Photonics Dictionary


Photoplethysmography (PPG) is a non-invasive optical technique used to detect changes in blood volume in tissues. It measures variations in light absorption caused by the pulsatile nature of blood flow. Typically, PPG is employed to monitor physiological parameters such as heart rate and blood oxygen saturation. The basic principle involves illuminating the skin or a tissue with a light source, often an LED, and detecting the transmitted or reflected light using a photodetector.

The key steps in photoplethysmography include:

Illumination: A light source is directed into the tissue, and the tissue absorbs and scatters the light.

Absorption by blood: Blood absorbs light differently based on its oxygenation and the pulsatile nature of blood flow. When arterial blood pulsates, it changes the amount of light absorbed by the tissue.

Photodetection: A photodetector detects the transmitted or reflected light. The variations in light intensity correspond to changes in blood volume, providing information about the pulsatile blood flow.

Signal processing: The collected signal is processed to extract physiological parameters, such as the heart rate and the oxygen saturation of hemoglobin in the blood.

PPG is commonly used in various medical and wearable technology applications. Key applications include:

Pulse oximetry: PPG is a crucial component of pulse oximeters, which measure oxygen saturation levels in the blood.

Heart rate monitoring: Wearable fitness trackers often use PPG to monitor heart rate continuously.

Blood pressure estimation: PPG signals can be used to estimate blood pressure non-invasively.

Sleep monitoring: PPG can be employed to assess sleep patterns and detect conditions like sleep apnea.

PPG provides a non-invasive and convenient method for monitoring cardiovascular and respiratory parameters, making it widely applicable in both clinical and consumer health settings.
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