Photoplethysmography (PPG) is used to measure heart rate, blood flow, and blood oxygen saturation.
Photoplethysmography is the technique used in smartwatches (like the Apple Watch and Fitbit) to measure your heart rate. These watches use a green light-emitting diode (LED) which is aimed at the skin and measures the light that is reflected. Photoplethysmography occurs because red blood absorbs green light, so the amount of light reflected changes as blood pulses through tiny blood vessels close to the skin. By measuring the changes in light absorption, PPG can provide information about different cardiovascular parameters. This is also the most common use of PPG.
Photoplethysmography is also used to measure oxygen saturation, for example, in a pulse oximeter. Oxygen saturation, which represents the percent amount of hemoglobin molecules in blood that is carrying oxygen, can be estimated using two different parts of the PPG waveform and examining the ratio of their amplitudes.
PPG has found wide use in medical settings due to its simplicity, and cost-effectiveness. As we mentioned, it is commonly used to provide continuous monitoring of heart rate and oxygen saturation. However, PPG can also be used in clinical settings for conditions like peripheral vascular disease, pulse waveform analysis, and assessment of autonomic nervous system function.
Sources:
Cheriyedath, S. (2019, February 27). Photoplethysmography (PPG). News. Retrieved November 11, 2022, from https://www.news-medical.net/health/Photoplethysmography-(PPG).aspx