Abstract

Reduced parasympathetic activity is associated with emotion regulation difficulties and increased cardiovascular risk (CVR), both of which are prevalent in Post-Traumatic Stress Disorder (PTSD). Consequently, understanding the relationship between autonomic nervous system (ANS) functioning and emotion regulation in PTSD is critical for both psychological and physical health. The present thesis investigates the psychological and physiological processes linking PTSD, autonomic functioning, and emotion regulation difficulties.

Chapter One provides an overall introduction to the thesis. The chapter first examines DSM-5 PTSD diagnostic criteria and symptom clusters, before evaluating psychophysiological explanations of PTSD. The chapter then introduces Heart Rate Variability (HRV) as an index of autonomic nervous system functioning and discusses psychophysiological theories to explain the association between HRV and emotion regulation. Finally, the concept of emotion regulation is explored in depth, highlighting how it manifests both physiologically and cognitively, and how it is affected in those with PTSD. Chapter One concludes by providing the rationale for the overarching aim of the thesis and the methodology adopted in subsequent chapters to address the aim.

Chapter Two presents a comprehensive multilevel meta-analysis comparing short-term (5-minute) and long-term (24-hour) Vagally-Mediated HRV (vmHRV) in PTSD populations. The findings indicated that short-term recordings appear more sensitive to acute autonomic fluctuations but are susceptible to confounding variables. Conversely, long-term recordings provide more stable assessments of parasympathetic function but may overlook acute changes that occur in response to contextual demands. The results highlight the need for standardised vmHRV measurement protocols in PTSD studies and informed the methodology of the subsequent empirical studies presented in Chapter Five and Six.

Chapter Three examined self-reported emotion regulation difficulties in individuals with and without PTSD. The findings revealed that whilst overall emotion regulation difficulties are associated with PTSD, specific facets of emotion regulation, such as impulse control and goal-directed behaviour, exhibit a stronger association with PTSD than other facets. The findings challenge the assumption of global emotion regulation deficits in PTSD and highlight the importance of recognising that not all facets are equally affected in PTSD. Consequently, the findings advocate for targeted PTSD treatments to address the specific emotion regulation difficulties experienced by an individual. Additionally, the findings informed the design of the remaining studies presented in the thesis, which aligned vmHRV with self-reported emotion regulation difficulties to identify which facets of emotion regulation are associated with autonomic functioning.

Chapter Four employed a multivariate meta-analytic approach to examine the relationship between self-reported emotion regulation difficulties and vmHRV in trauma-exposed populations. The results demonstrated that vmHRV correlates more robustly with difficulties in specific facets of emotion regulation such as difficulties with goal directed behaviour and impulse control. These findings provided preliminary evidence that vmHRV may reflect specific facets of emotion regulation.

Chapter Five empirically investigated the relationship between PTSD symptom severity, vmHRV, and self-reported emotion regulation difficulties. The findings indicated a threshold effect whereby diminished vmHRV was only observed in individuals with severe PTSD symptoms but not in those with moderate symptoms. Interestingly, the moderate PTSD symptom group reported greater regulation difficulties in some emotion regulation facets than the severe PTSD group, without corresponding autonomic dysregulation. The findings indicate a misalignment between the subjective emotional and physiological experiences of those with PTSD.

Chapter Six examined vmHRV changes during implicit and explicit emotion regulation challenges across groups with moderate and severe PTSD symptoms and controls. Contrary to existing findings, no differences in vmHRV were observed between groups during the emotion regulation challenges. Although no group differences in vmHRV responsivity were observed, interpretations grounded in the Polyvagal and Neurovisceral Integration Theories suggest that, in those with PTSD, vmHRV may fail to capture the underlying mechanisms responsible for autonomic dysregulation and emotion regulation difficulties. The findings highlight the complexity of the relationship between autonomic functioning and emotion regulation in PTSD. Together, the findings from this thesis highlight the need for integrated subjective and objective measures of emotion regulation and autonomic functioning in those with PTSD. In turn, the integration of physiological indices and subjective experiences may facilitate the development of individualised treatments that improve both emotional and cardiovascular outcomes for those affected by PTSD.