Concussion reduces blood flow to and oxygen levels in the brain, two new studies have found.1,2
In the first study, Canadian researchers found that blood flow and carbon dioxide levels in the brains of athletes are reduced under the stress of exercise for three to seven days after they suffer concussions.
Their study1 is reported in the December 2011 issue of the American College of Sports Medicine's journal Medicine & Science in Sports & Exercise.
In the second study,2 researchers at Cincinnati Children's Hospital found significant alterations in cerebral blood flow (CBF) in concussed adolescent athletes which persisted more than 30 days after injury in one-third of the athletes studied.
Their study is reported in the January 2012 issue of the journal Pediatrics.
Canadian study
The Canadian researchers compared cerebrovascular reactivity in post-concussion brains and healthy brains by measuring blood flow in their middle cerebral artery, monitoring the blood flow rate and carbon dioxide levels of 31 athletes (10 who had suffered a concussion within seven days prior to testing and 21 who were concussion-free for at least two months) at rest, while holding their breath and hyperventilating, and at recovery.
Healthy and concussed athletes at rest had similar results for blood flow rate and carbon dioxide levels. However, concussed athletes and healthy athletes differed under the physiological stress of breath-holding and hyperventilation. While healthy athletes' brains recovered quickly from holding their breath and hyperventilating, concussed athletes' brains failed to return to resting levels.
"Suffering a concussion may actually impair the brain's ability to recover after routine physiological stress," said lead researcher, J. Patrick Neary, Ph.D.Neary, of the University of Regina in Regina, Saskatchewan, Canada. "Throughout the testing protocol, concussed athletes had cerebrovascular abnormalities not seen in healthy athletes."
The findings support the revised team physician consensus statement on concussion released by the American College of Sports Medicine, which recommends against use of neuropsychological testing as the sole diagnostic tool in evaluating and managing concussions, or in making the all-important return-to-play decision.
"This provides further support that a physiologically challenging protocol, like the one [used in our study], is needed to confirm whether athletes are fully recovered from a concussion and able to return to play," said Neary.
Concussions can cause short- and long-term complications that affect an athlete's cognitive and emotional abilities. While the findings are promising, more research is needed on the pathophysiology of concussion to draw firm conclusions, the authors said.
Cincinnati study
Twelve children, ages 11 to 15, who had suffered sport-related concussion (SRC), two with loss of consciousness, underwent neurocognitive, MRI, magnetic resonance spectroscopy, and angiography tests at 3 days, 14 days and 30 days or greater after concussion. The neurocognitive tests using the Immediate Post-Concussion Assessment and Cognitive Testing (e.g. ImPACT) confirmed statistically signifcant differences in initial total symptom score and reaction time beteen the SRC and control groups, resolving by 14 days for total symptom score and 30 days for reaction time. While no evidence of structural injury or metabolic changes to the brain were found, significant alterations in cerebral blood flow was documented in the SRC group. At 14 days, only one-quarter (27%) of the participants showed improvement in CBF; at 30 days or more after SRC CBF had still not returned to normal in more than one-third (36%) of the athletes.
"Taken together, these CBF data suggest that pediatric sport-related concussion produces a patho-physiologic process resulting in altered CBF values with a variable and possibly protracted timeframe for resolution," writes lead author, Todd A. Maugans, M.D., of the Division of Pediatric Neurosurgery at Cincinnati Children's Hospital Medical Center.
Brains more vulnerable, more conservative management needed
"Considerable clnical evidence suggests a period of vulnerability after sport-related concussion, even after symptom resolution," says Maugans. "If a concussed child returns to quickly to strenuous physical activity or experiences a second concussion, symptoms and neuropsychological testing deficits frequently worsen. ... Furthermore, catastrophic outcomes such as second impact syndrome have been atributed to probable loss of cerebral autoregulation. Therefore, our results reinforce the concept that a protracted state of physiologic abnormality exists for some young athletes. This substantiates the need for further investigation and circumspect management of the concussed pediatric athlete," the study says.
Study supports cognitive rest prescription
Their findings have important implications for the management of pediatric concussions, says Maugans: first, because medications presently prescribed for severe postconcussive symptoms such as stimulants, beta blockers, calcium channel blockers, and triptans, have known effects on cerebral blood flow; and second, by validating the increasingly common prescription for cognitive rest. As it based on the concept of reducing cerebral metabolic demand in patients with reduced cerebral blood flow, the study shows that such "strategy is physiologically sound."
With such a small number of patients in the study, however, William P. Meehan, III, Director of the Sports Concussion Clinic in the Division of Sports Medicine at Children's Hospital Boston, was "not ready to make any changes in the medical management recommendation at this juncture. While it might cause some to reconsider the use of beta-blockers and calcium channel blockers, as the author suggests, I do not believe many physicians are currently using these as first-line agents."1. Neary J. et. al. Cerebrovascular Reactivity Impairment after Sport-Induced Concussion, Medicine & Science in Sports & Exercise 2011;43(12): 2241-2248.
2. Maugans T, Farley C, Altaye M, Leach J, Cecil K. Pediatric Sports-Related Concussion Produces Cerebral Blood Flow Alterations. Pediatrics 2012;129:28-37.
Most recently updated January 3, 2013
