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Lesson 5: Blood Pressure
5-1
LESSON 5
BLOOD PRESSURE
5-1. WHAT IS BLOOD PRESSURE?
Blood pressure refers to the force (pressure) with which the blood presses against the walls of the blood vessel. All blood vessels--large or small, artery or vein--have blood pressure. However, the term blood
pressure normally refers to the blood pressure of a major artery. Unlike the other vital signs discussed previously, it takes two numbers--the systolic pressure and the diastolic pressure--to describe this vital sign. Blood pressure is normally measured in millimeters of mercury (mm Hg). "Millimeters of mercury" is a standard unit for measuring pressure. It refers to how high a force (pressure) would cause a column of mercury (chemical symbol Hg) to rise in a tube. Figure 5-1 gives the general idea. The greater the pressure, the more mercury is forced up the tube.
Figure 5-1. "Millimeters of mercury" as a measure of pressure.
