What is the common formula for estimating mean arterial pressure (MAP)?

• A. MAP equals SBP
• B. MAP equals DBP
• C. MAP ≈ DBP + 1/3(SBP − DBP)
• D. MAP equals SBP − DBP

Answer: (C)

Mean arterial pressure reflects the average pressure in the arteries during the cardiac cycle, and the heart spends more time in diastole than in systole. Because of that weighting, a common and practical estimate adds a portion of the pulse pressure (the difference between systolic and diastolic pressures) to the diastolic pressure. The formula is MAP ≈ DBP + 1/3(SBP − DBP). This captures that most of the cycle pressure is near diastolic levels, with a smaller lift during the brief systolic rise.

For example, if systolic pressure is 120 and diastolic is 80, pulse pressure is 40, and MAP ≈ 80 + 1/3×40 ≈ 93 mmHg. If you only used systolic or diastolic pressure, you’d misrepresent the actual pressure driving tissues throughout the cycle. An equivalent way to express this weighting is MAP ≈ (SBP + 2×DBP)/3, which shows the same emphasis on diastole.