Characterizing the Optical Response of Human Tissues to Prolonged Pressure

Pressure Injuries are burdensome to the US healthcare system and significantly impact patient quality of life. Methods for reduction have focused almost exclusively on risk assessment and reductions in pressure and shear stresses. While extensive work has been performed to understand the etiology of pressure injuries, less focus has been placed on the use of non-invasive technologies to monitor tissues and predict injury. This thesis is a step in that direction. The aim of this thesis was to validate a brand new flexible Near Infrared sensing system and model the optical characteristics of tissues under pressure for clinically relevant time periods. The pilot study for this thesis was a descriptive cross-sectional analysis. 5 healthy college aged volunteers lay supine for 2 hours while spectroscopic recordings of their sacral tissues were collected. Results suggested that two physiological process were occurring at different tissue depths. In shallower tissue depths optical signals indicated that relative concentrations of HbO and HbR changed from their initial concentrations, whereas at deeper tissue depths changes in total blood volume occurred. This work is the beginning of a series of exploratory analysis for validating the NIRS device and investigating signals indicative of pressure injury. The NIRS device performed adequately, but multiple improvements to its design have been noted. Specifically, increased flexibility, durability, and sterility of future iterations will need to be addressed.