Chronic stress is a leading risk factor for heart diseases, diabetes, asthma and depression. However, physicians find it difficult to continuously track a person's stress levels throughout the day, as current techniques of electrocardiogram and blood pressure monitoring are not practical. There is thus a critical need for a non-invasive, ambulatory device to track physiological stress over extended periods of time. Such information would allow physicians to assess precisely the affect of stress and determine the most appropriate interventions.

The primary objective of this study was to investigate the relationship between non-invasive, physiological signal parameters and the stress level as perceived by the subject. The mapping of physiological parameters onto stress levels to accurately monitor the stress levels in a subject under various conditions will assist the diagnosis of subjects at risk of various stress related disorders.

An ambulatory, wireless device was developed with respiratory rate, galvanic skin response and heart rate sensors, which the subjects can wear comfortably while performing their everyday tasks. An experiment involving 13 activities with different stress levels was conducted on 22 subjects during which physiological data was collected using the developed device. While participating in the experiment, subjects had to record the stress level of each activity on a scale of 1 and 7. The data collected was processed in MATLAB, appropriate signal parameters extracted and then correlated with the subject's perceived stress levels.

Analysis of the data showed that the stress levels varied as the subjects progressed into different activities due to their varying current mental states. The perceived nature of stress varied considerably amongst the individuals with certain activities able to induce a stronger variation in stress compared to others. The derived features were shown to be effective in tracking the variation in stress induced in the subjects.

Results of the experiment showed that the developed device was effective in recording non-invasive physiological for use in tracking the stress levels and mental state of the subjects. Further work is being done to develop an effective model that accurately predicts stress levels based on the physiological data collected.


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