Utility of Heart Rate Variability and Exertional Task Completion During Recovery of Mild Traumatic Brain Injury in Active Duty Service Members

Introduction Primary care exertional testing is recommended for mild traumatic brain injury (mTBI) management in active duty service members (ADSM) before return-to-duty (RTD), yet there are no validated standardized tasks with objective physiological measures. Impairments to the automatic nervous system (ANS) after mTBI may last beyond symptom resolution and impact readiness for duty. Assessment of ANS functioning (heart rate variability, HRV) could provide an objective measure of mTBI recovery. Materials and Methods Eighteen ADSM with mTBI (2 weeks or less post-injury) and 18 age-matched healthy controls (HC) performed a protocol of two brief exertional tasks that challenge exertional and autonomic impairments: a 6-minute metronome-paced step-task and a 2-minute self-paced push-up task with built in rest periods. Heart rate variability components Respiratory Sinus Arrhythmia (RSA; parasympathetic input) and heart period (HP; average inter-beat-intervals), symptoms levels, and rate of perceived exertion (RPE) were measured prior, during, and after each task. All study procedures were approved by The U.S. Army Regional Health Command-Atlantic (RHC-A) IRB, #2019-001. Results Between group analyses of self-rated and HRV components demonstrated mTBI differences: higher RPE during recovery (B = 1.0, P < .01); increased symptoms under exertion (χ2(1,36) = 5.14, P < .03); lower RSA at Rest 1 (B = −1.0, P = .04) indicating longer recovery; higher RSA during push-ups (B = 1.22, P = .02; and higher Heart Period during both step (B = 75.34, P < .02) and push-up task (B = 84.43, P < .01)) indicating less vagal withdrawal compared to HCs. ADSM with mTBI were less likely to successfully complete both tasks (OR = 5.80, [1.79-18.82]). Conclusions These brief exertional tasks may prove useful in primary care to identify symptomatic responses to exercise. Heart rate variability measurement may expose autonomic dysfunction that could influence readiness for full return to duty.