Humphreys, Kenneth Gerard
An investigation of remote non-contact photoplethysmography and pulse oximetry.
PhD thesis, National University of Ireland Maynooth.
This thesis presents an investigation of non-contact remote pulse oximetry and photoplethysmography. A thorough description is given of the technique of pulse oximetry along with some physiological effects and some characteristics of light-tissue interaction that underlie pulse oximetry. A device is then described that is capable of capturing two photoplethysmograph (PPG) signals simultaneously in a multiplexed fashion. The device is comprised of a complementary metal oxide semiconductor (CMOS) camera and a dual wavelength array of light emitting diodes (LEDs) (760 nm and 880 nm). By alternately illuminating a region of tissue with each wavelength of light and detecting the backscattered light with the camera at a rate of 16 frames per second per wavelength, two PPG signals are simultaneously captured. This process forms the basis of pulse oximetry. A methodical investigation of the comparability of the camera-based device with a conventional clinical contact device is presented. The camera-based device is demonstrated to provide a comparable PPG waveform and measure of pulse rate and a description is given of how, with the inclusion of a calibration procedure, such a device could be used to estimate arterial oxygen saturation (SpO2). Some aspects of PPG signal acquisition that are unique to a camera-based device are highlighted and camera-based capture is shown to introduce both tractable complications and the potential for additional utility beyond that of a conventional contact device. Additionally this thesis describes a concept for camera-based reflection tomography with the potential to yield structural information about shallow vasculature and tissue morphology. Lastly this thesis describes areas of further work in relation to the development of clinically useful camera-based pulse oximetry, and areas of further research concerning the potential of camera-based photoplethysmography as an investigative tool.
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