A simulator to test automated non-invasive sphygmomanometers
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To identify possible causes of inaccuracy in the use of the Hawksley random-zero sphygmomanometer and methods that could reduce this.Four Hawksley random-zero sphygmomanometers were compared with a standard sphygmomanometer under static conditions. Two methods (standard and rapid) were used to release pressure from the inflated cuff with pressures recorded by independent blinded observers. The rate at which the hand valve released pressure was analysed. The effects of varying filling times and pressures on the size of the final zero correction were investigated.The Hawksley devices all under-recorded pressure compared with that measured by using a standard machine. A rapid means of pressure release approximately halved this error in each case. Pressure release through the hand valve was shown to have a characteristic and prolonged exponential decay. Using low filling times and pressures reduced the observed range of zeros seen, with the production of a correlation between the size of the zero and the inflation pressure used.These findings suggest that overestimation of the final zero correction is a common and major source of error in the use of the Hawksley sphygmomanometer. A simple change in the design of the final pressure release would improve the machine's reliability in clinical usage. The machine's zero mechanism is susceptible to unintentional misuse. Such misuse could occur when the machine is used in accordance with current sphygmomanometry guidelines.
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Hypertension is the most commonly managed problem in general practice. Systematic errors in blood pressure measurements caused by inadequate sphygmomanometer calibration are a common cause of over- and underidentification of hypertension.This article reviews sphygmomanometer error and makes recommendations regarding in service maintenance and calibration of sphygmomanometers.Most sphygmomanometer surveys report high rates of inadequate calibration and other faults, particularly in aneroid sphygmomanometers. Automatic electronic sphygmomanometers produce systematic errors in some patients. All sphygmomanometers should be checked and calibrated by an accredited laboratory at least annually. Aneroid sphygmomanometers should be calibrated every 6 months. Only properly validated automatic sphygmomanometers should be used. Practices should perform regular in house checks of sphygmomanometers. Good sphygmomanometer maintenance and traceable sphygmomanometer calibration will contribute to reducing the burden of cardiovascular disease and the number of patients overtreated for hypertension in Australia.
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Objective To identify possible causes of inaccuracy in the use of the Hawksley random-zero sphygmomanometer and methods that could reduce this. Methods Four Hawksley random-zero sphygmomanometers were compared with a standard sphygmomanometer under static conditions. Two methods (standard and rapid) were used to release pressure from the inflated cuff with pressures recorded by independent blinded observers. The rate at which the hand valve released pressure was analysed. The effects of varying filling times and pressures on the size of the final zero correction were investigated. Results The Hawksley devices all under-recorded pressure compared with that measured by using a standard machine. A rapid means of pressure release approximately halved this error in each case. Pressure release through the hand valve was shown to have a characteristic and prolonged exponential decay. Using low filling times and pressures reduced the observed range of zeros seen, with the production of a correlation between the size of the zero and the inflation pressure used. Conclusion These findings suggest that overestimation of the final zero correction is a common and major source of error in the use of the Hawksley sphygmomanometer. A simple change in the design of the final pressure release would improve the machine's reliability in clinical usage. The machine's zero mechanism is susceptible to unintentional misuse. Such misuse could occur when the machine is used in accordance with current sphygmomanometry guidelines.
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Seven types of sphygmomanometer were used in random order on each of nine hypertensive patients and the readings compared with simultaneous intra-arterial blood-pressure recordings. All the devices gave significantly different values for systolic pressure, and only two measured diastolic pressure without significant error. Systolic pressure was consistently underestimated (range 31-7 mm Hg), and all but one instrument overestimated diastolic pressure (range 10-2 mm Hg). The variability of readings was least with the standard mercury sphygmomanometer and the random-zero machine, while with some of the more automated devices single readings were in error up to -68/33 mm Hg. The strong correlations found between intra-arterial and cuff systolic pressures with all devices tested and significant correlations for diastolic pressure with all but one device indicate that, with one possible exception, the sphygmomanometers would give accurate results where a change in blood pressure was the main concern.
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To quantify overdetection and underdetection of hypertension caused by systematic sphygmomanometer errors permitted by the current European standard (EN 1060 'noninvasive sphygmomanometers').We carried out Monte Carlo simulation of measurement of blood pressure (BP) of the adult Australian population using sphygmomanometers showing systematic errors compliant with the EN 1060 standard. We repeated the simulations limiting systematic sphygmomanometer errors to +/-1 mmHg. Simulated BP measurements included systematic sphygmomanometer error, random intraindividual BP variability and random measurement error.After three visits, underdetection of hypertension is common owing to variability of BP measurements and systematic errors of sphygmomanometers. After three visits, the wide tolerances of EN 1060 are responsible for approximately 4.9 and 11% of underdetection of systolic and diastolic hypertension, respectively. Underdetection is worse in some groups, for example, permitted sphygmomanometer error causes 20% of all undetected systolic hypertension in 18-24 year-old women. The current standard also results in overdetection of hypertension. Permitted sphygmomanometer error causes 5.8 and 14% of the overdetection of systolic and diastolic hypertension, respectively, after three visits. Overdetection is worse in some groups, for example, after three visits, permitted sphygmomanometer error causes 19% of falsely detected diastolic hypertension in 18-24 year-old men. For all adults, reduction of permitted sphygmomanometer error to +/-1 mmHg achieves approximately the same improvement in hypertension detection as at least one additional visit to the clinician.Systematic sphygmomanometer errors permitted by the current standard are a preventable cause of clinically significant overdetection and underdetection of hypertension. The standard should be revised to make the effects of equipment related systematic errors negligible compared with the effects of physiological variability.
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Abstract The sphygmomanometer is a widely used device for non-invasive blood pressure measurement. Systematic measurement errors and uncertainties can affect measurements, consequently, impacting diagnosis or medication. In order to maintain the conformity of the instruments, sphygmomanometers are usually under control of legal metrology demanding periodical verifications. Automated sphygmomanometers are based on the oscillometric method, measuring small changes of arterial blood pressure occurring in the cuff. Once pressure working standards are unable to generate the oscillometric pulses, verifications are performed on the sphygmomanometer on its manometer mode, disregarding the contribution of the oscillometric mode to the uncertainties. The present study investigates the contribution of the oscillometric method to the expanded measurement uncertainty. We used a patient simulator in four sphygmomanometers available in the market for consumers. The results show that the contribution of the oscillometric mode to the expanded uncertainty can be significant, varying from 0.16 to 1.56 mmHg and from 0.12 to 1.55 mmHg, for 100 and 150 mmHg, respectively. We also observed different contributions to the uncertainty for systolic and diastolic blood pressure.
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Objective To estimate the contribution of inadequate sphygmomanometer calibration to over- and under-detection of hypertension. Design Monte Carlo simulation of the measurement of blood pressure (BP) of a population with calibrated and uncalibrated sphygmomanometers. Simulated BP measurements included systematic sphygmomanometer error and random variability. Main outcome measures The percentage of hypertensive adults (BP > 140/90 mmHg) not detected and the percentage of adults incorrectly classified hypertensive due to sphygmomanometer error. The percentage of the false positives and false negatives attributable to sphygmomanometer error. The number of additional visits patients need to make to obtain the same improvement in hypertension detection as is obtained by sphygmomanometer calibration. Results After three visits, uncalibrated sphygmomanometer error causes 20 and 28% of all undetected adult systolic and diastolic hypertension, respectively, and 15 and 31% of all falsely detected adult systolic and diastolic hypertension. In some groups, under-detection is worse; for example, sphygmomanometer error causes 27% of all missed systolic hypertension in 35–44-year-old females. In some age groups, over-detection is worse; for example, after three visits, sphygmomanometer error causes 63 and 50% of falsely detected systolic and diastolic hypertension in 18–24-year-old females, respectively. In-service sphygmomanometer calibration achieves the same or greater improvement in hypertension detection as an additional two visits. Conclusions Uncalibrated sphygmomanometers are a preventable cause of clinically significant over- and under-detection of hypertension. Sphygmomanometers should be calibrated regularly by accredited organizations or technicians. Standards and guidelines governing sphygmomanometers in service should be revised. Sphygmomanometer calibration is a cost-effective way of improving hypertension detection.
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This survey assessed the measurement of blood pressure and use of sphygmomanometers by general practitioners in Humberside and Yorkshire in 1988. All registered practitioners were sent a questionnaire--1223 (58%) returned it completed. Their responses showed that 269 (22%) had an aneroid sphygmomanometer only, and that 120 (10%) had a random zero sphygmomanometer; 700 (57%) had special cuffs for obese patients, and 558 (46%) had special cuffs for children; 228 (23.5%) had never had their sphygmomanometers serviced ('never' corresponding to a mean time of 5.75 years), while 23% had patients who measured their own blood pressure. These findings suggest that the British Hypertension Society's recommendations on servicing and cuff use are not always applied. A formal audit of the use of different types of sphygmomanometer in general practice may encourage and improve accuracy and uniformity in blood pressure recording.
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