Mean arterial pressure

In medicine, the mean arterial pressure (MAP) is an average blood pressure in an individual during a single cardiac cycle.^[1]

CalculationEdit

The Systemic Vascular Resistance (SVR), denoted ${\displaystyle R}$ is represented mathematically by the formula

${\displaystyle R=\Delta P/Q}$,^[2] where ${\displaystyle \Delta P}$ is the change in pressure across the systemic circulation from its beginning to its end and

${\displaystyle Q}$ is the flow through the vasculature (equal to cardiac output)

another type of equation is:

${\displaystyle MAP=[Systolic+2(Diastolic)]/3}$

In other words:

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

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

${\displaystyle MAP=(CO\cdot SVR)+CVP}$

where:

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

EstimationEdit

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.^[4]

This is only valid at normal resting heart rates during which ${\displaystyle MAP}$ can be approximated using the measured systolic (${\displaystyle SP}$) and diastolic (${\displaystyle DP}$) blood pressures:^[5][6][7]

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

or equivalently

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

or equivalently

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

or equivalently

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

where ${\displaystyle PP}$ is the pulse pressure, ${\displaystyle SP-DP}$

At high heart rates ${\displaystyle MAP}$ 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 ${\displaystyle MAP}$:

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

Where HR is the heart rate.^[8]

Clinical significanceEdit

${\displaystyle MAP}$ is considered to be the perfusion pressure seen by organs in the body.

It is believed that a ${\displaystyle MAP}$ that is greater than 70 mmHg is enough to sustain the organs of the average person. ${\displaystyle MAP}$ is normally between 65 and 110 mmHg.^[9] 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.^[10][11] 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.^[12]

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

This article uses material from the Wikipedia article  Metasyntactic variable, which is released under the  Creative Commons Attribution-ShareAlike 3.0 Unported License.