Diastolic Pressure Definition

We encounter them whenever we visit a doctor--two numbers, one on top of the other. A nurse may announce "120 over 80." But what do these numbers mean? Both numbers show the current state of our blood pressure. The number on top refers to our systolic blood pressure, while the one beneath refers to our diastolic blood pressure. These two help us determine our cardiovascular health.

Function

• According to the American Heart Association, our diastolic blood pressure works along with our systolic blood pressure to circulate blood through our body. Think of our cardiovascular system--or veins, arteries, capillaries and heart--as a closed system that requires pressure to function properly. The two types of blood pressure are forces that keep our blood pumping to our body and brain.

Identification

• Whereas systolic blood pressure occurs while the heart is pumping, diastolic pressure is present when the heart rests between beats. Think of diastolic pressure as though you were pumping a bicycle tire with a hand pump. When you press down on it, pushing air into the tire, you are creating the equivalent of systolic pressure. When pulling up for another pump, what's going on inside the tire is similar to diastolic pressure. Our arteries have elastic properties similar to the inner rubber tube of the tire, and the way blood pressure works is nearly the same in concept.

Features

• The American Heart Association defines diastolic pressure as resistance by the arteries against blood flow. It's similar to breathing--when we breathe in, our lungs expand with pressure outward, and when we exhale, the lungs contract causing pressure inward. As the systolic portion of blood pressure occurs, arteries are put under force, or "stretched," for the duration of the heart's beat. The following resistance of the arterial walls receding back inward on the bloodstream is diastolic blood pressure.

Expert Insight

• Normal diastolic pressure, says the AHA, is considered to be below 80 mm Hg (millimiters of mercury, a unit of pressure used to determine that of our blood). If your diastolic pressure is around 80, and your systolic reads out at 120 mm Hg, you have what medical experts call normal blood pressure. This is a sign of good heart health, and generally the lower the systolic and diastolic pressures are, the healthier your cardiovascular system is. Low blood pressure, or hypotension, is less of a concern than high blood pressure, and there is no generalized systolic and diastolic set of numbers that defines low blood pressure--it's usually only an issue if one is experiencing symptoms that a doctor has recognized. However, high blood pressure is a bigger problem.

Expert Insight

• A diastolic reading of 90 mm Hg or higher, says the AHA, is considered to be high blood pressure, or hypertension. The AHA also defines systolic blood pressure over 120 mm HG to be hypertension. The two will raise together because they are paired in their function. Hypertension can be mild or severe, and it can be managed through medication, diet, exercise and other activities as advised by a doctor. If you test yourself at one of those pharmacy blood pressure chairs and notice a high diastolic and systolic reading of more than 120/80 mm Hg, contact your doctor to ensure your continued health.