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Blood Pressure: Highs, Lows & What's Normal

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Blood pressure is one of the vital signs that doctors measure to assess general health. Having a high blood pressure, also called hypertension, that is not under control can result in heart problems, stroke, and other medical conditions.

About one in three U.S. adults have high blood pressure and only about half of these people have their high blood pressure under control, according to the Centers for Disease Control and Prevention (CDC). High blood pressure is sometimes referred to as the "silent killer" because it often has no symptoms. 

Certain lifestyle factors, such as diet and smoking habits, can greatly impact a person's risk of developing high blood pressure.

"Having a healthy lifestyle really makes a difference in your life because you can avoid high blood pressure," said Dr. Mary Ann Bauman, an internist at Integris Baptist Medical Center in Oklahoma City. "If you do have high blood pressure, make sure take your medication. You may not necessarily have symptoms until your blood pressure gets really high."

What is normal blood pressure?

Blood pressure reflects the force of blood as it hits the walls of the arteries. When the heart squeezes and pushes the blood out, the blood pushes against the walls of the blood vessels. People are born with very elastic vessels that can expand easily, and bounce back when the pressure on them is low. 

As people age, they get plaque buildup inside the blood vessels, and the flexible walls of the arteries become stiff. Now, when the heart squeezes and pushes the blood out, the blood vessels can't expand like they used to do and sustain higher pressure. Over time, the heart has to push so hard against the pressure that it starts to fail, Bauman said.

Blood pressure is recorded as two numbers and written as a ratio: the top number, called the systolic pressure, is the pressure as the heart beats. The bottom number, called the diastolic pressure, is the measurement as the heart relaxes between beats. 

Normal blood pressure is a systolic pressure of less than 120 millimeters of mercury (mm Hg) and a diastolic pressure of less than 80 mm Hg, or 120/80 mm Hg, according to the American Heart Association (AHA).

Having a blood pressure greater than 140/90 mm Hg is considered high blood pressure or hypertension.

A blood pressure level between normal and hypertension, is called prehypertension, meaning it is higher than normal, but not high enough to be considered hypertension.

A number of factors can raise blood pressure, including stress, smoking, caffeine, binge drinking, certain over-the-counter and prescribed medications and even cold temperatures. 

Those who are fit — including those who regularly exercise and professional athletes — tend to have lower blood pressures and heart rates, as do those who do not smoke and are a healthy weight.


 

Checking your blood pressure

Starting at age 20, the AHA recommends a blood pressure screening at your regular healthcare visit or once every 2 years, if your blood pressure is less than 120/80 mm Hg.

People who have high blood pressure are pre-hypertension are recommended to check their blood pressure at least three times a week, Bauman said.

People can check their blood pressure themselves. In fact, monitoring blood pressure at home may be better than doing so at the doctor's office, partly because people are especially susceptible to a spike in their blood pressure when they visit a doctor, a situation known as white coat hypertension. [Related: Heart Rate Monitors: How They Work]

"We have many studies that indicate people taking their blood pressure at home is much more accurate than at the doctor's office," Bauman said.

A manual or digital blood pressure monitor (sphygmomanometer) typically comes with instructions that should be followed carefully to get the most accurate results.

The first step is to find your pulse by pressing your index finger on the brachial artery, which is at the bend of your elbow, slightly to the inside center. On a manual monitor, place the head of the stethoscope in the general area, or for a digital monitor, place the cuff in this area.

For a manual monitor, you have to hold the pressure gauge in one hand (your weaker hand) and the bulb in the other hand. Inflate the cuff until it reads about 30 points above your normal systolic pressure. At this point, you should not hear your pulse in the stethoscope. When you hear the first heart beat, this is the systolic pressure. As you deflate the cuff, keep listening for a heart beat. When you can no longer hear it, that is your diastolic pressure.

A digital monitor does the inflation and deflation and recording of the systolic and diastolic heart rates.

Risk factors for hypertension and its consequences

Risk factors for high blood pressure include too much salt in the diet, excess weight, inactivity, and smoking.

The dangers of high blood pressure include hardening of the arteries, or atherosclerosis, kidney disease and heart disease. High blood pressure can also result in stroke, either because of a blocked arteries or a burst in a blood vessel.

Low blood pressure, known as hypotension, can also cause health problems such as fainting and dizziness. Quick, dramatic drops in blood pressure can reduce the adequate blood supply to the brain. Most of the time, hypotension goes undetected and is typically not dangerous unless it produces symptoms.

Treating high blood pressure

Treating high blood pressure includes lifestyle changes and prescription medication for those with readings of 140/90 or higher, according to the AHA.

"The first thing we tell people to do if their blood pressure is in prehypertension range, is to lose weight, exercise more, and reduce salt in diet," Bauman said. "If they reach higher levels, we then treat them with medications."

Additional reporting by Kim Ann Zimmermann, Live Science Contributor.

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Bahar Gholipour, Live Science Staff Writer

Bahar Gholipour

Bahar Gholipour is a staff reporter for Live Science covering neuroscience, odd medical cases and all things health. She holds a Master of Science degree in neuroscience from the École Normale Supérieure (ENS) in Paris, and has done graduate-level work in science journalism at the State University of New York at Stony Brook. She has worked as a research assistant at the Laboratoire de Neurosciences Cognitives at ENS.
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