FY12 Line-Supported Bio-Medical Initiative Program: Advanced Photoplethysmography (PPG) Sensors for Operational and Casualty Care Medicine

: Visible and near-infrared light interact via absorption and scattering with biomolecules, and a number of diagnostic tools based upon these interactions have been developed to indicate pathophysiological states and normal and diseased tissue. Additionally, the cyclic nature of these absorption or scattering events, such as those arising from cardiovascular or pulmonary physiology, has recently been shown to indicate trauma and cardiovascular status. The most commonly encountered diffuse optical technique is pulse oximetry, a form of photoplethysmography (PPG), where the distinct absorption behavior of oxygenation and non-oxygenation hemoglobin molecules forms a basis for determining arterial blood O2 saturation levels (SpO2). New analysis algorithms have shown that PPG can be used to indicate a variety of physiological conditions beyond hypoxic hypoxemia (i.e., low SpO2) including noncompressible hemorrhage, a condition notoriously difficult to diagnose without CT or MRI capabilities, and cardiac output, a variable difficult to measure in real time noninvasively. With support from the FY12 Biomedical Initiative Line, we embarked on a size, weight, and power (SWaP) analysis of PPG sensors, and collaborated with Professors Ki Chon and Yitzhak Mendelson from Worcester Polytechnic Institute to build a prototype ultra-low SWaP sensor. This report gives background and motivation for why PPG sensing is an important physiological modality, and details on the SWaP analysis and prototype development.