Blood Pressure

Mean Arterial Pressure

The term, mean arterial pressure (MAP) can be simply described as average blood pressure recorded in an individual. A single cardiac cycle is taken into consideration for the calculation of mean arterial pressure. Average arterial pressure is another term used to refer to MAP. Calculating the MAP is important from the point of getting an idea about a person’s health.

Overview of Mean Arterial Pressure

The mean arterial pressure normal range is 70-110 mmHg. A minimum MAP of 60 mmHg is necessary for proper perfusion (blood flow) to body organs like the kidneys, brain and coronary arteries. The measure of the MAP, therefore, becomes an indicator of the health of these organs. Some of the critical conditions in which the MAP needs to be monitored are as follows:
Monitoring the MAP of those cardiac patients who are on vasodilator infusion is necessary.
Head-injury patients need to be monitored for MAP.
The condition of septic shock also calls for MAP monitoring. In this condition, severe infection results into decreased tissue perfusion, causing reduction in oxygen delivery to body organs.
The blood pressure of a patient with dissecting abdominal aneurysm needs to be controlled within a narrow range. Any change in the blood pressure leads to increase in internal bleeding; it is, therefore, necessary to monitor the MAP.
The MAP should also be monitored on a regular basis during check-ups to get an idea of the state of health of our body systems. If the MAP falls below the normal range, the patient is said to become alchemic. In such a condition, body tissues get damaged.

Calculating MAP

The following formula is used for calculating the mean arterial pressure. The explanation regarding this formula is also presented below.

MAP = (CO × SVR) + CVP

The above mentioned terms CO, SVR, and CVP stand for cardiac output, systemic vascular resistance, and central venous pressure. Let us understand what these terms mean.

Cardiac Output
It is the measure of the volume of blood that is pumped out of the heart in a duration of 1 minute. Cardiac output is measured in terms of cubic dm (i.e. 1 liter). The rate of cardiac output, by either the left or right ventricle at a given point of time, is measured. The average cardiac output in the resting phase for males is 5.6 L/min; this value for females is 4.9 L/min.

Systemic Vascular Resistance
The term vascular resistance is used in reference with the resistance faced by blood flow in the circulatory system. There are two types of vascular resistance – systemic vascular resistance and pulmonary vascular resistance. The former (system vascular resistance) is the measure of resistance resulting from peripheral blood circulation. Vasculature of lungs also offers resistance to the flow of blood. This kind of resistance is referred to as pulmonary vascular resistance.

Central Venous Pressure
The pressure of blood in the thoracic vena cava (near the right atrium) is known as central venous pressure. This factor (central venous pressure) influences the mean arterial pressure by a small amount.

Perfusion Pressure and MAP Significance

The concept of perfusion pressure needs to be understood in order to study the topic of mean arterial pressure in a proper manner. The process of delivery of arterial blood to the biological tissues through the network of capillaries is referred to as perfusion; the process of perfusion is responsible for nutrition of the tissues to which blood is transported. It is necessary to check the perfusion pressure and mean arterial pressure in emergency situations to determine the well-being of a patient/person. The loss of balance in maintenance of MAP results into poor blood circulation and extreme conditions like underperfusion and overperfusion.
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