Brain Ischemia - Pathophysiology

Pathophysiology

During brain ischemia, the brain cannot perform aerobic metabolism due to the loss of oxygen and substrate. The brain is not able to switch to anaerobic metabolism and because it does not have any long term energy stored the levels of adenosine triphosphate (ATP) drop rapidly and approach zero within 4 minutes. In the absence of biochemical energy, cells begin to lose the ability to maintain electrochemical gradients. Consequently, there is a massive influx of calcium into the cytosol, a massive release of glutamate from synaptic vesicles, lipolysis, calpain activation, and the arrest of protein synthesis. Additionally, removal of metabolic wastes is slowed. The interruption of blood flow to the brain for ten seconds results in the immediate loss of consciousness. The interruption of blood flow for twenty seconds results in the stopping of electrical activity. An area called a penumbra, may result, wherein neurons do not receive enough blood to communicate, however do receive sufficient oxygenation to avoid cell death for a short period of time.