Cerebral perfusion pressure
Encyclopedia
Cerebral perfusion pressure, or CPP, is the net pressure
gradient causing blood flow to the brain
(brain perfusion
). It must be maintained within narrow limits because too little pressure could cause brain tissue to become ischemic (having inadequate blood flow), and too much could raise intracranial pressure
(ICP).
(CBF) such that
where:
where:
This definition may be more appropriate if considering the circulatory system in the brain as a Starling resistor
, where an external pressure (in this case, the intracranial pressure) causes decreased blood flow through the vessels. In this sense, more specifically, the cerebral perfusion pressure can be defined as either:
or
Physiologically, increased intracranial pressure
(ICP) causes decreased blood perfusion of brain cell
s by mainly two mechanisms:
Outside of the limits of autoregulation, raising MAP raises CPP and raising ICP lowers it (this is one reason that increasing ICP in traumatic brain injury
is potentially deadly). CPP is normally between 70 and 90 mmHg in an adult human, and cannot go below 70 mmHg for a sustained period without causing ischemic
brain damage
,
although some authorities regard 50-150 mmHg as a normal range for adults.
Children require pressures of at least 60 mmHg.
Within the autoregulatory range, as CPP falls there is, within seconds, vasodilatation of the cerebral resistance vessels, a fall in cerebrovascular resistance and a rise in cerebro-blood volume (CBV), and therefore CBF remains constant (see as ref. Aaslid, Lindegaard, Sorteberg, and Nornes 1989: http://stroke.ahajournals.org/cgi/reprint/20/1/45.pdf).
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
gradient causing blood flow to the brain
Cerebral blood flow
Cerebral blood flow, or CBF, is the blood supply to the brain in a given time. In an adult, CBF is typically 750 millitres per minute or 15% of the cardiac output. This equates to 50 to 54 millilitres of blood per 100 grams of brain tissue per minute. CBF is tightly regulated to meet the brain's...
(brain perfusion
Perfusion
In physiology, perfusion is the process of nutritive delivery of arterial blood to a capillary bed in the biological tissue. The word is derived from the French verb "perfuser" meaning to "pour over or through."...
). It must be maintained within narrow limits because too little pressure could cause brain tissue to become ischemic (having inadequate blood flow), and too much could raise intracranial pressure
Intracranial pressure
Intracranial pressure is the pressure inside the skull and thus in the brain tissue and cerebrospinal fluid . The body has various mechanisms by which it keeps the ICP stable, with CSF pressures varying by about 1 mmHg in normal adults through shifts in production and absorption of CSF...
(ICP).
From resistance
CPP can be defined as the pressure gradient causing cerebral blood flowCerebral blood flow
Cerebral blood flow, or CBF, is the blood supply to the brain in a given time. In an adult, CBF is typically 750 millitres per minute or 15% of the cardiac output. This equates to 50 to 54 millilitres of blood per 100 grams of brain tissue per minute. CBF is tightly regulated to meet the brain's...
(CBF) such that
where:
- CVR is cerebrovascular resistance
By intracranial pressure
An alternative definition of CPP is:
where:
- MAP is mean arterial pressureMean arterial pressureThe mean arterial pressure is a term used in medicine to describe an average blood pressure in an individual. It is defined as the average arterial pressure during a single cardiac cycle.-Calculation:...
- ICP is intracranial pressureIntracranial pressureIntracranial pressure is the pressure inside the skull and thus in the brain tissue and cerebrospinal fluid . The body has various mechanisms by which it keeps the ICP stable, with CSF pressures varying by about 1 mmHg in normal adults through shifts in production and absorption of CSF...
This definition may be more appropriate if considering the circulatory system in the brain as a Starling resistor
Starling resistor
The Starling resistor was invented by English physiologist Ernest Starling and used in an isolated-heart preparation during work which would later lead to the "Frank–Starling law of the heart"....
, where an external pressure (in this case, the intracranial pressure) causes decreased blood flow through the vessels. In this sense, more specifically, the cerebral perfusion pressure can be defined as either:
-
(if ICP is higher than JVP)
or
-
(if JVP is higher than ICP).
Physiologically, increased intracranial pressure
Intracranial pressure
Intracranial pressure is the pressure inside the skull and thus in the brain tissue and cerebrospinal fluid . The body has various mechanisms by which it keeps the ICP stable, with CSF pressures varying by about 1 mmHg in normal adults through shifts in production and absorption of CSF...
(ICP) causes decreased blood perfusion of brain cell
Brain Cell
Brain Cell is a mail art project begun by Ryosuke Cohen in June 1985. The project is basically a networked art project where individual artists create their own 30x42cm work of art with stamps, drawings, stickers and so forth. This is sent to Cohen, who prints each cell - 150 copies each - with a...
s by mainly two mechanisms:
- Increased ICP constitutes an increased interstitial hydrostatic pressure that, in turn, causes a decreased driving force for capillary filtrationStarling equationThe Starling equation is an equation that illustrates the role of hydrostatic and oncotic forces in the movement of fluid across capillary membranes.Capillary fluid movement may occur as a result of three processes:...
from intracerebral blood vessels. - Increased ICP compresses cerebral arteries, causing increased cerebrovascular resistance (CVR).
Autoregulation
Under normal circumstances (MAP between 60 to 150 mmHg and ICP about 10 mmHg) cerebral blood flow is relatively constant due to protective autoregulation.Outside of the limits of autoregulation, raising MAP raises CPP and raising ICP lowers it (this is one reason that increasing ICP in traumatic brain injury
Traumatic brain injury
Traumatic brain injury , also known as intracranial injury, occurs when an external force traumatically injures the brain. TBI can be classified based on severity, mechanism , or other features...
is potentially deadly). CPP is normally between 70 and 90 mmHg in an adult human, and cannot go below 70 mmHg for a sustained period without causing ischemic
Ischemia
In medicine, ischemia is a restriction in blood supply, generally due to factors in the blood vessels, with resultant damage or dysfunction of tissue. It may also be spelled ischaemia or ischæmia...
brain damage
Brain damage
"Brain damage" or "brain injury" is the destruction or degeneration of brain cells. Brain injuries occur due to a wide range of internal and external factors...
,
although some authorities regard 50-150 mmHg as a normal range for adults.
Children require pressures of at least 60 mmHg.
Within the autoregulatory range, as CPP falls there is, within seconds, vasodilatation of the cerebral resistance vessels, a fall in cerebrovascular resistance and a rise in cerebro-blood volume (CBV), and therefore CBF remains constant (see as ref. Aaslid, Lindegaard, Sorteberg, and Nornes 1989: http://stroke.ahajournals.org/cgi/reprint/20/1/45.pdf).
Others
- Sanders MJ and McKenna K. 2001. Mosby’s Paramedic Textbook, 2nd revised Ed. Chapter 22, "Head and Facial Trauma." Mosby.