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Setting-up of PPG scaling factors for SpO2% evaluation by smartphone

The recent literature proposes the smartphone's camera to evaluate the arterial blood oxygenation (SpO2%) with the characteristic of friendly and ubiquitous measurement instrument. Some issues remain open, making difficult the compensation of artefacts causing error in the estimation of the photoplethysmogram signal (PPG) and not guarantying that the measurement of SpO2% is correctly executed. In the research, a method is proposed for setting-up the parameters to compensate the effects of the environmental light sources. Initially, the method evaluates the quality of the PPG signals by analysing the light intensity in the red and green colour channels of the video frames of the patient fingertip. Successively, a proper digital procedure sets the scale factor of the PPG to compensate the effects of external light for improving the accurate evaluation of the SpO2%. In order to assess the effectiveness of the proposed method, the experimental results are compared with the gas chromatography analysis.