The Relationship between Mental Stress Induced Changes in Cortisol Levels and Vascular Responses Quantified by Waveform Analysis: Investigating Stress-Dependent Indices of Vascular Changes

Objective: Human salivary cortisol is a major possible physiological index for the evaluation of mental stresses and photoplethysmogram appearance is sensitive to stress-induced haemodynamic changes. The purpose of this experiment was to assess these features in laboratory settings under both stressful and non stressful situations. Methods: The effect of a mental stress test was assessed in 55 healthy young adults using salivary cortisol. Blood pressure and heart rate as well as photoplethysmogram appearance were measured as indices of mental stress-induced changes. Results: The results of medical examination showed that salivary cortisol levels were significantly elevated (P<;0.05) after viewing negative pictures of International Affective Picture System (IAPS) comparing with the baseline value obtained before test, but no significant difference (P>;0.05) was observed after viewing neutral pictures of it respectively. Significant increase of two parameters derived from PPG signals was observed (P<;0.01) after viewing negative pictures comparing with baseline detected before test but no significant difference (P>;0.05) after viewing neutral pictures either. A significant mean heart rate drop (P<;0.05) was found after viewing neutral pictures. Conclusion: Mental stress results in an elevation in salivary cortisol levels as well as haemodynamic changes reflected in photoplethysmogram appearance. The relationship between these features in different stressful conditions provides a simplified means of estimating stress and the surrogate measures in addition to subjective rating scale.