Development and Evaluation of a Smartphone Application for Self-estimation of Daily Mental Stress Level

Abstract

Heart rate variability (HRV) is known to represent the activity of the autonomic nervous system and is used as a measure for stress levels. Generally, HRV is calculated from the heart rate or the pulse wave using an electrocardiogram (ECG) that is physically-taxing. However, for those with psychological strains and disorders, a handy device that can be used at any time is necessary in order to detect mental illness in its early stages and to prevent it from becoming worse. Therefore, we focused on the idea of using a popular device, the smartphone, and we developed a real-time, HRV-calculating application that uses a photoplethysmogram (PPG) obtained with the smartphone's camera. The user-friendly interface of the application was designed for use by a wide range of age groups. We conducted two experiments and compared the HRV data obtained by our application with ECG measurements to verify the application's accuracy. Once a certain level of accuracy was reached, we evaluated the usability of our application among young and elderly users. The results showed that improvements are necessary in terms of the interface, measuring time, and other performance indices.