Development of aphotopletysmography based methodfor investigating changes in bloodvolume pulsations : for the purpose of pressure ulcer prevention

Abstract: The aim of this thesis is to develop and evaluate a prototype for measuring volumetric changes of the blood with PPG. The prototype consist of a sensor plate controlled in Lab-view and algorithms for signal processing and analysis of results developed in Matlab. A study divided into three parts is performed, where the collected data is used for further development and alternations of the prototype between the study parts. A measurement in the study is divided into three stages before, during and after pressure, where the subject is changing body position between each stage in order to either apply or relieve pressure from the sensor plate. The amplitude changes of the recorded signals are analysed and the results from the stable parts of the measurements are presented as the ratio between before and during pressure. A ratio separated from 1 either show a decrease or an increase of pulsating blood volume as a response to the applied pressure. The results from the study show that there are both large spatial variations and large variations over time in the measurements. Today the prototype does not give repeatable results and there are several uncertainties in the measurement method. An optimal sensor plate would be flexible and have several LEDs over a larger area in order to give reliable result despite spatial variations.