What is the significance of the mean arterial pressure?

Why is mean arterial pressure not equal to systolic pressure minus diastolic pressure dived by 2?

• Answer:

  This is because the lengths of systole and diastole are different. Usually in a resting individual having his or her blood pressure taken, the amount of time spent in diastole is longer than the amount of time spent in systole. The length of time the heart is in diastole is approximately twice as long as it is in systole. Systole only occurs when the heart is actively contracting, the rest of the time is diastole. So mean arterial pressure is usually closer to one's diastolic pressure than systolic. As one's heart-rate increases and the length of diastole shortens, the mean arterial pressure is much closer to just the average of systolic blood pressure and diastolic pressure.