Accrued reductions in heart rate following transcutaneous vagal nerve stimulation in adults with posttraumatic stress disorder

FIGURE 1. Hypothesized comparison between acute and accrued effects of transcutaneous cervical vagus nerve stimulation (tcVNS) over time. tcVNS causes an acute impact on physiological markers initially. The magnitude of this effect decreases over time at a relatively faster rate than the accrued effects asserted by this analysis. The accrued effects increase initially, and these effects are endured longer than the acute effects.

FIGURE 2. Processing pipeline for time series analysis. The first 5 min of data for each participant were used as a baseline to normalize the heart rate data. These values were then averaged among the participants. The data points were averaged for each condition to produce the condensed plots. The time series analysis was conducted by plotting each data point over the first four hours of data collection.

FIGURE 3. (a,b) Condensed comparison between relative change in heart rate for participants receiving either active or sham stimulation during each condition of protocol. Participants receiving active stimulation experienced a greater accrued decrease in their heart rate when compared to sham participants. On average, participants with Post-Traumatic Stress Disorder (PTSD) experienced a decrease in heart rate during the conditions with trauma recall and stimulation. Heart rate increases and returns above baseline for active and sham participants without PTSD and sham participants with PTSD during neutral scripts 3 and 4. However, heart rate remains below baseline during both neutral scripts 3 and 4. Furthermore, these effects remain even during trauma recall 3 and 4.

FIGURE 4. Time series analysis of relative changes in heart rate for Post-Traumatic Stress Disorder (PTSD) and non-PTSD participants during each condition of protocol. In the PTSD active group (red line), heart rate decreased during stimulation and remained below pre-stimulation levels thereafter, with no post-stimulation increases above baseline (indicated by 0.00 on the y-axis). During trauma recall in the third script, heart rate for the PTSD active group increased but returned to approximately baseline, contrasting with the PTSD sham group’s response (blue line). Participants without PTSD showed no significant differences between active (red line) and sham (blue line) groups.