Mean arterial pressure (MAP) is an average calculated blood pressure in an individual during a single cardiac cycle. Although methods of estimating MAP vary, a common calculation is to take one-third of the pulse pressure (the difference between the systolic and diastolic pressures), and add that amount to the diastolic pressure. A normal MAP is about 90 mmHg. MAP is altered by cardiac output and systemic vascular resistance. It is used to estimate the risk of cardiovascular diseases, where a MAP of 90 mmHg or less is low risk, and a MAP of greater than 96 mmHg represents "stage one hypertension" with increased risk.
Basic calculation The mean arterial pressure is calculated as the sum of the diastolic blood pressure plus the difference of the systolic pressure to the diastolic pressure, with the difference divided by three, as shown in the equation below. For example, a diastolic pressure of 70 mm Hg and a systolic pressure of 100 mm Hg would yield by means of the calculator below a MAP of 80 mm Hg. Mean arterial pressure = diastolic blood pressure + (systolic blood pressure - diastolic blood pressure)/3
Testing
Mean arterial pressure can be measured directly or estimated from systolic and diastolic blood pressure by using a formula. In the direct approach, mean arterial pressure can be calculated exactly using an arterial catheter with a transducer; this device inserted into the bloodstream measures arterial pressure over time. A less exact but less invasive approach is to use a blood pressure cuff or an oscillometric blood pressure device to determine systolic and diastolic blood pressure; these values can be plugged into a formula to estimate mean arterial pressure.
Estimating
While MAP can only be measured directly by invasive monitoring, there are several formulas for estimating MAP in terms of easy-to-measure quantities such as systolic and diastolic blood pressure. One common formula is to double the lower (diastolic) blood pressure, add it to the higher (systolic) blood pressure, and divide the resulting sum by 3 to estimate MAP:
M A P ≈ ( 2 D P + S P ) / 3 = ( 2 / 3 ) D P + ( 1 / 3 ) S P {\displaystyle MAP\approx (2DP+SP)/3=(2/3)DP+(1/3)SP}
This is equivalent to taking one-third of the pulse pressure (systolic minus diastolic pressure) and adding it to the diastolic pressure:
M A P ≈ D P + 1 / 3 ( S P − D P ) {\displaystyle MAP\approx 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 {\displaystyle R} ), which is represented mathematically by the formula
R = Δ P / Q {\displaystyle R=\Delta P/Q}
where Δ P {\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:
S V R = ( M A P − C V P ) / C O {\displaystyle SVR=(MAP-CVP)/CO}
Therefore, MAP can be determined by rearranging the equation to:
M A P = ( C O ⋅ S V R ) + C V P {\displaystyle MAP=(CO\cdot SVR)+CVP}
where:
C O {\displaystyle CO} is cardiac output
S V R {\displaystyle SVR} is systemic vascular resistance
C V P {\displaystyle CVP} is central venous pressure and usually is small enough to be neglected in this formula.
M A P ≈ C O ⋅ S V R {\displaystyle MAP\approx CO\cdot SVR}
This is only valid at normal resting heart rates during which M A P {\displaystyle MAP} can be approximated using the measured systolic ( S P {\displaystyle SP} ) and diastolic ( D P {\displaystyle DP} ) blood pressures.
Elevated heart rate At high heart rates M A P {\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 M A P {\displaystyle MAP} for elevated heart rates use:
M A P ≃ D P + 0.01 × exp ( 4.14 − 40.74 / H R ) × P P {\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
Most accurate The version of the MAP equation multiplying 0.412 by pulse pressure and adding diastolic blood pressure is indicated to correlate better than other versions of the equation with left ventricular hypertrophy, carotid wall thickness and aortic stiffness. It is expressed:
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