Blood pressure the pressure of blood against the walls of the main arteries. Pressure is highest during systole, when the ventricles are contracting (systolic pressure), and lowest during diastole, when the ventricles are relaxing and refilling (diastolic pressure).

Blood pressure is measured in millimetres of mercury (mmHg) by means of a *sphygmomanometer at the brachial artery of the arm, where the pressure is most similar to that of blood leaving the heart. The normal range varies with age, but a young adult would be expected to have a systolic pressure of around 120 mmHg and a diastolic pressure of 80 mmHg at rest. These are recorded as 120/80 mmHg.

Individual variations are common. Muscular exertion and emotional factors, such as fear, stress, and excitement, all raise systolic blood pressure (see HYPERTENSION). Systolic blood pressure is normally at its lowest during sleep. Severe shock may lead to an abnormally low blood pressure and possible circulatory failure (see HYPOTENSION). Blood pressure is adjusted to its normal level by the "sympathetic nervous system and hormonal controls.

Unit 5,

Reference: Oxford Concise Colour Medical Dictionary (7th Edition, Kindle Edition) Oxford University Press 2020 ISBN-13: 978-0198836629, p1069