The guidelines also redefined the various categories of hypertension. It eliminated the category of prehypertension, which had been defined as systolic blood pressure of 120 to 139 mm Hg or diastolic pressure (the lower number in a reading) of 80 to 89 mm Hg. Instead, people with those readings are now categorized as having either elevated pressure (120 to 129 systolic and less than 80 diastolic) or Stage 1 hypertension (130 to 139 systolic or 80 to 89 diastolic).
The guidelines, from the American Heart Association (AHA) and the American College of Cardiology (ACC), now define high blood pressure as 130 mm Hg or higher for the systolic blood pressure measurement, or 80 mm Hg or higher for the diastolic blood pressure measurement. (Systolic is the top number, and diastolic is the bottom number, in a blood pressure reading.) Previously, high blood pressure was defined as 140 mm Hg or higher for the systolic measurement and 90 or higher for the diastolic measurement.
Much is being made of the fact that the new definitions of high blood pressure will mean roughly half of all US citizens will be considered to have high blood pressure, but when you really look at the numbers, as cardiologists already have, not that many more people will actually be advised to take medications. Although the public has good reason to be suspicious of “big pharma,” that’s not what this is about.
Hypertension occurs in around 0.2 to 3% of newborns; however, blood pressure is not measured routinely in healthy newborns.[33] Hypertension is more common in high risk newborns. A variety of factors, such as gestational age, postconceptional age and birth weight needs to be taken into account when deciding if a blood pressure is normal in a newborn.[33]

When your heart contracts and squeezes blood out into your network of arteries, the pressure inside those blood vessels is at its highest. This is called systolic pressure and it’s the top number on your blood pressure reading. In between beats, the heart relaxes and the pressure drops. This is your diastolic blood pressure, and it’s the reading’s bottom number.

Moderate or severe bleeding can quickly deplete an individual's body of blood, leading to low blood pressure or orthostatic hypotension. Bleeding can result from trauma, surgical complications, or from gastrointestinal abnormalities such as ulcers, tumors, or diverticulosis. Occasionally, the bleeding may be so severe and rapid (for example, bleeding from a ruptured aortic aneurysm) that it causes shock and death rapidly.
Low blood pressure (hypotension) is pressure so low it causes symptoms or signs due to the low flow of blood through the arteries and veins. When the flow of blood is too low to deliver enough oxygen and nutrients to vital organs such as the brain, heart, and kidney, the organs do not function normally and may be temporarily or permanently damaged.
High blood pressure is more common in older people. At age 45, more men have hypertension than women. By age 65, this is reversed and more women are affected. People with diabetes have a greater risk of hypertension than those without diabetes. Having a close family member with high blood pressure also increases your risk of developing it. About 60% of all people with diabetes also have hypertension.
At the most basic level, hypotension can cause dizziness or blurry vision, which may increase the risk of falling or contribute to accidents. In more serious cases, it reduces the blood flow to the brain and other vital organs. This decreases the amount of oxygen and nutrients being delivered to these organs and impairs their ability to carry out normal functions. Hypotension may also indicate a more serious underlying health condition.
If you have high blood pressure, it is important to get routine medical care and to follow your prescribed treatment plan, which will include heart-healthy lifestyle changes and possibly medicines. Heart-healthy lifestyle changes can prevent high blood pressure, reduce elevated blood pressure, help control existing high blood pressure, and prevent complications, such as heart attack, heart failure, stroke, vascular dementia, or chronic kidney disease.
Some people have low blood pressure all the time. They have no symptoms and their low readings are normal for them. In other people, blood pressure drops below normal because of a medical condition or certain medicines. Some people may have symptoms of low blood pressure when standing up too quickly. Low blood pressure is a problem only if it causes dizziness, fainting or in extreme cases, shock.
Vasovagal syncope can be treated with several types of drugs such as beta blockers, for example, propanolol (Inderal, Inderal LA) and selective serotonin reuptake inhibitors such as fluoxetine (Prozac), escitalopram oxalate (Lexapro), paroxetine (Paxil), sertraline (Zoloft), citalopram (Celexa), and fluvoxamine (Luvox). Fludrocortisone (Florinef) (a drug that prevents dehydration by causing the kidney(s) to retain water) also may be used. A pacemaker can also be helpful when a patient fails drug therapy.

^ Aronow WS, Fleg JL, Pepine CJ, Artinian NT, Bakris G, Brown AS, Ferdinand KC, Ann Forciea M, Frishman WH, Jaigobin C, Kostis JB, Mancia G, Oparil S, Ortiz E, Reisin E, Rich MW, Schocken DD, Weber MA, Wesley DJ, Harrington RA, Bates ER, Bhatt DL, Bridges CR, Eisenberg MJ, Ferrari VA, Fisher JD, Gardner TJ, Gentile F, Gilson MF, Hlatky MA, Jacobs AK, Kaul S, Moliterno DJ, Mukherjee D, Rosenson RS, Stein JH, Weitz HH, Wesley DJ (2011). "ACCF/AHA 2011 expert consensus document on hypertension in the elderly: a report of the American College of Cardiology Foundation Task Force on Clinical Expert Consensus Documents developed in collaboration with the American Academy of Neurology, American Geriatrics Society, American Society for Preventive Cardiology, American Society of Hypertension, American Society of Nephrology, Association of Black Cardiologists, and European Society of Hypertension". J Am Soc Hypertens. 5 (4): 259–352. doi:10.1016/j.jash.2011.06.001. PMID 21771565.
Health care providers measure blood pressure with a sphygmomanometer (sfig-mo-muh-NAH-muh-ter), which has a cuff that's wrapped around the upper arm and pumped up to create pressure. When the cuff is inflated, it squeezes a large artery in the arm, stopping the blood flow for a moment. Blood pressure is measured as air is gradually let out of the cuff, which allows blood to flow through the artery again.

Low blood pressure due to nervous system damage (multiple system atrophy with orthostatic hypotension). Also called Shy-Drager syndrome, this rare disorder causes progressive damage to the autonomic nervous system, which controls involuntary functions such as blood pressure, heart rate, breathing and digestion. It's associated with having very high blood pressure while lying down.

Blood pressure is the force of your blood pushing against the walls of your arteries. Each time your heart beats, it pumps out blood into the arteries. Your blood pressure is highest when your heart beats, pumping the blood. This is called systolic pressure. When your heart is at rest, between beats, your blood pressure falls. This is the diastolic pressure. Your blood pressure reading uses these two numbers. Usually they're written one above or before the other, such as 120/80. If your blood pressure reading is 90/60 or lower, you have low blood pressure.