Understanding Your Blood Pressure: What Do Your Diastolic and Systolic Values Actually Measure?

Doctors explain what these two numerical values mean in the context of your heart's health.

When it comes to your heart's health, you know that having normal blood pressure levels is important. When those levels get too high—a condition known as hypertension—our health falters; this can be quite damaging to the body, leading to damaged arteries, aneurysms, and heart disease over time, according to the American Heart Association. But knowing that your blood pressure is high is one thing—understanding what it actually measures is another. Ahead, two cardiologists break this important reading down and share how the two numerics involved—the diastolic and systolic values—play a part.

blood pressure readying on home test
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What is blood pressure?

In simplest terms, your blood pressure is the force of your blood against the walls of your blood vessels, explains Jennifer Wong, M.D., a cardiologist and medical director of Non-Invasive Cardiology at MemorialCare Heart and Vascular Institute at Orange Coast Medical Center in Fountain Valley, California. There are two different values involved: diastolic and systolic. "The systolic blood pressure is the peak pressure during a heartbeat while the heart is 'squeezing,' and the diastolic blood pressure is the lowest pressure between two beats while the heart is 'relaxed,'" she explains.

How is blood pressure measured?

Blood pressure is measured using an instrument called a sphygmomanometer, or blood pressure monitor. You've probably had this device wrapped around your arm several times—in fact, it is utilized at the beginning of virtually every doctor visit. "The sphygmomanometer cuff is typically wrapped around the upper arm to compress the brachial artery, inflated above the expected systolic pressure, and then the pressure is slowly released," explains Dr. Wong. "When the cuff's pressure equals the systolic pressure, blood begins to flow past the cuff, creating the Korotkoff sounds of blood flow turbulence that can be heard with a stethoscope." The systolic value is measured when the sounds first appear; when the sounds stop, the diastolic numeric is produced.

How can you prevent high blood pressure?

Hypertension does not always come with warning signs, which is why staying up to date with your yearly physical and maintaining a healthy lifestyle that's conducive to normal blood pressure levels is essential. Some key lifestyle modifications to make to prevent or reduce this condition, says Dr. Wong, include limiting salt intake to 2.3 grams of sodium per day, adding in a potassium supplement (unless contraindicated by kidney disease), losing weight, getting in moderate-intensity aerobic exercise for 40 minutes three to four times per week, and reducing the number of alcoholic beverages you drink per week. "The Dietary Approaches to Stop Hypertension, or DASH diet, which is high in vegetables, fruits, low-fat dairy products, whole grains, poultry, fish, and nuts and low in sweets, sugar-sweetened beverages, and red meats, has also been shown to reduce blood pressure," she says.

If you're unable to lower your blood pressure levels through lifestyle changes alone, there are several classes of medications that are effective. "It is typical that most adults will require more than one medication to treat their blood pressure," adds Howard S. Weintraub, M.D., the Clinical Director at the NYU Center for the Prevention of Cardiovascular Disease. And if you know you are prone to this condition? Dr. Weintraub recommends purchasing a blood pressure monitor for your home and measuring it several times a day. "Typically, we recommend once in the morning within about 30 minutes of awakening and the second later in the afternoon or early evening," he says. If you notice that your blood pressure levels aren't lowering, reach out to your primary care physician who can schedule further testing to rule out more serious conditions.

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