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What Is the Mean Arterial Pressure?

Systolic blood pressure is the top number when reading blood pressure levels, and generally doctors recommend it be below 140.
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  • Written By: Erik J.J. Goserud
  • Edited By: A. Joseph
  • Last Modified Date: 18 December 2014
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Mean arterial pressure (MAP) is a measure of the average blood pressure in a person at a given moment. This value is primarily calculated using two equations or a simplified version of either. The most frequently used equation is MAP = (CO x SVR) + CVP, where "CO" represents cardiac output, "SVR" represents systemic vascular resistance and "CVP" is equal to central venous pressure. Mean arterial pressure, which is measured in millimeters of mercury (mmHG), is significant in that it reflects the perfusion pressure to the organs of the body. This value in a healthy individual should be 70-110 mmHg.

Conventionally, blood pressure is measured using two values. Systolic blood pressure, the first value, reflects the average pressure exerted on the arterial walls during the contraction of the heart; a cardiac phase known as systole. The second number is diastolic blood pressure, which represents the average arterial pressure during the relaxation period of the heart, or diastole. Although this conventional method is accurate in describing blood pressure during the two most distinct cardiac phases, mean arterial pressure intends to provide a more generalized measure of blood pressure over the course of the cardiac cycle.

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To understand more about mean arterial pressure, one must make sense of the equation from which this value is derived. Again, the equation used is MAP = (CO x SVR) + CVP. The central venous pressure (CVP) is commonly left out of the equation because of its nominal value, typically close to zero. Therefore, MAP = CO x SVR.

Cardiac output (CO) is the volume of blood that cycles through the heart during a one-minute interval. CO is equal to the heart rate (HR) times the stroke volume (SV), so an increase in heart rate or stroke volume, with other variables constant, will cause an increase in mean arterial pressure, and vice versa. Systemic vascular resistance measures the resistance that the heart must overcome because of the vascular system in order to contract and eject blood into the arteries. Like cardiac output, this is directly related to MAP.

The second equation, MAP = diastolic pressure + 1/3 (systolic pressure - diastolic pressure), is referenced as a more convenient but typically less accurate form of calculating MAP. The difference in systolic and diastolic blood pressure is know as pulse pressure. This simplifies the equation to MAP = DP + 1/3 PP.

If the human body is functioning properly, mean arterial pressure will be measured at 70-110 mmHG. This means that the organs of the body are receiving enough blood to provide adequate perfusion of oxygen and other nutrients. When MAP falls below 60 mmHg, a person's organs might be at risk because of a deficiency in the nutrients that are necessary to sustain life.

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