Which of the following is the correct equation for MAP?

Therefore, changes in either CO or SVR will affect MAP. As shown in the graph, increasing CO increases MAP. Likewise, increasing SVR increases MAP at any given CO. If CO and SVR change reciprocally and proportionately, then MAP will not change. For example, if CO doubles and SVR decreases by one-half, MAP does not change (if CVP = 0). It is important to note that variables found in equation 1 are all interdependent. This means that changing one variable can change each of the other variables.

In practice, MAP is not determined by knowing the CO and SVR, but rather by direct or indirect measurements of arterial pressure. From the aortic pressure trace over time (see figure), the shape of the pressure trace yields a mean pressure value (geometric mean) that is less than the arithmetic average of the systolic and diastolic pressures as shown to the right.

At normal resting heart rates, MAP can be approximated by the following equation:

For example, if systolic pressure is 120 mmHg and diastolic pressure is 80 mmHg (as shown in the figure), then the mean arterial pressure is approximately 93 mmHg using this calculation. At high heart rates, however, MAP is closer to the arithmetic average of systolic and diastolic pressure (therefore, almost 100 mmHg in this example) because of the change in shape of the arterial pressure pulse (it becomes narrower). To determine mean arterial pressure with absolute accuracy, analog electronic circuitry or digital techniques are used. In normal clinical practice, however, systolic and diastolic pressures are measured using a sphygmomanometer. MAP is determined only when SVR needs to be calculated.

To learn what factors alter cardiac output and systemic vascular resistance, and therefore alter arterial pressure, CLICK HERE

Representation of the arterial pressure waveform over one cardiac cycle. The notch in the curve is associated with closing of the aortic valve.

MeSH

In medicine, the mean arterial pressure (MAP) is an average blood pressure in an individual during a single cardiac cycle.[1] MAP is altered by cardiac output and systemic vascular resistance.[2]

Testing[edit]

Mean arterial pressure can be measured directly or determined by using a formula.[2] The least invasive method is the use of an blood pressure cuff 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.[3] Invasively, an arterial catheter with a transducer is placed and the mean pressure is determined by the subsequent waveform.[4]

Calculation[edit]

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.[5]

Normal heart rate[edit]

The most common formula for calculating mean arterial pressure is:

MAP=DP+1/3(SP−DP){\displaystyle MAP=DP+1/3(SP-DP)}

[6]

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.[2]

Another way to find the MAP is to use the Systemic Vascular Resistance equated (R{\displaystyle R}

), which is represented mathematically by the formula

R=ΔP/Q{\displaystyle R=\Delta P/Q}

where ΔP{\displaystyle \Delta P}

is the change in pressure across the systemic circulation from its beginning to its end and Q{\displaystyle Q} is the flow through the vasculature (equal to cardiac output).

In other words:

SVR=(MAP−CVP)/CO{\displaystyle SVR=(MAP-CVP)/CO}

Therefore, Mean arterial pressure can be determined by rearranging the equation to:

MAP=(CO⋅SVR)+CVP{\displaystyle MAP=(CO\cdot SVR)+CVP}

where:

This is only valid at normal resting heart rates during which MAP{\displaystyle MAP}

can be approximated using the measured systolic (SP{\displaystyle SP}) and diastolic (DP{\displaystyle DP}) blood pressures:[8][9][10]

Elevated heart rate[edit]

At high heart rates MAP{\displaystyle MAP} is more closely approximated by the arithmetic mean of systolic and diastolic pressures because of the change in shape of the arterial pressure pulse.

For a more accurate formula of MAP{\displaystyle MAP} for elevated heart rates use:

MAP≃DP+0.01×exp⁡(4.14−40.74/HR)×PP{\displaystyle 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[11]

Most accurate[edit]

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.[12] It is expressed:

MAP=DBP+(0.412×PP){\displaystyle MAP=DBP+(0.412\times PP)}

where:

• DBP = diastolic pressure
• MAP = mean arterial pressure
• PP = pulse pressure

Young Patients[edit]

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×PP){\displaystyle 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.[13]

Neonates[edit]

For neonates, because of their altered physiology, a different formula has been proposed for a more precise reading:

MAP=DBP+(0.466×PP){\displaystyle 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.[14]

Other formula versions[edit]

Other formulas used to calculate mean arterial pressure are:

MAP=DBP+0.33(PP+5){\displaystyle MAP=DBP+0.33(PP+5)}

[15]

or

MAP=DBP+[0.33+(0.0012×HR)]×PP{\displaystyle MAP=DBP+[0.33+(0.0012\times HR)]\times PP}

[16]

or

MAP=DAP+PP/3{\displaystyle MAP=DAP+PP/3}

[17]

or

MAP=DAP+PP/3+5mmHg{\displaystyle MAP=DAP+PP/3+5mmHg}

[18]

• MAP = mean arterial pressure
• PP = pulse pressure
• DAP = diastolic aortic pressure
• DPB = diastolic blood pressure

Clinical significance[edit]

Thresholds for 24 hr. mean arterial pressure (MAP)[19]24 hr. MAP category24 hr. MAPNormal<90 mmHgElevated blood pressure90 to <92 mmHgStage 1 hypertension92 to <96 mmHgStage 2 hypertension>96 mmHg

Mean arterial pressure is considered to be the perfusion pressure seen by organs in the body. It is believed that a MAP that is greater than 70 mmHg is enough to sustain the organs of the average person. MAP is normally between 65 and 110 mmHg.[20]

Hypotension[edit]

In patients with sepsis, the vasopressor dosage may be titrated on the basis of estimated MAP.[5]

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.[21][22] MAP may be used like systolic blood pressure in monitoring and treating target blood pressure. Both have been shown advantageous targets for sepsis, major trauma, 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.[23]

Hypertension[edit]

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.[19]

What is the equation for MAP?

What is the formula for calculating mean arterial pressure quizlet?

How was formula for mean arterial pressure derived?

Why is MAP divided 3?