Autonomic and Endocrine assessments through Heart Rate Variability and Salivary Cortisol: from Clinical to Laboratory Studies

This thesis investigated the utility of Heart Rate Variability (HRV) and salivary cortisol as non-invasive markers of autonomic and HPA axis function across clinical, ecological, and laboratory experimental contexts. In the first study, HRV and cortisol were assessed in newborns of healthy and gestational diabetes mellitus (GDM) mothers within the first 24 hours of life. GDM-exposed neonates exhibited altered autonomic regulation with sex- specific patterns: females showed reduced heart rate without HRV changes, while males displayed increased vagally mediated HRV with unchanged heart rate. Cortisol patterns were similar between groups, decreasing after the initial post-delivery peak. These findings suggest that GDM may modulate early ANS reactivity to birth, with modified vagal modulation shortly after birth, and highlight the importance of considering sex differences in autonomic development. The second study explored HRV and cortisol in relation to gut microbiota and stress-related symptoms in adults. Lower vagally mediated HRV was linked to higher depressive symptoms and microbiota dysbiosis (higher Prevotella, lower Faecalibacterium, Alistipes, and Gemmiger), supporting its modulatory role of microbiota– gut–brain axis function. In contrast, cortisol indices (Cortisol awakening response, Diurnal cortisol slope) showed weaker and less consistent associations with psychological and microbial measures, suggesting more context-dependent utility. The third study confirmed that the immersive multimodal virtual enviromente stress test (IMVEST) reliably elicits a psychophysiological stress response, reflected in increased perceived stress, elevated heart rate, reduced vagally mediated HRV, and salivary cortisol elevation. Stress-responsive miRNAs (miR-21, miR-25, miR-29a, miR-200a) were detectable in the saliva of participants and were modulated by acute stress, though correlations with psychophysiological traits were not observed, possibly due to high baseline stress levels or the analytical approach. Overall, these studies demonstrate the versatility of HRV and salivary cortisol for assessing 8 autonomic and neuroendocrine regulation, respectively. HRV was particularly sensitive to sex differences, intrauterine exposures, and gut–brain interactions, whereas salivary cortisol provided complementary, context-dependent insights. Together, these measures offer a robust framework for investigating physiological regulation, stress responsiveness, and mental health across the lifespan.