What do blood pressure numbers mean?

DEAR DOCTOR K:

At my last checkup, my blood pressure was 130/85. I’d like to have a better understanding of what those numbers mean.

DEAR READER:

Your heart is a pump, pushing blood throughout your body 60 to 80 times a minute. After each pump it relaxes, fills up with more blood and then pumps again. The heart pumps blood out through blood vessels called arteries, and collects blood returning from the body in blood vessels called veins.

One way to think about the pressure in the arteries as the heart pumps is to visualize a garden hose. You turn on the faucet a little and feel the water coming out the end of the hose, striking your finger. Now you open up the faucet a little more, and the water hits your finger more forcefully. That’s what happens in your arteries every time the heart pumps. It’s like opening up the faucet for a few seconds, then closing the faucet a little and then opening it up again.

The top number in your blood pressure is the systolic pressure. It reflects the amount of pressure in your arteries when your heart pumps.

The bottom number is the diastolic pressure. It represents the pressure in between heartbeats, when the heart is relaxing.

Blood pressure is measured in millimeters of mercury (mm Hg). Hypertension, or high blood pressure, is defined as having a systolic reading of at least 140 mm Hg or a diastolic reading of at least 90 mm Hg, or both.

Why do doctors measure your blood pressure every time you come for a visit? Because nothing could be more important. A lot of people have high blood pressure. In my opinion, undiagnosed and untreated high blood pressure is one of the biggest threats to our health in the United States. High blood pressure greatly increases a person’s risk for heart disease, stroke, kidney failure and blindness.

Why does high blood pressure weaken the heart? Because it makes the heart work harder, beat after beat. It also injures the arteries and increases the tendency for plaques of atherosclerosis to form in them. Sometimes it causes the arteries to rupture. President Franklin Roosevelt, for example, died when his high blood pressure caused a hemorrhage in his brain.

What makes high blood pressure so dangerous is that it can be really high without causing any symptoms — until it suddenly causes big symptoms, such as the pain of a heart attack or the paralysis of a stroke. That’s why measuring it regularly is so important.

Today we have simple machines that let us measure our own high blood pressure at home. I have high blood pressure, and I regularly make sure my medicines are keeping it in check.

We also have much more powerful blood pressure medicines today than ever before. President Roosevelt’s doctors had nothing more to offer him during his time, even though he was the most powerful person in the world.

We have more information on blood pressure in our Special Health Report, “Hypertension: Controlling the ‘Silent Killer.'” You can find out more about it here.