Psychological Stress Index Measuring System And Analysis Method

The purpose of this study is developing a home-made and non-invasive opticsystem to assess psychological stress index (PSI) by using oxyhemoglobin saturationby pulse oximetry (SpO2) which is measured easily and don’t need high-pricedequipment. And the system can be applied to measuring Heart Rate (HR), andobserve the Heart Rate Variability (HRV). Stress index is obtained by usingplethysmograph amplitude (PPGA) and heart beat interval (HBI), which are extractedfrom SpO2signals. Therefore, we can quantify the mental condition and establish anew way to assess mental condition. It can provide long-term care for users.Replacing formerly used electrodes, the users of any age can immediately operate andmeasure correctly.The home-made system is composed of a hardware measuring system based on anoninvasive photoplethysmographic (PPG) signal measuring device to acquireoxyhemoglobin saturation using pulse oximetry (SpO2) signals and a further softwarepackage which includes the method used to filter and analyze the signals for HR,HRV and PSI. We use PPGA and HBI extracted from SpO2to obtain the stress indexand quantify it from0to100. Therefore, the pulse oximeter can display SpO2concentration, HR and PSI. We can obtain both the details of psychological andphysiological information at the same time. The method can be applied on a patient athome. When measuring the PPG signal, there are a lot of noises, so empirical modedecomposition (EMD) method is applied to remove high frequency and lowfrequency noise content.The experiment consists of three parts. Firstly, designing an experiment formeasuring heartbeat using the system to observe whether the EMD method can reallyinhibit noise or not on one volunteer with10minutes repeated for10times. Secondly,use the hardware system and analysis method on another10volunteer students to testtheir HR and HRV before and after receiving cold face immersion. Finally, we usedour hardware system and analysis method on another10volunteer students to testtheir PSI when they under the stress of English presentation.The results of the first experiment analyzed by T test are similar to commercial instrument (p>0.05), but the results using EMD are better when there is aninterference in the process of measurement. The second part experiment using the fastFourier transform (FFT) method was subdivided into two stages. The results showedthat HR values at each stage were similar to commercial instrument (p>0.05) andchanging from high (i.e.,70.86±6.72) to low (i.e.,68.38±6.68) during the twostages (p <0.05). For HRV analysis, the LF is significantly reduced from0.33±0.03to0.31±0.03but HF is significantly increased from0.41±0.07to0.43±0.07whichindicates that cold face immersion has increased parasympathetic and decreasedsympathetic actions. Hence, the ratio of LF/HF power changes significantly fromhigh (0.85±0.17) to low (0.74±0.17) before and after adding stimulation. The thirdpart experiment was separated into three stages: preparation, presentation anddiscussion, and relaxation. The PSI values of these three stages were48.9±16.2,59.4±8.1, and21.3±8.2, respectively. The experiment results were excellent, andshowed PSI values changing from low, to high, and back to low during these threestages.As the reason referred above, it confirms that the developed system can measurePPG to calculate HR and observe the HRV and PSI. So the findings of this researchmay be useful for developing a low-cost and a miniaturized pulse oxymeter systemfor the purpose of portability, convenience, and operability.