Development of novel physiological analysis methods based on dual-wavelength phtoplethysmographic signals time differences

Photoplethysmographic (PPG) signals are obtained by changes in the amount of arterial blood, which in turn depends on the heart activities. PPG has been used as an advantageous measurement technique in biological and physiological assessments. Most previous analyses of PPG signal were based on time and frequency domain characteristics or shape of the simple PPG signal with a unique wavelength of light. In the present thesis, for the first time, time difference variations between two simultaneous unlike PPG signals were extracted and proposed as a new strategy for the analysis of dual-wavelength PPG signals. An improved dual-channel PPG biosensor was developed to obtain simultaneous PPG signals with different wavelengths. Then, time differences between the obtained PPG pairs were extracted in each heartbeat and used for various physiological conditions monitoring. The extracted time difference features were analyzed in different studies. Statistical analysis and classification algorithms were used to analyze the obtained data. Results showed that different PPG signals had significant time difference variations (time shifts relative to each other) with changes in a psychophysical state of investigated subjects. This earlier unreported phenomenon would have been a novel and interesting finding. In addition, analyses and classification results showed that the used time difference features had very good potential to classify various bio-physiological conditions.