Hyperacute Brain Hemodynamic and Neurocognitive Function Response to Repetitive Sub-Concussive Head Impacts

Abstract

Traumatic brain injury (TBI) is a major public health concern, affecting as many as 3 million people each year in the U.S. Athletes participating in high-contact sports are at even greater risk of head injury, especially mild traumatic brain injury (mTBI) otherwise known as concussion. Physiological changes following concussion via fMRI have been a target of study since generally no changes are observed with conventional imaging such as MRI and CT. However, little is known about the hyperacute effect, defined as the first minutes after impact, as many imaging techniques are limited to time for travel and set up for scanning. Additionally, there is limited understanding of the effects of sub-concussive head impacts, which constitute a lower impact force, and no objective symptoms of a concussion. Previous concussion studies lead us to believe there may be physiological changes occurring immediately after repetitive sub- concussive impacts that are transient. Real-time, portable neuroimaging could serve as a most effective metric in monitoring sub-concussive impacts and determine brain dysfunction at the hyperacute level. The objective of these studies is to understand the immediate physiological response to the brain following sub-concussive impacts in terms of brain blood flow, oxygenation status, neurocognitive function, and balance. This was done by using two advanced portable neuroimaging techniques, i.e., transcranial Doppler (TCD) ultrasound and functional near infrared spectroscopy (fNIRS), that allow for real-time measurements following real-world head impact kinematic data captured by wearable sensor- based mouth guards. Data was collected from multiple athletes including soccer players performing multiple soccer headers, as well as mixed martial arts (MMA) athletes during sparring sessions.We found increased changes in brain oxygenation following 10 soccer headers for the soccer athletes, as well as after contact sparring sessions for the MMA athletes. These results were similar to trends seen in concussion or TBI studies but to a much lesser extent. MMA athletes also had significantly increased blood flow velocity (BFV) values in the middle cerebral artery (MCA) following the contact sparring sessions, which was not observed for the soccer athletes. Head kinematics were also correlated with changes in BFV for the MMA athletes. These are the first studies to observe hemodynamic changes within minutes after multiple sub-concussive level impacts using non-invasive portable imaging technology. The results of this work could provide metrics for improved monitoring of head impacts and decision-making tools in contact sports, and in the future minimizing risk of repeated injury, prolonged symptoms, and more severe physiological dysfunction.