In medicine

Medicine

Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....

, ischemia (from Greek

Greek language

Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 ισχαιμία, ischaimía; isch- root denoting a restriction or thinning or to make or grow thin/lean, haema blood

Blood

Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....

) is a restriction in blood supply, generally due to factors in the blood vessel

Blood vessel

The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...

s, with resultant damage or dysfunction of tissue. It may also be spelled ischaemia or ischæmia. It also means local anemia in a given part of a body sometimes resulting from congestion (such as vasoconstriction

Vasoconstriction

Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, particularly the large arteries, small arterioles and veins. The process is the opposite of vasodilation, the widening of blood vessels. The process is particularly important in...

, thrombosis

Thrombosis

Thrombosis is the formation of a blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel is injured, the body uses platelets and fibrin to form a blood clot to prevent blood loss...

 or embolism

Embolism

In medicine, an embolism is the event of lodging of an embolus into a narrow capillary vessel of an arterial bed which causes a blockage in a distant part of the body.Embolization is...

).

Ischemic means having or showing symptoms of ischemia, while nonischemic means "not related to or showing signs of ischemia".

Mechanism

Rather than hypoxia

Hypoxia (medical)

Hypoxia, or hypoxiation, is a pathological condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise...

 (a more general term denoting a shortage of oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

, usually a result of lack of oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 in the air being breathed), ischemia is an absolute or relative shortage of the blood supply to an organ, i.e. a shortage of oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

, glucose

Glucose

Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...

 and other blood-borne fuels. A relative shortage means the mismatch of blood supply (oxygen/fuel delivery) and blood request for adequate metabolism of tissue. Ischemia results in tissue damage because of a lack of oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 and nutrients http://www.ncbi.nlm.nih.gov/pubmed/19751827. Ultimately, this can cause severe damage because of the potential for a build-up of metabolic wastes.

Ischemia can also be described as an inadequate flow of blood to a part of the body, caused by constriction or blockage of the blood vessels supplying it. Ischemia of heart muscle produces angina pectoris.

This can be due to

• Atherosclerosis
  Atherosclerosis
  Atherosclerosis is a condition in which an artery wall thickens as a result of the accumulation of fatty materials such as cholesterol...
  
   (lipid-laden plaques obstructing the lumen
  Lumen
  Lumen can mean:* Lumen , the SI unit of luminous flux* Lumen , the cavity or channel within a tubular structure* Thylakoid lumen, the inner membrane space of the chloroplast* Phenobarbital...
  
   of arteries
  Artery
  Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries....
  
  )
• Hypoglycemia
  Hypoglycemia
  Hypoglycemia or hypoglycæmia is the medical term for a state produced by a lower than normal level of blood glucose. The term literally means "under-sweet blood"...
  
   (lower than normal level of glucose)
• Tachycardia
  Tachycardia
  Tachycardia comes from the Greek words tachys and kardia . Tachycardia typically refers to a heart rate that exceeds the normal range for a resting heart rate...
  
   (abnormally rapid beating of the heart
  Heart
  The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
  
  )
• Hypotension
  Hypotension
  In physiology and medicine, hypotension is abnormally low blood pressure, especially in the arteries of the systemic circulation. It is best understood as a physiologic state, rather than a disease. It is often associated with shock, though not necessarily indicative of it. Hypotension is the...
  
   (low blood pressure, e.g. in septic shock
  Septic shock
  Septic shock is a medical emergency caused by decreased tissue perfusion and oxygen delivery as a result of severe infection and sepsis, though the microbe may be systemic or localized to a particular site. It can cause multiple organ dysfunction syndrome and death...
  
  , heart failure)
• Thromboembolism (blood clots)
• Outside compression of a blood vessel, e.g. by a tumor
  Tumor
  A tumor or tumour is commonly used as a synonym for a neoplasm that appears enlarged in size. Tumor is not synonymous with cancer...
  
   or in the case of superior mesenteric artery syndrome
  Superior mesenteric artery syndrome
  Superior mesenteric artery syndrome is a very rare, life-threatening gastro-vascular disorder characterized by a compression of the third portion of the duodenum by the abdominal aorta and the overlying superior mesenteric artery...
  
  
• Embolism
  Embolism
  In medicine, an embolism is the event of lodging of an embolus into a narrow capillary vessel of an arterial bed which causes a blockage in a distant part of the body.Embolization is...
  
   (foreign bodies in the circulation, e.g. amniotic fluid embolism
  Amniotic fluid embolism
  Amniotic fluid embolism is a rare and incompletely understood obstetric emergency in which amniotic fluid, fetal cells, hair, or other debris enters the mother's blood stream via the placental bed of the uterus and triggers an allergic reaction. This reaction then results in cardiorespiratory ...
  
  )
• Sickle cell disease (abnormally shaped red blood cells)
• Induced g-force
  G-force
  The g-force associated with an object is its acceleration relative to free-fall. This acceleration experienced by an object is due to the vector sum of non-gravitational forces acting on an object free to move. The accelerations that are not produced by gravity are termed proper accelerations, and...
  
  s which restrict the blood flow and force the blood to the extremities of the body, as in acrobatics and military flying
• Localized extreme cold, such as by frostbite
  Frostbite
  Frostbite is the medical condition where localized damage is caused to skin and other tissues due to extreme cold. Frostbite is most likely to happen in body parts farthest from the heart and those with large exposed areas...
  
   or improper cold compression therapy
  Cold compression therapy
  Cold Compression Therapy combines two of the principles of R.I.C.E. to reduce pain and swelling from a sports or activity injury to soft tissues and recommended by orthopedic surgeons following surgery...
  
  
• Tourniquet application
• An increased level of glutamate receptor
  Glutamate receptor
  Glutamate receptors are synaptic receptors located primarily on the membranes of neuronal cells. Glutamate is one of the 20 amino acids used to assemble proteins and as a result is abundant in many areas of the body, but it also functions as a neurotransmitter and is particularly abundant in the...
  
   stimulation
• arteriovenous malformation
  Arteriovenous malformation
  Arteriovenous malformation or AVM is an abnormal connection between veins and arteries, usually congenital. This pathology is widely known because of its occurrence in the central nervous system, but can appear in any location. An arteriovenous malformation is a vascular anomaly. It is a...
  
  s, and peripheral artery occlusive disease
  Peripheral artery occlusive disease
  Peripheral vascular disease , commonly referred to as peripheral arterial disease or peripheral artery occlusive disease , refers to the obstruction of large arteries not within the coronary, aortic arch vasculature, or brain. PVD can result from atherosclerosis, inflammatory processes leading to...
  
  .

The heart

Heart

The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...

, the kidney

Kidney

The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...

s, and the brain

Brain

The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...

 are among the organs that are the most quickly damaged by loss of blood flow for any period of time.

Consequences

Since oxygen is mainly bound to hemoglobin

Hemoglobin

Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates, with the exception of the fish family Channichthyidae, as well as the tissues of some invertebrates...

 in red blood cell

Red blood cell

Red blood cells are the most common type of blood cell and the vertebrate organism's principal means of delivering oxygen to the body tissues via the blood flow through the circulatory system...

s, insufficient blood supply causes tissue to become hypoxic, or, if no oxygen is supplied at all, anoxic

Hypoxia (medical)

Hypoxia, or hypoxiation, is a pathological condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise...

. In very aerobic tissues such as heart and brain, at body temperature necrosis

Necrosis

Necrosis is the premature death of cells in living tissue. Necrosis is caused by factors external to the cell or tissue, such as infection, toxins, or trauma. This is in contrast to apoptosis, which is a naturally occurring cause of cellular death...

 due to ischemia usually takes about 3–4 minutes before becoming irreversible. Administration of "clot-buster" drugs such as Alteplase (given for stroke and heart attack) within this time period, together with some collateral circulation to the ischemic area is a main factor in patient recoveries. However, complete cessation of oxygenation of such organs for more than 20 minutes typically results in irreversible damage.

Ischemia is a feature of heart disease

Heart disease

Heart disease, cardiac disease or cardiopathy is an umbrella term for a variety of diseases affecting the heart. , it is the leading cause of death in the United States, England, Canada and Wales, accounting for 25.4% of the total deaths in the United States.-Types:-Coronary heart disease:Coronary...

s, transient ischemic attack

Transient ischemic attack

A transient ischemic attack is a transient episode of neurologic dysfunction caused by ischemia – either focal brain, spinal cord or retinal – without acute infarction...

s, cerebrovascular accident

Stroke

A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...

s, ruptured sensitive to inadequate blood supply. Ischemia in brain tissue, for example due to stroke or head injury

Traumatic brain injury

Traumatic brain injury , also known as intracranial injury, occurs when an external force traumatically injures the brain. TBI can be classified based on severity, mechanism , or other features...

, causes a process called the ischemic cascade

Ischemic cascade

The ischemic cascade is a series of biochemical reactions that are initiated in the brain and other aerobic tissues after seconds to minutes of ischemia . This is typically secondary to stroke, injury, or cardiac arrest due to heart attack. Most ischemic neurons that die do so due to the...

 to be unleashed, in which proteolytic

Proteolysis

Proteolysis is the directed degradation of proteins by cellular enzymes called proteases or by intramolecular digestion.-Purposes:Proteolysis is used by the cell for several purposes...

 enzymes, reactive oxygen species

Reactive oxygen species

Reactive oxygen species are chemically reactive molecules containing oxygen. Examples include oxygen ions and peroxides. Reactive oxygen species are highly reactive due to the presence of unpaired valence shell electrons....

, and other harmful chemicals damage and may ultimately kill brain tissue.

Restoration of blood flow after a period of ischemia can actually be more damaging than the ischemia. Reintroduction of oxygen causes a greater production of damaging free radicals

Radical (chemistry)

Radicals are atoms, molecules, or ions with unpaired electrons on an open shell configuration. Free radicals may have positive, negative, or zero charge...

 as well as allowing, via removal of the extracellular acidotic

Acidosis

Acidosis is an increased acidity in the blood and other body tissue . If not further qualified, it usually refers to acidity of the blood plasma....

 conditions, influx of calcium and thus calcium overloading. Overall this results in reperfusion injury

Reperfusion injury

Reperfusion injury is the tissue damage caused when blood supply returns to the tissue after a period of ischemia or lack of oxygen. The absence of oxygen and nutrients from blood during the ischemic period creates a condition in which the restoration of circulation results in inflammation and...

 which can result in potentially fatal cardiac arrhythmias, also necrosis can be greatly accelerated.

Variations

There are various types of ischemia, organized by the organ experiencing the ischemic insult. The mechanism of ischemia may differ based on the organ involved.

Cardiac ischemia

Cardiac ischemia may be asymptomatic or may cause chest pain, known as angina pectoris. It occurs when the heart muscle, or myocardium, receives insufficient blood flow. This most frequently results from atherosclerosis

Atherosclerosis

Atherosclerosis is a condition in which an artery wall thickens as a result of the accumulation of fatty materials such as cholesterol...

, which is the long-term accumulation of cholesterol-rich plaques in the coronary arteries. Ischemic heart disease is the most common cause of death in most Western countries and a major cause of hospital admissions.

Bowel

Both large and small bowel can be affected by ischemia. Ischemia of the large intestine

Large intestine

The large intestine is the third-to-last part of the digestive system — — in vertebrate animals. Its function is to absorb water from the remaining indigestible food matter, and then to pass useless waste material from the body...

 may result in an inflammatory process known as ischemic colitis

Ischemic colitis

Ischemic colitis is a medical condition in which inflammation and injury of the large intestine result from inadequate blood supply. Although uncommon in the general population, ischemic colitis occurs with greater frequency in the elderly, and is the most common form of bowel ischemia...

. Ischemia of the small bowel is called mesenteric ischemia

Mesenteric ischemia

Mesenteric ischemia is a medical condition in which inflammation and injury of the small intestine result from inadequate blood supply. Causes of the reduced blood flow can include changes in the systemic circulation or local factors such as constriction of blood vessels or a blood clot...

.

Brain

Brain ischemia is insufficient blood flow to the brain

Brain

The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...

, and can be acute (i.e., rapid) or chronic (i.e., long-lasting). Acute ischemic stroke is a neurologic emergency that may be reversible if treated rapidly. Chronic ischemia of the brain may result in a form of dementia

Dementia

Dementia is a serious loss of cognitive ability in a previously unimpaired person, beyond what might be expected from normal aging...

 called vascular dementia.

Limb

Lack of blood flow to a limb results in acute limb ischemia.

Cutaneous

Reduced blood flow to the skin layers may result in mottling or uneven, patchy discoloration of the skin

See also

• Cerebral ischemia
  Cerebral ischemia
  Brain ischemia, also known as cerebral ischemia, is a condition in which there is insufficient blood flow to the brain to meet metabolic demand. This leads to poor oxygen supply or cerebral hypoxia and thus to the death of brain tissue or cerebral infarction / ischemic stroke...
  
  
• Infarction
  Infarction
  In medicine, infarction refers to tissue death that is caused by a local lack of oxygen due to obstruction of the tissue's blood supply. The resulting lesion is referred to as an infarct.-Causes:...
  
  
• Inhibitor protein
  Inhibitor protein
  The inhibitor protein is situated in the mitochondrial matrix and protects the cell against rapid ATP hydrolysis during momentary ischaemia. In oxygen absence, the pH of the matrix drops...
  
  
• Ischemic cascade
  Ischemic cascade
  The ischemic cascade is a series of biochemical reactions that are initiated in the brain and other aerobic tissues after seconds to minutes of ischemia . This is typically secondary to stroke, injury, or cardiac arrest due to heart attack. Most ischemic neurons that die do so due to the...
  
  
• Reperfusion injury
  Reperfusion injury
  Reperfusion injury is the tissue damage caused when blood supply returns to the tissue after a period of ischemia or lack of oxygen. The absence of oxygen and nutrients from blood during the ischemic period creates a condition in which the restoration of circulation results in inflammation and...
  
  
• Trauma triad of death