Study Of Mental Stress Evaluation Using Heart Rate Variability

The psychological stress is a feeling of strain and pressure.Nowadays everyone has to suffer different level of psychological stress unavoidably.The psychological stress mainly comes from our society,life and competition,which is harmful to the psychological health.In fact,everyone can bear a certain level of stress.However,when man is suffered from the stress beyond the acceptable level,man may behave abnormally.At present,there are two categories for the evaluation of the psychological stress,the subjective and objective categories.In recent years the analysis of the heart rate variability(HRV),one method of the objective category,has achieved great progress in the field of the mental health diagnosis.The HRV is the physiological phenomenon of variation in the time interval between heartbeats,which is measured by the variation in the beat-to-beat interval.It is regulated by the neurohumoral regulation,so that the body gets used to various physiological state and pathological conditions.When man is under stress,the autonomic nervous system(ANS)is disordered,namely the parasympathetic nervous system increases its activity while the sympathetic nervous system decreases its activity.The HRV can provide the quantitative parameters of the activity between the sympathetic and parasympathetic system and the ANS balance,the blood pressure and the function of the cardiovascular system.Hence,the HRV can be used objectively and effectively to evaluate the psychological stress of an individual.This dissertation focus on the development of the psychological stress rating system(PSRS)based on the HRV,which is used to assess the psychological stress quantitatively.Based on the signal acquisition of the electrocardiography and pulse wave under four different conditions,the corresponding HRV curves are obtained.Furthermore,the HRV curves are analyzed in time-domain,in frequency-domain and nonlinearly in order to obtain the parameters mentioned above.Based on the relation between the parameters and the level of the psychological stress,the mathematical model is built and the PSRS is developed based on the Qt software design platform.The PSRS consists of the data acquisition module,the data management module,the data analysis module and the result display module.The PSRS integrates all functionalities(the data acquisition and processing of the electrocardiography and pulse wave signals,the calculation of the HRV parameters,the selection of feature parameters and the establishment of the mathematical model for the psychological stress level)to achieve the quantitative assessment of the psychological mental stress level.