Mean arterial pressure

The mean arterial pressure (MAP) is a term used in medicine to describe an average blood pressure in an individual.^[1] It is defined as the average arterial pressure during a single cardiac cycle.

Calculation

Total Peripheral Resistance (TPR) is represented mathematically by the formula:

R = ΔP/Q^[2]

R is TPR. ΔP is the change in pressure across the systemic circulation from its beginning to its end. Q is the flow through the vasculature (equal to cardiac output)

In other words:

Total Peripheral Resistance = (Mean Arterial Pressure - Mean Venous Pressure) / Cardiac Output

Therefore, Mean arterial pressure can be determined from:^[3]

$MAP = (CO \cdot SVR) + CVP$

where:

• $CO$ is cardiac output
• $SVR$ is systemic vascular resistance
• $CVP$ is central venous pressure and usually small enough to be neglected in this formula.

Estimation

At normal resting heart rates $MAP$ can be approximated using the more easily measured systolic and diastolic pressures, $SP$ and $DP$:^[4][5][6]

$MAP \simeq DP + \frac{1}{3}(SP - DP)$

or equivalently

$MAP \simeq \frac{2}{3}(DP) + \frac{1}{3}(SP)$

or equivalently

$MAP \simeq \frac{(2 \times DP) + SP}{3}$

or equivalently

$MAP \simeq DP + \frac{1}{3}PP$

where $PP$ is the pulse pressure, $SP-DP$

At high heart rates $MAP$ is more closely approximated by the arithmetic mean of systolic and diastolic pressures because of the change in shape of the arterial pressure pulse.

For a generalized formula of $MAP$:

$MAP \simeq DP + 0.01 \times \exp(4.14 - 40.74 / HR) (SP - DP)$

Where HR is the heart rate.^[7]

Clinical significance

$MAP$ is considered to be the perfusion pressure seen by organs in the body.

It is believed that a $MAP$ that is greater than 60 mmHg is enough to sustain the organs of the average person. $MAP$ is normally between 65 and 110 mmHg.^[8] MAP may be used similarly to Systolic blood pressure in for target blood pressure. Both have been shown advantageous targets for sepsis, trauma, stroke, intracranial bleed, and hypertensive emergencies.^[9]

If the $MAP$ falls below this number for an appreciable time, vital organs will not get enough Oxygen perfusion, and will become hypoxic, a condition called ischemia.

See also

• Blood pressure
• Hypertension
• Pulse pressure

References

1. Zheng L, Sun Z, Li J, et al. (July 2008). "Pulse pressure and mean arterial pressure in relation to ischemic stroke among patients with uncontrolled hypertension in rural areas of China". Stroke 39 (7): 1932–7. doi:10.1161/STROKEAHA.107.510677. PMID 18451345.
2. Total peripheral resistance, Wikipedia
3. Cardiovascular Physiology Concepts: Mean Arterial Pressure, Richard E. Klabunde, Ph.D
4. Physiology: 3/3ch7/s3ch7_4 - Essentials of Human Physiology
5. Cardiovascular Physiology (page 3)
6. http://www.clinicalreview.com Physiology Review
7. Calculation of mean arterial pressure during exercise as a function of heart rate.
8. impactEDnurse (May 31, 2007). "mean arterial pressure". impactednurse.com. Archived from the original on December 12, 2013. Retrieved 2013-12-12.
9. Magder SA (2014). "The highs and lows of blood pressure: toward meaningful clinical targets in patients with shock.". Crit Care Med. 42 (5): 1241–51. doi:10.1097/ccm.0000000000000324. PMID 24736333.

External links

• Mean Arterial Pressure Calculator
• More Information on usage of the Mean Arterial Pressure