Comprehensive Literature Review on the Use of Heart Rate Variability as a Biomarker for Concussion Recovery
Objective:
In this comprehensive review, we will determine whether heart rate variability (HRV) can serve as a biomarker of incomplete concussion recovery.
Background:
HRV is an index of parasympathetic activity, quantifying the variance between successive heart beats. HRV is often abnormal after severe traumatic brain injury (TBI), but has not been widely studied after concussion until recently. Studies have begun testing the hypothesis that HRV can serve as a biomarker of recovery because the regions vulnerable to concussional forces (e.g., limbic cortex, hypothalamus, and midbrain nuclei) are also key structures in the central autonomic network.
Design/Methods:
To derive a consensus from this work, we performed a comprehensive literature review of studies that compared HRV in concussed and control populations in varying conditions (e.g., rest, exertion, recovery). From 22 studies (19 adults, 2 adolescents, 1 mixed ages), we extracted HRV metrics in time and frequency domains. We then quantified the proportion of studies showing increased, decreased, or no difference in HRV across concussed and control subjects.
Results:
The majority of studies measured HRV during rest, which revealed the most consistent finding of decreased HRV (e.g. HF, RMSSD, and SDNN) in concussed compared to control subjects (12/19 studies). This finding was independent of injury mechanism, chronicity, sex, and age. Moreover, most concussed subjects were asymptomatic. Other findings, such as differences in HRV metrics after sympathetic provocations (i.e., standing, aerobic exercise, hand grip) and parasympathetic provocations (i.e., eye pressure and face cooling) were less consistent or poorly represented. More recently, studies are focusing on adolescents (3/23 studies), sex differences (2/23 studies), and longitudinal protocols (4/23 studies).
Conclusions:
Our review suggests that HRV may be a proxy for incomplete physiological recovery beyond symptoms. This positions HRV as an adjunct to concussion care, which has become more feasible in the advent of new consumer wearables.
Disclaimer: Abstracts were not reviewed by Neurology® and do not reflect the views of Neurology® editors or staff.