After a concussion…

92% of repeat concussions occur within 10 days of the initial injury,

and

75% occur within the first week after a concussion

Immediately after an impact to the brain, a cascade of events can occur that changes the way the body functions:

• The brain neurotransmitter (messenger) glutamate is release at a rate of up to 50% greater than normal
  • High glutamate levels are toxic to nerve cells!
• Potassium exits the brain cells up to 4 times greater than the normal rate
  • Unconsciousness occurs as potassium levels exceed a critical concentration
• Calcium enters the brain at 5 times the normal rate
• Blood flow to the brain decreases by up to 50% within minutes of the initial impact
• Glutamate levels return to baseline levels within 3.5 minutes after impact
  • Potassium restoration takes approximately 20 minutes
  • Calcium levels are not restored for up to 3 days
• Blood flow levels are not restored until 7-10 days post injury

The brain works into overtime to restore normal chemical balances resulting in an energy crisis termed hypermetabolism. This occurs because less oxygen and glucose, which the body uses as energy sources, are available and there is less blood flow to bring these energy sources to the brain.

The brain then enters a state of hypometabolism (resting depression) which can last 5-10+ days until blood flow levels in the brain are returned to normal. During this time frame the body is working on healing the brain.

Based on the severity of the concussion, the brain takes a minimum of 7-10 days to return to a normal chemical and blood flow balance, making the necessity to avoid repeated trauma all the more important during this time frame.

This begs the question of whether the above concussed athletes were ready to return in the first place!

References:   Giza CC, Hovda DA. The neurometabolic cascade of concussion. J of Athletic Training. 2001; 36(3): 228-235.

Giza CC, Hovda DA.  The New Neurometabolic Cascade of Concussion.  Neurosurgery. 2014; 75(3) supplement:24-33.