You've had your blood pressure read and know what's normal, but do you know what the numbers mean and what they measure?

You've had your blood pressure read and you may know what's considered normal blood pressure, but do you know what those numbers measure and what they mean? If you're one of the approximately 70 million adults in the US with high blood pressure - also known as hypertension - you should know, because high blood pressure can lead to a host of problems, such as artery damage, stroke, heart attack and even kidney and eye damage.

If your blood pressure is high, your heart muscle is pumping against high resistance. Given enough time pumping against high resistance, the heart will hypertrophy, or grow bigger. This can lead to impaired blood flow, arrhythmia and cardiac arrest.

The Measurements

Blood pressure is depicted as a fraction or a division equation, with a larger number on top and a small number on the bottom, separated by a slash. The top number is systolic blood pressure, which measures the pressure inside the arteries when the heart contracts or beats. The bottom number, diastolic blood pressure, measures the pressure in the arteries at rest, between heartbeats. So, a blood pressure reading that's 120/80 means the systolic blood pressure is 120 and diastolic is 80.

Tools of the Trade

Blood pressure is measured in millimeters of mercury or mm Hg. Why mercury? Take a closer look at the blood pressure cuff the nurse or doctor puts around your arm. The cuff is called a sphygmomanometer and, even today, many contain mercury to measure barometric pressure in the arteries.

The cuff is inflated to squeeze the artery and prevent blood from flowing, then the air is released. When the blood starts flowing again, the doctor or nurse will look at the pressure reading and determine the systolic blood pressure. When the pulse goes away, we're measuring diastolic blood pressure.

Most doctors will test blood pressure at least once more after a reading comes back high. Often if the initial screening finds high blood pressure, a physician will ask the patient to relax and then measure again. Anxiety can raise blood pressure. Sometimes someone can have high blood pressure in one arm and not the other due to a problem with their veins.

What's Normal and What's Not

A blood pressure reading of less than 120 mm Hg systolic and less than 80 mm Hg diastolic is considered normal blood pressure; between 120 and 139 systolic or 80 to 89 diastolic is prehypertension; above 140 systolic or 90 diastolic is hypertension.

Does that mean lower is better? Not necessarily. Hypotension, or low blood pressure, can lead to blurry vision, confusion, dizziness, fainting, lightheadedness, nausea and vomiting, fatigue and weakness. Sudden and drastic drops in blood pressure can starve vital organs like the heart and brain of oxygen. Hypotension, unlike hypertension, doesn't have a hard and fast range. As long as your low blood pressure doesn't cause any symptoms, you don't need to worry.

Recognized for its outstanding stroke care, both Coliseum Medical Centers and Coliseum Northside Hospital have been accredited by the Joint Commission as a Primary Stroke Center. For the ninth year in a row, Coliseum Medical Centers has received "Get With the Guidelines" Certification in stroke by the American Heart Association. Coliseum Medical Centers' Inpatient Rehabilitation Center is the only Joint Commission certified Stroke Rehabilitation Center in the area.

To learn more about stroke or to take a free online stroke risk assessment, visit our website.

This content originally appeared on Sharecare.com.