Evaluation of Stress Response Using Smartphone PPG for Anxiety and Depression Monitoring

Diminished stress reactivity is frequently reported in individuals with depression and anxiety. Smartphone-camera photoplethysmography (SCPPG) could offer an innovative, objective, and ambulatory metric for monitoring these conditions. This study aims to evaluate the use of SCPPG to monitor anxiety and depression by analyzing stress responses. Specifically, it examines the autonomic nervous system through heart rate variability using pulse rate variability (PRV) metrics derived from SCPPG. The study involved 79 participants, including patients diagnosed with generalized anxiety disorder and major depressive disorder (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> = 22), as well as a control group (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> = 57). SCPPG signals were compared with those from a validated device during a stress-inducing protocol, consisting of baseline, stress tests (Trail Making Test and Stroop Test), and recovery phases. Pearson’s correlation and Bland-Altman analysis were used to assess the agreement. The results indicate a high correlation (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</i> ≥ 0.96, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i> < 0.001) between PRV metrics derived from SCPPG and those from reference devices. Additionally, exhibited minimal bias (Δ ≤ 2%) with the exception of RMSSD (Δ = 12%). Notably, SCPPG reliably detects stress reactivity differences between patient and control groups across all PRV metrics (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i> < 0.05). The study highlights the significance of SCPPG in understanding and personalizing mental health treatments, considering factors such as stress reactivity and recovery. Future research directions include longitudinal studies and improving SCPPG accuracy, particularly for patients with tremors or during dynamic tasks.