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Automatic electronic oscillometric blood pressure monitors (BPMs) are inaccurate in certain individuals though they have been validated, largely due to its disclosed algorithms. It is recommended that oscillometric devices should be calibrated by auscultation when first used but it’s difficult to practice. Here, we introduced a smartphone based technique to verify the accuracy of BPMs.
33 consecutive subjects were enrolled and 6 brands of BPMs were tested in this study. During measurement of electronic oscillometric BPMs, Korotkoff sounds were simultaneously collected by a stethoscope head beneath the cuff connected with a cellphone. And then an App called Accutension Stetho (http://accutension.com/accutension_stetho.html) could yield an auscultatory BP reading as reference using the synchronized cuff pressures displayed on the BPMs. BP differences between the BPMs and Accutension Stetho were then analyzed with our designed scoring system to rank the accuracy of these BPMs. The scoring system was based on three metrics: percentage distribution of BP differences from 0-9mmHg, mean value and SD of BP differences and deflating errors.
The score of accuracy among the 6 BPMs (BeurerBM26, Microlife 3MUI-4D, AND UA-771, Mabis 04-596-008, Yuwell YE6660A, OmronHEM7051) were 78.49, 63.83, 52.83, 49.75, 47.25, and 43.41 in turn. Pearson correlation coefficient and ICC of the readings between Accutension Stetho and BPMs showed good consistence (P<0.05). The deflating rate among the 6 BPMs were: 2.23, 3.48, 6.10, 2.44, 3.66 and 4.85 mmHg/beat, respectively. The deflating error which defined as deflating prior to the end of the Korotkoff sounds existed in 4 BPMs except for Beurer and Microlife, while Yuwell had the highest incidence.
Accutension Stetho could detect the BP difference between oscillometric BPMs readings and its real auscultatory readings simultaneously. Diastolic BP can be overestimated by device’s deflating prior to the end of the Korotkoff sounds. Using the scoring system we designed, the accuracy of BPMs could be ranked among the same subjects or on certain individual.