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Finding sensitive and specific markers for sports-related concussion is both challenging and clinically important. Such biomarkers might be helpful in the management of patients with concussion (i.e. diagnosis, monitoring and risk prediction). Among many parameters, blood flow-pressure metrics and heart rate variability (HRV) have been used to gauge concussion outcomes. Reports on the relation between HRV and both acute and prolonged concussion recovery are conflicting. While some authors report on differences in the low-frequency (LF) component of HRV during postural manipulations and postexercise conditions, others observe no significant differences in various HRV measures. Despite the early success of using the HRV LF for concussion recovery, the interpretation of the LF is debated. Recent research suggests the LF power is a net effect of several intrinsic modulatory factors from both sympathetic and parasympathetic branches of the autonomic nervous system, vagally mediated baroreflex and even some respiratory influences at lower respiratory rate. There are only a few well-controlled concussion studies that specifically examine the contribution of the autonomic nervous system branches with HRV for concussion management. This study reviews the most recent HRV- concussion literature and the underlying HRV physiology. It also highlights cerebral blood flow studies related to concussion and the importance of multimodal assessment of various biological signals. It is hoped that a better understanding of the physiology behind HRV might generate cost-effective, repeatable and reliable protocols, all of which will improve the interpretation of HRV throughout concussion recovery., (© 2017 Scandinavian Society of Clinical Physiology and Nuclear Medicine. Published by John Wiley & Sons Ltd.)

Background: Clinicians typically rely on neuropsychological and balance tests to track concussion recovery. The aforementioned tests imply impairments that are based on performance, but these tests do not directly measure brain physiology throughout concussion recovery. Because of these issues, an objective biomarker that can index severity and the recovery timeline is needed. Moreover, the number of concussions occurring at a recreational level requires the biomarker to be easily administered in a cost effective manner, and the results easily interpreted., Methods: To address these issues, near-infrared spectroscopy was used to assess the relative changes in oxy (HbO 2 )- and deoxyhaemoglobin and the associated standard deviations (SD) in the prefrontal cortex. Resting haemoglobin, and haemoglobin changes in response to hypercapnia (five repeated 20s breath holds), was measured in all participants. Data were aggregated into healthy baselines (n = 115), and concussed participants on days 1-3 (n = 14), 4-6 (n = 8), and 7-14 (n = 11). The data were statistically compared using a 1 × 4 ANOVA., Results: Resting HbO 2 values progressively lowered from days 1-3 to 7-14 (with no differences compared to controls). The second major finding showed that hypercapnic HbO 2 SD was significantly lower than resting values on days 1-3 and 4-6, but reversed back towards the healthy control group on day 7-14., Conclusion: Monitoring cerebral oxygenation changes is a viable biomarker to assess the physiological state of the brain following concussion., (© 2017 Scandinavian Society of Clinical Physiology and Nuclear Medicine. Published by John Wiley & Sons Ltd.)

Ballistocardiography (BCG) is a non-invasive technology that has been used to record ultra-low-frequency vibrations of the heart allowing for the measurement of cardiac cycle events including timing and amplitudes of contraction. Recent developments in BCG have made this technology simple to use, as well as time- and cost-efficient in comparison with other more complicated and invasive techniques used to evaluate cardiac performance. Recent technological advances are considerably greater since the advent of microprocessors and laptop computers. Along with the history of BCG, this paper reviews the present and future potential benefits of using BCG to measure cardiac cycle events and its application to clinical and applied research., (© 2012 The Authors Clinical Physiology and Functional Imaging © 2012 Scandinavian Society of Clinical Physiology and Nuclear Medicine.)

Mild traumatic brain injury (mTBI) or sport-induced concussion has recently become a prominent concern not only in the athletic setting (i.e. sports venue) but also in the general population. The majority of research to date has aimed at understanding the neurological and neuropsychological outcomes of injury as well as return-to-play guidelines. Remaining relatively unexamined has been the pathophysiological aspect of mTBI. Recent technological advances including transcranial Doppler ultrasound and near infrared spectroscopy have allowed researchers to examine the systemic effects of mTBI from rest to exercise, and during both asymptomatic and symptomatic conditions. In this review, we focus on the current research available from both human and experimental (animal) studies surrounding the pathophysiology of mTBI. First, the quest for a unified definition of mTBI, its historical development and implications for future research is discussed. Finally, the impact of mTBI on the control and regulation of cerebral blood flow, cerebrovascular reactivity, cerebral oxygenation and neuroautonomic cardiovascular regulation, all of which may be compromised with mTBI, is discussed., (© 2010 The Authors. Clinical Physiology and Functional Imaging © 2010 Scandinavian Society of Clinical Physiology and Nuclear Medicine.)