Self-blood pressure (BP) monitoring presents several advantages compared with office BP measurement as it provides multiple readings under standardized conditions and avoids the white-coat effect 1–3. Oscillometric devices are becoming increasingly popular, especially for self-measurement of BP at home. The accuracy of BP measuring devices is of prime importance and all of them should be validated according to agreed criteria 2,4. The aim of the present study was to verify the accuracy of the UA-651 (Fig. 1) (UA-611 without AC adapter), an oscillometric device developed by the A&D Company for self-BP measurement at the upper arm, according to the International Protocol revision 2010 of the European Society of Hypertension (ESH) 5.
Materials and methods
The UA-651 device is a compact and fully automated monitor developed by the A&D Company (Tokyo, Japan), which measures BP at the upper arm using the oscillometric technique. Systolic BP, diastolic BP, and heart rate are displayed on a liquid crystal digital display. The device detects BP values during the deflation period. Power supply is provided by four batteries or through an AC adapter. The same device without AC adapter is marketed under the name UA-611. There are three cuffs provided by the manufacturer that are suitable for upper arm circumferences ranging between 22 and 32 cm (standard adult cuff), between 23 and 37 cm (semilarge cuff), and between 31 and 45 cm (large cuff).
Forty test measurements were carried out. No problems were encountered. The observer agreement was evaluated according to the ESH protocol 5 and was −1.0±2.0 mmHg for systolic BP and −0.8±2.2 mmHg for diastolic BP.
The International Protocol revision 2010 of the ESH requires the enrollment of 33 patients who are divided into three groups according to their BP range 5. The number of observer test measurements in each pressure range must be between 22 and 44. The difference between the range with the highest count and that with the lowest count cannot exceed 19. Ideally, the recruitment BPs should be in the range 90–180 mmHg for systolic BP and 40–130 mmHg for diastolic BP. However, if patients with BPs beyond these ranges are available, they may be included but only to a maximum of four such pressures. The discrepancy between the reading provided by the sphygmomanometer and the mean of the observer’s measurements is allocated to four zones of accuracy, which is determined by the number of differences in these ranges.
Participants and recruitment
The UA-651 device was evaluated in 42 adult individuals (20 men) with BPs within the ranges required by the protocol. The participants were recruited from the outpatient clinics, wards, and from among the medical staff at the Department of Medicine, University of Padova, Padua, Italy. Nine participants (seven men) were excluded because their BP was within the BP ranges already completed, leaving an overall number of 33 participants (13 men and 20 women). Recruitment details and participant characteristics are reported in Tables 1–3. There was some difficulty in recruiting patients with BP in the high ranges, but apart from this, there was no problem. The study was approved by the Ethics Committee of the University of Padova, and written informed consent was provided by the participants.
The validation team included three individuals (two observers and one supervisor). The two observers involved in the validation (C.F. and E.B.) had received adequate training by an expert in BP measurement. The BP was measured in a quiet room at a comfortable temperature, without any noise that could interfere with the auscultation of BP. During the test, the participants were evaluated in the sitting position, and sequential same arm measurements were taken. The two observers were blinded to the measurements obtained by each other and to the device readings. BP measurements were taken with a mercury sphygmomanometer at the upper arm, using an adult cuff with a bladder that was at least 80% of the arm circumference and had a width that was at least 40% of the same. The mean value of the first observer’s measurement was used to categorize the participant into a low, medium, or high BP range, separately for systolic BP and diastolic BP (Table 3). Four sequential readings were taken by observers 1 and 2 using a double-headed stethoscope and a mercury sphygmomanometer (BP1, BP3, BP5, and BP7), whereas three BP readings were taken by the supervisor using the test instrument (BP2, BP4, and BP6). At least 60 s were allowed between two measurements. The differences between the readings provided by the device and the mean observer measurements were calculated. Therefore, each device measurement was compared with the previous and the next mean observer measurement. Correlations between device–observer differences and other clinical variables were calculated using Pearson’s test with Bonferroni adjustment for multiple tests. Between-sex comparisons were evaluated using an unpaired t-test adjusting for age and arm circumference. A P-value of less than 0.05 was considered statistically significant. For analyses, the Systat, version 11 statistical package (SPAA Inc., Evanston, Illinois, USA) was used.
The results of the study are presented in Tables 4–6. The observer measurements showed a good agreement. The device–observer disagreement was −0.4±4.4 mmHg for systolic BP and −1.3±3.5 for diastolic BP. The validation results fulfilled all the 2010 ESH revision Protocol criteria for the general population and passed all validation grades. No correlation was found between the systolic or diastolic BP discrepancies and age, body weight and height, arm circumference, and mean device and observer BP level (all P>0.10). The BP discrepancies did not vary according to sex (P>0.11).
The present study showed that the A&D UA-651 BP monitor fulfilled the recently proposed ESH standards for use in the general adult population because it passed all phases of the 2010 ESH revised Protocol. The recruitment of individuals in the high BP range proved to be difficult and accounted for the extra number of screened participants. The UA-651 BP device proved to be accurate across the entire range of age, BP level, body size, and arm circumference, and its performance did not vary according to sex. Visual inspection of the device–observer discrepancies (Fig. 2) confirmed that the error was unrelated to patient BP levels and that the discrepancies were not higher at the extremes of BP. Only one observer–device systolic BP difference was beyond the +15/−15 mmHg range (+20 mmHg) probably because of an unnoticed arm movement or muscular contraction during the deflation phase that may have affected the accuracy of measurement.
As the UA-651 device (UA-611 without AC adapter) has reached the required ESH standards, it can be recommended for self-BP monitoring in the general population.
Conflicts of interest
There are no conflicts of interest.
1. Ohkubo T, Imai Y, Tsuji I, Nagai K, Kato J, Kikuchi N, et al..Home blood pressure
measurement has a stronger predictive power for mortality than does screening blood pressure measurement: a population-based observation in Osama, Japan.J Hypertens1998;16:971–975.
2. Parati G, Stergiou GS, Asmar R, Bilo G, de Leeuw P, Imai Y, et al..European Society of Hypertension practice guidelines for home blood pressure
monitoring.J Hum Hypertens2010;24:779–785.
3. Mancia G, Fagard R, Narkiewicz K, Redón J, Zanchetti A, Böhm M, et al..2013 ESH/ESC Guidelines for the management of arterial hypertension: the Task Force for the management of arterial hypertension of the European Society of Hypertension (ESH) and of the European Society of Cardiology (ESC).J Hypertens2013;31:1281–1357.
4. Palatini P, Frick GN.Techniques for self-measurement
of blood pressure: limitations and needs for future research.J Clin Hypertens2012;14:139–143.
5. O’Brien E, Atkins N, Stergiou G, Karpettas N, Parati G, Asmar R, et al..European Society of Hypertension International Protocol revision 2010 for the validation
of blood pressure measuring devices in adults.Blood Press Monit2010;15:23–38.