What is ischaemia?
Ischaemia (also spelled as ischemia, depending on dialect) is defined as a lack of oxygen to a certain organ in the body due to blockage of the blood in the circulation. Since I’m referring to the brain here, when I refer to ischaemia, I mean ischaemia of the brain. Ischaemia can either be transient (temporary) or permanent.
What are the types of brain ischemia?
Ischaemia (lack of oxygen) of the brain can either be global (throughout the entire brain) as seen on the picture above, or focally (in the centre of the brain). The prognosis for the person that gets this condition is dependent on the severity of the ischaemia.
Global ischaemia is defined as a lack of oxygen due to low blood pressure: (blood pressure= systolic/diastolic pressure) if measured, the systolic pressure would be below 50mmHg. The parts of the brain that are most likely to be influenced by global ischaemia include the pyrimidial cells in the hippocampus, the Purkinje cells in the cerebellum and the pyrimidial cells in the neocortex. Circumstances that would make the blood pressure go this low include severe shock and cardiac arrest (heart attack). The neurons within the brain would start to die off due to the lack of oxygen (as well as lack of glucose). Unfortunately, if this condition is severe, the prognosis is poor: the person who suffered from global ischaemia might end up in a vegetative state or potentially end up brain dead: this would be detected by a flat line on an EEG (electroencephalogram) as well as a lack of reflexes and no breathing. The brain waves can be checked out by placing electrodes on the brain like the picture above. However, if the condition is caught early enough, the prognosis is good and there is a chance that after a period, the brain is able to rewire itself due to its plasticity.
Changes During Global Ischaemia
The changes are illustrated in the Smart Art Graphic below:
Focal Cerebral Ischaemia
There are two subtypes of focal cerebral ischaemia: haemorrhagic and non-haemorrhagic ischaemia. The lack of oxygen in the brain can lead to infarction (death of the tissue) and the prognosis of the person depends on where the ischaemia occurs. A major factor that determines the final prognosis is collateral flow: the parts of the brain that have little collateral flow are the thalamus, basal ganglia and deep white matter.
What is collateral flow?
It’s similar to being on the road: if you want to get a certain destination, you have to figure out how many potential routes there are to drive and which one is the quickest or the most direct. The more routes there are, the less likely there is to be a gridlock in order to reach the final destination, as the traffic would be distributed more finely.
The same thing happens in the brain: the more routes there are, the less likely that something is bound to go wrong if blood is blocked, as the blood can be diverted to other vessels. If there is only one blood vessel to a certain area of the brain, if it becomes blocked, there would be a major traffic jam! Blood commonly gets blocked by means of thrombi (blood clots) or emboli (smaller pieces of clots thrown from a main clot).
The treatment of the infarcts associated with focal cerebral ischaemia depends on the subtype. Nonhaemorrhagic infarcts can be treated with thrombolytic therapies which breakdown the thrombus or embolus.
Recovery from Focal Cerebral Ischaemia
The recovery process from focal cerebral ischaemia is shown in the Smart Art Graphic below:
*H/I= haemorrhagic infarction