MAP Calculator (Mean Arterial Pressure)

Table of contents:
Mean Arterial Pressure (MAP) is a measure of blood pressure. It measures the average blood pressure in an individual during a single cardiac cycle, the beginning of one heartbeat to the next.

This cycle is made of 2 distinct periods of relaxation and contraction of the heart, although the system works through the four quadrants of the heart. The diastole phase corresponds to two-thirds of the cardiac cycle, while the systole phase occupied only one-third. The relaxation of the muscle is the diastole period, and the period of muscle contraction is the systole. It is the systolic period where blood is pumped. After the systolic period within this cycle, the muscle immediately relaxes, drawing blood in from lungs, and other systems, before the next pump, or beat of the heart.

Blood pressure is effectively a measurement of the velocity at which the blood passes through the valves of the heart.

Blood enters the heart through the venous valve, and blood is pumped out through the arterial valve to the arteries, for distribution around the body. As the arteries carry the blood away from the heart, blood pressure measures how hard the blood pushes the wall of arteries. 
The measurement for blood pressure is in millimeters of mercury (mmHg).

There are two numbers in measuring blood pressure. The systolic pressure, the first measure, reflects how hard to blood pushes against the sides of the arteries during the systolic period, that is when the heart muscle contracts, and pumps blood. The second is a measure of pressure in the diastolic period when the heart muscle relaxes and draws blood back into the heart.

Blood pressure is measured using a Baumanometer which uses pressure sensitive cuff, to measure arterial pressure in the arm. The pressures are measured as XX/YY, where XX is systolic and YY is diastolic pressure as defined above. 
For example, the blood pressure reading 120/80 means that a person has a systolic blood pressure (SBP) or 120 mmHg, and a diastolic blood pressure (DBP) of 80 mmHg.

Defining Mean Arterial Pressure

It is the average blood pressure during a single cycle and is calculated as the average of the systolic and diastolic pressures as measured.  More specifically, the Mean Arterial Pressure is defined as an approximation of the time-weighted average for blood pressure in the arteries during the cardiac cycle. 

MAP is not an arithmetic average, because the cardiac cycle is actually a four-part process, and the measurement is more weighted on the diastolic phase. 
Mean Arterial Pressure is shown by the formula:

This takes into account the systolic and diastolic blood pressure as a weighted average, according to the relevant weighting within the cardiac cycle.
A normal MAP is between 70 – 100 mmHg.

Measuring Blood Pressure

In medical contexts, the Baumanometer, or sphygmomanometer would be used to measure blood pressure accurately. There is no way to measure blood pressure accurately without the use of specific equipment. 

This equipment has changed and developed over time.
Manual machines include the mercury sphygmomanometer, which requires a doctor to read the blood pressure as shown by a column of mercury.

After tightening the cuff, a doctor would listen at the brachial artery for the characteristic whooshing sound as the cuff is released, to measure the systolic pressure, shown on the sphygmomanometer.

The diastolic pressure is the figure shown at the point where the doctor can no longer hear the pounding, before the next beat of the heart. Other devices include the Aneroid sphygmomanometer, which is more mechanical and uses a dial to represent pressure. These require calibration and are generally less accurate.

More modern, electronic machines utilize the same basic mechanism, but the results are reported on a screen.

Digital meters use oscillometric measurements, and calculations are made electronically. These machines automatically output the MAP and pulse pressure.

Pulse Pressure

Pulse pressure is calculated as the difference between systolic blood pressure and diastolic blood pressure.

This value correlates to the volume of blood ejected during a contraction of the left heart ventricle to the aorta and other arteries. This is the stroke volume. The bigger the stroke volume, the higher the value of the pulse pressure.

Stroke volume increases for several reasons, some as simple as the experience of exercise. Compliance of the aorta is something that harms pulse pressure. Compliance is the ability to stretch in response to the pressure inside a vessel-like organ of our body.

The aorta has high compliance, as it is relatively elastic. This elasticity allows our pulse pressure to remain at a healthy level of around 40 mmHg.

There are a number of conditions, such as plaque build-up within the blood vessels, or a condition known as aortic dissection (a state in which blood gets between the walls of the aorta) leading to stiffness, and a lack of elasticity of the vessels.

Normal Blood Pressure

As stated above, a normal MAP is between 70 and 100 mmHg, and the MAP should not fall below 60 mmHg.

The normal blood pressure for a healthy adult falls between 90 mmHg and 119 mmHg for the systolic pressure and 60 mmHg to 79mmHg for diastolic blood pressure.

Systolic blood pressure that hovers between 120 mmHg and 140 mmHg is an indication of prehypertension.

It is a good idea to seek medical advice for any concerning conditions relating to the heart, pulse, or blood pressure.

MAP Calculator (Mean Arterial Pressure)

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