OEM MAX What is Blood Pressure? NIBP®

What is Blood Pressure?
Blood pressure is the pressure of the circulating blood against the walls of the arteries. The heart acts as a
pump, which moves and maintains the blood flow throughout the body. Blood pressure is dependent upon
the energy of the heart action, elasticity of the arterial walls and blood volume and viscosity. Anything that
affects heart rate will affect blood pressure.
Blood pressure is usually measured in millimeters of mercury (mmHg). You will see numbers written like this:
B/P 120/80, MAP 93.
Systolic Pressure
The upper number, 120 in this example, is the systolic pressure. This is the maximum pressure present in
the artery and occurs during systole when the ventricles contract and the pulse of blood is ejected into the
aorta. The systolic pressure becomes higher as the blood travels away from the heart. This reading is critical
because your system requires a minimum amount of pressure to get blood to your brain and other body
parts, but too much pressure can cause damage to the vessels.
Diastolic Pressure
The lower number, 80 in this example, is the diastolic pressure. This is the amount of pressure present in
the system between beats. The aortic valve is closed and the left ventricle is in diastole, dilated and filling
with blood. Too high a pressure can cause damage to the artery walls; too low a pressure will prevent the
myocardium (heart muscle) from getting the blood it needs. Diastolic pressure decreases slightly as the
blood travels away from the heart. The diastolic pressure will increase with age as the arteries become less
elastic and do not relax as much.
Mean Arterial Pressure
MAP is an indicator of the cardiovascular status and tissue perfusion. It is a good indicator for trending data
because it does not fluctuate as widely under normal circumstances. In an invasive measurement, MAP is a
calculated number based on the Systolic and the Diastolic Pressures. In an oscillometric measurement, MAP
is the cuff pressure at which the maximum pressure pulse amplitude is obtained.
1. Geddes LA, ME, PhD, Handbook of Blood Pressure Measurement, Humana Press, Clifton NJ, 1991.
2. Forster FK and Turney D, Journal of Biomechanical Engineering, Vol. 108, pp 359-364, Nov 1986.
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MAXNIBP What is BP Rev 0.2 5102010