The more pressure the blood exerts on the artery walls, the higher the blood pressure will be. The size of small arteries also affects the blood pressure.

 

Blood pressure is highest when the heart beats to push blood out into the arteries: this is called systolic pressure. When the heart relaxes to fill with blood again, the pressure is at its lowest point and is called diastolic pressure. When blood pressure is measured, the systolic pressure is stated first and the diastolic pressure second. Blood pressure is measured in millimeters of mercury (mm Hg). For example, if a person's systolic pressure is 120 and diastolic pressure is 80, it is written as 120/80 mm Hg. A normal reading is considered as less than 120 over less than 80. Many different actions or situations can normally raise blood pressure, such as physical activity or stressful situations. . These temporary increases in blood pressure are not considered hypertension. A diagnosis of hypertension is made only when a person has multiple high blood pressure readings over a period of time. The cause of hypertension is not known in 90 to 95 percent of the people who have it. Hypertension without a known cause is called primary or essential hypertension.