Diastolic pressure

Blood pressure
Medical diagnostics
A sphygmomanometer, a device used for measuring arterial pressure
MeSH	D001795
[]

Blood pressure (BP) is the pressure of circulating blood on the walls of blood vessels. When used without further specification, "blood pressure" usually refers to the arterial pressure in the systemic circulation. Blood pressure is usually expressed in terms of the systolic (maximum during one heart beat) pressure over diastolic (minimum in between two heart beats) pressure and is measured in millimeters of mercury (mmHg), above the surrounding atmospheric pressure (considered to be zero for convenience).

It is one of the vital signs, along with respiratory rate, heart rate, oxygen saturation, and body temperature. Normal resting blood pressure in an adult is approximately 120 mmHg systolic, and 80 mmHg diastolic, abbreviated "120/80 mmHg".

Traditionally, blood pressure is measured non-invasively using a mercury manometer because these gauges are dependent upon only gravity, thus inherently more accurate than alternative types of pressure gauges. In research, the values obtained by an experienced knowledgeable physician using a mercury manometer and stethoscope listening for the Korotkoff sounds are typically within 10 mmHg of the pressures measured via higher sophistication internal measurements of central aortic pressures at heart level. Other methods, which have become more dominant (for cost, time, convenience and concerns about potential mercury toxicity issues) are inherently less accurate.

Blood pressure is determined, moment by moment, by the balance between heart output versus total peripheral resistance and varies depending on situation, emotional state, activity, and relative health/disease states. It is regulated by the brain via both the nervous and endocrine systems.