BLOG: How temperature affects concussion recovery
by W. Dalton Dietrich III, PhD
I’ve been researching the role of mild hypothermia and hyperthermia on health outcomes for more than 35 years. What the basic and more recent clinical science tells us very clearly is that small variations in brain temperature can impact many secondary pathophysiological events that influence the early and long-term consequences of brain and spinal cord injury.
Strenuous exercise such as cycling or running can potentially raise the body’s core from its normal temperature around 37°C to a state of mild hyperthermia (about 39°C to 40°C, or similar to a mild/moderate fever). The brain heats up, too, and may be warmer than the rest of the body.
Using jugular vein temperature as a surrogate marker for brain temperature, studies have shown that the brain can still significantly be hyperthermic a full hour after ceasing extensive periods of exercise.
This is important because we have clinical evidence documenting the detrimental effects of elevated temperature levels on recovery after moderate to severe traumatic brain injury (TBI). The National Institutes of Health and Department of Defense have been interested in this research, because it means that civilians or soldiers who sustain a brain injury during active periods of strenuous activities in a hot climate might be susceptible to a slower recovery or more damage.
Recent preclinical research suggests that mild hyperthermia may also affect recovery from a concussion, or mild traumatic brain injury (mTBI). In a published study (Sakurai et al.), rats with normal temperature and those whose brain temperature had been raised to 39°C were subjected to a simulated mTBI. The rats with hyperthermia were more likely to have long-term cognitive problems and showed more neuropathological changes in the brain than the rats with normal temperature.
Do humans and rats react the same way to hyperthermia? We don’t know yet, but it seems reasonable to expect they would. The hippocampus, a region of the brain involved in learning and memory, has many similar functions in rats and humans, and learning and memory are both highly vulnerable to mTBI. Current studies in the laboratory are also examining the effects of brain temperature on other systems commonly affected by concussion, including vestibular function.
Interestingly, reducing the temperature by cooling after the mTBI may reduce the risk of long-term behavioral and structural damage. This points to potential mitigation strategies in settings where concussions are more common, such as the athletic field or those sustained during war. If you watch closely during some warm-weather professional football games, you might notice that when lineman come off the field, their shoulder pads may be connected to a tube that circulates cold water to help cool down the athlete. Many athletes will also wrap a cool towel around the neck or head to help them cool down during a game. These measures may be primarily for comfort, but they can also reduce core temperatures by cooling the skin and blood coursing through blood vessels, which may improve outcomes if the athlete sustains a head injury.
In addition to being proactive, we can also be reactive. Immediately following a known or suspected concussion, high-tech strategies like cooling helmets and other devices could be used, but even moving a player into the shade or an air-conditioned building could be helpful. We are just beginning to see clinical studies published (Atkins et al.) that have evaluated whether temperature correlates to long-term outcomes following concussion and how temperature might interact with many other factors related to injury and recovery.
As we dig deeper into the science, we find that so-called “simple” insults like a mild concussion are much more complex in terms of their underlying mechanisms of injury. Potential relationships to later-occurring neurodegenerative disorders and effects on remote organ systems are also demanding more research attention. As we continue to work on understanding the consequences of brain injury, targeted temperature management strategies including therapeutic hypothermia may be one of many exciting directions for improving function and patient quality of life.
Atkins CM, et al. F1000Res. 2017;doi:10.12688/f1000research.
Sakurai A, et al. J Neurotrauma. 2012;doi:10.1089/neu.2011.2152.
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W. Dalton Dietrich III, PhD, is scientific director of the Miami Project to Cure Paralysis at the University of Miami Miller School of Medicine. He is the Kinetic Concepts Distinguished Chair in Neurosurgery; senior associate dean for discovery science; professor of neurological surgery, neurology, biomedical engineering and cell biology; and co-director of the Institute for Neural Engineering. For the past 10 years, he has served as Editor-in-Chief of the journal, Therapeutic Hypothermia and Temperature Management.
Disclosure: Dietrich reports no relevant financial disclosures.
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