Photoplethysmography

PPG observations are delayed and modulated by peripheral vascular physiology. Real-world smartphone PPG acquisition can distort morphology through motion, pressure changes, and ambient light fluctuation. Most PPG systems discard waveform morphology and reconstructed phase-space geometry. Raw PPG-related CSI distributions differed across datasets because of sensor physics, sampling rate, acquisition setting, and label derivation. Smartphones and wearables can acquire PPG for frequent or continuous cardiac monitoring.