The ChatPPG library
Technical guides to PPG sensors, signal processing, HRV, SpO2, and wearable accuracy. Explore the methods and their published evidence.
Showing 301–308 of 308 articles · Latest first
SpO2 & OximetryDetailed blood oxygen level chart showing normal SpO2 ranges by age and health condition. Learn the difference between SpO2 and SaO2, how wearables measure oxygen continuously, and what the oxygen-hemoglobin dissociation curve means for your readings.
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PPG & Signal ProcessingA comprehensive technical guide to photoplethysmography (PPG) explaining how PPG sensors work, the physics of light-tissue interaction, transmission vs reflectance modes, signal components, and modern applications in wearables and clinical devices.
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Arrhythmia & ECGExpert-selected best heart rate monitors for 2026 covering every use case from general wellness to clinical AFib detection. Includes PPG sensor analysis, accuracy comparisons, and recommendations for the Apple Watch Series 10, Garmin Forerunner 965, Oura Ring 4, WHOOP 5.0, Polar H10, Fitbit Charge 6, and Apple Watch Ultra 2.
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PPG & Signal ProcessingA comprehensive technical guide to PPG motion artifact removal covering adaptive filtering (LMS, RLS, NLMS), ICA, EMD, wavelet decomposition, SVD, and deep learning methods. Includes algorithm comparison, pipeline design, benchmark datasets, and real-time implementation considerations.
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SpO2 & OximetryA technical deep dive into PPG wavelength selection comparing green (520-530nm), red (660nm), and infrared (940nm) light for heart rate monitoring, SpO2 measurement, and wearable sensor design. Covers absorption spectra, skin tone considerations, motion artifact behavior, and multi-wavelength approaches.
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Arrhythmia & ECGA comprehensive review of wearable atrial fibrillation detection covering PPG-based irregular rhythm detection, ECG-enabled smartwatches, the Apple Heart Study, Fitbit Heart Study, FDA clearances, sensitivity and specificity data, and clinical guidelines for screening versus diagnosis.
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Blood PressureAn industry analysis of cuffless blood pressure monitoring technologies including PTT, PWV, PPG morphology, ultrasound, and tonometry. Covers calibration challenges, regulatory hurdles, current players (Samsung, Aktiia, Biobeat, Valencell), and a realistic timeline for when truly calibration-free devices will be available.
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Arrhythmia & ECGGillinov et al. 2017 (n=50): Apple Watch concordance vs ECG was 0.92; Polar H7 chest strap 0.996. No device was accurate on an elliptical with arm levers.
Read the articleUse the library to explore optical sensing, waveform morphology, motion artifacts, and wearable design. Follow article references to the original research and consider the population, device, and conditions behind each result. How to read the library ↗