Uncertainty estimation in the sphygmomanometers calibration according to OIML R16-1 from a legal metrology perspective

Abstract

Objective: To estimate the uncertainty in the calibration of sphygmomanometers according to OIML R16-1 from a legal metrology perspective. Materials and methods: Four (4) sphygmomanometers of different brands with a resolution of 2 mmHg were selected to perform the calibration, using several direct comparisons between a sphygmomanometer and a digital standard manometer with a resolution of 0.01 mmHg, generating pressure with a pneumatic clamp. The uncertainty was estimated using the Guide to the Expression of Uncertainty in Measurement (GUM) and the OIML R16-1 international recommendation. Two measurement series were computed, each with upward and decent sequence, to achieve 4 measurements each time with the corresponding errors. Results and discussion: Several uncertainty representations were achieved, in particular expressions such as type A, type B, and expanded, employing a physic modeling and a non-stochastic mathematic model. From the sphygmomanometer measurement series in calibration processes, the uncertainty contributions were analyzed, finding that the dominant uncertainty source, in most cases, is derived from the equipment resolution, followed by repeatability and hysteresis in the sphygmomanometer test processes. Conclusions: The proposed structure for estimating uncertainty follows international regulations and can be used in procedures for approval of models with a final impact on patient safety.