Figure 2.

Outline of the Siamese architecture and analysis workflow. Two copies of the same neural network share parameters and are used to compare the current photoplethysmography (PPG)-derived spectrogram to the calibration sample (the first available sample) and is trained to extract features that enable estimating the change in blood pressure (BP) (systolic, mean, and diastolic) from the current value relative to the calibration sample. CNN = convolutional neural network, ReLU = rectified linear unit.