Like HowStuffWorks on Facebook!

What is hypertension?

Most visits to the doctor include a blood pressure reading, whether you're feeling ill or in for a routine checkup. Let's say the nurse puts the cuff around your arm, inflates it and tells you that your reading is 145 over 95. Wonder what that means?

Health professionals use the following scale to categorize blood pressure readings:

  • Normal = less than 120/80 mm Hg
  • Prehypertension = 120-139/80-89 mm Hg
  • Hypertension = greater than 140/90 mm Hg
  • Stage I Hypertension = 140-159/90-99 mm Hg
  • Stage II Hypertension = 160 or greater/100 or greater mm Hg

Blood pressure is how much force your blood uses as it pumps blood through your body. Readings are broken into two numbers, systolic and diastolic. The systolic number -- 145 in the above example, or the higher number -- represents how strongly your blood flows while your heart is contracting, and the diastolic number -- 95 in the above example, or the lower number -- represents how strongly your blood flows when your heart is relaxed between heartbeats. The higher your blood pressure, the harder your heart is working to pump blood through your body. A person with a blood pressure reading of 145 over 95 has high blood pressure, known as hypertension.

Hypertension is a silent killer and without proper diagnosis and treatment it can damage vital organs including the brain (stroke), kidneys (kidney failure), legs (peripheral artery disease) and eyes (hypertensive retinopathy and blindness). And, of course, the heart.

When blood flows through our arteries at such high pressure over a long period of time it stretches the arterial walls and weakens blood vessels. Weakened blood vessels can rupture, causing strokes and aneurysms. Additionally, blood clots, cholesterol and plaque can become trapped in hardened, scarred arteries leading to tissue damage, heart attacks and strokes.

Symptoms that most of us would associate with illness such as headaches, vision problems, nausea and vomiting don't commonly appear until blood pressure has risen to severely high levels.