Mean arterial pressure, which is commonly known as MAP, is the function of systolic and diastolic blood pressure. It is also known as the average arterial pressure during a single cardiac cycle. In medicine this term is usually used to describe the average blood pressure of an individual. It is very easy to calculate the mean arterial pressure of an individual by knowing his systolic and diastolic pressure.
- Systole pressure is the pressure exerted on the heart during the contraction of the ventricles and diastolic pressure is the pressure exerted on the heart during the relaxation of the ventricles.
- It is observed that the time taken by systole phase is about half of the time taken by the diastole phase. Therefore, we cannot simply divide the sum of systolic and diastolic pressure by two i.e. taking average of both the pressures to obtain mean arterial pressure.
- To calculate mean arterial pressure you first have to calculate the systolic and diastolic pressure. This can be measured using a sphygmomanometer.
There are many formulas for calculating the MAP or the mean arterial pressure.
- This formula does not use systolic and diastolic pressures, but it is more accurate than the other formulae.
MAP = ( CO × SVR ) + CVP
In the above formula,
- CO is the cardiac output. Cardiac output is the quantity of blood pumped by the heart either by the left ventricle or right ventricle in a time interval of one minute.
- SVR is the systemic vascular resistance. This the resistance to flow that must be overcome to push the blood throughout the circulatory system.
- CVP is the central venous pressure. It determines the quantity of the blood returning to the heart and ability of the heart to pump the blood into the arterial system.
- Knowing all the values, you can calculate the MAP by simply substituting them in the above formula.
- There are many other formulae to calculate the mean arterial blood pressure. These formulae are used to calculate the mean arterial pressure at the normal resting heart rates.
MAP = DP + ⅓ (SP – DP)
OR
MAP = ⅔ (DP) + ⅓ (SP)
OR
MAP = (2 × DP) + SP
3
OR
MAP = DP + ⅓ PP
Here, PP is the pulse pressure i.e. SP-DP
Example
- Conside a patient having blood pressure 120/60 . Here 120 is the systolic blood pressure and 60 is the diastolic blood pressure.
- His pulse pressure would be
Pulse pressure = PP =SP – DP
PP = 120 – 60
PP= 60
Thereforre the pulse pressure of the patient is 60.
- Now, to calculate the MAP consider the formula
MAP = DP + ⅓ PP
MAP = 60 + 60/3
MAP = 60 + 20
MAP=80 mmHg
- It is generally considered that the MAP which is greater than 60 mmHg will help in sustaining the organs of a person.
- If this decreases, then the organ will not get sufficient amount of blood resulting in a condition called ischemia i.e local anemia in some part of the body.
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