Modelling of light tissue interactions in Photoplethysmography
Principal Investigators: Dr J Phillips, Prof P Kyriacou
Researchers: Ms S Chatterjee
Funding: City University London
Photoplethysmography is widely accepted clinical method to monitor blood perfusion in tissue, mostly obtained by the use of pulse-oximeter probe. Although there has been noticeable technological advancements in the technique, the basic functionality underlying photoplethysmography is still not fully elucidated. Photoplethysmography relies on photometric principles, however the complex light-tissue interaction associated with the procedure makes it difficult to explain by simple application of Beer-Lambert's law or any other straightforward theory. Also, pulse-oximetry is limited for the applications in the situations like low perfusion, as in states like hypovolemia and hypothermia, which still demand better explanation. To address all these problems, an effort is being made to prepare a Monte Carlo algorithm based light-tissue interaction model to describe photoplethysmography. A three dimensional multilayer tissue model, with pulsatile blood flow, is being developed and will be explored to investigate the optical interaction with it in a pulse-oximetry set up for a range of probe configurations and physiological states. The outcome of such a study is invaluable for basic understanding of photoplethysmography as well as aiding to designing of more precise and accurate optical sensors.