MAP calculation: which equation approximates MAP?

• A. DBP + 1/3(SBP − DBP)
• B. SBP − DBP
• C. (SBP + DBP)/2
• D. SBP

Answer: (A)

Mean arterial pressure reflects the average pressure in the arteries over an entire heartbeat, and the weighting of pressures across the cycle is guided by how long the heart spends in each phase. Since diastole lasts longer than systole, the MAP sits closer to diastolic pressure, with a portion added from the systolic rise. The practical estimate DBP plus one third of the pulse pressure captures this timing, because pulse pressure equals SBP minus DBP and one third of that rise is applied to the diastolic baseline to reflect the longer diastolic period. This yields MAP ≈ DBP + 1/3(SBP − DBP).

Why this is the best choice: it combines both pressures and weights them according to the time spent at each pressure during the cycle, providing a closer approximation to the true average than a simple arithmetic mean or using only one of the pressures. The other options either isolate the peak pressure, represent only the pressure difference without time weighting, or assume equal time at SBP and DBP—none of which matches the physiological reality of the cardiac cycle.