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Ischemia
 
 
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In medicine
Medicine

Medicine is the art and science of healing. It encompasses a range of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
, ischemia (Greek
Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
 ?s?a?µ?a, isch- is restriction, hema or haema is blood
Blood

Blood is a specialized bodily fluid that delivers necessary substances to the body's Cell s ? such as nutrients and oxygen ? and transports 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 transport blood throughout the body. There are three major types of blood vessels: the artery, which carry the blood away from the heart, the capillary, which enable the actual exchange of water and chemicals between the blood and the tissues; and the veins, which carry blood from...
s, with resultant damage or dysfunction of tissue. It may also be spelled ischaemia or ischæmia.

er than in hypoxia
Hypoxia (medical)

Hypoxia is a Pathology 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 (usually a result of lack of oxygen in the air being breathed), ischemia is an absolute or relative shortage of the blood supply to an organ.






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In medicine
Medicine

Medicine is the art and science of healing. It encompasses a range of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
, ischemia (Greek
Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
 ?s?a?µ?a, isch- is restriction, hema or haema is blood
Blood

Blood is a specialized bodily fluid that delivers necessary substances to the body's Cell s ? such as nutrients and oxygen ? and transports 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 transport blood throughout the body. There are three major types of blood vessels: the artery, which carry the blood away from the heart, the capillary, which enable the actual exchange of water and chemicals between the blood and the tissues; and the veins, which carry blood from...
s, with resultant damage or dysfunction of tissue. It may also be spelled ischaemia or ischæmia.

Mechanism

Rather than in hypoxia
Hypoxia (medical)

Hypoxia is a Pathology 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 (usually a result of lack of oxygen in the air being breathed), ischemia is an absolute or relative shortage of the blood supply to an organ. Relative shortage means the mismatch of blood supply (oxygen delivery) and blood request for adequate oxygenation of tissue. Ischemia results in tissue damage because of a lack of oxygen and nutrients. Ultimately, this causes great damage because of a buildup 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
  • Tachycardia
    Tachycardia

    The word tachycardia comes from the Greek words tachys and kardia .Tachycardia typically refers to a heartrate that exceeds the range of the normal resting heartrate, based upon age:...
     (abnormally rapid beating of the heart
    Heart

    The heart is a muscle organ in all vertebrates responsible for pumping blood through the blood vessels by repeated, rhythmic contractions, or a similar structure in annelids, mollusks, and arthropods....
    )
  • Atherosclerosis
    Atherosclerosis

    Atherosclerosis is a syndrome affecting artery blood vessels. It is a chronic inflammatory response in the walls of arteries, in large part due to the accumulation of macrophage white blood cells and promoted by low density lipoproteins without adequate removal of fats and cholesterol from the macrophages by functional high density lipoprot...
     (lipid-laden plaques obstructing the lumen of arteries
    Artery

    Arteries are blood vessels that carry blood away from the heart. All arteries, with the exception of the pulmonary and umbilical arteries, carry oxygenated blood....
    )
  • Hypotension
    Hypotension

    In physiology and medicine, hypotension refers to an abnormally low blood pressure. This is best understood as a physiologic state, rather than a disease....
     (low blood pressure, e.g. in septic shock
    Septic shock

    Septic shock is a serious medicine condition caused by decreased tissue perfusion and oxygen delivery as a result of infection and sepsis, though the microbe may be systemic or localized to a particular site....
    , heart failure)
  • Thromboembolism (blood clots)
  • Outside compression of a blood vessel, e.g. by a tumor
    Tumor

    A tumor or tumour is the name for a swelling or lesion formed by an abnormal growth of cells . Tumor is not synonymous with cancer. A tumor can be Benign neoplasm, Carcinoma in situ or malignant, whereas cancer is by definition malignant....
  • Embolism
    Embolism

    In medicine, an embolism occurs when an object migrates from one part of the body and causes a blockage of a blood vessel in another part of the body....
     (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....
    )
  • Sickle cell disease (abnormally shaped hemoglobin)
  • Induced g-force
    G-force

    The g-force of an object is its acceleration relative to free-fall. The unit of measure used is informally but commonly known as the "gee" , symbolized as g . An acceleration of 1 g is generally considered as equal to standard gravity , which is defined as precisely metre per second square...
    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 wherein localized damage is caused to skin and other biological tissue due to extreme cold.Frostbite is most likely to happen in body parts farthest from the heart and those with large exposed areas....
    , ice
    Ice

    Ice is a solid phases of matter, usually crystalline solid, of a non-metallic substance that is liquid or gas at room temperature, such as ammonia ice or methane ice....
    , or improper Cold compression therapy
    Cold compression therapy

    Cold Compression Therapy combines two of the principles of RICE to reduce pain and swelling from a sports or activity injury to soft tissues. The therapy is especially useful for sprains, strains, pulled muscles and pulled ligaments....


Consequences

Since oxygen is mainly bound to hemoglobin
Hemoglobin

Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of vertebrates, and 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 body's principal means of delivering oxygen to the body tissues via the blood....
s, insufficient blood supply causes tissue to become hypoxic, or, if no oxygen is supplied at all, anoxic
Hypoxia (medical)

Hypoxia is a Pathology 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....
. This can cause oncosis (i.e. cell death by lysis). In very aerobic tissues such as heart and brain, at body temperature necrosis
Necrosis

Necrosis is the name given to premature death of cell s and living biological tissue. Necrosis is caused by external factors, such as infection, toxins, or trauma....
 due to ischemia usually takes about 3-4 hours before becoming irreversible. This and typically some collateral circulation to the ischemic area accounts for the efficacy of "clot-buster" drugs such as Alteplase, given for stroke and heart attack within this time period. 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 is an umbrella term for a variety for different diseases affecting the heart. As of 2007, it is the leading cause of death in the United States, England, Canada and Wales, killing one person every 34 seconds in the United States alone....
s, transient ischemic attack
Transient ischemic attack

A transient ischemic attack is caused by the changes in the blood supply to a particular area of the brain, resulting in brief neurologic dysfunction that persists, by definition, for less than 24 hours; if symptoms persist then it is categorized as a stroke....
s, cerebrovascular accident
Stroke

A stroke is the rapidly developing loss of brain function due to a disturbance in the blood supply to the brain. According to the National Stroke Association, a "stroke" occurs when a blood clot blocks and artery or a blood vessel breaks, interrupting blood flow to an area of the brain....
s, ruptured arteriovenous malformation
Arteriovenous malformation

Arteriovenous malformation or AVM in the majority of cases is a congenital disorder consisting of a connection between veins and arteries, this pathology is universally known because of its occurrence in the central nervous system, but can appear in any location....
s, and peripheral artery occlusive disease
Peripheral artery occlusive disease

Peripheral vascular disease , also known as peripheral artery disease or peripheral artery occlusive disease , includes all diseases caused by the obstruction of large artery in the arms and legs....
. The heart
Heart

The heart is a muscle organ in all vertebrates responsible for pumping blood through the blood vessels by repeated, rhythmic contractions, or a similar structure in annelids, mollusks, and arthropods....
, the kidney
Kidney

The kidneys are Organ that have numerous biological roles. Their primary role is to maintain the homeostasis balance of bodily fluids by filtering and secreting Metabolomics#Metabolitess and minerals from the blood and excreting them, along with water , as urine....
s, and the brain
Brain

The brain is the center of the nervous system in all vertebrate, and most invertebrate, animals. Some primitive animals such as cnidarian and echinoderm have a decentralized nervous system without a brain, while sponges lack any nervous system at all....
 are among the organs that are the most sensitive to inadequate blood supply. Ischemia in brain tissue, for example due to stroke or head injury
Traumatic brain injury

Traumatic brain injury occurs when an outside force physical trauma 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 take place in the brain and other aerobic tissues after seconds to minutes of ischemia ....
 to be unleashed, in which proteolytic
Proteolysis

Proteolysis is the directed degradation of proteins by cellular enzymes called proteases or by intramolecular digestion....
 enzymes, reactive oxygen species
Reactive oxygen species

Reactive oxygen species are ions or very small molecules that include oxygen ions, radical , and peroxides, both inorganic and organic peroxide....
, 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)

In chemistry, radicals are atoms, molecules or ions with unpaired electrons on an otherwise open shell configuration. These unpaired electrons are usually highly chemical reaction, so radicals are likely to take part in chemical reactions....
, resulting in reperfusion injury
Reperfusion injury

Reperfusion injury refers to damage to tissue caused when blood supply returns to the tissue after a period of ischemia. The absence of oxygen and nutrients from blood creates a condition in which the restoration of circulatory system results in inflammation and oxidation damage through the induction of oxidative stress rather than restorat...
. With reperfusion injury, necrosis can be greatly accelerated.

Variations

The mechanism of ischemia depends on the type. One important type is cardiac ischemia, another is bowel ischemia.

Cardiac ischemia

Cardiac ischemia may cause chest pain, known as angina pectoris

Detection
Initial evaluation of chest-pain patients involves a 12 lead electrocardiogram
Electrocardiogram

An electrocardiogram is a recording of the electricity activity of the heart over time produced by an electrocardiograph, usually in a Non-invasive recording via skin electrodes....
 (ECG) and cardiac markers such as troponin
Troponin

Troponin is a complex of three regulatory proteins that is integral to muscle contraction in skeletal muscle and cardiac muscle, but not smooth muscle....
s. These tests are highly specific but very insensitive and often leave the requirement for further testing to achieve an accurate diagnosis. Magnetocardiography
Magnetocardiography

Magnetocardiography is a technique to measure the magnetic fields produced by electrical activity in the heart using extremely sensitive devices such as the Superconducting Quantum Interference Device ....
 (MCG) imaging utilises superconducting quantum interference devices (SQUIDs) to detect the weak magnetic fields generated by the heart's electrical fields. There is a direct correlation between abnormal cardiac depolarisation or repolarisation and abnormality in the magnetic field map. In July 2004, the Food and Drug Administration
Food and Drug Administration

The U.S. Food and Drug Administration is an Government agency of the United States Department of Health and Human Services and is responsible for regulating and supervising the safety of foods, dietary supplements, Medications, vaccines, Biopharmaceutical, blood transfusion, medical devices, Electromagnetic radiation-emitting devices, veteri...
 (FDA) approved the CardioMag Imaging MCG as a safe device for the non-invasive detection of ischemia.

Bowel ischemia

An ischemia in the large bowel caused by an inflammation results in 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....
. An ischemia in the small bowel, on the other hand, caused by an inflammation results in 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 vasoconstriction or a blood clot....
.

Cutaneous ischemia

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 the reduction of blood flow to the brain. Brain ischemia has been connected to cerebral hypoxia and, if prolonged, to cerebral infarction....
  • Infarction
    Infarction

    In medicine, an infarction results in the death of a macroscopic area of tissue in an organ due to loss of adequate blood supply. This dead tissue is then known as necrosis....
  • Ischemic cascade
    Ischemic cascade

    The ischemic cascade is a series of biochemical reactions that take place in the brain and other aerobic tissues after seconds to minutes of ischemia ....
  • Reperfusion injury
    Reperfusion injury

    Reperfusion injury refers to damage to tissue caused when blood supply returns to the tissue after a period of ischemia. The absence of oxygen and nutrients from blood creates a condition in which the restoration of circulatory system results in inflammation and oxidation damage through the induction of oxidative stress rather than restorat...