Nonlinear Dynamic Modeling of Blood Pressure Waveform: Towards an Accurate Cuffless Monitoring System

The objective is to develop a cuffless modelling approach to accurately estimate the blood pressure (BP) waveform and extract important BP features, such as the systolic BP (SBP), diastolic BP (DBP), and mean BP (MAP). Access to the full waveform has significant advantages over previous cuffless BP estimation tools in terms of accuracy and access to additional cardiovascular health markers (e.g., cardiac output), as well as potentially providing arterial stiffness and identifying different cardiovascular diseases. Nonlinear autoregressive models with exogenous input (NARX) are implemented using an artificial neural network to predict the BP waveforms using electrocardiography (ECG), and/or photoplethysmography (PPG) signals as inputs. The efficacy of the model is compared with a pulse arrival time (PAT) model using 15 subjects from the MIMIC II database. Two training modes are considered: training on the first eight minutes of data for each subject (Predictive training) and testing on the rest (up to 5.2 hours); and training on the first and the last eight minutes (Interval training) and testing the model in between. Predictive training and Interval training exhibited similar results initially, while Interval training resulted in higher accuracy over longer periods. The proposed method models the BP as a dynamical system leading to better accuracy in the estimation of SBP, DBP and MAP when compared to the PAT model. Moreover, the NARX model, with its ability to provide the BP waveform, yields more insight into patient health.