Normal blood pressure is a range. How to read it and when to see a doctor

Nearly half of adults have hypertension, according to the Centers for Disease Control and Prevention.

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By Maxine Lipner

Checking up on blood pressure is easier than ever with at-home monitors and drugstore blood pressure cuffs that are widely available. And, it’s a valuable tool for people to be able to monitor their own levels, since nearly half of adults have high blood pressure, according to the Centers for Disease Control and Prevention.

“It can be extremely valuable for patients to know their blood pressure," Dr. Robert Segal, board-certified cardiologist and founder of Manhattan Cardiology in New York City told TODAY. "High blood pressure usually has no symptoms ... In 2017, nearly one half million deaths in the United States included high blood pressure as the primary or contributing cause. Knowing your blood pressure is a matter of life and death.”

But, it’s also important to understand how the readings work. Unlike a bathroom scale where a pound or two of weight gain might make sense based on momentary indulgences, blood pressure is one of those numbers that may seem to rise and fall with no clear reason. The downside of blood pressure self-monitoring is that people may become alarmed with normal changes and sometimes that stress itself can send someone’s pressure sailing.

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When to take a blood pressure reading

Blood pressure can fluctuate on a daily basis due to myriad factors and it’s important to consider the source, Segal said. Things like stress, exercise, laughter, medication, caffeine, illness and sex can all contribute to pressure swings that are likely not a cause for concern.

Even the time of day blood pressure is monitored can affect the numbers.

“When you’re waking up, your blood pressure is on the lower level,” Segal said.

Meanwhile, a dramatic uptick may be seen if pressure is taken during the workday, in a high-stress environment or right after exercise. Those are not the best times to monitor.

When done properly, the best readings to understand what a person’s “normal” range is can be found at home, according to Segal.

To keep fluctuations at a minimum, and get a better baseline reading, there are a few things to consider:

  • Make sure the home monitor fits well
  • Take the pressure right before eating or in the evening about 30 minutes after dinner when most people are least stressed
  • Avoid taking any medications first
  • Keep as calm as possible

Segal finds that using an arm blood pressure cuff is more reliable than one that wraps around the wrist. When checking the pressure, the arm should be at the level of the heart.

“So, if you’re lying down, the arm should be beside you and if you’re sitting up, put your arm, let’s say, on a desk,” Segal said.

Understanding the numbers

Coming armed with the blood pressure numbers to show a doctor can help guide conversations. Understanding them is also vital. The top number is known as the systolic pressure.

“That measures the amount of pressure that your heart generates while pumping blood through your arteries to the rest of your body,” Segal said.

Meanwhile, the diastolic reading, which is the bottom number, measures the amount of pressure when the heart is at rest.

“While both numbers are important, you should be taking into greater consideration that top number,” Segal said, adding that it most readily points to risk of stroke and heart disease.

The American Heart Association pegs normal blood pressure as less than 120/80. The prehypertension range is anything from 120 to 139 as that top number.

“Prehypertension is not an illness like hypertension; rather it’s a warning that illness is looming,” Segal said. “Those with prehypertension are twice as likely to develop high blood pressure than those with normal blood pressure.”

Hypertension crosses into actual disease at the 140/90 blood pressure level. On the other end, low blood pressure includes readings of 90/60 or less.

A dramatic drop in blood pressure from what’s typical for someone may also spell trouble. It can cause dizziness or cloudiness and may require some action. So, if someone’s blood pressure is typically 130/80 and this suddenly drops to a 100/70 reading, technically this is not low blood pressure, but a drop that may be cause for concern.

“A 10, 20 or 30 percent drop may be significant for you,” Segal said.

Knowing what your baseline blood pressure is can be a big help to getting the proper medical treatment. A doctor may not realize the reading is unusual unless the person raises concern that the reading is off.

Anyone who has ongoing medical issues that are known to raise blood pressure like long-term illnesses, drug addiction, high-stress lifestyles or poor sleeping patterns may also have different from normal changes which can signal there’s a problem that needs professional attention from a doctor.

“Then fluctuations are not OK,” he said.

Having a consistent regimen for taking blood pressure -- and knowing the usual numbers -- can be a powerful asset for good heart health and blood pressure.

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