CLOSE
Getty Images
Getty Images

How Do Blood Pressure Tests Work, And What Do Those Numbers Mean?

Getty Images
Getty Images


Getting your blood pressure taken is a standard part of most visits to the doctor, but the details might seem mysterious—so read on.

What It Is

Blood pressure (BP) is the force exerted by circulating blood on the walls of the arteries as it's pumped from the heart. When we talk about it, we're usually referring specifically to the pressure as measured on the upper arm at the brachial artery.

Average blood pressure varies from person to person and is influenced by a number of factors, including age, gender, diet, stress, exercise and alcohol use. For an individual, blood pressure changes over the course of the day and even varies during a single heartbeat between a systolic (maximum) pressure, when the heart beats and pumps blood and the ventricles are contracting, and a diastolic (minimum) pressure, when the heart is at rest between beats and the ventricles are filled with blood.

That arm band the doctor uses to measure your BP is called a sphygmomanometer (from the Greek sphygmus ("pulse") + the scientific term manometer (pressure meter). The instrument consists of an inflatable cuff, a measuring unit and, for manual models, an inflation bulb and valve. The pressure of the cuff used to be measured on manual sphygmomanometers by observing a mercury column in the measuring unit and reading the BP as millimeters of mercury (mmHg). The risk of mercury leaks has led to the increased use of aneroid manual and even digital sphygmomanometers, but the mercury ones are still considered more accurate. Even if a mercury column isn't used, mmHg is still the unit of measurement for BP.

How It's Measured

During an exam, the cuff is placed around the upper arm at roughly the same height as the heart and inflated with the bulb until the artery is closed. Using the stethoscope, the doctor slowly releases the pressure in the cuff and listens. What they're listening for are the Korotkoff sounds, named for the Russian physician who described them in 1905. The first Korotkoff sound occurs when the pressure of the cuff is the same as the pressure produced by the heart and only some blood is able to pass through the upper arm in spurts, resulting in turbulence and an audible whooshing or pounding sound. The doctor records the pressure at which this sound is heard as the systolic blood pressure.

As the pressure in the cuff is further released, the sound changes in quality, becomes quieter (running through the second, third, and fourth Korotkoff sounds) and, when the cuff stops restricting blood flow enough to allow smooth flow with no turbulence, stops altogether. This silence is the fifth Korotkoff sound and the pressure at which it happens is recorded as the diastolic blood pressure.

The fraction that the doctor records as your blood pressure is the systolic pressure over the diastolic pressure, giving you the measure of both the pressure when your heart is exerting maximum pressure and when it's relaxed.

According to the American Heart Association, blood pressure readings break down like this:

Normal Blood Pressure: 120 systolic pressure and 80 diastolic pressure or less

Prehypertension:120-139 systolic pressure or 80-89 diastolic pressure

High Blood Pressure (Hypertension) Stage 1: 140-159 systolic pressure or 90-99 diastolic pressure

High Blood Pressure Stage 2: 160+ systolic pressure or 100+ diastolic pressure

Hypertensive Crisis (emergency care needed): 180+ systolic pressure or 110+ diastolic pressure

nextArticle.image_alt|e
Cameron Spencer, Getty Images
arrow
Big Questions
How Do Aerial Skiers Perfect Their Jumps?
Cameron Spencer, Getty Images
Cameron Spencer, Getty Images

If you've ever watched an aerial skier in action, you know that some of the maneuvers these athletes pull off are downright jaw-dropping—and you've probably seen more than a few of these skiers land on their rear ends at some point. The jumps are incredible, but they're also so technical that one seemingly insignificant motion can drop a skier on his or her tail.

Given that the skiers can fly up to 60 feet in the air and come down on a 37-degree grade, it seems like just going out and trying a new trick would be a good way to break your neck. That's why you'll need one unexpected piece of equipment if you want to start training for aerials: a towel.

Instead of perfecting their flips and twists over the snow, aerial skiers try out their new maneuvers on ramps that launch them over huge swimming pools. The U.S. national team has facilities in Park City, Utah and Lake Placid, New York that include specially designed pools to help competitors perfect their next big moves. The pools have highly aerated patches of bubbles in their centers that decrease the surface tension to make the water a bit softer for the skiers' landings.

If you're an aspiring aerial skier, expect to get fairly wet. New skiers have to make a minimum of 200 successful jumps into water before they even get their first crack at the snow, and these jumps have to get a thumbs up from coaches in order for the skier to move on.

This sort of meticulous preparation doesn't end once you hit the big-time, either. American Ashley Caldwell, one of the most decorated athletes in the sport, is competing in her third Olympics in Pyeongchang, but failed to advance past the qualifiers on February 15, as she wasn't able to land either one of the two triple-flipping jumps she attempted. Still, it's this very sort of risk-taking that has brought her to the top of her game, and caused friction with more than one of her past coaches.

"Why win with less when you can win with more?" Caldwell said of her competition mentality. “I don’t want to go out there and show the world my easiest trick. I want to show the world my best trick, me putting everything on the line to be the best.”

You can check out some of Team USA's moves in the video below:

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

nextArticle.image_alt|e
iStock
arrow
Big Questions
Is There Really Such Thing As 'Muscle Memory'?
iStock
iStock

Is there really such a thing as 'muscle memory'? For example, in the sense of your fingers remembering where the keys of the keyboard are?

C Stuart Hardwick:

Yes and no. There is no literal memory in the muscles, but the thing people call “muscle memory” exists, though the name is a misnomer.

A better name might be “subconscious memory,” as the information is stored in the brain, but is most readily accessible—or only accessible—by non-conscious means.

What “non-conscious” refers to here is the brain’s enormous capacity to train up what might almost be called “subroutines,” that exist outside our conscious experience. I like the term for this that at least one researcher in the field uses: “zombie agency.”

Zombie agents are non-conscious, or sub-conscious (in the literal, not the Freudian sense) that can do essentially everything you can do except make value judgments. So, for example, you don’t consciously know how to control your muscles in order to walk —in all likelihood, you wouldn’t know where to begin—but your zombie agents do, and they’ll take you wherever you want to go, dodging curbs and puppies, and “waking you” when appropriate to decide which babies to stop and kiss.

Zombie agents can be rather startling things. When you suddenly become aware that you’ve driven halfway across town in the direction of the office instead of going to the shoe store Saturday morning, you have zombie agents to thank. You “wake” as if from slumber, and with the frightening realization that you’ve been flying down the highway at prodigious speed while your mind was on other things. You feel as if you’ve been asleep, and in a way you have—but a very funny kind of sleep in which it is only the uppermost layer of abstract reason that is disassociated from the rest of conscious experience. Your zombie agents have been driving to work, responding to traffic, adjusting the radio, noting the check engine light, all the things you think of as “you, driving the car,” except the big one: deciding where to go. That part was on automatic pilot (which is another good way to think of this).

This is at the advanced end of the spectrum. Typing your friend’s phone number using “muscle memory” is at the other, but it’s the same phenomenon.

We didn’t evolve to remember phone numbers, so we aren’t very good at it. In fact, we are so bad at it, we invent all sorts of mnemonic devices (memory aids) to help us [in] relating numbers to words or spacial memory, either of which are closer to the hunting and gathering we are evolved for. The illusion of “muscle memory” arises because we are supremely well adapted to manual manipulation and tool-making. We don’t need to invent a memory aid to help us remember what we do with our hands, we only have to practice.

So the conscious mind says “dial Tabby’s number,” and our fingers—or more correctly, the zombie agent which learned that task—do it. Similarly, after sufficient training, we can do the same thing with tasks like “play a major fifth,” "drive to work,” or “pull an Airbus A380 up for a go-around.”

It feels like muscle memory because the conscious mind—the part you experience as being you—is acting like a coach driver, steering the efforts of a team of zombie agents, all harnesses to collective action. But it isn’t muscle memory, it's just memory—though it may be stored (or at least some of it) in the deeper, motor cortex parts of the brain.

This post originally appeared on Quora. Click here to view.

SECTIONS

arrow
LIVE SMARTER
More from mental floss studios