Expansion
Diastolic pressure plus one third of the pulse pressure
Expansion
MAP = diastolic pressure + (pulse pressure / 3)
For a blood pressure of 120/80:
- Pulse pressure = 120 - 80 = 40
- MAP = 80 + 13 = about 93 mmHg
The weighting towards diastole reflects the fact that diastole lasts about twice as long as systole at resting heart rates. At fast rates the two durations converge and the mean moves closer to the arithmetic average, so the formula becomes less accurate.
MAP is the pressure that matters for organ perfusion, because it is the driving pressure averaged over the whole cycle. A MAP of about 65 mmHg is the usual resuscitation threshold, since below this most organs fall off the flat part of their autoregulatory curve.
It also links the two central equations: MAP = cardiac output x systemic vascular resistance.