Blood pressure (BP) is the pressure of circulating blood on the walls of blood vessels. Most of this pressure is due to the work done by the heart in pumping blood round the circulation. 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 pressure (maximum during one heartbeat) over diastolic pressure (minimum in between two heartbeats) and is measured in millimeters of mercury (mmHg), above the surrounding atmospheric pressure.
Blood pressure 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 millimetres of mercury (16 kPa) systolic, and 80 millimetres of mercury (11 kPa) diastolic, abbreviated "120/80 mmHg".
Traditionally, blood pressure was measured non-invasively using ausculation with a mercury-tube sphygmomanometer. Ausculation is still generally considered to be the gold standard of accuracy for non-invasive blood pressure readings in clinic. However, semi-automated methods have become common, largely due to concerns about potential mercury toxicity, although cost, ease of use and applicability to ambulatory blood pressure or home blood pressure measurements have also influenced this trend. Early automated alternatives to mercury-tube sphygmomanometers were often seriously inaccurate, but modern devices validated to international standards achieve average difference between two standardized reading methods of 5 mm Hg or less and a standard deviation of less than 8 mm Hg. Most of these semi-automated methods measure blood pressure using oscillometry.
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, blood pressure is regulated by baroreceptors which act via the brain to influence nervous and endocrine systems.
Blood pressure that is too low is called hypotension, and pressure that is consistently high is hypertension. Both have many causes and may be of sudden onset or of long duration. Long-term hypertension is a risk factor for many diseases, including heart disease, stroke and kidney failure. Long-term hypertension is more common than long-term hypotension, which is usually only diagnosed when it causes symptoms.
A sphygmomanometer, a device used for measuring arterial pressure
|Category||systolic BP, mmHg||diastolic BP, mmHg|
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.
The table shows the most recent classification (2018) of office (or clinic) blood pressure by The Task Force for the management of arterial hypertension of the European Society of Cardiology (ESC) and the European Society of Hypertension (ESH). Similar thresholds had been adopted by the American Heart Association for adults who are 18 years and older, but in November 2017 the American Heart Association announced revised definitions for blood pressure categories that increased the number of people considered to have high blood pressure.
Blood pressure fluctuates from minute to minute and normally shows a circadian rhythm over a 24-hour period, with highest readings in the early morning and evenings and lowest readings at night. Loss of the normal fall in blood pressure at night is associated with a greater future risk of cardiovascular disease and there is evidence that night-time blood pressure is a stronger predictor of cardiovascular events than day-time blood pressure. Blood pressure varies over longer time periods (months to years) and this variability predicts adverse outcomes. Blood pressure also changes in response to temperature, noise, emotional stress, consumption of food or liquid, dietary factors, physical activity, changes in posture, such as standing-up, drugs, and disease. The variability in blood pressure and the better predictive value of ambulatory blood pressure measurements has led to some authorities, such as The National Institute for Health and Care Excellence (NICE) in UK, to advocate the use of ambulatory blood pressure as the preferred method for diagnosis of hypertension.
Various other factors, such as age and sex, also influence a person's blood pressure. Differences between left 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 or obstructive arterial disease.
There is no accepted diagnostic standard for hypotension, although pressures less than 90/60 are commonly regarded as hypotensive. In practice blood pressure is considered too low only if symptoms are present.
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.
The average blood pressure for full-term infants:
|Stage||Approximate age||Systolic BP, mmHg||Diastolic BP, mmHg|
|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|
In children, the normal ranges for blood pressure are lower than for adults and depend on height. Reference blood pressure values have been developed for children in different countries, based on the distribution of blood pressure in children of these countries.
In adults in most societies, systolic blood pressure tends to rise from early adulthood onward, up to at least age 70; diastolic pressure tends to begin to rise at the same time but to start to fall earlier in mid-life, approximately age 55. Mean blood pressure rises from early adulthood, plateauing in mid-life, while pulse pressure rises quite markedly after the age of 40. Consequently, in many older people, systolic blood pressure often exceeds the normal adult range, if the diastolic pressure is in the normal range this is termed isolated systolic hypertension. The rise in pulse pressure with age is attributed to increased stiffness of the arteries. An age-related rise in blood pressure is not considered healthy and is not observed in some isolated unacculturated communities.
|Central venous pressure||3–8|
|Right ventricular pressure||systolic||15–30|
|Pulmonary artery pressure||systolic||15–30|
|Left ventricular pressure||systolic||100–140|
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 vein or in the atria of the heart. It is much less than arterial pressure, with common values of 5 mmHg in the right atrium and 8 mmHg in the left atrium.
Variants of venous pressure include:
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.
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; typically this is of the order of ~7mm Hg.
Levels of arterial pressure put mechanical stress on the arterial walls. Higher pressures increase heart workload and progression of unhealthy tissue growth (atheroma) that develops within the walls of arteries. The higher the pressure, the more stress that is present and the more atheroma tend to progress and the heart muscle tends to thicken, enlarge and become weaker over time.
Persistent hypertension is one of the risk factors for strokes, heart attacks, heart failure and arterial aneurysms, and is the leading cause of chronic kidney failure. Even moderate elevation of arterial pressure leads to shortened life expectancy. 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.
In the past, most attention was paid to diastolic pressure; but nowadays it is recognized that both high systolic pressure and high pulse pressure (the numerical difference between systolic and diastolic pressures) are also risk factors. In some cases, it appears that a decrease in excessive diastolic pressure can actually increase risk, due probably to the increased difference between systolic and diastolic pressures (see the article on pulse pressure). If systolic blood pressure is elevated (>140 mmHg) with a normal diastolic blood pressure (<90 mmHg), it is called "isolated systolic hypertension" and may present a health concern.
For those with heart valve regurgitation, a change in its severity may be associated with a change in diastolic pressure. In a study of people with heart valve regurgitation that compared measurements 2 weeks apart for each person, there was an increased severity of aortic and mitral regurgitation when diastolic blood pressure increased, whereas when diastolic blood pressure decreased, there was a decreased severity.
Causes of low arterial pressure include:
A large fall in blood pressure upon standing (persistent systolic/diastolic blood pressure decrease of >20/10 mm Hg) 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 axon reflex, the 'skeletal muscle pump' and 'respiratory pump'. Together these mechanisms normally stabilize blood pressure within a minute or less. If these compensatory mechanisms fail and arterial pressure and blood 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. Usually this failure of compensation is due to diseases or drugs that affect the sympathetic nervous system. 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.
Normal fluctuation in blood pressure is adaptive and necessary. Fluctuations in pressure that are significantly greater than the norm are associated with greater white matter hyperintensity, a finding consistent with reduced local cerebral blood flow and a heightened risk of cerebrovascular disease. Within both high and low blood pressure groups, a greater degree of fluctuation was found to correlate with an increase in cerebrovascular disease compared to those with less variability, suggesting the consideration of the clinical management of blood pressure fluctuations, even among normotensive older adults. Older individuals and those who had received blood pressure medications were more likely to exhibit larger fluctuations in pressure.
During each heartbeat, blood pressure varies between a maximum (systolic) and a minimum (diastolic) pressure. The blood pressure in the circulation is principally due to the pumping action of the heart. Differences in mean blood pressure drive the flow of blood around the circulation. The rate of mean blood flow depends on both blood pressure and the resistance to flow presented by the blood vessels. In the absence of hydrostatic effects (e.g. standing), mean blood pressure decreases as the circulating blood moves away from the heart through arteries and capillaries due to viscous losses of energy. Mean blood pressure drops over the whole circulation, although most of the fall occurs along the small arteries and arterioles. Pulsatility also diminishes in the smaller elements of the arterial circulation, although some transmitted pulsatility is observed in capillaries.
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.
A simple view of the hemodynamics of systemic arterial pressure is based around mean arterial pressure (MAP) and pulse pressure. Most influences on blood pressure can be understood in terms of their effect on cardiac output and systemic vascular resistance. Cardiac output is the product of stroke volume and heart rate, and stroke volume is influenced by blood volume. In the short-term, the greater the blood volume, the higher the cardiac output. This may explain in part the relationship between dietary salt intake and increased blood pressure, where increased salt intake may increase blood volume potentially resulting in higher arterial pressure. However, this varies with the individual and is highly dependent on autonomic nervous system response and the renin–angiotensin system. In the longer-term the relationship between volume and blood pressure is more complex. In simple terms systemic vascular resistance is mainly determined by the caliber of small arteries and arterioles. The resistance attributable to a blood vessel depends on its radius as described by the Hagen-Poiseuille's equation (resistance∝1/radius4). Hence, 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 number of vessels, particularly the smaller numerous, arterioles and capillaries. The presence of an arterial stenosis increases resistance to flow, however this increase in resistance rarely increases systemic blood pressure because its contribution to total systemic resistance is small, although it may profoundly decrease downstream flow. Substances called vasoconstrictors reduce the caliber of blood vessels, thereby increasing blood pressure. 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. Reductions in capillary density, termed capillary rarefaction, may also contribute to increased resistance in some circumstances.
In practice, each individual's autonomic nervous system and other systems regulating blood pressure, notably the kidney, 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.
In practice, the contribution of CVP (which is small) is generally ignored and so
MAP can be estimated from measurements of the systolic pressure and the diastolic pressure 
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.
The endogenous regulation of arterial pressure is not completely understood, but the following mechanisms of regulating arterial pressure have been well-characterized:
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.
Currently, the RAS is targeted pharmacologically by ACE inhibitors and angiotensin II receptor antagonists, also known as angiotensin receptor blockers (ARBs). The aldosterone system is directly targeted by spironolactone, an aldosterone antagonist. The fluid retention may be targeted by diuretics; the antihypertensive effect of diuretics is due to its effect on blood volume. Generally, the baroreceptor reflex is not targeted in hypertension because if blocked, individuals may suffer from orthostatic hypotension and fainting.
Arterial pressure is most commonly measured via a sphygmomanometer, which uses the height of a column of mercury, or an aneroid gauge, to reflect the blood pressure by auscultation. The most common automated blood pressure measurement technique is based on the oscillometric method. Fully automated oscillometric measurement has been available since 1981. This principle has recently been used to measure blood pressure with a smartphone. Measuring pressure invasively, 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. So-called cuffless measurements, these methods open the door to more comfortable and acceptable blood pressure monitors. See by instance, a cuffless blood pressure monitor at the wrist that uses only optical sensors 
Blood pressure in non-human mammals is similar to human blood pressure. In contrast, heart rate differs markedly, largely depending on the size of the animal (larger animals have slower heart rates). As in humans, blood pressure in animals differs by age, sex, time of day and circumstances: measurements made in laboratories or anesthesia may not be representative of values under free-living conditions. Rats, mice, dogs and rabbits have been used extensively to study the causes of high blood pressure.
|Species||Systolic blood pressure,
|Diastolic blood pressure,
beats per minute
Hypertension in cats and dogs is diagnosed if the blood pressure is greater than 150 mm Hg (systolic) and/or 95 mm Hg (diastolic).
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
Amlodipine, sold under the brand name Norvasc among others, is a medication used to treat high blood pressure and coronary artery disease. While not typically recommended in heart failure, amlodipine may be used if other medications are not sufficient for high blood pressure or heart-related chest pain. Amlodipine is taken by mouth and has an effect for at least a day.Common side effects include swelling, feeling tired, abdominal pain, and nausea. Serious side effects include low blood pressure or a heart attack. Whether use is safe during pregnancy or breastfeeding is unclear. When used by people with liver problems, and in elderly individuals, doses should be decreased. Amlodipine works partly by increasing the size of arteries. It is a long-acting calcium channel blocker of the dihydropyridine (DHP) type.Amlodipine was first patented in 1986 with commercial sale beginning in 1990. It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system. It is available as a generic medication. Wholesale cost in the developing world is US$0.003 to 0.066 per day for a typical dose as of 2015. In the United States, a month's supply costs less than $25. In 2016 it was the 5th most prescribed medication in the United States with more than 75 million prescriptions.Antihypertensive drug
Antihypertensives are a class of drugs that are used to treat hypertension (high blood pressure). Antihypertensive therapy seeks to prevent the complications of high blood pressure, such as stroke and myocardial infarction. Evidence suggests that reduction of the blood pressure by 5 mmHg can decrease the risk of stroke by 34%, of ischaemic heart disease by 21%, and reduce the likelihood of dementia, heart failure, and mortality from cardiovascular disease. There are many classes of antihypertensives, which lower blood pressure by different means. Among the most important and most widely used drugs are thiazide diuretics, calcium channel blockers, ACE inhibitors, angiotensin II receptor antagonists (ARBs), and beta blockers.
Which type of medication to use initially for hypertension has been the subject of several large studies and resulting national guidelines. The fundamental goal of treatment should be the prevention of the important endpoints of hypertension, such as heart attack, stroke and heart failure. Patient age, associated clinical conditions and end-organ damage also play a part in determining dosage and type of medication administered. The several classes of antihypertensives differ in side effect profiles, ability to prevent endpoints, and cost. The choice of more expensive agents, where cheaper ones would be equally effective, may have negative impacts on national healthcare budgets. As of 2018, the best available evidence favors low-dose thiazide diuretics as the first-line treatment of choice for high blood pressure when drugs are necessary. Although clinical evidence shows calcium channel blockers and thiazide-type diuretics are preferred first-line treatments for most people (from both efficacy and cost points of view), an ACE inhibitor is recommended by NICE in the UK for those under 55 years old.Baroreflex
The baroreflex or baroreceptor reflex is one of the body's homeostatic mechanisms that helps to maintain blood pressure at nearly constant levels. The baroreflex provides a rapid negative feedback loop in which an elevated blood pressure reflexively causes the heart rate to decrease and also causes blood pressure to decrease. Decreased blood pressure decreases baroreflex activation and causes heart rate to increase and to restore blood pressure levels. The baroreflex can begin to act in less than the duration of a cardiac cycle (fractions of a second) and thus baroreflex adjustments are key factors in dealing with postural hypotension, the tendency for blood pressure to decrease on standing due to gravity.
The system relies on specialized neurons, known as baroreceptors, in the aortic arch, carotid sinuses, and elsewhere to monitor changes in blood pressure and relay them to the Medulla. Baroreceptors are stretch receptors and respond to the pressure induced stretching of the blood vessel in which they are found. Baroreflex induced changes in blood pressure are mediated by both branches of the autonomic nervous system: the parasympathetic and sympathetic nerves. Baroreceptors are active even at normal blood pressures so that their activity informs the brain about both increases and decreases in blood pressure.
The body contains two other, slower acting systems to regulate blood pressure: the heart releases atrial natriuretic peptide when blood pressure is too high, and the kidneys sense and correct low blood pressure with the renin–angiotensin system.Calcium channel blocker
Calcium channel blockers (CCB), calcium channel antagonists or calcium antagonists are several medications that disrupt the movement of calcium (Ca2+) through calcium channels. Calcium channel blockers are used as antihypertensive drugs, i.e., as medications to decrease blood pressure in patients with hypertension. CCBs are particularly effective against large vessel stiffness, one of the common causes of elevated systolic blood pressure in elderly patients. Calcium channel blockers are also frequently used to alter heart rate, to prevent cerebral vasospasm, and to reduce chest pain caused by angina pectoris.
N-type, L-type, and T-type voltage-dependent calcium channels are present in the zona glomerulosa of the human adrenal gland, and CCBs can directly influence the biosynthesis of aldosterone in adrenocortical cells, with consequent impact on the clinical treatment of hypertension with these agents.CCBs have been shown to be slightly more effective than beta blockers at lowering cardiovascular mortality, but they are associated with more side effects. Potential major risks however were mainly found to be associated with short-acting CCBs.Cardiology
Cardiology (from Greek καρδίᾱ kardiā, "heart" and -λογία -logia, "study") is a branch of medicine dealing with disorders of the heart as well as parts of the circulatory system. The field includes medical diagnosis and treatment of congenital heart defects, coronary artery disease, heart failure, valvular heart disease and electrophysiology. Physicians who specialize in this field of medicine are called cardiologists, a specialty of internal medicine. Pediatric cardiologists are pediatricians who specialize in cardiology. Physicians who specialize in cardiac surgery are called cardiothoracic surgeons or cardiac surgeons, a specialty of general surgery.
Although the cardiovascular system is inextricably linked to blood, cardiology is relatively unconcerned with hematology and its diseases. Some obvious exceptions that affect the function of the heart would be blood tests (electrolyte disturbances, troponins), decreased oxygen carrying capacity (anemia, hypovolemic shock), and coagulopathies.Cardiovascular disease
Cardiovascular disease (CVD) is a class of diseases that involve the heart or blood vessels. CVD includes coronary artery diseases (CAD) such as angina and myocardial infarction (commonly known as a heart attack). Other CVDs include stroke, heart failure, hypertensive heart disease, rheumatic heart disease, cardiomyopathy, heart arrhythmia, congenital heart disease, valvular heart disease, carditis, aortic aneurysms, peripheral artery disease, thromboembolic disease, and venous thrombosis.The underlying mechanisms vary depending on the disease. Coronary artery disease, stroke, and peripheral artery disease involve atherosclerosis. This may be caused by high blood pressure, smoking, diabetes mellitus, lack of exercise, obesity, high blood cholesterol, poor diet, and excessive alcohol consumption, among others. High blood pressure is estimated to account for approximately 13% of CVD deaths, while tobacco accounts for 9%, diabetes 6%, lack of exercise 6% and obesity 5%. Rheumatic heart disease may follow untreated strep throat.It is estimated that up to 90% of CVD may be preventable. Prevention of CVD involves improving risk factors through: healthy eating, exercise, avoidance of tobacco smoke and limiting alcohol intake. Treating risk factors, such as high blood pressure, blood lipids and diabetes is also beneficial. Treating people who have strep throat with antibiotics can decrease the risk of rheumatic heart disease. The use of aspirin in people, who are otherwise healthy, is of unclear benefit.Cardiovascular diseases are the leading cause of death globally. This is true in all areas of the world except Africa. Together CVD resulted in 17.9 million deaths (32.1%) in 2015, up from 12.3 million (25.8%) in 1990. Deaths, at a given age, from CVD are more common and have been increasing in much of the developing world, while rates have declined in most of the developed world since the 1970s. Coronary artery disease and stroke account for 80% of CVD deaths in males and 75% of CVD deaths in females. Most cardiovascular disease affects older adults. In the United States 11% of people between 20 and 40 have CVD, while 37% between 40 and 60, 71% of people between 60 and 80, and 85% of people over 80 have CVD. The average age of death from coronary artery disease in the developed world is around 80 while it is around 68 in the developing world. Diagnosis of disease typically occurs seven to ten years earlier in men as compared to women.Clonidine
Clonidine, sold as the brand name Catapres among others, is a medication used to treat high blood pressure, attention deficit hyperactivity disorder, drug withdrawal (alcohol, opioids, or smoking), menopausal flushing, diarrhea, and certain pain conditions. It is used by mouth, by injection, or as a skin patch. Onset of action is typically within an hour with the effects on blood pressure lasting for up to eight hours.Common side effect include dry mouth, dizziness, headaches, and sleepiness. Severe side effects may include seeing or hearing things that other people do not, heart arrhythmias, and confusion. If rapidly stopped, withdrawal effects may occur. Use during pregnancy or breastfeeding is not recommended. Clonidine lowers blood pressure by stimulating α2 receptors in the brain, which results in relaxation of many arteries.Clonidine came into medical use in 1966. It is available as a generic medication. As of 2019 a month of medication costs the NHS about 8£. In the United States this amount costs about US$2.70 as of 2019. In 2016 it was the 76th most prescribed medication in the United States with more than 10 million prescriptions.Hemodynamics
Hemodynamics or hæmodynamics is the dynamics of blood flow. The circulatory system is controlled by homeostatic mechanisms, such as hydraulic circuits are controlled by control systems. Hemodynamic response continuously monitors and adjusts to conditions in the body and its environment. Thus hemodynamics explains the physical laws that govern the flow of blood in the blood vessels.
Blood flow ensures the transportation of nutrients, hormones, metabolic wastes, O2 and CO2 throughout the body to maintain cell-level metabolism, the regulation of the pH, osmotic pressure and temperature of the whole body, and the protection from microbial and mechanical harms.Blood is a non-Newtonian fluid, best studied using rheology rather than hydrodynamics. Blood vessels are not rigid tubes, so classic hydrodynamics and fluids mechanics based on the use of classical viscometers are not capable of explaining hemodynamics.The study of the blood flow is called hemodynamics. The study of the properties of the blood flow is called hemorheology.Hypertension
Hypertension (HTN or HT), also known as high blood pressure (HBP), is a long-term medical condition in which the blood pressure in the arteries is persistently elevated. High blood pressure typically does not cause symptoms. Long-term high blood pressure, however, is a major risk factor for coronary artery disease, stroke, heart failure, atrial fibrillation, peripheral vascular disease, vision loss, chronic kidney disease, and dementia.High blood pressure is classified as either primary (essential) high blood pressure or secondary high blood pressure. About 90–95% of cases are primary, defined as high blood pressure due to nonspecific lifestyle and genetic factors. Lifestyle factors that increase the risk include excess salt in the diet, excess body weight, smoking, and alcohol use. The remaining 5–10% of cases are categorized as secondary high blood pressure, defined as high blood pressure due to an identifiable cause, such as chronic kidney disease, narrowing of the kidney arteries, an endocrine disorder, or the use of birth control pills.Blood pressure is expressed by two measurements, the systolic and diastolic pressures, which are the maximum and minimum pressures, respectively. For most adults, normal blood pressure at rest is within the range of 100–130 millimeters mercury (mmHg) systolic and 60–80 mmHg diastolic. For most adults, high blood pressure is present if the resting blood pressure is persistently at or above 130/80 or 140/90 mmHg. Different numbers apply to children. Ambulatory blood pressure monitoring over a 24-hour period appears more accurate than office-based blood pressure measurement.Lifestyle changes and medications can lower blood pressure and decrease the risk of health complications. Lifestyle changes include weight loss, physical exercise, decreased salt intake, reducing alcohol intake, and a healthy diet. If lifestyle changes are not sufficient then blood pressure medications are used. Up to three medications can control blood pressure in 90% of people. The treatment of moderately high arterial blood pressure (defined as >160/100 mmHg) with medications is associated with an improved life expectancy. The effect of treatment of blood pressure between 130/80 mmHg and 160/100 mmHg is less clear, with some reviews finding benefit and others finding unclear benefit. High blood pressure affects between 16 and 37% of the population globally. In 2010 hypertension was believed to have been a factor in 18% of all deaths (9.4 million globally).Hypotension
Hypotension is low blood pressure, especially in the arteries of the systemic circulation. Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood. A systolic blood pressure of less than 90 millimeters of mercury (mm Hg) or diastolic of less than 60 mm Hg is generally considered to be hypotension. However, in practice, blood pressure is considered too low only if noticeable symptoms are present.Hypotension is the opposite of hypertension, which is high blood pressure. It is best understood as a physiological state, rather than a disease. Severely low blood pressure can deprive the brain and other vital organs of oxygen and nutrients, leading to a life-threatening condition called shock.
For some people who exercise and are in top physical condition, low blood pressure is a sign of good health and fitness. A single session of exercise can induce hypotension and water-based exercise can induce important hypotension response.
For many people, excessively low blood pressure can cause dizziness and fainting or indicate serious heart, endocrine or neurological disorders.
Treatment of hypotension may include the use of intravenous fluids or vasopressors. When using vasopressors, trying to achieve a mean arterial pressure (MAP) of greater than 70 mm Hg does not appear to result in better outcomes than trying to achieve a MAP of greater than 65 mm Hg in adults.Intracerebral hemorrhage
Intracerebral hemorrhage (ICH), also known as cerebral bleed, is a type of intracranial bleed that occurs within the brain tissue or ventricles. Symptoms can include headache, one-sided weakness, vomiting, seizures, decreased level of consciousness, and neck stiffness. Often symptoms get worse over time. Fever is also common. In many cases bleeding is present in both the brain tissue and the ventricles.Causes include brain trauma, aneurysms, arteriovenous malformations, and brain tumors. The largest risk factors for spontaneous bleeding are high blood pressure and amyloidosis. Other risk factors include alcoholism, low cholesterol, blood thinners, and cocaine use. Diagnosis is typically by CT scan. Other conditions that may present similarly include ischemic stroke.Treatment should typically be carried out in an intensive care unit. Guidelines recommended decreasing the blood pressure to a systolic of 140 mmHg. Blood thinners should be reversed if possible and blood sugar kept in the normal range. Surgery to place a ventricular drain may be used to treat hydrocephalus but corticosteroids should not be used. Surgery to remove the blood is useful in certain cases.Cerebral bleeding affects about 2.5 per 10,000 people each year. It occurs more often in males and older people. About 44% of those affected die within a month. A good outcome occurs in about 20% of those affected. Strokes were first divided into their two major types, bleeding and insufficient blood flow, in 1823.Kidney failure
Kidney failure, also known as end-stage kidney disease, is a medical condition in which the kidneys no longer function. It is divided into acute kidney failure (cases that develop rapidly) and chronic kidney failure (those that are long term). Symptoms may include leg swelling, feeling tired, vomiting, loss of appetite, or confusion. Complications of acute disease may include uremia, high blood potassium, or volume overload. Complications of chronic disease may include heart disease, high blood pressure, or anemia.Causes of acute kidney failure include low blood pressure, blockage of the urinary tract, certain medications, muscle breakdown, and hemolytic uremic syndrome. Causes of chronic kidney failure include diabetes, high blood pressure, nephrotic syndrome, and polycystic kidney disease. Diagnosis of acute disease is often based on a combination of factors such as decrease urine production or increased serum creatinine. Diagnosis of chronic disease is typically based on a glomerular filtration rate (GFR) of less than 15 or the need for renal replacement therapy. It is also equivalent to stage 5 chronic kidney disease.Treatment of acute disease typically depends on the underlying cause. Treatment of chronic disease may include hemodialysis, peritoneal dialysis, or a kidney transplant. Hemodialysis uses a machine to filter the blood outside the body. In peritoneal dialysis specific fluid is placed into the abdominal cavity and then drained, with this process being repeated multiple times per day. Kidney transplantation involves surgically placing a kidney from someone else and then taking immunosuppressant medication to prevent rejection. Other recommended measures from chronic disease include staying active and specific dietary changes.In the United States acute disease affects about 3 per 1,000 people a year. Chronic disease affects about 1 in 1,000 people with 3 per 10,000 people newly develop the condition each year. Acute disease is often reversible while chronic disease often is not. With appropriate treatment many with chronic disease can continue working.Losartan
Losartan, sold under the trade name Cozaar among others, is a medication mainly used to treat high blood pressure. Other uses include for diabetic kidney disease, heart failure, and left ventricular enlargement. It is taken by mouth. It may be used together with other blood pressure medication. Up to six weeks may be required for the full effects to occur.Common side effects include muscle cramps, stuffy nose, cough, and high blood potassium. Severe side effects may include angioedema, low blood pressure, and kidney problems. Use during pregnancy may result in harm to the baby. Use is not recommended during breastfeeding. It is in the angiotensin II receptor antagonist family of medication and works by blocking angiotensin II.Losartan was approved for medical use in the United States in 1995. It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system. It is available as a generic medication. The wholesale cost in the developing world is about US$0.28–3.45 per month as of 2015. In the United States, as of 2017, the wholesale cost of a typical dose is $1.13 per month. In 2016 it was the 9th most prescribed medication in the United States with more than 49 million prescriptions. A version combined with hydrochlorothiazide is available.Orthostatic hypotension
Orthostatic hypotension, also known as postural hypotension, occurs when a person's blood pressure falls when suddenly standing up from a lying or sitting position. It is defined as a fall in systolic blood pressure of at least 20 mm Hg or diastolic blood pressure of at least 10 mm Hg when a person assumes a standing position. It occurs predominantly by delayed constriction of the lower body blood vessels, which is normally required to maintain an adequate blood pressure when changing position to standing. As a result, blood pools in the blood vessels of the legs for a longer period and less is returned to the heart, thereby leading to a reduced cardiac output. Mild orthostatic hypotension is common and can occur briefly in anyone, although it is prevalent in particular among the elderly and those with known low blood pressure. Severe drops in blood pressure can lead to fainting, with a possibility of injury.
There are numerous possible causes for orthostatic hypotension, such as certain medications (e.g. alpha blockers), autonomic neuropathy, decreased blood volume, and age-related blood vessel stiffness.
Apart from addressing the underlying cause, orthostatic hypotension may be treated with a recommendation to increase salt and water intake (to increase the blood volume), wearing compression stockings, and sometimes medication (fludrocortisone, midodrine or others).Pre-eclampsia
Pre-eclampsia (PE) is a disorder of pregnancy characterized by the onset of high blood pressure and often a significant amount of protein in the urine. When it arises, the condition begins after 20 weeks of pregnancy. In severe disease there may be red blood cell breakdown, a low blood platelet count, impaired liver function, kidney dysfunction, swelling, shortness of breath due to fluid in the lungs, or visual disturbances. Pre-eclampsia increases the risk of poor outcomes for both the mother and the baby. If left untreated, it may result in seizures at which point it is known as eclampsia.Risk factors for pre-eclampsia include obesity, prior hypertension, older age, and diabetes mellitus. It is also more frequent in a woman's first pregnancy and if she is carrying twins. The underlying mechanism involves abnormal formation of blood vessels in the placenta amongst other factors. Most cases are diagnosed before delivery. Rarely, pre-eclampsia may begin in the period after delivery. While historically both high blood pressure and protein in the urine were required to make the diagnosis, some definitions also include those with hypertension and any associated organ dysfunction. Blood pressure is defined as high when it is greater than 140 mmHg systolic or 90 mmHg diastolic at two separate times, more than four hours apart in a woman after twenty weeks of pregnancy. Pre-eclampsia is routinely screened for during prenatal care.Recommendations for prevention include: aspirin in those at high risk, calcium supplementation in areas with low intake, and treatment of prior hypertension with medications. In those with pre-eclampsia delivery of the baby and placenta is an effective treatment. When delivery becomes recommended depends on how severe the pre-eclampsia and how far along in pregnancy a woman is. Blood pressure medication, such as labetalol and methyldopa, may be used to improve the mother's condition before delivery. Magnesium sulfate may be used to prevent eclampsia in those with severe disease. Bedrest and salt intake have not been found to be useful for either treatment or prevention.Pre-eclampsia affects 2–8% of pregnancies worldwide. Hypertensive disorders of pregnancy (which include pre-eclampsia) are one of the most common causes of death due to pregnancy. They resulted in 46,900 deaths in 2015. Pre-eclampsia usually occurs after 32 weeks; however, if it occurs earlier it is associated with worse outcomes. Women who have had pre-eclampsia are at increased risk of heart disease and stroke later in life. The word "eclampsia" is from the Greek term for lightning. The first known description of the condition was by Hippocrates in the 5th century BC.Renin–angiotensin system
The renin–angiotensin system (RAS), or renin–angiotensin–aldosterone system (RAAS), is a hormone system that regulates blood pressure and fluid balance.
When renal blood flow is reduced, juxtaglomerular cells in the kidneys convert the precursor prorenin (already present in the blood) into renin and secrete it directly into circulation. Plasma renin then carries out the conversion of angiotensinogen, released by the liver, to angiotensin I. Angiotensin I is subsequently converted to angiotensin II by the angiotensin-converting enzyme (ACE) found on the surface of vascular endothelial cells, predominantly those of the lungs. Angiotensin II is a potent vasoconstrictive peptide that causes blood vessels to narrow, resulting in increased blood pressure. Angiotensin II also stimulates the secretion of the hormone aldosterone from the adrenal cortex. Aldosterone causes the renal tubules to increase the reabsorption of sodium and water into the blood, while at the same time causing the excretion of potassium (to maintain electrolyte balance). This increases the volume of extracellular fluid in the body, which also increases blood pressure.
If the RAS is abnormally active, blood pressure will be too high. There are many drugs that interrupt different steps in this system to lower blood pressure. These drugs are one of the primary ways to control high blood pressure, heart failure, kidney failure, and harmful effects of diabetes.Sepsis
Sepsis is a life-threatening condition that arises when the body's response to infection causes injury to its own tissues and organs. Common signs and symptoms include fever, increased heart rate, increased breathing rate, and confusion. There may also be symptoms related to a specific infection, such as a cough with pneumonia, or painful urination with a kidney infection. In the very young, old, and people with a weakened immune system, there may be no symptoms of a specific infection and the body temperature may be low or normal, rather than high. Severe sepsis is sepsis causing poor organ function or insufficient blood flow. Insufficient blood flow may be evident by low blood pressure, high blood lactate, or low urine output. Septic shock is low blood pressure due to sepsis that does not improve after fluid replacement.Sepsis is caused by an inflammatory immune response triggered by an infection. Most commonly, the infection is bacterial, but it may also be fungal, viral, or protozoan. Common locations for the primary infection include the lungs, brain, urinary tract, skin, and abdominal organs. Risk factors include very young age, older age, a weakened immune system from conditions such as cancer or diabetes, major trauma, or burns. An older method of diagnosis was based on meeting at least two systemic inflammatory response syndrome (SIRS) criteria due to a presumed infection. In 2016, SIRS was replaced with a shortened sequential organ failure assessment score (SOFA score) known as the quick SOFA score (qSOFA) which is two of the following three: increased breathing rate, change in level of consciousness, and low blood pressure. Blood cultures are recommended preferably before antibiotics are started, however, infection of the blood is not required for the diagnosis. Medical imaging should be used to look for the possible location of infection. Other potential causes of similar signs and symptoms include anaphylaxis, adrenal insufficiency, low blood volume, heart failure, and pulmonary embolism.Sepsis is usually treated with intravenous fluids and antibiotics. Typically, antibiotics are given as soon as possible. Often, ongoing care is performed in an intensive care unit. If fluid replacement is not enough to maintain blood pressure, medications that raise blood pressure may be used. Mechanical ventilation and dialysis may be needed to support the function of the lungs and kidneys, respectively. To guide treatment, a central venous catheter and an arterial catheter may be placed for access to the bloodstream. Other measurements such as cardiac output and superior vena cava oxygen saturation may be used. People with sepsis need preventive measures for deep vein thrombosis, stress ulcers and pressure ulcers, unless other conditions prevent such interventions. Some might benefit from tight control of blood sugar levels with insulin. The use of corticosteroids is controversial. Drotrecogin alfa, originally marketed for severe sepsis, has not been found to be helpful, and was withdrawn from sale in 2011.Disease severity partly determines the outcome. The risk of death from sepsis is as high as 30%, from severe sepsis as high as 50%, and from septic shock as high as 80%. The number of cases worldwide is unknown as there is little data from the developing world. Estimates suggest sepsis affects millions of people a year. In the developed world approximately 0.2 to 3 people per 1000 are affected by sepsis yearly, resulting in about a million cases per year in the United States. Rates of disease have been increasing. Sepsis is more common among males than females. The medical condition has been described since the time of Hippocrates. The terms "septicemia" and "blood poisoning" have been used in various ways and are no longer recommended.Shock (circulatory)
Shock is the state of not enough blood flow to the tissues of the body as a result of problems with the circulatory system. Initial symptoms may include weakness, fast heart rate, fast breathing, sweating, anxiety, and increased thirst. This may be followed by confusion, unconsciousness, or cardiac arrest as complications worsen.Shock is divided into four main types based on the underlying cause: low volume, cardiogenic, obstructive, and distributive shock. Low volume shock may be from bleeding, vomiting, or pancreatitis. Cardiogenic shock may be due to a heart attack or cardiac contusion. Obstructive shock may be due to cardiac tamponade or a tension pneumothorax. Distributed shock may be due to sepsis, spinal cord injury, or certain overdoses.The diagnosis is generally based on a combination of symptoms, physical examination, and laboratory tests. A decreased pulse pressure (systolic blood pressure minus diastolic blood pressure) or a fast heart rate raises concerns. The heart rate divided by systolic blood pressure, known as the shock index (SI), of greater than 0.8 supports the diagnosis more than low blood pressure or a fast heart rate in isolation.Treatment of shock is based on the likely underlying cause. An open airway and sufficient breathing should be established. Any ongoing bleeding should be stopped, which may require surgery or embolization. Intravenous fluid, such as Ringer's lactate or packed red blood cells, is often given. Efforts to maintain a normal body temperature are also important. Vasopressors may be useful in certain cases. Shock is both common and has a high risk of death. In the United States about 1.2 million people present to the emergency room each year with shock and their risk of death is between 20 and 50%.Sphygmomanometer
A sphygmomanometer, also known as a blood pressure meter, blood pressure monitor, or blood pressure gauge, is a device used to measure blood pressure, composed of an inflatable cuff to collapse and then release the artery under the cuff in a controlled manner, and a mercury or mechanical manometer to measure the pressure. It is always used in conjunction with a means to determine at what pressure blood flow is just starting, and at what pressure it is unimpeded. Manual sphygmomanometers are used in conjunction with a stethoscope.
A sphygmomanometer consists of an inflatable cuff, a measuring unit (the mercury manometer, or aneroid gauge), and a mechanism for inflation which may be a manually operated bulb and valve or a pump operated electrically.