Mean arterial pressure
Also known as: MAP
Mean arterial pressure (MAP) is the average pressure in a person's arteries over one cardiac cycle. Because it reflects the driving force for blood flow to the organs, it is the pressure value used to judge whether tissues are being adequately perfused.
Mean arterial pressure is not the simple average of systolic and diastolic pressure, because the heart spends roughly twice as long in diastole as in systole at a normal heart rate. The standard estimate weights it accordingly: MAP = diastolic pressure + ⅓ (systolic − diastolic), where the term in parentheses is the pulse pressure. For a blood pressure of 120/80, MAP is 80 + ⅓(40), or about 93 mmHg. A MAP of at least 60 to 65 mmHg is generally regarded as the minimum needed to perfuse the vital organs.
MAP can also be expressed through its physiologic determinants: MAP = cardiac output × total peripheral resistance. Cardiac output is itself heart rate times stroke volume, so anything that changes rate, contractility, preload, afterload, or vessel tone moves MAP. This equation explains why vasodilation lowers pressure even when the heart is pumping normally, and why vasopressors raise it by increasing resistance.
Regulation happens on two timescales. Rapid control comes from the baroreceptor reflex — stretch receptors in the carotid sinus and aortic arch adjust sympathetic and parasympathetic output within seconds of a pressure change. Longer-term control runs through the kidneys and the renin-angiotensin-aldosterone system, which adjust sodium and water balance and therefore blood volume. Because MAP represents the perfusion pressure into the brain, cerebral perfusion pressure is calculated as MAP minus intracranial pressure.
MAP crosses several exams. USMLE Step 1 physiology tests the formula, the determinants, and baroreceptor regulation; the NCLEX covers it in hemodynamic monitoring and critical care, where maintaining a target MAP guides fluid and vasopressor management; and the CSCS covers it among the acute cardiovascular responses to aerobic exercise.
Key takeaways
- MAP is the time-weighted average arterial pressure across the cardiac cycle, not a simple mean of systolic and diastolic.
- Estimate it as diastolic pressure plus one third of the pulse pressure.
- MAP equals cardiac output multiplied by total peripheral resistance.
- A MAP of roughly 60 to 65 mmHg is the usual threshold for adequate organ perfusion.
- Baroreceptors adjust MAP within seconds; the renin-angiotensin-aldosterone system controls it over the long term.