Relationships between respiratory sinus arrhythmia and anxiety

Abstract

Anxiety disorders are global health concerns. Accurate identification of these disorders is significant for timely intervention to result in optimum recovery. Current identification of anxiety disorders relies heavily on self-reports. Incorporation of potential biological markers in the diagnostic process can complement information from self-reports to augment the diagnostic accuracy regarding such disorders. According to the literature, both the polyvagal theory and neurovisceral integration model posit that cardiac vagal tone is essential for adaptive emotion regulation, which can be reflected by respiratory sinus arrhythmia (RSA), a proxy measure of the cardiac vagal tone. There are different indices of RSA, namely baseline resting RSA (resting condition) and RSA reactivity (elicited by stress). Also, the profile of RSA can be in a suppression or augmentation pattern. Given the fact that emotion dysregulation is one of the precipitating factors of anxiety disorders and respiratory sinus arrhythmia (RSA) is a proxy measure of the cardiac vagal tone, understanding the relationship between emotion regulation and RSA will enable important insights into the identification and pathophysiological mechanism of anxiety disorders to be made. This thesis contains reports on two studies. Study 1 investigated the relationship between RSA and panic disorder. Twenty patients diagnosed with panic disorder and 13 agematched healthy controls participated in this study. Their RSA at resting condition was measured. Besides, their RSA reactivity patterns were assessed by an acute stress induction protocol by the Montreal Imaging Stress Test (MIST). The results showed that, relative to the controls, the clinical participants had a significantly lower resting RSA but similar RSA reactivity. While the RSA reactivity profile of the controls showed suppression during the stress induction process, that of patients was characterized by continual augmentation across all experimental conditions. The RSA indices of patients were also compared to 124 healthy young adults participating in Study 2 of the present project. Again, the patients had a significantly lower resting RSA than the healthy young adults. The RSA reactivity of patients was also significantly lower. More strikingly, their direction of reactivity was opposite to that of young adult controls. The key observation was that resting RSA could distinguish patients with panic disorder, and RSA augmentation in response to stress may also mark the difference from healthy controls. This supported the potential value of RSA assessment as a clinical tool for the identification of anxiety disorders. Study 2 investigated the relationship between emotion regulation strategies and RSA. One hundred and twenty-four healthy young adults were assessed for the habitual use of cognitive reappraisal and expressive suppression as emotion regulation strategies. It was found that cognitive reappraisal marginally mediates the relationship between resting RSA after going through the experimental stressor and anxiety level of the past one week. However, this mediation role could only be found in participants with a RSA suppression profile but not in those with a RSA augmentation profile. The mediation role of emotion regulation strategy found between RSA and anxiety enhanced the understanding of how cardiac vagal tone affects the use of regulatory strategies and the physiological limitation for individuals who may not be good at implementing it. The findings of the present project show that RSA assessment could enhance the diagnostic process of anxiety disorders. It may also facilitate psychological intervention through matching the emotion regulation strategy with the physiological condition.