Non-invasive techniques for assessment of peripheral blood flow at different vascular depths

University dissertation from Västerås : Mälardalen University

Abstract: Missing or reduced blood flow can lead to pressure ulcers. Monitoring blood flow in areas prone to pressure ulcer development would be a valuable tool for prevention of pressure ulcers.PPG and LDF are both established non invasive optical techniques that can be used to estimate the changes in blood flow in different tissue volumes. The aim of this thesis was to combine the established techniques, LDF and PPG, into one flexible silicon probe intended for evaluation of peripheral blood flow in tissue volumes prone to pressure ulcer development. Further, a temperature sensor was integrated.Two probe configurations combining LDF and PPG has been evaluated regarding the ability to separate between shallow, medium and deep blood flow variations, and skin temperature changes. Further, techniques to reduce or totally avoid interference between LDF and PPG have been investigated.The probes can be used to discriminate between blood flows at different vascular depths. The vascular depths reached by the different channels correspond to the depths of interest when investigating pressure ulcer aetiology. The probe itself has shown not to affect the skin surface temperature, neither due to the silicon sheet or the light. The skin temperature can be expected to rise and approach the body core temperature by lying in supine position alone, which has to be taken into consideration when designing studies.By switching between the different light sources, interference can be totally avoided. When rapid blood flow variations at several vascular depths are of interest to evaluate, a peripheral placement of the LDF-fibre and an increased illumination power of the PPG-LEDs might be used to minimize the interference between LDF and PPG.Both probes have shown potential to be used for investigation of the processes in pressure ulcer development.