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

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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

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Big Questions
Who Was Chuck Taylor?
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From Betty Crocker to Tommy Bahama, plenty of popular labels are "named" after fake people. But one product with a bona fide backstory to its moniker is Converse's Chuck Taylor All-Star sneakers. The durable gym shoes are beloved by everyone from jocks to hipsters. But who's the man behind the cursive signature on the trademark circular ankle patch?

As journalist Abraham Aamidor recounted in his 2006 book Chuck Taylor, All Star: The True Story of the Man behind the Most Famous Athletic Shoe in History, Chuck Taylor was a former pro basketball player-turned-Converse salesman whose personal brand and tireless salesmanship were instrumental to the shoes' success.

Charles Hollis Taylor was born on July 24, 1901, and raised in southern Indiana. Basketball—the brand-new sport invented by James Naismith in 1891—was beginning to take the Hoosier State by storm. Taylor joined his high school team, the Columbus High School Bull Dogs, and was named captain.

After graduation, instead of heading off to college, Taylor launched his semi-pro career playing basketball with the Columbus Commercials. He’d go on to play for a handful of other teams across the Midwest, including the the Akron Firestone Non-Skids in Ohio, before finally moving to Chicago in 1922 to work as a sales representative for the Converse Rubber Shoe Co. (The company's name was eventually shortened to Converse, Inc.)

Founded in Malden, Massachusetts, in 1908 as a rubber shoe manufacturer, Converse first began producing canvas shoes in 1915, since there wasn't a year-round market for galoshes. They introduced their All-Star canvas sports shoes two years later, in 1917. It’s unclear whether Chuck was initially recruited to also play ball for Converse (by 1926, the brand was sponsoring a traveling team) or if he was simply employed to work in sales. However, we do know that he quickly proved himself to be indispensable to the company.

Taylor listened carefully to customer feedback, and passed on suggestions for shoe improvements—including more padding under the ball of the foot, a different rubber compound in the sole to avoid scuffs, and a patch to protect the ankle—to his regional office. He also relied on his basketball skills to impress prospective clients, hosting free Chuck Taylor basketball clinics around the country to teach high school and college players his signature moves on the court.

In addition to his myriad other job duties, Taylor played for and managed the All-Stars, a traveling team sponsored by Converse to promote their new All Star shoes, and launched and helped publish the Converse Basketball Yearbook, which covered the game of basketball on an annual basis.

After leaving the All-Stars, Taylor continued to publicize his shoe—and own personal brand—by hobnobbing with customers at small-town sporting goods stores and making “special appearances” at local basketball games. There, he’d be included in the starting lineup of a local team during a pivotal game.

Taylor’s star grew so bright that in 1932, Converse added his signature to the ankle patch of the All Star shoes. From that point on, they were known as Chuck Taylor All-Stars. Still, Taylor—who reportedly took shameless advantage of his expense account and earned a good salary—is believed to have never received royalties for the use of his name.

In 1969, Taylor was inducted into the Basketball Hall of Fame. The same year, he died from a heart attack on June 23, at the age of 67. Around this time, athletic shoes manufactured by companies like Adidas and Nike began replacing Converse on the court, and soon both Taylor and his namesake kicks were beloved by a different sort of customer.

Still, even though Taylor's star has faded over the decades, fans of his shoe continue to carry on his legacy: Today, Converse sells more than 270,000 pairs of Chuck Taylors a day, 365 days a year, to retro-loving customers who can't get enough of the athlete's looping cursive signature.

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

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Big Questions
What Is the Difference Between Generic and Name Brand Ibuprofen?
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What is the difference between generic ibuprofen vs. name brands?

Yali Friedman:

I just published a paper that answers this question: Are Generic Drugs Less Safe than their Branded Equivalents?

Here’s the tl;dr version:

Generic drugs are versions of drugs made by companies other than the company which originally developed the drug.

To gain FDA approval, a generic drug must:

  • Contain the same active ingredients as the innovator drug (inactive ingredients may vary)
  • Be identical in strength, dosage form, and route of administration
  • Have the same use indications
  • Be bioequivalent
  • Meet the same batch requirements for identity, strength, purity, and quality
  • Be manufactured under the same strict standards of FDA's good manufacturing practice regulations required for innovator products

I hope you found this answer useful. Feel free to reach out at www.thinkbiotech.com. For more on generic drugs, you can see our resources and whitepapers at Pharmaceutical strategic guidance and whitepapers

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

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