The tension in the main arteries that is created by the beating of the heart and the resistance to flow and elasticity of the blood vessels. The highest and lowest pressures are called the systolic and diastolic pressures respectively and may be measured using a blood pressure cuff and sphygmomanometer and expressed in millimetres of mercury. Systolic pressure is seen during systole, when the ventricles of the heart are contracting, whilst diastolic pressure is seen during diastole, when the ventricles are relaxing. The values are written as a fraction, with the systolic pressure on top; the normal range for a young adult would be 120/80, though there can be a considerable variation in individuals.
An increase in blood pressure may be due to physical effort, or to stress and emotional factors, and is called hypertension. An abnormally low blood pressure, called hypotension, may be caused by shock or circulation diseases.
See also Diastolic Pressure and Systolic Pressure.
