Near Infrared Device for Tissue Inflammation Evaluation

Abstract

A photoplethysmographic (PPG) near infrared (850nm) system has been developed for the non-invasive assessment of superficial tissues’ (skin) swelling and redness. The PPG signal is treated to avoid ambient light and to extract the DC (direct current) and AC (alternate current) components. These components are then subtracted from the same components acquired on a reference site on the same subject. The resulting measures are used in a model able to classify different states of inflammation of the tissues. Numerical results permit to follow the inflammation state and to evaluate possible medical and physiotherapy interventions. To avoid artefacts due to compression of the skin by the instrument, a pressure sensor has been also embedded on the optical sensing head of the system, so that the measures are considered as valid only if they are taken within the same range of applied pressure on the skin. This is important to get comparable PPG measures. Heart rate and hemoglobin oxygen saturation measures are a by-product out of the system and they can be exploited for other purposes or they can be taken into account for a better evaluation of the inflammation state. Although the system is still a research prototype and no real model is available about how inflammation affects the optical properties of the skin, the very first qualitative results show a strong sensibility of the system to skin alterations due to acute inflammation.