## Blood pressure

• Blood pressure
Medical diagnostics
A sphygmomanometer, a device used for measuring arterial pressure
MeSH D001795
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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 pressure in large arteries of 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 was measured non-invasively using a mercury manometer and this is still generally considered the gold standard. More recently other semi-automated methods have become common, largely due to concerns about potential mercury toxicity, although cost and ease of use have also influenced this trend. Early alternatives to mercury sphygmomanometers were often inaccurate, but more modern validated devices have similar accuracy to mercury devices.

Blood pressure is influenced by cardiac output, total peripheral resistance and arterial stiffness and varies depending on situation, emotional state, activity, and relative health/disease states. In the short term it is regulated by baroreceptors which act via the brain to influence nervous and endocrine systems.

Classification of blood pressure for adults
Category systolic, mmHg diastolic, mmHg
Hypotension
< 90
< 60
Desired
90–119

90–129
60–79

60–84
Prehypertension (high normal)
120–139

130–139
80–89

85–89
Stage 1 hypertension
140–159
90–99
Stage 2 hypertension
160–179
100–109
Hypertensive urgency
≥ 180
≥ 110
Isolated systolic hypertension
≥ 160
< 90
Reference ranges for blood pressure in children
Stage Approximate age Systolic Diastolic
Infants 1 to 12 months 75–100 50–70
Toddlers and preschoolers 1 to 5 years 80–110 50–80
School age 6 to 12 years 85–120 50–80
Adolescents 13 to 18 years 95–140 60–90
Site Normal
pressure range
(in mmHg)
Central venous pressure 3–8
Right ventricular pressure systolic 15–30
diastolic 3–8
Pulmonary artery pressure systolic 15–30
diastolic 4–12
Pulmonary vein/

Pulmonary capillary wedge pressure

2–15
Left ventricular pressure systolic 100–140
diastolic 3-12

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• Central venous pressure, which is a good approximation of right atrial pressure, which is a major determinant of right ventricular end diastolic volume. (However, there can be exceptions in some cases.)
• The jugular venous pressure (JVP) is the indirectly observed pressure over the venous system. It can be useful in the differentiation of different forms of heart and lung disease.
• The portal venous pressure is the blood pressure in the portal vein. It is normally 5–10 mmHg
• Blood volume: the greater the blood volume, the higher the cardiac output. There is some relationship between dietary salt intake and increased blood volume, potentially resulting in higher arterial pressure, though this varies with the individual and is highly dependent on autonomic nervous system response and the renin–angiotensin system.
• Cardiac output: the pumping action of the heart is ultimately responsible for blood pressure. Increases or decreases in cardiac output can result in increases or decreases respectively in blood pressure.
• Systemic vascular resistance: the higher the resistance to blood flow, the higher the arterial pressure upstream needs to be to maintain flow. In simple terms, resistance is related to vessel radius by the Hagen-Poiseuille's equation (resistance∝1/radius4, so the smaller the radius, the very much higher the resistance). Other physical factors that affect resistance include: vessel length (the longer the vessel, the higher the resistance), blood viscosity (the higher the viscosity, the higher the resistance) and the presence of an arterial stenosis (a narrow stenosis increases resistance to flow, however this increase in resistance rarely if ever increases systemic blood pressure, it decreases downstream flow). Substances called vasoconstrictors can reduce the calibre of blood vessels, thereby increasing blood pressure. Vasodilators (such as nitroglycerin) increase the calibre of blood vessels, thereby decreasing arterial pressure.
• Systolic 65–95 mmHg
• Diastolic 30–60 mmHg
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