A Quadratic Analysis of Trait Anxiety and Heart Rate Variability

Trait anxiety refers to an individual’s sensitivity to perceived threat. Though it is not itself diagnosable according to the DSM-5, trait anxiety scales are often administered in a clinical context and serve as an indicator for anxiety disorders. High levels of trait anxiety can result in prolonged periods of intense worry and dysfunction, even in those who are not diagnosed with an anxiety disorder. Previous studies have attempted to understand the relationship between trait anxiety and reactivity of the autonomic nervous system, especially in relation to vagal tone, but have found inconsistent results. One possible explanation for this inconsistency is that these studies primarily tested a linear relationship between trait anxiety and parasympathetic nervous system reactivity. It is possible that low HRV may be associated with increased trait anxiety, consistent with other types of emotion dysregulation, but high levels of heart rate variability become maladaptive and are also associated with higher trait anxiety. A quadratic relationship, sometimes referred to as the “too much of a good thing effect,” was tested in order to determine whether both low and high levels of heart rate variability, an indicator of parasympathetic reactivity, would increase trait anxiety. Previous studies did not establish an ideal condition or domain of measurement for heart rate variability, so an exploratory analysis was conducted where regressions were used for both time-domain and frequency-domain measurements of HRV. Analyses were run using data that was collected both during a task and during resting state to see if there was any particular condition where a quadratic relationship may be present. Because gender differences have previously been established in relation to anxiety, each regression was run a second time, split by gender. Results indicated neither a quadratic nor a linear relationship between trait anxiety and heart rate variability under any of these conditions. This study reinforces the possibility that individual differences in trait anxiety are not solely mediated by autonomic nervous system reactivity, but rather a combination of factors possibly including, but not limited to, autonomic nervous system reactivity