Continuous Non-Invasive Arterial Blood Pressure Measurement Using Photoplethysmography

Arterial Blood Pressure is one of the primary indicators used to monitor health. It is often useful to continuously observe fluctuations in the systolic and diastolic blood pressure in post-operative patients. Conventional devices like a sphygmomanometer are non-invasive methods of reading blood pressure, but are not continuous. Another commonly used technique, which is invasive, is an intra- arterial blood pressure sensing mechanism. A non-invasive method to continuously track variations in blood pressure is very useful as it has the advantages of not being intrusive and hence eliminating the need to surgically implant a device to sense intra-arterial pressure and the risk of infection. In this project, different methods of processing the photoplethysmogram signal are analyzed with the aim of identifying the components of the signal that vary with blood pressure, and can distinctly report the systolic and diastolic values. The data collected from 20 subjects is statistically analyzed. Pressure was also calculated from measured photoplethysmogram, using principles from photonics and biomechanics. This method was found to be the closest approximation to real-time pressure. Analysis of different parameters of the photoplethysmogram indicates that even though it depends upon pressure to a certain extent, there is no simple relationship that is valid or consistent over a reasonable period of time. However, with some improvements to the sensitivity of the device and by using the calculated pressure from the photoplethysmogram, the real-time blood pressure can be measure