Modeling of the Cuffless Blood Pressure Measurement Errors for the Evaluation of a Wearable Medical Device

The two widely used standards for validating the conventional cuff-based BP devices are those set up by the American Association for the Advancement of Medical Instrumentation (AAMI) and the British Hypertension Society (BHS) respectively. It was reported that although both standards work well for most BP devices, they do not agree with each other in all circumstances. Previous attempts to model the measurement errors as Gaussian could not explain the phenomena. Results of this study indicate that the general t distribution fits better to the BP measurement errors reported in previous literatures and collected from our clinical experiments. Furthermore, the theoretical mapping of the AAMI accuracy criteria and BHS grading system derived from the t distribution model can better reflect the real situations, where some devices can pass the BBS criteria but fail that of the AAMI. Based on this mapping relationship, it is found that current standards work well for devices with error distribution close to Gaussian but they may not be suitable for the newly developed wearable BP measuring devices used in the experiment, where the errors followed a t distribution with a smaller degree of freedom. It is suggested that a statistical measure that takes into account both the probability and the absolute value of the extreme errors could be introduced into the standard in order to better evaluate this kind of wearable, cuffless BP measuring devices.