Heart Rate Variability in Young Adults with Persisting Post‐Concussion Symptoms

Abstract

Objective Recovery following a concussion generally occurs within 7 to 10 days. However, between 10 to 50% of adults experience persistent post-concussion symptoms (PPCS). Alterations in cardiac autonomic function, which may lead to heart rate (HR) dysregulation, could explain some of those persisting symptoms. Our aim was to examine short-term resting heart rate variability (HRV), commonly used as an indicator of cardiac autonomic balance, in a group of subjects with PPCS. Hypothesis HRV parameters associated with cardiac vagal tone will be lower, while parameters associated with cardiac sympathetic activity (SYMP) will be higher in subjects with PPCS when compared to controls. Methods HRV was quantified in individuals experiencing PPCS for more than 4 wks [n=9 (5M/4F); 25 ± 6 y; body mass index (BMI): 25 ± 4 kg/m2] compared to matched healthy controls [n=18 (10M/8F); 27 ± 5 y; BMI: 23 ± 3 kg/m2]. Electrical activity of the heart was recorded continuously for 5 min in resting supine position (3-lead ECG). Signals were reviewed for artifacts and processed using Ensemble-R software (Elucimed, Wellington, NZ). Time-domain analysis of HRV provided the square root of the mean squared differences of successive NN intervals (RMSSD), and the number of interval differences, between successive intervals, greater than 50ms (pNN50). Using spectral power analysis, relative low frequency (LF) power, relative high frequency (HF) power and LF/HF ratio were obtained. RMSSD, pNN50 and relative HF power are generally associated with cardiac vagal tone, whilst relative LF power and LF/HF ratio reflect a mix of cardiac SYMP and vagal activity. Results Mean LF/HF ratio was elevated in PPCS compared to controls (2.4 ± 1.9 vs. 0.9 ± 0.5; p=0.020), owing mainly to a lower relative HF power (28.1 ± 15.8 % vs. 48.5 ± 15.8 %; p=0.004), whilst relative LF power did not differ between groups (p=0.053). There were no significant differences in RMSSD and PNN50 between groups. Conclusion As hypothesized, LF/HF ratio was increased. This shift in cardiac autonomic balance appears to result from a reduction in cardiac vagal tone in young adults with PPCS when assessed in the frequency domain.