Muscle Sympathetic Nerve Reactivity to Trier Social Stress Test
Authors: Bigalke Jeremy A. , Greenlund Ian M. , Nicevski Jennifer R. , Tikkanen Anne L. , Carter Jason R. 
Published: May 2022

Muscle sympathetic nerve activity (MSNA) responses to laboratory mental stress are highly variable, making characterization of the sympathoneural response difficult to infer. However, most commonly used mental stress tasks (i.e., mental arithmetic, Stroop Color Word Task, etc.) are primarily cognitive tasks. Further, interpretation of MSNA reactivity to these stressors can be challenging due to irregular breathing patterns, limb movement, etc. The current study assesses MSNA reactivity to the Trier Social Stress Test (TSST), an ecologically valid evaluative social stress task that utilizes an anticipatory stress period free of confounds such as irregular breathing and movement found in other mental stress tasks. The primary purpose of the present study was to assess MSNA during the stress‐anticipation period, as well as during the socially evaluated portion of the task. We hypothesized that MSNA would be elevated during both phases of the task. Sixteen healthy adults (12 female, 26 ± 1 years, 24 ± 1 kg/m2) participated in a morning autonomic function test consisting of simultaneous recordings of heart rate (HR, electrocardiogram), beat‐to‐beat blood pressure (finger plethysmography), and MSNA (microneurography) during a 10‐minute resting baseline followed by the TSST. The TSST consists of a speech preparation period (5 min), a public speech (5 min), and mental arithmetic task (5 min) in front of two laboratory judges and video recording. After completion of the TSST, participants were assessed throughout a 5‐minute recovery. MSNA was obtained throughout all tasks in 12 individuals. Compared to baseline, mean arterial pressure (MAP) significantly increased during the anticipatory phase (Δ8 ± 2 mmHg, p<.001), increased further during the speech (Δ25 ± 3 mmHg, p<.001) and arithmetic (Δ23 ± 3 mmHg, p<.001), and returned to anticipatory levels during recovery (Δ10 ± 1 mmHg, p<.001). Similarly, HR was elevated during the anticipatory (Δ8 ± 2 bpm, p=.002), and increased further during the speech (Δ24 ± 5 bpm, p<.001) and arithmetic (Δ19 ± 4 bpm, p<.001) phases, but fully returned to baseline levels during recovery (Δ2 ± 1 bpm p=.232). MSNA burst frequency was significantly reduced during the anticipatory phase (Δ‐5 ± 2 bursts/min, p=.014) and tended to be reduced during mental arithmetic (Δ‐5 ± 2 bursts/min, p=.058), while MSNA burst incidence was reduced during the anticipatory (Δ‐9 ± 3 bursts/100hb, p=.008) and arithmetic (Δ‐11 ± 4 bursts/100hb, p=.016) phases. In 7 individuals, MSNA signal quality allowed assessment of MSNA total area. While total MSNA appeared to increase during the speech portion of the TSST, this effect did not reach significance (Δ8906 ± 4547 arbitrary units, p=.098). Contrary to our hypothesis, while blood pressure and HR were significantly elevated, MSNA was reduced in response to social stress, likely due to baroreflex inhibition. Further, our findings exhibit previously observed inter‐individual variability in MSNA responsiveness to mental stress, even during anticipatory stress, suggesting that this variability is conserved between various laboratory stressors.