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[6] [7] Regional volume reduction is not uniform; some brain regions shrink at a rate of up to 1% per year, whereas others remain relatively stable until the end of the life-span. [8] The brain is very complex, and is composed of many different areas and types of tissue, or matter.
The brain volume decreases roughly 5% per decade after forty. It is currently unclear why brain volume decreases with age. However, a few causes may include cell death, decreased cell volume, and changes in synaptic structure.
In general, cytotoxic edema is linked to cell death in the brain through excessive cellular swelling. [1] During cerebral ischemia for example, the blood–brain barrier remains intact but decreased blood flow and glucose supply leads to a disruption in cellular metabolism and creation of energy sources, such as adenosine triphosphate (ATP). [1]
About 15% of the blood volume is present in the arteries, 40% in the veins, and 45% in the nerve tissue and capillaries. [2] There is a difference between the cerebral blood volume of gray and white matter. The cerebral blood volume value of gray matter is about 3.5 +/- 0.4 ml/100g, and the white matter is about 1.7 +/- 0.4 ml/100g.
Brain ischemia has been linked to a variety of diseases or abnormalities. Individuals with sickle cell anemia, compressed blood vessels, ventricular tachycardia, plaque buildup in the arteries, blood clots, extremely low blood pressure as a result of heart attack, and congenital heart defects have a higher predisposition to brain ischemia in comparison to the average population.
For example, an increase in lesion volume (e.g., epidural hematoma) will be compensated by the downward displacement of CSF and venous blood. [24] Additionally, there is some evidence that brain tissue itself may provide an additional buffer for elevated ICP in circumstances of acute intracranial mass effect via cell volume regulation. [25] [26]
The condition is more concerning if it starts suddenly, or pain or shortness of breath is present. [2] Treatment depends on the underlying cause. [2] If the underlying mechanism involves sodium retention, decreased salt intake and a diuretic may be used. [2] Elevating the legs and support stockings may be useful for edema of the legs. [3]
This relationship is dictated by the Monro-Kellie doctrine, which states that as the brain swells, intracranial pressure (ICP) rises and cerebral perfusion decreases. As the brain swelling exceeds a certain point called the critical closing pressure (CrCP), the arterioles feeding the brain oxygen-rich blood will collapse, and the brain becomes ...