Photoplethysmography: Towards a non-invasive pressure measurement technique

There is a need for a non-invasive and continuous blood pressure monitor. Photoplethysmography (PPG) is one of the techniques that were investigated for this purpose in an in vitro model where the relationship between the PPG and pressure-volume (P-V) changes was investigated. Pressure and red (R) infrared (IR) PPG signals were recorded continuously in an arterial model that simulates fluid flow utilizing a pulsatile pump. Flow rates were controlled through three set-points of pumping frequencies at low and high stroke volumes. Normalized Pulse Volume (NPV) is defined as the light intensity ratio at each wavelength, R (NPVR) and IR (NPVIR). Adjusted Pulse Volume (APV) was determined for both wavelengths. It was found that the optimum method for estimation of the pulsatile volume is through APV, which has a remarkable correlation (r2=0.99, p<0.001) with the assumed exponential P-V model. APV obtained significantly better fit when compared to NPVIR (r2=0.73, z=25.85, p<0.001) and NPVR (r2=0.95, z=12.26, p