How is mean arterial pressure (MAP) calculated from SBP and DBP?

• A. MAP ≈ DBP + (SBP − DBP)/3.
• B. MAP ≈ SBP − DBP.
• C. MAP ≈ (SBP + DBP)/2.
• D. MAP ≈ SBP/DBP.

Answer: (C)

Mean arterial pressure is the average pressure in the arteries over a full heartbeat, weighted toward the portion of the cycle spent in diastole because diastole lasts longer. The standard approximation uses diastolic pressure plus one third of the pulse pressure (the difference between systolic and diastolic). In formula form, MAP ≈ DBP + 1/3 × (SBP − DBP), which is also written as MAP ≈ (SBP + 2 × DBP)/3. For example, with SBP 120 and DBP 80, pulse pressure is 40, so MAP ≈ 80 + 1/3 × 40 = 93.3 mmHg. The simple average of SBP and DBP (SBP + DBP)/2 would give 100 mmHg here, overestimating MAP because it treats systole and diastole as equal time periods. The pulse pressure alone (SBP − DBP) or the ratio SBP/DBP does not represent MAP.