What is Blood Pressure?

Blood is carried from the heart to all parts of your body in vessels called arteries. Blood pressure is the force of the blood pushing against the walls of the arteries. Each time the heart beats (about 60-70 times a minute at rest), it pumps out blood into the arteries. Your blood pressure is at its highest when the heart beats, pumping the blood. This is called systolic pressure. When the heart is at rest, between beats, your blood pressure falls. This is the diastolic pressure. Blood pressure is always given as these two numbers, the systolic and diastolic pressures. Both are important. Usually they are written one above or before the other, such as 120/80 mmHg. The top number is the systolic and the bottom the diastolic. When the two measurements are written down, the systolic pressure is the first or top number, and the diastolic pressure is the second or bottom number (for example, 120/80). If your blood pressure is 120/80, you say that it is "120 over 80." Blood pressure changes during the day. It is lowest as you sleep and rises when you get up. It also can rise when you are excited, nervous, or active. Still, for most of your waking hours, your blood pressure stays pretty much the same when you are sitting or standing still. That level should be lower than 120/80. When the level stays high, 140/90 or higher, you have high blood pressure. With high blood pressure, the heart works harder, your arteries take a beating, and your chances of a stroke, heart attack, and kidney problems are greater.
What causes it?In many people with high blood pressure, a single specific cause is not known. This is called essential or primary high blood pressure. Research is continuing to find causes. In some people, high blood pressure is the result of another medical problem or medication. When the cause is known, this is called secondary high blood pressure.
This section � National Heart, Lung, and Blood Institute
What is high blood pressure?

A blood pressure of 140/90 or higher is considered high blood pressure. Both numbers are important. If one or both numbers are usually high, you have high blood pressure. If you are being treated for high blood pressure, you still have high blood pressure even if you have repeated readings in the normal range. There are two levels of high blood pressure: Stage 1 and Stage 2 (see the chart below). Categories for Blood Pressure Levels in Adults* (In mmHg, millimeters of mercury)
Category
Systolic(Top number)
Diastolic(Bottom number)
Normal
Less than 120
Less than 80
Prehypertension
120-139
80-89
High Blood Pressure
Systolic
Diastolic
Stage 1
140-159
90-99
Stage 2
160 or higher
100 or higher* For adults 18 and older who:
Are not on medicine for high blood pressure
Are not having a short-term serious illness
Do not have other conditions such as diabetes and kidney disease Note: When systolic and diastolic blood pressures fall into different categories, the higher category should be used to classify blood pressure level. For example, 160/80 would be stage 2 high blood pressure. There is an exception to the above definition of high blood pressure. A blood pressure of 130/80 or higher is considered high blood pressure in persons with diabetes and chronic kidney disease.
Hypertension & Women
Does menopause affect blood pressure?
Do oral contraceptives raise blood pressure?
High blood pressure and bone weakening.
High Blood Pressure Isn't Well Controlled in Older Women.
Symptoms of High Blood Pressure
How do I know when my blood pressure is high?
What are the symptoms of high blood pressure?
Headaches & High Blood Pressure
Is Headache Related to Increases of Blood Pressure?
Study Proves Headaches Are Not Related to Blood Pressure
Measuring High Blood Pressure
What are Korotkoff sounds?
What is an electrocardiogram?
Do You Have 'White Coat Hypertension'?
Stress & High Blood Pressure
Panic attacks more common in people with high blood pressure.
Does stress cause hypertension?
'Fight or flight' response raises blood pressure -- even while you're asleep
Miscellaneous
What is the prevalence of hypertension?
What is essential hypertension and where does it come from?
How blood pressure is regulated?
What is postural hypotension?
What is coarctation of the aorta?
Are there different types of blood pressure disorders?
What is a pheochromocytoma?
What is an aldosterone secreting tumor?
Is it safe to use nasal decongestants if you have high blood pressure?
How does atherosclerosis begin?
How does magnesium affect blood pressure?
Who has high blood pressure?
High blood pressure: Awareness and treatment
What happens inside your body if high blood pressure is not controlled?
Controlling Blood Pressure Works
Does tea offset the effects of caffeine on blood pressure?
Aspirin is ineffective in preventing heart disease when the blood pressure is high.
Is there a particular type of personality associated with high blood pressure?
Common Ingredient in Cold and Diet Medications Associated with Stroke
High Blood Pressure and Obesity May Be Caused by the Same Gene
New Program Aims to Improve Outcomes for People with Diabetes
Doctors Urged to Treat High Systolic Blood Pressure More Aggressively
Heart Disease Remains the #1 Cause of Hospitalization
Can Acupuncture Lower Blood Pressure?
Study Suggests Viagra Is Safe for Cardiac Patients
High BP - It's a Guy Thing
Treating Depression Fails to Reduce Heart Attacks
Successes and Failures in Hypertension
Lifetime Risk of Hypertension Is 90%
Why Aren't Doctors Treating High Systolic BP?
What Is A Hypertensive Crisis?
Related Diseases
What is a heart attack (myocardial infarction)?
What is angina pectoris?
What is coronary artery disease?
High Blood Pressure Might Affect Your Thinking, Too