Cerebral blood volume is the volume of blood in the skull that supplies oxygen and nutrients to the brain and meninges. Cerebral blood volume is closely related to cerebral blood flow. Severe changes in blood volume can increase intracranial pressure or result in an inadequate supply of oxygen.
What is cerebral blood volume?
Cerebral blood volume is the volume of blood in the skull that supplies oxygen and nutrients to the brain and meninges. The blood volume is equal to the total amount of blood in the human body. Depending on the localization, different blood volumes exist. For example, cerebral blood volume is the total amount of blood in the neurocranium (skull). The blood at this localization is used to supply the brain and meninges (meninges). The supply of blood is also a supply of nutrients. In addition, the blood supply ensures the supply of oxygen, on which every tissue of the human body is absolutely dependent. Oxygen binds to hemoglobin in human blood and is thus transported together with hemoglobin to the smallest vessels. The binding loosens depending on parameters such as the pH value. In this way, the oxygen is released again and can be absorbed by the individual tissues. These processes make the blood a transport medium for vital substances. The cerebral blood volume is accordingly important for the central nervous system and especially the brain. If the supply of oxygen remains inadequate, body tissues die. This has correspondingly serious consequences in connection with a vital organ such as the brain.
Function and task
The human skull always has a similar anatomy. For example, the average human skull contains 1500 grams of brain mass, which in turn consists of gray and white matter. In addition to an average of 75 milliliters of cerebrospinal fluid (brain water), there are also about 100 to 130 milliliters of blood in the brain. This blood is the cerebral blood and makes up the cerebral blood volume. Cerebral blood is distributed among various vessels. Of the total cerebral volume, about 15 percent is carried by the arteries there. About 40 percent, on the other hand, is carried by the cerebral veins. The tissue of the brain and the capillaries thus contain the remaining 45 percent of the total cerebral volume on average. Cerebral blood volume is associated with specific tissue values. The gray matter of the brain has values of about 3.5 milliliters per 100 grams. The white matter has values of about 1.75 milliliters per 100 grams. This means that the white matter contains only about half the blood volume that is found in the gray matter. The white matter consists of portions of the central nervous system that contain axons of neurons. Cerebral blood volume is closely related to the concept of cerebral blood flow. For the brain, for example, science assumes a blood flow of about 15 to 20 percent of the cardiac output. This cardiac output in turn is about 5l/min. This gives a blood flow of around 1000 milliliters per minute for the cerebral blood flow at a mass of around 1.5 kilograms. Cerebral blood flow depends not only on cerebral blood volume but also on mean arterial blood pressure, intracranial pressure, and vascular resistance of cerebral vessels.
Diseases and disorders
Any changes in cerebral blood volume can be accompanied by serious symptoms and, for this reason, have high clinical relevance. Serious consequences are mainly associated with a significant increase in cerebral blood volume. Such an increase in the volume of blood in the cerebral skull can be caused, for example, by a hematoma. A second possibility is an acute hemorrhage within the brain. Once this change violates the Monro-Kellie doctrine, the increase in volume of cerebral blood can sometimes cause life-threatening increases in intracranial pressure. The Monro-Kellie doctrine dates back to the 19th century and refers to the sum of all components in the cerebral skull. According to the doctrine, the proportions of brain tissue, blood, and cerebrospinal fluid must remain constant for intracranial pressure to remain constant. The total intracranial volume available is limited to 1600 milliliters. Any increase above this volume limit will therefore increase the intracranial pressure.For this reason, increases in cerebral blood volume can produce intracranial pressure signs indicative of an increase in intracranial pressure. With an increase in intracranial pressure, the individual parts of the brain sometimes become trapped. Depending on the part of the brain affected, irreversible consequences may result. Not only an increase in cerebral blood volume, but also a significant reduction can have serious consequences. Such a reduction occurs, for example, in the course of a stroke. When the brain no longer receives sufficient blood, it becomes proportionately or even completely insufficiently perfused. This insufficient blood supply can result in a reduced supply of nutrients and oxygen. In particular, the undersupply of oxygen is devastating to the tissues of the brain and causes individual nerve cells to die. If the blood supply and with it the oxygen supply to the brain is no longer guaranteed over a longer period of time, brain death occurs. Although major changes in cerebral blood volume can have the consequences described and thus represent serious disease phenomena, minor fluctuations in cerebral blood volume do not necessarily cause symptoms.
