blood pressure
the pressure exerted by the blood against the walls of blood vessels, especially arteries. It varies with the strength of the heartbeat, the elasticity of the artery walls and resistance of the arterioles, and the person’s health, age, and state of activity. Blood pressure is measured using an instrument called a sphygmomanometer. The pressure measured during heart contraction (see systolic blood pressure) is higher than that measured when the heart is relaxed (see diastolic blood pressure). The readings are recorded (in millimeters of mercury) as systolic/diastolic; the normal resting blood pressure for an adult is less than 120/80. See also hypertension.