# Mean arterial pressure

In medicine, the mean arterial pressure (MAP) is an average blood pressure in an individual during a single cardiac cycle.

## Calculation

Systemic Vascular Resistance (SVR) is represented mathematically by the formula:mean arterial pressure

R = ΔP/Q

R is SVR. 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:

Systemic Vascular Resistance = (Mean Arterial Pressure - Mean Venous Pressure) / Cardiac Output

Therefore, Mean arterial pressure can be determined from:

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

While MAP can only be measured directly by invasive monitoring it can be approximately estimated using a formula in which the lower (diastolic) blood pressure is doubled and added to the higher (systolic) blood pressure and that composite sum then is divided by 3 to estimate MAP. In patients with sepsis, the vasopressor dosage may be titrated on the basis of estimated MAP.

This is only valid at normal resting heart rates during which $MAP$ can be approximated using the measured systolic ($SP$ ) and diastolic ($DP$ ) blood pressures:

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

## 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 70 mmHg is enough to sustain the organs of the average person. $MAP$ is normally between 65 and 110 mmHg.. Even 1 minute at a mean arterial pressure of 50 mmHg, or accumulative effects over short periods, increases the risk of mortality by 5% and can result in organ failure or complications . MAP may be used similarly to systolic blood pressure in monitoring and treating[clarification needed] for target blood pressure. Both have been shown advantageous targets for sepsis, major trauma, stroke, intracranial bleed, and hypertensive emergencies.

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.