The Effects of Multiple Concussions on Heart Rate Variability at Rest, Steady State Exercise, and Recovery

The Effects of Multiple Concussions on Heart Rate Variability at Rest,

Steady-State Exercise, and Recovery

Marisa A. Harrington and Lynneth A. Stuart-Hill

School of Exercise Science, Physical, and Health Education, University of Victoria, BC, Canada

Abstract

Methods Results

Figure 2. LFnu and HFnu results as seen during recovery from exercise with the

95% confidence interval as represented by the error bar.

References

This study investigated the long-term effects of concussions on heart-rate variability (HRV) to examine the link between neurological and cardiovascular health and functioning. A total of 28 participants were recruited; 14 subjects (26.2 ± 12.3 years, 9 males) who had suffered 2 or more concussions (3.4 ± 1.6) within the last 10 years with varying levels of symptom severity, and 14 control participants matched for age, sex, and VO₂ peak. Subjects rested for 12 minutes before performing an exercise protocol on a cycle ergometer consisting of a 6 minute steady-state submaximal load followed by an incremental test to exhaustion (VO₂ peak) followed by a 12-minute recovery period. HRV was measured continuously throughout the testing protocol. LF nu was greater in concussed participants during the recovery phase (t(26) = 2.625, p = 0.014), while recovery HF nu was larger in controls (t(26) = -2.617, p = 0.015). Recovery LF/HF ratio was greater in concussed participants than the respective controls (t(26) = 2.119, p = 0.044). The results show that multiple concussions suffered within a long-term time period can affect HRV response during recovery from exercise.

Introduction

Concussions have been shown to cause injury to both the central and autonomic nervous systems [1, 3]. Autonomic injury occurs through dysregulation of parasympathetic and sympathetic outflow [2]. This can make strenuous activities, such as exercise, more stressful as the body may experience a heightened state of activation through continuous systemic sympathetic control. Heart rate variability (HRV) is a reputable measure of autonomic balance that measures heart rate (HR) over time to determine predominant cardiovascular autonomic activity, specifically parasympathetic (vagal) tone [4]. HRV has been used as a predictor for future cardiovascular event and mortality across a wide variation of populations, including concussed individuals. The aim of this study was to examine if multiple concussions suffered within the last 10 years had an effect on frequency domain HRV values during rest, steady-state exercise (SS), or recovery. Ø Concussion group: 2+ concussions within the last 10 years, and last concussion at least 4 months prior to testing. Ø Control group: matched for age, sex & VO₂ peak Ø Data collection: Ø Questionnaire regarding concussion diagnoses and symptomatology Ø Anthropometrics Ø Protocol: Supine pre-exercise rest (12 minutes) followed by graded exercise on a Lode Stationary Cycle Ergometer starting at a load of 70 W, and

increasing 10 W._min-1 _{until an RER of 0.94-0.96 was reached (held for 6}

min) (SS). After SS, incremental load increases resumed until VO₂peak followed by supine post-exercise recovery HRV (12 minutes). Ø Data management: Frequency domain HRV variables pre-during and post-exercise were determined using Kubios (Finland; Version 3.0.0). Independent samples t-tests were used to compare HRV values between concussed and control participants with a 95% confidence interval (SPSS Version 24). Ø There were no difference in LF, HF and LF/HF ratio between the control and concussed groups at rest and during exercise. Ø LFnu was significantly higher in the concussed group during recovery, while HFnu was significantly greater in controls. The concussed group also showed a significantly higher LF/HF ratio during recovery. Ø These results imply that concussed participants experienced longer cardiac sympathetic activation compared to controls, who had an increase in parasympathetic output following in recovery from exercise. These also show that the autonomic impairments from concussion can last for an extended period of time since injury. [1] Gall, B., Parkhouse, W., & Goodman, D. (2004). Heart rate variability of recently concussed athletes at rest and exercise. Med Sci Sports Exerc, 36(8), 1269–1274 [2] McCrory, P., Meeuwisse, W., Dvorak, J., Aubry, M., Bailes, J., Broglio, S., … Vos, P. E. (2017). Consensus statement on concussion in sport—the 5th international conference on concussion in sport held in Berlin, October 2016. British Journal of Sports Medicine, 51(October 2016), bjsports-2017-097699. [3] Senthinathan, A., Mainwaring, L. M., & Hutchison, M. (2017). Heart rate variability of athletes across concussion recovery milestones: A preliminary study. Clinical Journal of Sport Medicine, 27(3), 288-295. [4] Tsuji, H., Larson, M. G. M., Venditti, F. J. F. J., Manders, E. E. S., Evans, J. J. C., Feldman, C. L. C., & Levy, D. (1996). Impact of reduced heart rate variability on risk for cardiac events. Circulation, 94(11), 2850–2855. 0.000000 10.000000 20.000000 30.000000 40.000000 50.000000 60.000000 70.000000 80.000000 90.000000 100.000000 LF nu HF nu nu Concussed Control * ** * *

Purpose

Major Findings

Results

0 2 4 6 8 10 12 14 LF/HF ms 2 Concussed Control Figure 1. LF/HF ratio in recovery from exercise with the 95% confidence interval as represented by the error bar. Concussed Group Control Group n = 14 Age = 26.2 years ± 12.3 Weight = 74.5 kg ± 13.4 Sex = 9M, 5F VO₂peak = 42.7 ml-1._kg-1._{min ± 11.0} Number of reported concussions = 3.4 ± 1.6 Number of diagnosed concussions = 2.5 ± 1.7 n = 14 Age = 27.4 years ± 14.1 Weight = 73.1 kg ± 11.7 Sex = 9M, 5F VO₂peak = 43.5 ml-1._kg-1._{min ± 11.6}

Participants

*note: significantly different at p<0.05 level *note: significantly different at p<0.05 level * * This research was supported by the Jamie Cassels Undergraduate Research Award., University of Victoria