How Much Does Stress Cost? A Case–Control Study on Vagally Mediated Heart Rate Variability Responses in Anxious and Non-Anxious Individuals During a Cognitive Task

<b>Background</b>: Heart rate (HR) and HR variability (HRV) are valid indices of psychophysical stress. Healthy individuals typically exhibit high vagal tone, as indicated by vagally mediated HRV (vmHRV) values. Despite current knowledge, HRV differences between anxious subjects and controls during a cognitive task have not yet been studied. <b>Methods</b>: Anxious people were compared to controls through the State-Trait Anxiety Inventory (STAI-Y), both considering State Anxiety (S-Anxiety) and Trait Anxiety (T-Anxiety) one at a time. Subsequently, a psychophysiological stress profile (PSP) was conducted to record HRV values (i.e., SDNN, RMSSD, and HF) at baseline and under induced stress with an electrocardiogram (ECG). During the stress test, the digit span forward task was conducted. <b>Results</b>: Significant differences were described by dividing the sample by S-Anxiety in the baseline values of log-HF (t = 2.68; <i>p</i> = 0.05; d = 0.85) and log-RMSSD (t = 2.34; <i>p</i> = 0.01; d = 0.74). Dividing the sample by T-Anxiety, significant differences were found in the reactivity (t = -2.26; <i>p</i> = 0.03; d = -0.70) and recovery (t = 2.11; <i>p</i> = 0.04; d = 0.66) log-HF values. Additionally, reactivity log-HF and recovery log-RMSSD values demonstrated significant discriminative power of 68% and 68%, respectively, in accurately identifying individuals with anxiety, as measured by T-Anxiety. Lastly, an association was found between the baseline HR value and the equivalent point of digit span forward in both the anxious (r = 0.59, <i>p</i> = 0.01) and control (r = -0.45, <i>p</i> = 0.05) groups. <b>Conclusions</b>: Although a high vmHRV is considered a protective factor against stress, our findings found that a reduced HRV modulation can distinguish a group of people with significant symptoms of anxiety and hinder cognitive efficiency.