Introduction

Accurate blood pressure (BP) measurement is the basis for the diagnosis, classification, and understanding of the effects of drug treatment and follow-up of hypertension by healthcare professionals [1]. It can be said that BP measurement accompanies hypertensive patients throughout their lives. At the same time, there is a need for regular BP monitoring in healthy populations to identify hypertensive patients at an early stage for secondary or even primary prevention of cardiovascular disease [2].

Patients prefer electronic BP monitors for their convenience. The accuracy of electronic BP monitors must be validated. The members of the AAMI, ESH and ISO committees have reached a consensus on an optimal validation standard, AAMI/ESH/ISO universal standard (ISO 81060-2:2018+Amd.1:2020), which is now considered the standard protocol for the validation of non-invasive BP devices [3–6].

An automated oscillometric upper-arm BP monitor, DBP-1333b (hereafter referred to as the test device), was developed and manufactured by JOYTECH Healthcare Co., Ltd. (Hangzhou, China) for family and clinical use. The aim of this study was to validate its efficacy in adult population according to AAMI/ESH/ISO universal standard (ISO 81060-2:2018+Amd.1:2020).

Methods

This trial was approved by the ethics committee of the Affiliated Suzhou Science and Technology Town Hospital of Nanjing Medical University before it was conducted (Ethics number: IRB202303-003).

Participants

For this study, participants were recruited from patients who sought medical treatment at the Affiliated Suzhou Science and Technology Town Hospital of Nanjing Medical University. Inclusion criteria for subjects: (1) age >12 years, regardless of sex; (2) informed consent and voluntary participation in the study; (3) able to communicate well with research physicians, have good compliance, and be able to follow the requirements of the clinical research. Exclusion criteria: (1) allergy to the materials of the cuffs of the sphygmomanometers; (2) severe arrhythmia; (3) persons with impaired consciousness who cannot be fully informed. According to the AAMI/ESH/ISO universal standard (ISO 81060-2:2018+Amd.1:2020) for a general population validation study at least 85 individuals aged older than 12 years are required. Collected data from ≥3 sets of each subject, with a minimum of 255 sets in total. Demographic data including age, sex, height, weight, history of hypertension, and arm circumference were recorded. Each participant provided informed consent for the study.

Instruments

The test device was the DBP-1333b, which uses the principle of oscillometry to measure SBP, DBP and pulse rate through the human arm. The pressure range of this device is 0–300 mmHg and the pulse rate range is 30–180 beats per minute. The arm circumference range of the cuff is 22–42 cm. It is equipped with additional functions such as low-voltage alarm, irregular heartbeat reminder and automatic storage of BP readings.

Use a reference sphygmomanometer that complies with the requirements of ISO81060-1. The reference device was the XJ11D, which is a mercury BP monitor. It was used in conjunction with a stethoscope to measure BP by auscultation. Multiple reference cuffs, consisting of an inflatable inner bladder and a non-inflatable external cuff, were used according to the subject’s arm size and met the requirements of the ISO standard of the cuffs.

Observer training and assessment

Two observers used a mercury sphygmomanometer (XJ11D) to measure the subjects’ BP and recorded their own readings independently. An independent (third) supervisor recorded the measurement results of the test device. Each observer’s measurements were not visible to the other. Observers were trained on mercury BP measurement according to the Universal Standard and conducted sufficient practice.

Procedures

Validate the accuracy of test device in a quiet and comfortable environment. The subject’s legs should not be crossed with their feet being flat on the floor. The measurement site was at the level of the subject’s left ventricle. Avoid talking during the measurement. The cuff was worn on the exposed upper arm of the participants.

The same arm sequential method was used. To determine the reference DBP, the observers used the fifth phase of Korotkof sound (K5). The participant was excluded if the fifth phase (K5) was not audible. If any monitor detected a significant irregular heartbeat, the reading was excluded. If the difference between any pair of SBP or DBP measured by the observers was greater than 4 mmHg, the data were excluded. Data from participants were excluded if any two reference SBP determinations differed by more than 12 mmHg or if any two reference DBP determinations differed by more than 8 mmHg. The average of the two observers’ readings was used as the reference BP for this measurement.

Analysis

Statistical analyses were performed using SPSS. Means, standard deviations and frequency counts (percentages) were used for statistical description. According to the requirements of AAMI/ESH/ISO universal standard (ISO 81060-2:2018+Amd.1:2020), the test device should meet two criteria. For Criterion 1: take the difference between the SBP and DBP of the test and reference device for each valid data set and calculate the mean and SD of all differences. For Criterion 2: take the average BP values of each set of the test and reference device for each subject and calculate the SD of the average values for all subjects. The average difference between the measurement results of the test and reference device was displayed with Bland-Altman plots (Figs. 1–4). Figure 5 showed the differences between the test device and reference (Y axis) versus arm circumference (X axis) for SBP and DBP.

Fig. 1:

Distribution diagram for difference value of SBP (mmHg) measured by the test device and the reference device (262 sets of data).

Fig. 2:

Distribution diagram for difference value of DBP (mmHg) measured by the test device and the reference device (262 sets of data).

Fig. 3:

Distribution diagram for difference value of SBP (mmHg) measured by the test device and the reference device (90 sets of data).

Fig. 4:

Distribution diagram for difference value of DBP (mmHg) measured by the test device and the reference device (90 sets of data).

Fig. 5:

(a) Distribution diagram for the differences between the test device and reference (Y axis) versus arm circumference (X axis) for SBP. (b) Distribution diagram for the differences between the test device and reference (Y axis) versus arm circumference (X axis) for DBP.

Results

A total of 95 people were recruited for this study, of whom 4 were excluded because the difference in DBP between the reference device was more than 8 mmHg. One participant was excluded because she was 12 years old. No one was excluded because of the hearing problem of the Korotkoff K5 sound. 8 sets of data were excluded for the following reasons: 3 sets of data were excluded because of missing data measured by the reference device; 3 sets of data were excluded because the DBP measured by the two observers differed by more than 4 mmHg; 1 set of data was excluded because the SBP measured by the two observers differed by more than 4 mmHg; and 1 set of data was excluded because the DBP measured by the reference device differed by more than 8 mmHg from the previous two sets of data. A total of 262 sets of effective measurement data from 90 participants were analyzed. Among them, 44 were males (48.9%) and 46 were females (51.1%). The participants’ average age was 51.21 ± 15.86 years (range: 22–87 years). There were 6 patients with diabetes (6.7%), 5 patients with peripheral arterial disease (5.6%), 28 senior patients (age ≥ 60 years, 31.1%) and 11 patients with renal failure (12.2%). The average arm circumference was 31.49 ± 5.14 cm (range: 22.00–41.00 cm). The mean SBP measured by the test device was 122.99 ± 20.63 mmHg (range: 84.00-194.00 mmHg) and the mean DBP was 74.26 ± 11.23 mmHg (range: 45.00–104.00 mmHg). Mean SBP measured by the reference device was 122.80 ± 21.52 mmHg (range: 87.00–191.00 mmHg) and mean DBP was 74.85 ± 12.39 mmHg (range: 54.50–104.00 mmHg). Three types of cuff sizes were used in the validation. General criteria requirements for age, sex, arm circumference, BP, and special population distribution were met. See Table 1 for detailed information.

Table 1 - Characteristics of the study participants (n = 90) Variable the ISO 81060-2:2018 standard (n, %) Value (%) Age, y (range) 51.21 ± 15.86 years (22–87 years)  >12 years and <18 years / 0 (0.0%)  ≥18 years old and <60 years old / 62 (68.9%)  ≥60 years / 28 (31.1%) Men: women, n (%) Men (≥26, ≥30%); women (≥26, ≥30%) 44 (48.9%): 46 (51.1%) Arm circumstance, cm (range) 31.49 ± 5.14 cm (22.0–41.0 cm)  ≥ 22.0 and ≤ 27.0 cm ≥17, ≥20% 20 (22.2%)  > 27.0 and ≤ 32.0 cm ≥17, ≥20% 31 (34.4%)  > 32.0 and ≤ 37.0 cm ≥17, ≥20% 19 (21.1%)  > 37.0 and ≤ 42.0 cm ≥17, ≥20% 20 (22.2%)  ≥ 22.0 and ≤ 24.5 cm ≥9, ≥10% 9 (10.0%)  ≥ 39.5 and ≤ 42.0 cm ≥9, ≥10% 10 (11.1%) SBP, mmHg (range)  ≤100 mmHg ≥5% 48 (13.6%)  ≥160 mmHg ≥5% 29 (8.2%)  ≥140 mmHg ≥20% 76 (21.6%) DBP, mmHg (range)  ≤60 mmHg ≥5% 39 (11.1%)  ≥100 mmHg ≥5% 18 (5.1%)  ≥85 mmHg ≥20% 89 (25.3%) Cuff sizes (label arm circumference range) Arm circumference interval of subjects in the validation Number of subjects  18–26 ≥22 cm and ≤24 cm 8  22–32 >24 cm and ≤32 cm 43  32–42 >32 cm and ≤42 cm 39

Data are expressed as the means ± SD or percentages or number.

262 valid paired measurements according to Criterion 1 showed that the mean difference in SBP was 0.19 mmHg, with a SD of 7.45 mmHg and the mean difference in DBP was −0.59 mmHg, with a SD of 6.47 mmHg. The average difference between SBP and DBP was less than 5 mmHg; the SD was less than 8 mmHg. The result met the Criterion 1. The Bland-Altman plots of the differences in SBP and DBP between the test and reference device are shown in Figs. 1 and 2.

Ninety-one valid paired individual average according to Criterion 2 showed that the SD of SBP between the test and reference device was 5.79 mmHg and the SD was less than 6.95 mmHg; the SD of DBP was 5.58 mmHg and the SD was less than 6.93 mmHg, which met Criterion 2. The Bland-Altman plots of the differences in SBP and DBP between the test and reference device are shown in Figs. 3 and 4.

Discussion

This study validated the accuracy of DBP-1333b measurement in adult population based on AAMI/ESH/ISO universal standard (ISO 81060-2:2018+Amd.1:2020). The results showed that the measurement results of the test and reference device were very close, meeting all the accuracy requirements of international standards.

The DBP-1333b uses the oscillographic method to measure BP. By detecting the amplitude of the pulse wave transmitted from the brachial artery to the cuff, the pulse pressure curve is recorded and then the corresponding algorithm is used to continuously calculate the BP value. The device is easy to use and is not as susceptible to external noise as the fifth phase (K5) method. The additional functions of the DBP-1333b, such as irregular heartbeat reminder, memory function, Bluetooth function, etc., help to store measurement data and send it to intelligent devices for BP monitoring. During this validation process, all of the additional functions performed well.

The results of the research showed that DBP-1333b met the two criteria of AAMI/ESH/ISO universal standard (ISO 81060-2:2018+Amd.1:2020). However, several groups of test and reference device measurements showed a high degree of variability. The reason for this may be that BP itself is a vital sign that fluctuates easily and is affected by many factors. Although we used a number of methods to control the influencing factors as much as possible during the trial, influencing factors such as emotions are still difficult to control. It is possible that these may have contributed to the differences in the measurements of these groups.

The test device had good stability, no device failures, and were easily to operate. This study had several limitations, such as the inclusion of participants that did not include pregnant women or people with cardiac arrhythmia, and future research needs to be validated in these populations.

Conclusion

The DBP-1333b met the validation criteria of AAMI/ESH/ISO universal standard (ISO 81060-2:2018+Amd.1:2020) and can therefore be recommended for clinical and self/family BP measurement in adults.

Acknowledgements

This study was funded by the JOYTECH Healthcare Co., Ltd., Hangzhou, China, through the Affiliated Suzhou Science and Technology Town Hospital of Nanjing Medical University Account for Research.

Guocun Hou conceived and implemented this study. Yulu Wu wrote the initial draft of the paper. Jiaying Wang and Jia Zhi provided important suggestions. All authors read and approved the final manuscript.

Conflicts of interest

There are no conflicts of interest.

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