You've seen your blood pressure readings, but do you know what the numbers mean? Our primer explains.

© Rmarmion | Dreamstime.com

You’ve probably had a blood pressure reading dozens or maybe hundreds of times in your life. Unless you get a result that gives a nurse or doctor pause, you may not think much about those numbers. Or maybe you’ve wondered, “What is high blood pressure, and what does it reveal about what’s going on inside my body?”

High blood pressure, also known as hypertension, is an all-too-common condition that can lead to a wide range of health problems. It’s one of the leading enlarged heart causes, as well as a major risk factor for some serious cardiovascular health complications.One of the most misleading things about high blood pressure is that it’s usually present without obvious symptoms, says Washington University cardiologist Lynne Seacord, MD.

“Many people fail to treat their high blood pressure because they can’t ‘feel’ that it’s high,” Dr. Seacord says. “Even when they’re told it’s high, they think, ‘Well, I don’t need to treat it because I feel fine.’ Yet, it is high and causing a lot of changes, including their risk of heart attack, stroke, and heart failure later in life.”

To avoid taking hypertension too lightly, it helps to understand what blood pressure itself is—and also what high blood pressure is.

What Does Blood Pressure Represent?

Blood constantly travels through the arteries and veins throughout your body. The arteries deliver oxygenated blood to your tissues and organs, while veins bring oxygen-depleted blood back to the heart.

The force of blood flow against the interior walls of the arteries is your blood pressure. The pressure rises and falls with every heartbeat. When your heart contracts and squeezes blood out through the aorta and pulmonary artery, the pressure is at its highest. When the heart relaxes and fills up with blood in between each heartbeat, the pressure is at its lowest.

That’s why you get two numbers on your blood pressure reading. The top number is the systolic pressure—the force of blood as it’s being pushed through your arteries. The bottom number is the diastolic pressure, the force the bloodstream exerts when the heart is at rest.

Know Your Numbers

So what is normal blood pressure, and what is high blood pressure?

According to the American Heart Association, a healthy or normal blood pressure is a systolic pressure of less than 120 mm Hg (millimeters of mercury) and a diastolic pressure of less than 80 mm Hg.

High blood pressure starts when your systolic pressure gets to 140 mm Hg or your diastolic is at least 90 mm Hg. In between—a systolic pressure of 120 to 139 mm Hg or a diastolic pressure of 80 to 89 mm Hg—is a condition known as prehypertension. It should be considered a red flag that your blood pressure needs attention.

Those standards underwent a revision in late 2017, when new hypertension guidelines issued by the American College of Cardiology (ACC) and American Heart Association (AHA) redefined the threshold for high blood pressure.
The new thresholds, as described in our post New Hypertension Guidelines: Rethinking Blood Pressure Standards, look like this:

• Normal: Less than 120 mmHg systolic and less than 80 mmHg diastolic
• Elevated: 120 to 129 mmHg systolic and less than 80 mmHg diastolic
• Hypertension Stage 1: 130 to 139 mmHg systolic or 80 to 89 mmHg diastolic
• Hypertension Stage 2: systolic pressure of 140 mmHg or higher or diastolic pressure of 90 mmHg or higher
• Hypertensive urgency: Systolic blood pressure greater than 180 mmHg and/or diastolic pressure greater than 120 mmHg
• Hypertensive emergency: Systolic blood pressure greater than 180 mmHg and/or diastolic pressure greater than 120 mmHg, plus target organ damage

It’s important to note that not all medical care providers have adopted the new standards. One thing is for sure, though: If your blood pressure reaches 180/110 mm Hg, that’s considered a hypertensive crisis and it requires emergency care.

Avoid High Blood Pressure Complications

Now that you understand high blood pressure from a numbers standpoint, consider what’s happening to your heart and blood vessels if you have hypertension.

When blood pressure is elevated for a long time, all that additional force against the arterial walls takes a toll. Arteries narrow and become less elastic—a condition called atherosclerosis, or hardening of the arteries. This situation is made worse as plaque made up of cholesterol, fats, and other substances builds up in the arteries.

Atherosclerosis in the arteries supplying your heart muscle with blood is called coronary artery disease (CAD), and can lead to a heart attack. If the narrowing occurs in the arteries supplying your brain with blood, the possible consequence is a stroke. In the legs, it’s called peripheral artery disease (PAD).

Hard-Working Heart: Health Issues

Hypertension also makes the heart work harder. Overwork leads to cardiomegaly, also known as an enlarged heart. Causes of cardiomegaly also include CAD, but the main culprit is high blood pressure. An enlarged heart doesn’t pump blood as effectively as it should throughout the body. This can lead to heart failure.

Research led by João Lima, MD, director of cardiovascular imaging at the Johns Hopkins School of Medicine’s Heart and Vascular Institute, found that pre-hypertension and even blood pressure at the high end of the normal range, can cause problems that can weaken the heart muscle and its pumping ability.

“Our results suggest the heart muscle may be more exquisitely sensitive to the effects of even subtle elevations in blood pressure than we thought,” Dr. Lima says.

Heart valve disease and kidney disease are other enlarged heart causes, but both those problems are made worse by high blood pressure.

High blood pressure is also associated with such issues as memory loss, erectile dysfunction, kidney damage, fluid in the lungs, and even vision problems.

What Is High Blood Pressure? Treatment Options

A regular exercise routine goes a long way in keeping your blood pressure under control.

As Dr. Seacord noted, just because you “feel fine” doesn’t mean the numbers of your blood pressure reading can be ignored. If you haven’t had your blood pressure checked lately, have it done soon. And if your doctor is telling you to manage your blood pressure, pay attention and follow his or her instructions carefully. (See our post “Blood Pressure Chart: Where Do Your Numbers Fit?.”

Many people need more than one medication to control blood pressure, so be prepared for a little trial and error to find out which combination is best for you. The good news is that if you can maintain a healthy weight, cut back on your sodium intake, and exercise most (if not all) days of the week, you may be able to keep the medications to a minimum. (See also “What Blood Pressure Is Too High?”)

High blood pressure can usually be brought back down to normal levels, but not on its own. Taking care of your blood pressure means taking care of more than just your heart and blood vessels. It means improving your overall health and quality of life.