1026 - Differences in Heart Rate Variability in Individuals with mTBI

Objectives: The primary goal of this study was to focus on
individuals with acute mTBI and to examine autonomic metrics – specifically in HRV during head-up tilt table testing (a condition intended to provide an autonomic stressor and symptom provocation) – compared to a healthy control group.

Design: Head-up tilt table testing was performed in individuals with mTBI < 14 days of injury, and age-/sex-matched health controls; HRV (RMSSD) was calculated in resting and head-up tilt phases, and change scores between conditions were computed. HR was also evaluated as a percentage of maximum heart rate (% max HR) at
predefined time points during tilt table testing, including supine and upright positions (first 5 minutes with supine, middle 5 minutes with upright). Kubios was utilized to calculate
HRV variables. Two sample equal t-tests were used to evaluated group differences between change scores across groups (mTBI vs controls).

Results: The reported sample consists of 27 controls and 33 acute mTBI participants. There were no statistically significant differences in resting, maximum or mean HR (p = 0.12, 0.27, 0.15 respectively). However, there was a significant difference in RMSSD change scores between upright and supine testing in mTBI vs control groups (p = 0.00009), where mTBI subjects demonstrated a relative reduction in RMSSD during head-up tilt, while RMSSD tended to increase in controls.

Conclusions: We found evidence of reduced HRV (via RMSSD) in individuals with mTBI
compared to healthy controls. These findings support prior reports suggestive of altered HRV in
mTBI, which are detectable in this study during the acute phase post-mTBI injury. Further, we note that RMSSD, a measure of autonomic response to acute stress, is impaired in mTBI during head-up tilt table challenge. These
findings prompt ongoing study, including larger group sizes and longitudinal investigation to
determine if these changes resolve with symptomatic recovery.