Mean Arterial Pressure
Average blood pressure during a cardiac cycle.
Formula
Variables
Example
120/80 ⇒ 93 mmHg
How it works
Mean arterial pressure estimates the average pressure pushing blood through the arteries over one heartbeat. It is not the simple midpoint of systolic and diastolic pressure because the heart spends more time in diastole than systole, so the diastolic value gets more weight. The formula adds the diastolic pressure to one-third of the pulse pressure, which is a practical approximation for a normal resting heart rate.
When to use it
Use this when you want a quick estimate of overall arterial pressure from a blood pressure reading, especially in physiology, nursing, or emergency care. It is commonly used to judge whether organs are likely receiving enough blood flow.
Worked example, step by step
Suppose a patient has a blood pressure of 138/86 mmHg. SBP = 138 mmHg, DBP = 86 mmHg Pulse pressure = SBP - DBP = 138 - 86 = 52 mmHg One-third of pulse pressure = 1/3 × 52 = 17.3 mmHg MAP = DBP + 1/3(SBP - DBP) = 86 + 17.3 = 103.3 mmHg Final answer: MAP ≈ 103 mmHg
Common mistakes to avoid
- Using the average of systolic and diastolic pressure instead of giving diastolic extra weight
- Forgetting to subtract DBP from SBP before taking one-third
- Treating MAP as exact for every heart rate, even though the 1/3 rule is only an approximation
Did You Know?
Mean arterial pressure, not the headline systolic number, is what truly determines organ blood supply.
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