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Application of high & low brightness LEDs to human tissue to capture photoplethysmogram at a finger tip

Photoplethysmography (PPG) is the process of applying a light source and photo sensor to an appendage, such as a finger or a toe, and measuring the light that is reflected by the skin. At each contraction of the heart, blood is forced through the peripheral vessels producing engorgement of the vessels under the light source, there by modifying the amount of light reflected to the photo sensor. Arterial pressure is one of the most important physiological parameters for the noninvasive diagnosis and monitoring of cardiovascular diseases. The aim of the project is to develop a reflectance type photoplethysmographic sensor to record the peripheral pulse wave by using various sources. In this study total 21 sources (diffused and clear LEDs) of 3mm and 5mm diameter were used. Opt101 was used as a detector for all the sources and effect the of various sources on PPG in the form of peak-peak voltage was studied. The photoplethysmographic signals are obtained from 8 subjects of different age group and gender. It was seen that the penetration of IR light into the human tissue is more than that of the visible light. Peak-peak voltage of PPG waveform for a clear LED with 3mm diameter was highest than any other LED of the same wavelength and diameter.