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How Does Blood Pressure Work?

Understanding your systolic and diastolic numbers is one of the best ways to maintain healthy blood pressure.
ByJordan Rosenfeld|
Digital blood pressure monitors allow people to check their systolic and diastolic numbers at home.
Digital blood pressure monitors allow people to check their systolic and diastolic numbers at home. | Kinga Krzeminska/Moment/Getty Images

You can’t actually feel your blood pressure, but it’s one of the body’s most important indicators of cardiovascular health. Here’s the lowdown on how blood pressure works—and what it means for your overall wellness.

Your heart is the master pump for all the blood in your body. With every heartbeat, your heart pushes your blood to all the vital parts of your body, such as muscles and bones, through a network of arteries, capillaries, and veins. As blood flows through the tube-like arteries, it presses up against the walls of the blood vessels with varying degrees of strength. The strength or weakness of this pressure is called your blood pressure (BP).

  1. Systolic vs. Diastolic Numbers
  2. What Is Considered High Blood Pressure?

Systolic vs. Diastolic Numbers

Each time your heart squeezes, moving your blood to its various destinations, your blood pressure goes up—this number is referred to by a blood pressure reading as “systolic.” Then, as the heart relaxes after each contraction, your blood pressure goes down; that is called the “diastolic” reading. Together, these two numbers are presented as a score, systolic over diastolic: Your doctor might tell you that your BP is “120 over 80.”

According to the American Heart Association (AHA), normal blood pressure should reflect systolic pressure under 120 and diastolic pressure under 80. These measurements are usually determined with an automatic blood pressure cuff. When blood passes under the cuff, the arm increases in circumference ever so slightly, and by measuring the amplitude of the oscillations at a continuous interval of pressures, blood pressure can be calculated.

What Is Considered High Blood Pressure?

If you have high blood pressure, a.k.a. hypertension, your heart is working too hard to pump the blood through your body. The AHA categorizes blood pressure into the following stages:

Category

Systolic (Top Number)

Diastolic (Bottom Number)

Healthy/Normal

Less than 120

Less than 80

Elevated

120-129

Less than 80

High (Stage 1)

130-139

80-89

High (Stage 2)

140 or higher

90 or higher

Hypertensive Crisis

180 or higher

120 or higher

According to the AHA, elevated blood pressure is 120–129/less than 80; hypertension stage 1 is 130–139 (systolic) or 80–89 (diastolic); and hypertension stage 2 is 140 or higher (systolic) or 90 or higher (diastolic). If your blood pressure hits 180/120, you're in hypertensive crisis, and you should seek help immediately.

If your systolic and diastolic numbers fall into the the elevated or hypertensive categories, your doctor will recommend changes to your diet and physical activity routine and possible medication. High blood pressure can be a side effect of other diseases, such as diabetes, and if left untreated, high BP can lead to heart attack, organ damage, stroke, and other serious issues.

In addition, your blood pressure can temporarily rise due to stress, pregnancy, and even some common medications, including over-the-counter pain relievers and antidepressants. One high reading will not necessarily mean you have hypertension—but it’s good to be vigilant.

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