The minimum numbers required for each blood pressure group.

Transcription

1 Validation of Stabil-O-Graph device for self-measurement of blood pressure according to the British Hypertension Society (BHS) standards and protocols. Dr. G.H.M ten Oever (a), Dr. Cortez-Campeáo (b), Dr. J. Bour (c), (a) G.H.M. ten Oever, General Practicioner, Roermond, The Netherlands, (b) Dr. med. Dionisio Cortez_Campeáo, Internal Medicine, Praxis Cortez-Capeáo / Flender, Sinsheim, Germany. (c) Dr. J. Bour, C.E.S. de Pharmacologie cardio-vasculaire et renale, Centre Hospitalier Lemire, Saint Avold, France Introduction During the past few years, the number of models of self-measurement blood pressure monitor for home us has considerably increased. There are dozens of models on the shelves: some with manufactures trademarks, some with those of trade houses, which order the devices on an original equipment manufacturing (OEM) basis. One of the basic characteristics of the monitors is accuracy of measurement of blood pressure. An impartial assessment criterion on the accuracy is clinical testing, during which readings obtained with the devices that are being tested are compared with standard sphygmomanometer results. Techniques of testing are regulated by national and international standards and protocols, the most popular of these being those of the Association for Advancement of Medical Instruments (AAMI) (1) and the British Hypertension Society (BHS) (2.3) The Self measurement blood pressure device Stabil-O-Graph is simple en easy to handle self-measurement blood pressure device one button operated device with large LCD screen showing systolic and diastolic blood pressure + pulse rate per minute. The SBPM device Stabil-O-Graph can memorize 50 measurements taken and these measurements can be downloaded to a Hypertension Management program. This allows you to store the measurement data under the patients name. The average BP of the last three (3) measured values is calculated automatically. The measuring range of the SBPM device Stabil-O-Graph is mmhg for SBP, mmhg for DBP and b/min for the Pulse Rate. The data-transfer to the Hypertension Management Software (Windows 95/98/NT/2000/XP) is done via infra-red-interface. The SBPM device Stabil-O-Graph contains an alarm-clock function which can be programmed for pre-scheduled BP measurements. Subjects and Methods The self-measurement blood pressure monitor Stabil-O-Graph (Company IEM GmbH, Stolberg, Germany) has been tested according to the standards and protocol (BHS 1990 protocol and BHS 1993 revised protocol) of the British Hypertension Society (BHS). The main validation test was performed in non-selected subjects for a total of 882 device measurements. In total 126 subjects (59 men and 67 women), aged from 16 to 85 mean age was years -, informed about the purpose of the test, were recruited, The tests were carried out in a group of subjects of the Centre Hospitalier Limére, St. Avold, France (Cardiology Department), General Practice Dr. G.H.M. ten Oever (GP), Roermond, The Netherlands and Dialysis Centre Dr. D. Cortez-Campeáo, Sinsheim, Germany. Patients with cardiac arrhythmia were not involved in the study. Subject Selection Subject selection was based on the requirements of the 1990 and 1993 revised BHS protocol. In selecting 126 subjects with a wide range of blood pressure it was likely that there were a representative range of arm circumferences. All subjects were not selected on the basis of arm circumference. The selection of subjects was not sufficient to specify merely that subjects had blood pressure within a specified range of pressure, because there might have been a tendency to recruit more subjects in the lower pressure range than those with higher pressures. Pressure ranges were therefore specified according to the 1990 and 1993 revised BHS protocol. The blood pressure used in the analysis was the entry blood pressure at the time of static validation, and was not measured at the time of recruitment for validation.

2 The minimum numbers required for each blood pressure group. Numbers Sex Age Range Arm Circumference 85 subjects Blood Pressure Range SBP (mmhg) < > 180 n DBP (mmhg) < > 110 n SBP: systolic blood pressure; DBP: diastolic blood pressure Testing Protocol The validation standards and protocol was based on the requirements of 1990 and 1993 revised BHS protocol. The method used was the sequential same-arm comparison protocol. Sequential same-arm measurements between the test instrument (self-measurement blood pressure device Stabil-O-Graph ) and a standard and calibrated mercury sphygmamanometer were carried out as followed. BP-A Entry blood pressure, observers 1 and 2 each with mercury standard. This blood pressure determined the blood pressure range to which the subject was allocated in subsequent analysis, it was not included in the analysis of this phase. BP-B Device (Stabil-O-Graph ) detection blood pressure, observer 3. This blood pressure was determined to permit the test instrument to determine the blood pressure characteristics of the subject, it was included in the analysis. BP-1 Observers 1 and 2 with mercury standard BP-2 Observer with test instrument (Stabil-O-Graph ) BP-3 Observers 1 and 2 with mercury standard BP-4 Observer with test instrument (Stabil-O-Graph ) BP-5 Observers 1 and 2 with mercury standard BP-6 Observer with test instrument (Stabil-O-Graph ) BP-7 Observers 1 and 2 with mercury standard At least 30 seconds were allowed between each measurement to avoid venous congestion, but no more than 60 seconds to minimize variability. Analysis was done separately by observers 1 and 2, using three pair of readings from each subjects. This resulted in a total of pairs of readings for each observer. To compare one observer and the test instruments, the data on the 126 subjects were analysed using the pairs BP-1 versus BP-2, BP-3 versus BP-4 and BP5 versus BP6. Than similarly data analysis were used using the pairs BP-2 versus BP-3, BP-4 versus BP-5 and BP-6 versus BP-7. The result which was more favourable to the test device (Stabil-O-Graph ) was selected.

3 Accuracy Criteria The percentages of test instrument ((Stabil-O-Graph ) measurement differing from the mercury standard by < 5, < 10 and < 15 mmhg were calculated separately for each observer and separately for systolic and diastolic blood pressure. The device was graded A, B, C or D separately for each observer, according to the criteria. The final grade for each systolic and diastolic blood pressure was the better grade obtained by the two observers. The difference (device-observer), for systolic and diastolic blood pressure separately (we used the date on which the finale grade was based), was plotted against the mean of the device (Stabil-O- Graph ) blood pressure and the observer blood pressure, using all 378points. Results All the analysis was carried out for the observers using three pairs of reading from each subject. In total 378 pairs of measurements by the test device (Stabil-O-Graph ) and observer were available for analysis. Individual readings were compared for two observers. The mean difference (observer 2 minus observer 1) between the measurements of the 2 observers (n= 378) were 0.1 mmhg for SBP and 0.0 mmhg for DBP, the related SDs being 2.2 mmhg and 2.3 mmhg, respectively. Additionally, in accordance with the AAMI guidelines, the proportion of readings agreeing to within 5,10 and 15 mmhg was calculated. Approximately 96 % of the SBP and 96 % of the DBP readings obtained by observers were within the 5 mmhg difference limit. Furthermore, % of the SBP and DBP readings were within 10 mmhg. This data agreed with AAMI recommendation. All measurements performed were successful. The simultaneous same-arm approach was used to compare the measurements taken by the observers and the SBPM test device Stabil- O-Graph. This according to the 1990 and 1993 BHS recommendations, in order to calculate the grading level of the test-device Stabil-O-Graph. The proportion of values agreeing to within, 5, 10 and 15 mmhg was 66 %, 89 %, and 96 % for SBP and 68 %, 92 %, and 98 % for DBP for the observers and device. Overall A/A grade for BHS.

4 The numbers for the SBPN Stabil-O-Graph test device blood pressure group. Numbers 126 subjects Sex (58 male/67 female) Age Range (16 85 year of age) Arm Circumference ( cm) Blood Pressure Range SBP (mmhg) < > 180 n 8(8) 57(20) 32(20) 20(20) 9(8) DBP (mmhg) < > 110 n 10(8) 43(20) 45(20) 20(20) 8(8) SBP: systolic blood pressure; DBP: diastolic blood pressure Absolute difference between standard and test-device (mmhg) Grade < 5 < 10 < 15 A 60% 85% 95% B 50% 75% 90% C 40 % 65% 85% D Less than C Less than C Less than C Absolute difference between standard and SBPM Stabil-O-Graph (mmhg) Grade < 5 < 10 < 15 A (SBP) 66% 89% 96% A (DBP) 66% 92% 98% Discussion The self-measuring blood pressure devices are more and more widely spread for the purpose of home monitoring and dynamic control of blood pressure. For their correct application, the accuracy of the devices determined at clinical testing is highly important. Comparative analysis has shown that only 50% of popular models of self-measuring blood pressure devices meet the requirements of AAMI accuracy and 15-20% those of BHS. The testing of the self-measuring blood pressure devices Stabil-O-Graph was carried out under the 1990 and 1993 BHS protocol, and with an assessment of accuracy in ranges of blood pressure level. It has shown high reliability, high accuracy under the requirements of the BHS and also AAMI. The self-measurement blood pressure device Stabil-O-Graph received the BHS grade A/A according to the British Hypertension Society validation standards and protocol. The data analysis results of the validation of the self-measurement blood pressure device Stabil-O-Graph agreed with AAMI recommendation. References: 1. Association for the Advancement of Medical Instruments. American national standard: electronic or automated sphygmomanometers. Arlington, Virginia: Association for the Advancement of Medical Instrumentation; O Brien E., Petrie J., Littler W., de Swiet M., Padfield PL., O Malley K., et al. The British Hypertension Society protocol for the evaluation of automated and semiautomated blood pressure measuring device with special reference to ambulatory systems. J.Hypertens 1990; 8: O Brien E., Petrie J., Little WA., de Swiet M., Padfield Pl., Altman D., et al. The British Hypertension Society Protocol for the evaluation of blood pressure measuring devices. J.Hypertens 1993; 11 (suppl 2):S43-S Pickering TG., Ambulatory Monitoring and Blood Pressure Variability. London: Science press: O Brien E., Mee F., Tan KS., Atkins N., O Malley K.,: Training and assessment of observers for blood pressure measurement in hypertension research. J Hum Hypertension 1991, 5: Clare R. Jones, Kirsten Taylor Chowienczyk, Lucille Poston and Andrew H. Shennan,; Avalation of the Mobil-O-Graph (version 12) ambulatory blood pressure monitor. Blood Pressure Monitoring, Vol. 5.No 4. August 2000.

5 World Health Organization-International Society of Hypertension Guidelines for the Management of Hypertension. Guidelines Subcommittee. JOH. Vol.117.No 2. Febr. 1999; The Authors like to thank Mr. Theo van de Kerkhof (RN) and Mr. Alexander Wolf (IEM GmbH) for there excellent support during the validation, and the assistance in technical knowledge concerning the Stabil-O-Graph and the HMS-software