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-tubesphygmomanometer.[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
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]
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]
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]
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]
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:
Central venous pressure, which is a good approximation of right atrial pressure,[39] which is a major determinant of right ventricular end diastolic volume. (However, there can be exceptions in some cases.)[40]
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 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][45] 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.[46][47]
Certain researchers have argued for physicians to begin using aortic pressure, as opposed to peripheral blood pressure, as a guide for clinical decisions.[48][45] The way antihypertensive drugs impact peripheral blood pressure can often be very different from the way they impact central aortic pressure.[49]
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;[50] typically this is proximally ~7 mmHg.[50]
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.
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.[51]
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.[51] Even moderate elevation of arterial pressure leads to shortened life expectancy.[51] 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.[52]
Both high
isolated systolic hypertension and may present a health concern.[51][57] According to the 2017 [58] 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".[51]
For those with
aortic and mitral regurgitation when diastolic blood pressure increased, whereas when diastolic blood pressure decreased, there was a decreased severity.[59]
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.[60]
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.[63] Usually this failure of compensation is due to disease, or drugs that affect the sympathetic nervous system.[62] 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.
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[64] brain small vessel disease,[65] and dementia[66] independent of the average blood pressure level. Recent evidence from clinical trials has also linked variation in blood pressure to mortality,[67][68] stroke,[69] heart failure,[70] and cardiac changes that may give rise to heart failure.[71] These data have prompted discussion of whether excessive variation in blood pressure should be treated, even among normotensive older adults.[72]
Older individuals and those who had received blood pressure medications are more likely to exhibit larger fluctuations in pressure,[73] and there is some evidence that different antihypertensive agents have different effects on blood pressure variability;[66] whether these differences translate to benefits in outcome is uncertain.[66]
Physiology
During each heartbeat, blood pressure varies between a maximum (systolic) and a minimum (diastolic) pressure.
arterioles.[76] Pulsatility also diminishes in the smaller elements of the arterial circulation, although some transmitted pulsatility is observed in capillaries.[77]
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.[75]
Hemodynamics
Main article:
Vasodilators (such as nitroglycerin) increase the caliber of blood vessels, thereby decreasing arterial pressure. In the longer term a process termed remodeling also contributes to changing the caliber of small blood vessels and influencing resistance and reactivity to vasoactive agents.[87][88] Reductions in capillary density, termed capillary rarefaction, may also contribute to increased resistance in some circumstances.[89]
In practice, each individual's autonomic nervous system and other systems regulating blood pressure, notably the kidney,[90] respond to and regulate all these factors so that, although the above issues are important, they rarely act in isolation and the actual arterial pressure response of a given individual can vary widely in the short and long term.
The pulse pressure is the difference between the measured systolic and diastolic pressures,[91]
The pulse pressure is a consequence of the pulsatile nature of the cardiac output, i.e. the heartbeat. The magnitude of the pulse pressure is usually attributed to the interaction of the stroke volume of the heart, the compliance (ability to expand) of the arterial system—largely attributable to the aorta and large elastic arteries—and the resistance to flow in the arterial tree.[91]
Elevated pulse pressure has been found to be a stronger independent predictor of cardiovascular events, especially in older populations, than has systolic, diastolic, or mean arterial pressure.[53][54] This increased risk exists for both men and women and even when no other cardiovascular risk factors are present. The increased risk also exists even in cases in which diastolic pressure decreases over time while systolic remains steady.[56][55]
A meta-analysis in 2000 showed that a 10 mmHg increase in pulse pressure was associated with a 20% increased risk of cardiovascular mortality, and a 13% increase in risk for all coronary end points. The study authors also noted that, while risks of cardiovascular end points do increase with higher systolic pressures, at any given systolic blood pressure the risk of major cardiovascular end points increases, rather than decreases, with lower diastolic levels. This suggests that interventions that lower diastolic pressure without also lowering systolic pressure (and thus lowering pulse pressure) could actually be counterproductive.[93] There are no drugs currently approved to lower pulse pressure, although some antihypertensive drugs may modestly lower pulse pressure, while in some cases a drug that lowers overall blood pressure may actually have the counterproductive side effect of raising pulse pressure.[94]
Pulse pressure can both widen or narrow in people with
hemodynamic compromise. A pulse pressure of over 70 mmHg in patients with sepsis is correlated with an increased chance of survival and a more positive response to IV fluids.[95][96]
regulation of arterial pressure is not completely understood, but the following mechanisms of regulating arterial pressure have been well-characterized:
high pressure receptor zones detect changes in arterial pressure. These baroreceptors send signals ultimately to the medulla of the brain stem, specifically to the rostral ventrolateral medulla (RVLM). The medulla, by way of the autonomic nervous system, adjusts the mean arterial pressure by altering both the force and speed of the heart's contractions, as well as the systemic vascular resistance. The most important arterial baroreceptors are located in the left and right carotid sinuses and in the aortic arch.[101]
angiotensin II
.
Aldosterone release: This steroid hormone is released from the adrenal cortex in response to activation of the renin-angiotensin system, high serum potassium levels, or elevated adrenocorticotropic hormone (ACTH). Renin converts angiotensinogen to angiotensin I, which is converted by angiotensin converting enzyme to angiotensin II. Angiotensin II then signals to the adrenal cortex to release aldosterone.[102] Aldosterone stimulates sodium retention and potassium excretion by the kidneys and the consequent salt and water retention increases plasma volume, and indirectly, arterial pressure. Aldosterone may also exert direct pressor effects on vascular smooth muscle and central effects on sympathetic nervous system activity.[103]
Frank–Starling law of the heart
, in turn increasing arterial blood pressure.
These different mechanisms are not necessarily independent of each other, as indicated by the link between the RAS and aldosterone release. When blood pressure falls many physiological cascades commence in order to return the blood pressure to a more appropriate level.
The blood pressure fall is detected by a decrease in blood flow and thus a decrease in glomerular filtration rate (GFR).
Decrease in GFR is sensed as a decrease in Na+ levels by the macula densa.
The macula densa causes an increase in Na+ reabsorption, which causes water to follow in via osmosis and leads to an ultimate increase in plasma volume. Further, the macula densa releases adenosine which causes constriction of the afferent arterioles.
At the same time, the
juxtaglomerular cells sense the decrease in blood pressure and release renin
.
Renin converts
angiotensin I
(active form).
Angiotensin I flows in the bloodstream until it reaches the capillaries of the lungs where
angiotensin II
.
Angiotensin II is a vasoconstrictor that will increase blood flow to the heart and subsequently the preload, ultimately increasing the cardiac output.
, by penetrating the arterial wall to take the measurement, is much less common and usually restricted to a hospital setting.
Novel methods to measure blood pressure without penetrating the arterial wall, and without applying any pressure on patient's body are currently being explored.[107] So-called cuffless measurements, these methods open the door to more comfortable and acceptable blood pressure monitors. An example is a cuffless blood pressure monitor at the wrist that uses only optical sensors.[108]
One common problem in office blood pressure measurement in the United States is terminal digit preference. According to one study, approximately 40% of recorded measurements ended with the digit zero, whereas "without bias, 10%–20% of measurements are expected to end in zero"[109] Therefore, addressing digit preference is a key issue for improving blood pressure measurement accuracy.
In animals
Blood pressure levels in non-human mammals may vary depending on the species. Heart rate differs markedly, largely depending on the size of the animal (larger animals have slower heart rates).[110] The giraffe has a distinctly high arterial pressure of about 190 mm Hg, enabling blood perfusion through the 2 metres (6 ft 7 in)-long neck to the head.[111] In other species subjected to orthostatic blood pressure, such as arboreal snakes, blood pressure is higher than in non-arboreal snakes.[112] A heart near to the head (short heart-to-head distance) and a long tail with tight integument favor blood perfusion to the head.[113][114]
As in humans, blood pressure in animals differs by age, sex, time of day, and environmental circumstances:[115][116] measurements made in laboratories or under anesthesia may not be representative of values under free-living conditions. Rats, mice, dogs and rabbits have been used extensively to study the regulation of blood pressure.[117]
Blood pressure and heart rate of various mammals[115]
Species
Blood pressure mm Hg
Heart rate beats per minute
Systolic
Diastolic
Calves
140
70
75–146
Cats
155
68
100–259
Dogs
161
51
62–170
Goats
140
90
80–120
Guinea-pigs
140
90
240–300
Mice
120
75
580–680
Pigs
169
55
74–116
Rabbits
118
67
205–306
Rats
153
51
305–500
Rhesus monkeys
160
125
180–210
Sheep
140
80
63–210
Hypertension in cats and dogs
Hypertension in cats and dogs is generally diagnosed if the blood pressure is greater than 150[118] mm Hg (systolic), although sight hounds have higher blood pressures than most other dog breeds; a systolic pressure greater than 180 mmHg is considered abnormal in these dogs.[119]
. Table2: Comparison of ambulatory blood pressures and urinary norepinephrine and epinephrine excretion measured at work, home, and during sleep between European–American (n = 110) and African–American (n = 51) women
from the original on 2020-03-17. Retrieved 2018-12-23.
^Mayo Clinic staff (2009-05-23). "Low blood pressure (hypotension) – Causes". MayoClinic.com. Mayo Foundation for Medical Education and Research. Archived from the original on 2021-11-17. Retrieved 2010-10-19.
^"What Is Pulmonary Hypertension?". From Diseases and Conditions Index (DCI). National Heart, Lung, and Blood Institute. September 2008. Archived from the original on 27 April 2012. Retrieved 6 April 2009.