Subject-Based Model for Reconstructing Arterial Blood Pressure from Photoplethysmogram

Figure 1. A synchronized ABP and PPG signal. SBPi and DBPi in ABP refer to the ith systolic and diastolic blood pressure, respectively. Oi and Si stand for the ith onset and systolic peak, respectively. For the ith beat, the blue line is the systolic wave in ABP and PPG. This figure was used to show the correlation between ABP and PPG. Note that PPG = Photoplethysmogram, ABP = Arterial blood pressure, SBP = Systolic blood pressure, and DBP = Diastolic blood pressure.

Figure 2. Flowchart of the proposed method. For each record, the PPG was detrended, and the ABP was scaled in preprocessing. Then, they were segmented into 8.2 s. The first 80% of segments were used for training, and the last 20% were used for testing. For the test set, the ABP signal of the segments was stitched to generate the reference ABP. In addition, the model’s outputs were stitched to generate the reconstructed ABP. Note that PPG = Photoplethysmogram and ABP = Arterial blood pressure.

Figure 3. Histogram distributions of SBP and DBP of the data set. This figure shows that the dataset has a population with a large spectrum of blood pressure values. The used dataset can test the model’s performance under different blood pressures. Note that SBP = Systolic blood pressure and DBP = Diastolic blood pressure.

Figure 4. Architecture of the proposed network. The architecture consists of two concatenated U-Net architectures, the first acting as an encoder and the second as a decoder reconstructing ABP from PPG. Due to the shape of the whole architecture, this neural network was named W-Net.

Figure 5. Demonstration of the reconstruction of the ABP waveform, where ‘r’ and ‘rmse’ stand for the correlation coefficient and the relative mean squared error, respectively, and ‘MAESBP’ and ‘MAEDBP’ represent the mean absolute error of systolic and diastolic blood pressure, respectively. Note that PPG = Photoplethysmogram, ABP = Arterial blood pressure, SBP = Systolic blood pressure, and DBP = Diastolic blood pressure.

Figure 6. A segment of the optimal DTW warping path for the reference and reconstructed ABPs. The d¯ stands for the normalized DTW distance. This figure shows that the reconstructed ABP was highly similar to the reference ABP. Note that ABP = Arterial blood pressure and DTW = Dynamic time warping.