Blood Pressure Monitoring
Devices and Technology
Accuracy of aneroid sphygmomanometers in clinical usage: University of Michigan experience
a Division of Hypertension, University of Michigan Health System, Chelsea, Michigan 48118, USA b Department of Chemical Engineering, University of Michigan, Ann Arbor, Michigan, USA.
Correspondence and requests for reprints to Steven A Yarows, MD, Clinical Associate Professor of Internal Medicine, Division of Hypertension, University of Michigan Health System,128 Van Buren, Chelsea, Michigan 48118, USA. E-mail: [email protected]
Received 7 July 2000
Revised 12 March 2001
Accepted 19 March 2001
Abstract
Background
Aneroid manometers are frequently used to measure blood pressure. Aneroid manometers have moving parts that are subject to fatigue. The accuracy duration of the aneroid devices, like most digital devices, is unstudied. It has been accepted that if the aneroid device does not rest at ‘0’ it is inaccurate, but how often is the device inaccurate when it does rest at ‘0’?
Methods
A Universal Biometer DPM-III measuring unit was used for all of the measurements at 10 University of Michigan Health System sites. A total of 136 aneroid manometers were tested. Two additional aneroid devices were not tested, as the needle did not start within ‘0’. Static pressure measurements were made at nine levels for all devices: 50, 80, 90, 100, 120, 150, 200 and 250 mmHg.
Results
The average difference of the nine pressure settings of the whole group was 0.2±0.31 (95% confidence interval 0.1–0.2) mmHg. The largest number of devices that were not calibrated within ±3 mmHg was seen at the 150 mmHg setting with six (4.4%) of the devices failing. If an accuracy standard of ±2 mmHg was used, the largest number of devices failed at 250 mmHg (22 devices, 16.2%). The largest number of devices that were inaccurate was manufactured 6 years prior to testing and was from two sites.
Conclusions
Aneroid devices were accurate. A yearly calibration programme should be performed and a ±2 mmHg standard should be used. Portable aneroid manometers may need to be more frequently calibrated due to the trauma associated with dropping.