Blood pressure is usually expressed in terms of the systolic (maximum) pressure over diastolic (minimum) pressure and is measured in millimeters of mercury (mm Hg). It is one of the vital signs along with respiratory rate, heart rate, oxygen saturation, and body temperature.
https://en.wikipedia.org/wiki/Blood_pressure
The diastolic blood pressure number or the bottom number indicates the pressure in the arteries when the heart rests between beats. A normal diastolic blood pressure number is 80 or less. A diastolic blood pressure between 80 and 89 is normal but higher than ideal. A diastolic blood pressure number of 90 or higher, on repeated measurements, is considered to be hypertension or high blood pressure.
http://www.webmd.boots.com/hypertension-high-blood-pressure/guide/diastolic-systolic
The theory was that the body could tolerate occasional increases in systolic blood pressure, but consistently high diastolic pressure could lead to health problems. However, doctors now know that high systolic pressure is as important as high diastolic pressure — and even more important in people older than age 50.
http://www.mayoclinic.org/diseases-conditions/high-blood-pressure/expert-answers/hypertension/FAQ-20058527
The systolic blood pressure number is always said first, and then the diastolic blood pressure number is given. For example, your blood pressure may be read as “120 over 80” or written 120/80.
http://www.webmd.boots.com/hypertension-high-blood-pressure/guide/diastolic-systolic
Every blood pressure reading consists of two numbers or levels. They are shown as one number on top of the other. The first (or top) number is your systolic blood pressure. It is the highest level your blood pressure reaches when your heart beats. The second (or bottom) number is your diastolic blood pressure. It is the lowest level your blood pressure reaches as your heart relaxes between beats.
http://www.bloodpressureuk.org/BloodPressureandyou/Thebasics/Bloodpressure
So if you have isolated systolic hypertension, your doctor may recommend that your diastolic pressure not be reduced to less than 70 mm Hg in trying to reach your target systolic pressure. Isolated systolic hypertension can lead to serious health problems, such as: 1  Stroke. 2  Heart disease.
http://www.mayoclinic.org/diseases-conditions/high-blood-pressure/expert-answers/hypertension/FAQ-20058527
If you have a diastolic number — the bottom number of a blood pressure measurement — less than 90 millimeters of mercury (mm Hg) and a systolic number — the top number of a blood pressure measurement — greater than 140 mm Hg, you have a common type of high blood pressure called isolated systolic hypertension.
http://www.mayoclinic.org/diseases-conditions/high-blood-pressure/expert-answers/hypertension/FAQ-20058527
When your heart beats, it contracts and pushes blood through the arteries to the rest of your body. This force creates pressure on the arteries. This is called systolic blood pressure. A normal systolic blood pressure is 120 or below. A systolic blood pressure of 120-139 means you have normal blood pressure that is higher than ideal, or borderline high blood pressure. Even people with this level are at a greater risk of developing heart disease.
http://www.webmd.boots.com/hypertension-high-blood-pressure/guide/diastolic-systolic
Systolic: The blood pressure when the heart is contracting. It is specifically the maximum arterial pressure during contraction of the left ventricle of the heart. The time at which ventricular contraction occurs is called systole. In a blood pressure reading, the systolic pressure is typically the first number recorded. For example, with a blood pressure of 120/80 (120 over 80), the systolic pressure is 120. By 120 is meant 120 mm Hg (millimeters of mercury). A systolic murmur is a heart murmur heard during systole, the time the heart contracts, between the normal first and second heart sounds.
http://www.medicinenet.com/script/main/art.asp?articlekey=16163
Blood pressure (BP) is the pressure exerted by circulating blood upon the walls of blood vessels. When used without further specification, blood pressure usually refers to the arterial pressure in the systemic circulation. It is usually measured at a person's upper arm.
https://en.wikipedia.org/wiki/Blood_pressure
systolic definition blood pressure
Systolic blood pressure is the blood pressure when the hearth is contracting. A systolic is defined as the blood pressure when the heart is contracting.