Blood pressure

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Diastolic blood pressure
)
Blood pressure
A healthcare worker measuring blood pressure using a sphygmomanometer.
MeSHD001795
MedlinePlus007490
LOINC35094-2

Blood pressure (BP) is the

mmHg) above the surrounding atmospheric pressure, or in kilopascals (kPa). The difference between the systolic and diastolic pressures is known as pulse pressure,[1] while the average pressure during a cardiac cycle is known as mean arterial pressure.[2]

Blood pressure is one of the

body temperature—that healthcare professionals use in evaluating a patient's health. Normal resting blood pressure in an adult is approximately 120 millimetres of mercury (16 kPa) systolic over 80 millimetres of mercury (11 kPa) diastolic, denoted as "120/80 mmHg". Globally, the average blood pressure, age standardized, has remained about the same since 1975 to the present, at approx. 127/79 mmHg in men and 122/77 mmHg in women, although these average data mask significantly diverging regional trends.[3]

Traditionally, a health-care worker measured blood pressure non-invasively by

aneroid gauge or a mercury-tube sphygmomanometer.[4] Auscultation is still generally considered to be the gold standard of accuracy for non-invasive blood pressure readings in clinic.[5] However, semi-automated methods have become common, largely due to concerns about potential mercury toxicity,[6] although cost, ease of use and applicability to ambulatory blood pressure or home blood pressure measurements have also influenced this trend.[7] Early automated alternatives to mercury-tube sphygmomanometers were often seriously inaccurate, but modern devices validated to international standards achieve an average difference between two standardized reading methods of 5 mm Hg or less, and a standard deviation of less than 8 mm Hg.[7] Most of these semi-automated methods measure blood pressure using oscillometry (measurement by a pressure transducer in the cuff of the device of small oscillations of intra-cuff pressure accompanying heartbeat-induced changes in the volume of each pulse).[8]

Blood pressure is influenced by

systemic vascular resistance, blood volume and arterial stiffness, and varies depending on patient's situation, emotional state, activity and relative health or disease state. In the short term, blood pressure is regulated by baroreceptors, which act via the brain to influence the nervous and the endocrine
systems.

Blood pressure that is too low is called

. Long-term hypertension is more common than long-term hypotension.

Classification, normal and abnormal values

Systemic arterial pressure

Blood pressure classifications
Categories
mmHg
And/or
Diastolic blood pressure
, mmHg
Method Office 24h ambulatory Office 24h ambulatory
Hypotension[10] <110 <100 or <70 <60
American College of Cardiology/American Heart Association (2017)[11]
Normal <120 <115 and <80 <75
Elevated 120–129 115–124 and <80 <75
Hypertension, stage 1 130–139 125–129 or 80–89 75–79
Hypertension, stage 2 ≥140 ≥130 or ≥90 ≥80
European Society of Hypertension (2023)[12]
Optimal <120 and <80
Normal 120–129 and/or 80–84
High normal 130–139 and/or 85–89
Hypertension, grade 1 140–159 ≥130 and/or 90–99 ≥80
Hypertension, grade 2 160–179 and/or 100–109
Hypertension, grade 3 ≥180 and/or ≥110
Diastolic vs systolic blood pressure chart comparing European Society of Cardiology and European Society of Hypertension classification with reference ranges in children

The risk of cardiovascular disease increases progressively above 115/75 mmHg,[13] below this level there is limited evidence.[14]

Observational studies demonstrate that people who maintain arterial pressures at the low end of these pressure ranges have much better long-term cardiovascular health. There is an ongoing medical debate over what is the optimal level of blood pressure to target when using drugs to lower blood pressure with hypertension, particularly in older people.[15]

Blood pressure fluctuates from minute to minute and normally shows a circadian rhythm over a 24-hour period,

stress, consumption of food or liquid, dietary factors, physical activity, changes in posture (such as standing-up), drugs, and disease.[21] The variability in blood pressure and the better predictive value of ambulatory blood pressure measurements has led some authorities, such as the National Institute for Health and Care Excellence (NICE) in the UK, to advocate for the use of ambulatory blood pressure as the preferred method for diagnosis of hypertension.[22]

A digital sphygmomanometer used for measuring blood pressure

Various other factors, such as age and sex, also influence a person's blood pressure. Differences between left-arm and right-arm blood pressure measurements tend to be small. However, occasionally there is a consistent difference greater than 10 mmHg which may need further investigation, e.g. for peripheral arterial disease, obstructive arterial disease or aortic dissection.[23][24][25][26]

There is no accepted diagnostic standard for hypotension, although pressures less than 90/60 are commonly regarded as hypotensive.[27] In practice blood pressure is considered too low only if symptoms are present.[28]

Systemic arterial pressure and age

Fetal blood pressure

In pregnancy, it is the fetal heart and not the mother's heart that builds up the fetal blood pressure to drive blood through the fetal circulation. The blood pressure in the fetal aorta is approximately 30 mmHg at 20 weeks of gestation, and increases to approximately 45 mmHg at 40 weeks of gestation.[29]

The average blood pressure for full-term infants:[30]

  • Systolic 65–95 mmHg
  • Diastolic 30–60 mmHg

Childhood

Reference ranges for blood pressure (BP) in children[31]
Stage Approximate age Systolic BP,
mmHg
Diastolic BP,
mmHg
Infants 0–12 months 75–100 50–70
Toddlers and preschoolers 1–5 years 80–110 50–80
School age 6–12 years 85–120 50–80
Adolescents 13–18 years 95–140 60–90

In children the normal ranges for blood pressure are lower than for adults and depend on height.[32] Reference blood pressure values have been developed for children in different countries, based on the distribution of blood pressure in children of these countries.[33]

Aging adults

In adults in most societies, systolic blood pressure tends to rise from early adulthood onward, up to at least age 70;

isolated systolic hypertension. The rise in pulse pressure with age is attributed to increased stiffness of the arteries.[36] An age-related rise in blood pressure is not considered healthy and is not observed in some isolated unacculturated communities.[37]

Systemic venous pressure

Site Normal
pressure range
(in
mmHg)[38]
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

Blood pressure generally refers to the arterial pressure in the

systemic circulation. However, measurement of pressures in the venous system and the pulmonary vessels plays an important role in intensive care medicine but requires invasive measurement of pressure using a catheter
.

Venous pressure is the vascular pressure in a

right atrium
and 8 mmHg in the left atrium.

Variants of venous pressure include:

Pulmonary pressure

Normally, the pressure in the pulmonary artery is about 15 mmHg at rest.[42]

Increased blood pressure in the

capillaries of the lung causes pulmonary hypertension, leading to interstitial edema if the pressure increases to above 20 mmHg, and to pulmonary edema at pressures above 25 mmHg.[43]

Aortic pressure

Aortic pressure, also called central aortic blood pressure, or central blood pressure, is the blood pressure at the root of the aorta. Elevated aortic pressure has usually been found to be a more accurate predictor of both cardiovascular events and mortality, as well as structural changes in the heart, than has peripheral blood pressure (such as measured through the brachial artery).[44] Traditionally it involved an invasive procedure to measure aortic pressure, but now there are non-invasive methods of measuring it indirectly without a significant margin of error.[45][46]

Certain researchers have argued for physicians to begin using aortic pressure, as opposed to peripheral blood pressure, as a guide for clinical decisions.[44] The way antihypertensive drugs impact peripheral blood pressure can often be very different from the way they impact central aortic pressure.[47]

Mean systemic pressure

If the heart is stopped, blood pressure falls, but it does not fall to zero. The remaining pressure measured after cessation of the heart beat and redistribution of blood throughout the circulation is termed the mean systemic pressure or mean circulatory filling pressure;[48] typically this is proximally ~7 mmHg.[48]

Disorders of blood pressure

Disorders of blood pressure control include high blood pressure, low blood pressure, and blood pressure that shows excessive or maladaptive fluctuation.

High blood pressure

Overview of main complications of persistent high blood pressure.[49]

Arterial hypertension can be an indicator of other problems and may have long-term adverse effects. Sometimes it can be an acute problem, such as in a hypertensive emergency when blood pressure is more than 180/120 mmHg.[49]

Levels of arterial pressure put mechanical stress on the arterial walls. Higher pressures increase heart workload and progression of unhealthy tissue growth (

heart muscle
tends to thicken, enlarge and become weaker over time.

Persistent

chronic kidney failure.[49] Even moderate elevation of arterial pressure leads to shortened life expectancy.[49] At severely high pressures, mean arterial pressures 50% or more above average, a person can expect to live no more than a few years unless appropriately treated.[50]

Both high

isolated systolic hypertension and may present a health concern.[49][55] According to the 2017 [56] American Heart Association blood pressure guidelines state that a systolic blood pressure of 130–139 mmHg with a diastolic pressure of 80–89 mmHg is "stage one hypertension".[49]

For those with

aortic and mitral regurgitation when diastolic blood pressure increased, whereas when diastolic blood pressure decreased, there was a decreased severity.[57]

Low blood pressure

Blood pressure that is too low is known as hypotension. This is a medical concern if it causes signs or symptoms, such as dizziness, fainting, or in extreme cases, circulatory shock.[58]

Causes of low arterial pressure include:[59]

Orthostatic hypotension

A large fall in blood pressure upon standing (persistent systolic/diastolic blood pressure decrease of >20/10 mmHg) is termed orthostatic hypotension (postural hypotension) and represents a failure of the body to compensate for the effect of gravity on the circulation. Standing results in an increased hydrostatic pressure in the blood vessels of the lower limbs. The consequent distension of the veins below the diaphragm (venous pooling) causes ~500 ml of blood to be relocated from the chest and upper body. This results in a rapid decrease in central blood volume and a reduction of ventricular preload which in turn reduces stroke volume, and mean arterial pressure. Normally this is compensated for by multiple mechanisms, including activation of the autonomic nervous system which increases heart rate, myocardial contractility and systemic arterial vasoconstriction to preserve blood pressure and elicits venous vasoconstriction to decrease venous compliance. Decreased venous compliance also results from an intrinsic myogenic increase in venous smooth muscle tone in response to the elevated pressure in the veins of the lower body.

Other compensatory mechanisms include the veno-arteriolar

flow decrease beyond a certain point, the perfusion of the brain becomes critically compromised (i.e., the blood supply is not sufficient), causing lightheadedness, dizziness, weakness or fainting.[61] Usually this failure of compensation is due to disease, or drugs that affect the sympathetic nervous system.[60] A similar effect is observed following the experience of excessive gravitational forces (G-loading), such as routinely experienced by aerobatic or combat pilots 'pulling Gs
' where the extreme hydrostatic pressures exceed the ability of the body's compensatory mechanisms.

Variable or fluctuating blood pressure

Some fluctuation or variation in blood pressure is normal. Variation in blood pressure that is significantly greater than the norm is known as labile hypertension and is associated with increased risk of cardiovascular disease[62] brain small vessel disease,[63] and dementia[64] independent of the average blood pressure level. Recent evidence from clinical trials has also linked variation in blood pressure to mortality,[65][66] stroke,[67] heart failure,[68] and cardiac changes that may give rise to heart failure.[69] These data have prompted discussion of whether excessive variation in blood pressure should be treated, even among normotensive older adults.[70]

Older individuals and those who had received blood pressure medications are more likely to exhibit larger fluctuations in pressure,[71] and there is some evidence that different antihypertensive agents have different effects on blood pressure variability;[64] whether these differences translate to benefits in outcome is uncertain.[64]

Physiology

Cardiac systole and diastole
Blood flow velocity waveforms in the central retinal artery (red) and vein (blue), measured by laser Doppler imaging in the eye fundus of a healthy volunteer.

During each heartbeat, blood pressure varies between a maximum (systolic) and a minimum (diastolic) pressure.

arterioles.[74] Pulsatility also diminishes in the smaller elements of the arterial circulation, although some transmitted pulsatility is observed in capillaries.[75]

Schematic of pressures in the circulation

Gravity affects blood pressure via hydrostatic forces (e.g., during standing), and valves in veins, breathing, and pumping from contraction of skeletal muscles also influence blood pressure, particularly in veins.[73]

Hemodynamics