Ratio-Independent Blood Pressure Estimation by Modeling the Oscillometric Waveform Envelope

Oscillometry is the most common measurement method used in electronic blood pressure (BP) monitors. However, most of the existing oscillometric algorithms employ empirical ratios on the oscillometric waveform envelope (OMWE) to determine the systolic pressure (SP) and diastolic pressure (DP). As these algorithms do not consider the cardiovascular system parameters that may vary due to health conditions or age, the pressure estimates are not always reliable. In this paper, we develop a new mathematical model for the OMWE by incorporating an existing model of the cuff-arm-artery system. The unique feature of our developed model is that it explicitly represents the relationship between the OMWE and the SP and DP. Based on our developed model, we propose a new ratio-independent oscillometric BP estimation method. The proposed method is based on minimizing the sum of the squared errors between our model and the OMWE using the trust-region-reflective algorithm. Our proposed method is validated in a pilot study against Omron HEM-790IT and BpTRU BMP-100 BP monitors. It is found that the mean absolute error of the proposed method in estimating SP and DP is 4.60 and 4.53 mmHg, respectively, relative to the Omron monitor, and 3.66 and 2.84 mmHg, respectively, relative to the BpTRU monitor. The proposed model thus shows promise toward developing robust BP estimation methods.