Blood pressure is the force of blood exerted on the inside walls of blood vessels, and is one of the chief vital signs. It is measured by a health care professional using a sphygmomanometer. Blood pressure is expressed as a ratio (e.g. 190/110). The first number is the systolic pressure— the pressure when the ventricles are contracting, pumping blood into the arteries. The second number is the diastolic pressure— the pressure when ventricles are filling with blood and the heart is at rest. The ideal blood pressure for a healthy, adult male is 120/80.
Blood pressure is not static—that is, it is constantly fluctuating. Factors that may attribute to a change in blood pressure include stress, physical exertion, drugs, and even merely from standing up too quickly (referred to as orthostatic hypotension)
Hypertension (high blood pressure) and hypotension (low blood pressure) are abnormal medical conditions which can be hazardous to your health, though very easily treatable with proper medication, diet, and exercise.