |
| Total recruited, n | 85 | 85 |
Table 2.
Characteristics of the study participants
|
Validation for HEM‐6410T‐ZM (n = 85) |
Validation for HEM‐6410T‐ZL (n = 85) |
|
|---|---|---|
| Age, y (range) | 58.8 ± 11.6 (35‐79) | 54.9 ± 12.0 (21‐80) |
| Men: women, n (%) | 47 :38 (55.3, 44.7) | 42 :43 (49.4, 50.6) |
| Wrist circumference, cm (range) | 17.4 ± 0.9 (16.0‐18.9) | 19.1 ± 0.8 (18.0‐21.3) |
Data are expressed as the means ±standard deviations or percentages or number.
Table 3.
Reference SBP and DBP of the participants in each validation study
|
Validation for HEM‐6410T‐ZM (n = 255) |
Validation for HEM‐6410T‐ZL (n = 255) |
|
|---|---|---|
| Reference SBP, mmHg (range) |
126.3 ± 20.2 (92.8‐200.0) |
127.3 ± 20.1 (83.5‐194.0) |
| Percentage of high SBP (≥160mmHg), % | 5.5 | 7.1 |
| Percentage of medium SBP (≥140 mm Hg), % | 25.1 | 22.0 |
| Percentage of low SBP (≤100 mm Hg), % | 8.6 | 5.5 |
| Reference DBP, mmHg (range) |
77.3 ± 14.5 (49.0 ‐ 118.5) |
80.3 ± 12.9 (48.0 ‐ 113.0) |
| Percentage of high DBP (≥100 mm Hg), % | 5.9 | 5.1 |
| Percentage of medium DBP (≥85 mm Hg), % | 31.4 | 36.5 |
| Percentage of low DBP (≤60 mm Hg), % | 8.2 | 7.1 |
Data are expressed as means±standard deviation or percentages.
DBP, diastolic blood pressure; SBP, systolic blood pressure.
Table 4.
Results of each validation study
| Validation for HEM‐6410T‐ZM | Validation for HEM‐6410T‐ZL | |
|---|---|---|
| Difference of SBP for criterion 1, mm Hg |
−0.9 ± 7.6 (passed) |
2.4 ± 7.3 (passed) |
| Difference of SBP for criterion 2, mm Hg |
−0.9 ± 6.8 (passed) |
2.4 ± 6.46 (passed) |
| Difference of DBP for criterion 1, mm Hg |
−1.1 ± 6.1 (passed) |
0.7 ± 7.0 (passed) |
| Difference of DBP for criterion 2, mm Hg |
−1.1 ± 5.5 (passed) |
0.7 ± 6.5 (passed) |
Data are expressed as means ±standard deviations.
3.2. Validation results of the Omron HEM‐6410T‐ZL
In the study of HEM‐6410T‐ZL, 103 participants were screened for the validation studies. All participants were Japanese. We excluded 18 participants for the reasons shown in Table 1, resulting in a final participant group of 42 men (49.4%) and 43 women (50.6%) who underwent the study. Their average age was 54.9 ± 12.0 years (mean ±SD) (range: 21‐80 years). The mean wrist circumference was 19.1 ± 0.8 cm (range: 18.0‐21.3 cm) (Table 2). Regarding reference SBP, the percentages of high (≥160 mm Hg), medium (≥140 mm Hg), and low SBP (≤100 mm Hg) were 7.1% (5% criterion), 22.0% (20% criterion), and 5.5% (5% criterion), respectively. For reference DBP, the percentages of high (≥100 mm Hg), medium (≥85 mm Hg), and low DBP (≤60 mm Hg) were 5.1% (5% criterion), 36.5% (20% criterion), and 7.1% (5% criterion), respectively (Table 3). The differences of reference BP between the two observers were −0.2 ± 1.6 mm Hg and 0.03 ± 1.8 mm Hg for SBP and DBP, respectively. The mean differences between the reference BPs and HEM‐6410T‐ZL readings were 2.4 ± 7.3 mm Hg and 0.7 ± 7.0 mm Hg for SBP and DBP according to criterion 1. The mean differences between the reference BPs and HEM‐6410T‐ZL readings were 2.4 ± 6.46 mm Hg and 0.7 ± 6.5 mm Hg for SBP and DBP according to criterion 2 (Table 4). These results fulfilled the validation criteria of the ANSI/AAMI/ISO 81060‐2:2013 of ≤5 ± ≤8.0 mm Hg for criterion 1, and SDs <6.51 mm Hg and <6.9 for SBP and DBP for criterion 2.
Figure 2 shows Bland‐Altman plots for the differences between the Omron HEM‐6410T‐ZM readings and the observer measurements for SBP (A) and DBP (B) (N = 255), and the differences between the Omron HEM‐6410T‐ZL readings and the observer measurements for SBP (C) and DBP (C) (N = 255).
Figure 2.
Bland‐Altman plots for the differences between the Omron HEM‐6410T‐ZM readings and the observer measurements for SBP (A) and DBP (B) (N = 255), and the differences between the Omron HEM‐6410T‐ZL readings and the observer measurements for SBP (C) and DBP (D) (N = 255)
4. DISCUSSION
In the present study, we demonstrated that the Omron HEM‐6410T‐ZM and the Omron HEM‐6410T‐ZL, which are watch‐type wearable BP monitors, fulfilled the validation criteria of the ANSI/AAMI/ISO81060‐2:2013 guidelines when used in the sitting position with the wrist at heart level.
As far as we know, the Omron HEM‐6410T‐ZM and the Omron HEM‐6410T‐ZL are the world's first watch‐type wearable BP monitors to fulfill the validation criteria of the ANSI/AAMI/ISO81060‐2:2013 guidelines. The special features of the devices are their small size and their silent measurement function. Therefore, patients can measure their BP whenever and wherever they need to, such as at the workplace when they are experiencing stress. Devereux et al. demonstrated that BP measured in the workplace was more closely related to left ventricular mass index than clinic BP.17 As daytime MHT is often overlooked by home BP measurements, typically taken early in the morning and at bedtime, this watch‐type wearable BP monitor could be useful for detection of daytime MHT. Historically, ABPM has been used to measure daytime BP, and it has been demonstrated that work stress may increase ambulatory BP levels throughout the day.18 However, as the mental and physical burden in the use of ABPM is heavy, ABPM is not suitable for repeatable daily monitoring to identify daytime hypertension. Hence, such watch‐type wearable BP monitors as we have developed are expected to be a practical alternative to ABPM for evaluating daytime MHT. We recently proposed a “resonance hypothesis” for the triggering of CV events by BPV.19 According to this hypothesis, CV events are triggered by the synchronization of various BP surges such as BP surges induced by sleep apnea,20, 21 cold temperature, heavy stress, and physical activity,22 albeit with different time phases, producing an unexpected large dynamic BP surge.23 The watch‐type wearable BP monitor could be useful for assessing BP surges during the daytime, resulting in the prevention of unexpected CV events during the daytime.
The watch‐type BP monitor has the limitation that patients must set their wrist at their heart level for a precise reading. Some previous studies have demonstrated that BP differs by 7 mm Hg if the height difference between the heart level and cuff position is 10 cm24, 25 due to hydrostatic pressure. Therefore, a future study evaluating the accuracy of the watch‐type wearable BP monitor under real‐world conditions during the day will be needed in order to assess how the watch‐type wearable BP monitor is adopted and experienced by users for monitoring daytime BP. In addition to daytime BP monitoring, the watch‐type BP monitor is expected to be a good tool for nighttime BP monitoring due to its strong features. However, as the accuracy of the wrist‐type BP monitor might be affected by body or palm position,26, 27 its accuracy in the supine position should be carefully evaluated. As well as real‐world conditions during the day, a future study evaluating the accuracy of the watch‐type wearable BP monitor under real‐world conditions during sleep will be needed.
4.1. Limitation
The ranges of wrist circumferences accommodated by HEM‐6410T‐ZM and HEM‐6410T‐ZL (16‐19 cm and 18‐21.5 cm, respectively) are very narrow and do not fulfill the requirements of the criteria of ANSI/AAMI/ISO 81060‐2:2013 guideline.
5. CONCLUSIONS
In conclusion, both watch‐type wearable BP monitors (the Omron HEM‐6410T‐ZM and the Omron HEM‐6410T‐ZL) fulfilled both validation criterion 1 and criterion 2 of the ANSI/AAMI/ISO 81060‐2:2013 guidelines when used in the sitting position with the wrist at heart level.
CONFLICT OF INTEREST
Dr Mitsuo Kuwabara, Ms Kanako Harada, and Ms Yukiko Hishiki are employees of Omron Healthcare Co., Ltd.
ACKNOWLEDGMENTS
We gratefully acknowledge the volunteers who agreed to have their BP measured for the purpose of the present study. In addition, we gratefully acknowledge Mrs. Ayako Okura for her editorial support.
Kuwabara M, Harada K, Hishiki Y, Kario K. Validation of two watch‐type wearable blood pressure monitors according to the ANSI/AAMI/ISO81060‐2:2013 guidelines: Omron HEM‐6410T‐ZM and HEM‐6410T‐ZL. J Clin Hypertens. 2019;21:853–858. 10.1111/jch.13499
Funding information
This research was supported by research funds from Omron Healthcare and was conducted under the auspices of the SURGE (SUper ciRculation monitorinG with high tEchnology) R&D Center developed collaboratively between Jichi Medical University and Omron Healthcare.
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