Photoplethysmography
Photoplethysmography (PPG) Analysis · Also known as: PPG, Pulse oximetry, Reflectance photometry
Photoplethysmography (PPG) measures blood volume changes in tissue using light absorption, providing a non-invasive optical window into cardiovascular dynamics. Originally developed by Hertzman in 1937, PPG is now ubiquitous in pulse oximetry, smartwatches, and research applications for monitoring heart rate, blood oxygenation, and vascular function.
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When to use it
Use PPG when you need continuous, non-invasive monitoring of heart rate and vascular dynamics in clinical or personal health settings. PPG is ideal for wearables and field deployments because it requires only a light source and photodetector. Assumptions include adequate skin perfusion, stable optical coupling, and acceptable motion artifact levels. Performance degrades with dark skin pigmentation, ambient light interference, or excessive movement.
Strengths & limitations
- Non-invasive, portable, and inexpensive compared to ECG-based systems
- Provides both cardiac and vascular information from a single optical measurement
- Real-time implementable on wearable devices and smartphones
- Multi-wavelength PPG enables blood oxygen saturation (SpO2) estimation
- Sensitive to motion artifact; requires motion filtering or accelerometer fusion
- Accuracy reduced in low-perfusion states (shock, vasoconstriction, anesthesia)
- Confounded by skin pigmentation, tattoos, and nail polish
- Morphological features subject to changes in respiration and posture
Frequently asked
Why does PPG work better on fingertips than on wrists?
Fingertips have higher perfusion and thinner tissue layers, allowing better light penetration and stronger pulsatile signals. Wrists are thicker and have more ambient light interference, reducing signal quality but still adequate for wearable applications.
How is SpO2 calculated from multi-wavelength PPG?
Red and infrared (IR) light are absorbed differently by oxygenated vs deoxygenated hemoglobin. The ratio of red to IR absorption (after accounting for pulsatile and non-pulsatile components) is calibrated to SpO2 using empirical formulas.
Can PPG measure blood pressure?
PPG alone cannot measure absolute BP; the signal depends on vascular compliance and perfusion. Pulse transit time (time between ECG and PPG peaks) can estimate relative BP changes, but absolute calibration requires cuff measurement.
Sources
How to cite this page
ScholarGate. (2026, June 3). Photoplethysmography (PPG) Analysis. ScholarGate. https://scholargate.app/en/biomechanics/photoplethysmography
Which method?
Set this method beside its closest kin and read them side by side — the library lays the books on the table; the choice is yours.
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