42ndAnnual Conference: Effects of Traumatic Stress - Molecular and Hormonal Mechanisms

Abstract

Rationale/ statement of the problem: Stress is a complex phenomenon coordinated by several neural systems and has consequently been measured by several biomarkers. Salivary cortisol is the classical used stress biomarker representing the hypothalamic-pituitary-adrenal system. Heart rate variability (HRV), defined as the distance variability between consecutive R peaks, is increasingly used as marker of the autonomic nervous system and as a result also as a stress marker (defined as sympathetic over parasympathetic dominance). Associations between children’s salivary cortisol and HRV will be examined. Methods: In 190 children (5-10 year) of the Belgian ChiBS study salivary cortisol and HRV were sampled. Salivary cortisol samples were collected when waking up, 30 minutes and 60 minutes after wake-up and in the evening on two weekdays. HRV measurements in supine position were undertaken with Polar chest belts during 5 minutes. Apart from HRV time-domain analysis, also frequency-domain analysis was performed in the low-frequency (LF) and high-frequency (HF) bands. Multilevel growth curve modelling with adjustments for age, sex, physical activity and wake-up time was used to analyse the HRV associations with overall cortisol, cortisol awakening response (CAR) and cortisol diurnal decline. Results: Higher overall cortisol levels were negatively associated with mean RR, root mean square of successive differences (RMSSD), percentage of RR intervals differing more than 5 0ms (pNN50) and HF. A steeper diurnal decline was positively associated with normalised LF and the LF/HF ratio and negatively with HF. The CARwas positively associated with normalised LF and the LF/HF ratio and negatively with normalised HF. Conclusion: Higher salivary cortisol levels were associated with lower parasympathetic activity. A larger CAR and steeper diurnal decline were associated with a sympathetic over parasympathetic dominance. Consequently, the two main neural stress systems (represented by cortisol and HRV) show good agreement in reflecting children’s stress status, although not all parameters were significantly related. Measuring both pathways stays recommended as the pathways might be stimulated differently depending on the stressor.