The mean arterial pressure (MAP) is a term used in medicine to describe an average blood pressure in an individual. It is defined as the average arterial pressure during a single cardiac cycle.
Total Peripheral Resistance (TPR) is represented mathematically by the formula:mean arterial pressure
R = ΔP/Q
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:
M
A
P
=
(
C
O
⋅
S
V
R
)
+
C
V
P
where:
C
O
is cardiac output
S
V
R
is systemic vascular resistance
C
V
P
is central venous pressure and usually small enough to be neglected in this formula.
At normal resting heart rates
M
A
P
can be approximated using the more easily measured systolic and diastolic pressures,
S
P
and
D
P
:
M
A
P
≃
D
P
+
1
3
(
S
P
−
D
P
)
or equivalently
M
A
P
≃
2
3
(
D
P
)
+
1
3
(
S
P
)
or equivalently
M
A
P
≃
(
2
×
D
P
)
+
S
P
3
or equivalently
M
A
P
≃
D
P
+
1
3
P
P
where
P
P
is the pulse pressure,
S
P
−
D
P
At high heart rates
M
A
P
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
M
A
P
:
M
A
P
≃
D
P
+
0.01
×
exp
(
4.14
−
40.74
/
H
R
)
(
S
P
−
D
P
)
Where HR is the heart rate.
M
A
P
is considered to be the perfusion pressure seen by organs in the body.
It is believed that a
M
A
P
that is greater than 70 mmHg is enough to sustain the organs of the average person.
M
A
P
is normally between 65 and 110 mmHg. MAP may be used similarly to Systolic blood pressure in monitoring and treating for target blood pressure. Both have been shown advantageous targets for sepsis, trauma, stroke, intracranial bleed, and hypertensive emergencies.
If the
M
A
P
falls below this number for an appreciable time, vital organs will not get enough Oxygen perfusion, and will become hypoxic, a condition called ischemia.
