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In medicine, the mean arterial pressure (MAP) is an average blood pressure in an individual during a single
cardiac cycle The cardiac cycle is the performance of the human heart from the beginning of one heartbeat to the beginning of the next. It consists of two periods: one during which the heart muscle relaxes and refills with blood, called diastole, following ...
. MAP is altered by cardiac output and systemic vascular resistance.


Testing

Mean arterial pressure can be measured directly or determined by using a formula. The least invasive method is the use of an
blood pressure cuff A sphygmomanometer ( ), a blood pressure monitor, or blood pressure gauge, is a device used to measure blood pressure, composed of an inflatable cuff to collapse and then release the artery under the cuff in a controlled manner, and a mercury ...
which gives the values to calculate the mean pressure. A similar method is to use a oscillometric blood pressure device that works by a cuff only method where a microprocessor determines the systolic and diastolic blood pressure. Invasively, an
arterial catheter An arterial line (also art-line or a-line) is a thin catheter inserted into an artery. Use Arterial lines are most commonly used in intensive care medicine and anesthesia to monitor blood pressure directly and in real-time (rather than by in ...
with a transducer is placed and the mean pressure is determined by the subsequent waveform.


Calculation

While MAP can only be measured directly by invasive monitoring. The MAP can be estimated by using a formula in which the lower (diastolic) blood pressure is doubled and added to the higher (systolic) blood pressure and that composite sum then is divided by 3 to estimate MAP.Calculating the mean arterial pressure (MAP) Nursing center2011-12-08
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Normal heart rate

The most common formula for calculating mean arterial pressure is: MAP =DP+1/3(SP-DP) where: * DP = diastolic pressure * SP = systolic pressure * MAP = mean arterial pressure Systolic pressure minus diastolic pressure equals the pulse pressure which may be substituted in. Another way to find the MAP is to use the Systemic Vascular Resistance equated (R), which is represented mathematically by the formula :R = \Delta P/Q where \Delta P is the change in pressure across the systemic circulation from its beginning to its end and Q is the flow through the vasculature (equal to cardiac output). In other words: SVR = (MAP - CVP) / CO Therefore, Mean arterial pressure can be determined by rearranging the equation to: :MAP = (CO \cdot SVR) + CVP where: *CO is
cardiac output In cardiac physiology, cardiac output (CO), also known as heart output and often denoted by the symbols Q, \dot Q, or \dot Q_ , edited by Catherine E. Williamson, Phillip Bennett is the volumetric flow rate of the heart's pumping output: t ...
*SVR is systemic vascular resistance *CVP is
central venous pressure Central venous pressure (CVP) is the blood pressure in the venae cavae, near the right atrium of the heart. CVP reflects the amount of blood returning to the heart and the ability of the heart to pump the blood back into the arterial system. CVP ...
and usually is small enough to be neglected in this formula. This is only valid at normal resting heart rates during which MAP can be approximated using the
measured Measurement is the quantification of attributes of an object or event, which can be used to compare with other objects or events. In other words, measurement is a process of determining how large or small a physical quantity is as compared ...
systolic (SP) and
diastolic Diastole ( ) is the relaxed phase of the cardiac cycle when the chambers of the heart are re-filling with blood. The contrasting phase is systole when the heart chambers are contracting. Atrial diastole is the relaxing of the atria, and ventricu ...
(DP) blood pressures:


Elevated heart rate

At high heart rates MAP is more closely approximated by the
arithmetic mean In mathematics and statistics, the arithmetic mean ( ) or arithmetic average, or just the ''mean'' or the ''average'' (when the context is clear), is the sum of a collection of numbers divided by the count of numbers in the collection. The coll ...
of systolic and diastolic pressures because of the change in shape of the arterial pressure pulse. For a more accurate formula of MAP for elevated heart rates use: : MAP \simeq DP + 0.01 \times \exp(4.14 - 40.74 / HR) \times PP Where * HR = heart rate. * DP = diastolic pressure * MAP = mean arterial pressure * PP = pulse pressure which is systolic minus diastolic pressure


Most accurate

The version of the MAP equation multiplying 0.412 by pulse pressure and adding diastolic blood is indicated to correlate better than other versions of the equation with left ventricular hypertrophy, carotid wall thickness and aortic stiffness. It is expressed: MAP=DBP +(0.412\times PP) where: * DBP = diastolic pressure * MAP = mean arterial pressure * PP = pulse pressure


Young Patients

For young patients with congenital heart disease a slight alteration to the factor used found to be more precise. This was written as: MAP=DBP +(0.475\times PP) where: *DBP = diastolic pressure * MAP = mean arterial pressure * PP = pulse pressure This added precision means cerebral blood flow can be more accurately maintained in uncontrolled hypertension.


Neonates

For neonates, because of their altered physiology, a different formula has been proposed for a more precise reading: MAP=DBP +(0.466\times PP) where: *DBP = diastolic pressure * MAP = mean arterial pressure * PP = pulse pressure It has also been suggested that when getting readings from a neonates radial arterial line, mean arterial pressure can be approximated by averaging the systolic and diastolic pressure.


Other formula versions

Other formulas used to calculate mean arterial pressure are: MAP=DBP+0.33(PP+5) or MAP=DBP+ .33+(0.0012 \times HR)times PP or MAP=DAP + PP/3 or MAP = DAP+PP/3+5mmHg * MAP = mean arterial pressure * PP = pulse pressure * DAP = diastolic aortic pressure * DPB = diastolic blood pressure


Clinical significance

Mean arterial pressure is considered to be the perfusion pressure seen by
organs In biology, an organ is a collection of tissues joined in a structural unit to serve a common function. In the hierarchy of life, an organ lies between tissue and an organ system. Tissues are formed from same type cells to act together in a ...
in the body. It is believed that a MAP that is greater than 70
mmHg A millimetre of mercury is a manometric unit of pressure, formerly defined as the extra pressure generated by a column of mercury one millimetre high, and currently defined as exactly pascals. It is denoted mmHg or mm Hg. Although not an ...
is enough to sustain the organs of the average person. MAP is normally between 65 and 110
mmHg A millimetre of mercury is a manometric unit of pressure, formerly defined as the extra pressure generated by a column of mercury one millimetre high, and currently defined as exactly pascals. It is denoted mmHg or mm Hg. Although not an ...
.


Hypotension

In patients with
sepsis Sepsis, formerly known as septicemia (septicaemia in British English) or blood poisoning, is a life-threatening condition that arises when the body's response to infection causes injury to its own tissues and organs. This initial stage is follo ...
, the
vasopressor An antihypotensive agent, also known as a vasopressor agent or simply vasopressor, or pressor, is any substance, whether endogenous or a medication, that tends to raise low blood pressure. Some antihypotensive drugs act as vasoconstrictors to i ...
dosage may be
titrate Titration (also known as titrimetry and volumetric analysis) is a common laboratory method of quantitative chemical analysis to determine the concentration of an identified analyte (a substance to be analyzed). A reagent, termed the ''titrant' ...
d on the basis of estimated MAP. Even 1 minute at a mean arterial pressure of 50 mmHg, or accumulative effects over short periods, increases the risk of mortality by 5% and can result in organ failure or complications. MAP may be used like systolic blood pressure in monitoring and treating target blood pressure. Both have been shown advantageous targets for
sepsis Sepsis, formerly known as septicemia (septicaemia in British English) or blood poisoning, is a life-threatening condition that arises when the body's response to infection causes injury to its own tissues and organs. This initial stage is follo ...
,
major trauma Major trauma is any injury that has the potential to cause prolonged disability or death. There are many causes of major trauma, blunt and penetrating, including falls, motor vehicle collisions, stabbing wounds, and gunshot wounds. Dependin ...
, stroke, intracranial bleed. If the MAP falls below the target number for an appreciable time, vital organs will not get enough oxygen perfusion, and will become hypoxic, a condition called ischemia.


Hypertension

As the 24 hour mean arterial pressure increases, so does the risk of adverse cardiovascular events. MAP shows information about both the systolic and diastolic blood pressure In the management of high blood pressure, so it can be evaluated to ensure perfusion is maintained to the organs.


See also

* Blood pressure * Hypertension * Hypotension * Systemic vascular resistance *
Pulse pressure Pulse pressure is the difference between systolic and diastolic blood pressure. It is measured in millimeters of mercury (mmHg). It represents the force that the heart generates each time it contracts. Resting blood pressure is normally approx ...


References


External links


Mean Arterial Pressure Calculator

More Information on usage of the Mean Arterial Pressure
{{Cardiovascular physiology Diagnostic intensive care medicine Medical signs Blood pressure it:Pressione arteriosa differenziale