fig2

Figure 2. Illustration of time-based BP estimation that could be performed with a camera using hypothetical combinations of ECG, BCG, and PPG waveforms. PAT can be measured from the “r” wave of an ECG and a PPG wave (PAT₁, PAT₂, and PAT₃). PTT can be measured between the “h” wave of a BCG from head movement and a PPG wave (PTT₁, PTT₂, and PTT₃). PTT can also be measured between PPG waves from different body sites (PTT₄ and PTT₅). Note: the arterial waveform in the aorta is shown for reference; this is a simplified conceptual diagram; actual calculations can involve feature derivatives and other points of interest. ECG: Electrocardiogram; BCG: ballistocardiogram; PTT: pulse transit time; PEP: pre-ejection period; PAT: pulse arrival time.