quarta-feira, 3 de setembro de 2008

Allergy tests

Definition
Allergy tests indicate a person's allergic sensitivity to commonly encountered environmental substances.

Purpose
Allergy is a reaction of the immune system. Normally, the immune system responds to foreign microorganisms and particles, like pollen or dust, by producing specific proteins called antibodies that are capable of binding to identifying molecules, or antigens, on the foreign organisms. This reaction between antibody and antigen sets off a series of reactions designed to protect the body from infection. Sometimes, this same series of reactions is triggered by harmless, everyday substances. This is the condition known as allergy, and the offending substance is called an allergen. Common inhaled allergens include pollen, dust, and insect parts from tiny house mites. Common food allergens include nuts, fish, and milk.
Allergic reactions involve a special set of cells in the immune system known as mast cells. Mast cells serve as guards in the tissues where the body meets the outside world: the skin, the mucous membranes of the eyes and other areas, and the linings of the respiratory and digestive systems. Mast cells display a special type of antibody, called immunoglobulin type E (IgE), on their surface. Inside, mast cells store reactive chemicals in small packets, called granules. When the antibodies encounter allergens, they trigger the release of granules, which spill out their chemicals onto neighboring cells, including blood vessels and nerve cells. One of these chemicals, histamine, binds to the surfaces of these other cells, through special proteins called histamine receptors. Interaction of histamine with receptors on blood vessels causes neighboring cells to become leaky, leading to the fluid collection, swelling, and increased redness characteristic of a runny nose and red, irritated eyes. Histamine also stimulates pain receptors, causing the itchy, scratchy nose, eyes, and throat common in allergic rhinitis.
The particular allergens to which a person is sensitive can be determined through allergy testing. Allergy tests may be performed on the skin or using blood serum in a test tube. During skin tests, potential allergens are placed on the skin and the reaction is observed. In radio-allergosorbent allergy testing (RAST), a patient's blood serum is combined with allergen in a test tube to determine if serum antibodies react with the allergen. Provocation testing involves direct exposure to a likely allergen, either through inhalation or ingestion. Positive reactions from any of these tests may be used to narrow the candidates for the actual allergen causing the allergy.
Identification of the allergenic substance may allow the patient to avoid the substance and reduce allergic reactions. In addition, allergy testing may be done in those with asthma that is difficult to manage, eczema, or skin rashes to determine if an allergy is causing the condition or making it worse. Allergy tests may also be done before allergen desensitization to ensure the safety of more extensive exposure.
Skin testing is the most common type of allergy test. There are two forms: percutaneous and intradermal. In percutaneous or prick testing, allergen solutions are placed on the skin, and the skin is then pricked with a needle, allowing the allergen to enter the skin and become exposed to mast cells. Scratch testing, in which the skin is scratched instead of punctured, is used less often. Intradermal testing involves directly injecting allergen solutions into the skin. In both tests, a reddened, swollen spot develops at the injection site for each substance to which the person is sensitive. Skin reactivity is seen for allergens regardless of whether they usually affect the skin. In other words, airborne and food allergens cause skin reactions equally well.
The range of allergens used for testing is chosen to reflect possible sources in the environment and may include the following:
pollen from a variety of trees, common grasses, and weeds
mold and fungus spores
house dust
house mites
animal skin cells (dander) and saliva
food extracts
antibiotics
insect venoms
Radio-allergosorbent testing (RAST) is a laboratory test performed when a person may be too sensitive to risk skin testing or when medications or skin conditions prevent it.
Provocation testing is done to positively identify suspected allergens after preliminary skin testing. A purified preparation of the allergen is inhaled or ingested in increasing concentrations to determine if it will provoke a response. In 2004, scientists introduced an optical method to continuously measure the changes in nasal mucosa (lining) changes with an infrared light to help improve the accuracy of provocation testing. Food testing is much more tedious than inhalation testing, since full passage through the digestive system may take a day or more.

Precautions
While allergy tests are quite safe for most people, the possibility of a condition known as anaphylaxis exists. Anaphylaxis is a potentially dangerous condition that can result in difficulty breathing and a sharp drop in blood pressure. People with a known history of anaphylaxis should inform the testing clinician. Skin tests should never include a substance known to cause anaphylaxis in the person being tested.
Provocation tests may cause an allergic reaction. Therefore, treatment medications should be available following the tests, to be administered, if needed.

Description
In prick testing, a drop of each allergen to be tested is placed on the skin, usually on the forearm or the back. A typical battery of tests may involve two dozen allergen drops, including a drop of saline solution that should not provoke a reaction (negative control) and a drop of histamine that should provoke a reaction (positive control). A small needle is inserted through the drop, and used to prick the skin below. A new needle is used for each prick. The sites are examined over the next 20 minutes for evidence of swelling and redness, indicating a positive reaction. In some instances, a tracing of the set of reactions may be made by placing paper over the tested area. Similarly, in intradermal testing, separate injections are made for each allergen tested. Observations are made over the next 20 minutes.
In RAST testing, a blood sample is taken for use in the laboratory, where the antibody- containing serum is separated from the blood cells. The serum is then exposed to allergens bound to a solid medium. If a person has antibodies to a particular allergen, those antibodies will bind to the solid medium and remain behind after a rinse. Location of allergen-antibody combinations is done by adding antibody-reactive antibodies, so called anti-antibodies, that are chemically linked with a radioactive dye. By locating radioactive spots on the solid medium, the reactive allergens are discovered.
Provocation testing may be performed to identify airborne or food allergens. Inhalation testing is performed only after a patient's lung capacity and response to the medium used to dilute the allergen has been determined. Once this has been determined, the patient inhales increasingly concentrated samples of a particular allergen, followed each time by measurement of the exhalation capacity. Only one allergen is tested per day. Testing for food allergies is usually done by removing the suspect food from the diet for two weeks, followed by eating a single portion of the suspect food and follow-up monitoring.

Preparation
Skin testing is preceded by a brief examination of the skin. The patient should refrain from using anti-allergy drugs for at least 48 hours before testing. Prior to inhalation testing, patients with asthma who can tolerate it may be asked to stop any asthma medications. Testing for food allergies requires the person to avoid all suspect food for at least two weeks before testing.

Aftercare
Skin testing does not usually require any aftercare. A generalized redness and swelling may occur in the test area, but it will usually resolve within a day or two.
Inhalation tests may cause delayed asthma attacks, even if the antigen administered in the test initially produced no response. Severe initial reactions may justify close professional observation for at least 12 hours after testing.

Risks
Intradermal testing may inadvertently result in the injection of the allergen into the circulation, with an increased risk of adverse reactions. Inhalation tests may provoke an asthma attack. Exposure to new or unsuspected allergens in any test carries the risk of anaphylaxis. Because patients are monitored following allergy testing, an anaphylactic reaction is usually recognized and treated promptly. Occasionally, a delayed anaphylactic response can occur that will require immediate care. Proper patient education regarding how to recognize anaphylaxis is vital.

Normal results
Lack of redness or swelling on a skin test indicates no allergic response. In an inhalation test, the exhalation capacity should remain unchanged. In a food challenge, no symptoms should occur.

Abnormal results
Presence of redness or swelling, especially over 5 mm (1/4 inch) in diameter, indicates an allergic response. This does not mean the substance actually causes the patient's symptoms, however, since he or she may have no regular exposure to the allergen. In fact, the actual allergen may not have been included in the test array.
Following allergen inhalation, reduction in exhalation capacity of more than 20%, and for at least 10-20 minutes, indicates a positive reaction to the allergen.
Gastrointestinal symptoms within 24 hours following the ingestion of a suspected food allergen indicates a positive response.
Key Terms
Allergen

A substance that provokes an allergic response.
Anaphylaxis
Increased sensitivity caused by previous exposure to an allergen that can result in blood vessel dilation (swelling) and smooth muscle contraction. Anaphylaxis can result in sharp blood pressure drops and difficulty breathing.
Antibody
A specific protein produced by the immune system in response to a specific foreign protein or particle called an antigen.
Antigen
A foreign protein to which the body reacts by making antibodies.
Histamine

A chemical released by mast cells that activates pain receptors and causes cells to become leaky.
Mast cells
A type of immune system cell that is found in the lining of the nasal passages and eyelids, displays a type of antibody called immunoglobulin type E (IgE) on its cell surface, and participates in the allergic response by releasing histamine from intracellular granules.
For Your Information
Resources/Periodicals
Hampel, U., et al. "Optical Measurements of Nasal Swellings." IEEE Transactions on Biomedical Engineering (September 2004): 1673-1680.

Credits
Gale Encyclopedia of Medicine, Published December, 2002 by the Gale Group The Essay Author is Richard Robinson.

Allergies

Definition
Allergies are abnormal reactions of the immune system that occur in response to otherwise harmless substances.

Description
Allergies are among the most common of medical disorders. It is estimated that 60 million Americans, or more than one in every five people, suffer from some form of allergy, with similar proportions throughout much of the rest of the world. Allergy is the single largest reason for school absence and is a major source of lost productivity in the workplace.
An allergy is a type of immune reaction. Normally, the immune system responds to foreign microorganisms or particles by producing specific proteins called antibodies. These antibodies are capable of binding to identifying molecules, or antigens, on the foreign particle. This reaction between antibody and antigen sets off a series of chemical reactions designed to protect the body from infection. Sometimes, this same series of reactions is triggered by harmless, everyday substances such as pollen, dust, and animal danders. When this occurs, an allergy develops against the offending substance (an allergen.)
Mast cells, one of the major players in allergic reactions, capture and display a particular type of antibody, called immunoglobulin type E (IgE) that binds to allergens. Inside mast cells are small chemical-filled packets called granules. Granules contain a variety of potent chemicals, including histamine.
Immunologists separate allergic reactions into two main types: immediate hypersensitivity reactions, which are predominantly mast cell-mediated and occur within minutes of contact with allergen; and delayed hypersensitivity reactions, mediated by T cells (a type of white blood cells) and occurring hours to days after exposure.
Inhaled or ingested allergens usually cause immediate hypersensitivity reactions. Allergens bind to IgE antibodies on the surface of mast cells, which spill the contents of their granules out onto neighboring cells, including blood vessels and nerve cells. Histamine binds to the surfaces of these other cells through special proteins called histamine receptors. Interaction of histamine with receptors on blood vessels causes increased leakiness, leading to the fluid collection, swelling and increased redness. Histamine also stimulates pain receptors, making tissue more sensitive and irritable. Symptoms last from one to several hours following contact.
In the upper airways and eyes, immediate hypersensitivity reactions cause the runny nose and itchy, bloodshot eyes typical of allergic rhinitis. In the gastrointestinal tract, these reactions lead to swelling and irritation of the intestinal lining, which causes the cramping and diarrhea typical of food allergy. Allergens that enter the circulation may cause hives, angioedema, anaphylaxis, or atopic dermatitis.
Allergens on the skin usually cause delayed hypersensitivity reaction. Roving T cells contact the allergen, setting in motion a more prolonged immune response. This type of allergic response may develop over several days following contact with the allergen, and symptoms may persist for a week or more.

Causes and symptoms
Allergens enter the body through four main routes: the airways, the skin, the gastrointestinal tract, and the circulatory system.
Airborne allergens cause the sneezing, runny nose, and itchy, bloodshot eyes of hay fever (allergic rhinitis). Airborne allergens can also affect the lining of the lungs, causing asthma, or conjunctivitis (pink eye). Exposure to cockroach allergens has been associated with the development of asthma. Airborne allergens from household pets are another common source of environmental exposure.
Allergens in food can cause itching and swelling of the lips and throat, cramps, and diarrhea. When absorbed into the bloodstream, they may cause hives (urticaria) or more severe reactions involving recurrent, non-inflammatory swelling of the skin, mucous membranes, organs, and brain (angioedema). Some food allergens may cause anaphylaxis, a potentially life-threatening condition marked by tissue swelling, airway constriction, and drop in blood pressure. Allergies to foods such as cow's milk, eggs, nuts, fish, and legumes (peanuts and soybeans) are common. Allergies to fruits and vegetables may also occur.
In contact with the skin, allergens can cause reddening, itching, and blistering, called contact dermatitis. Skin reactions can also occur from allergens introduced through the airways or gastrointestinal tract. This type of reaction is known as atopic dermatitis. Dermatitis may arise from an allergic response (such as from poison ivy), or exposure to an irritant causing nonimmune damage to skin cells (such as soap, cold, and chemical agents).
Injection of allergens, from insect bites and stings or drug administration, can introduce allergens directly into the circulation, where they may cause system-wide responses (including anaphylaxis), as well as the local ones of swelling and irritation at the injection site.
People with allergies are not equally sensitive to all allergens. Some may have severe allergic rhinitis but no food allergies, for instance, or be extremely sensitive to nuts but not to any other food. Allergies may get worse over time. For example, childhood ragweed allergy may progress to year-round dust and pollen allergy. On the other hand, a person may lose allergic sensitivity. Infant or childhood atopic dermatitis disappears in almost all people. More commonly, what seems to be loss of sensitivity is instead a reduced exposure to allergens or an increased tolerance for the same level of symptoms.
While allergy to specific allergens is not inherited, the likelihood of developing some type of allergy seems to be, at least for many people. If neither parent has allergies, the chances of a child developing allergy is approximately 10-20%; if one parent has allergies, it is 30-50%; and if both have allergies, it is 40-75%. One source of this genetic predisposition is in the ability to produce higher levels of IgE in response to allergens. Those who produce more IgE will develop a stronger allergic sensitivity.

COMMON ALLERGENS
The most common airborne allergens are the following:
plant pollens
animal fur and dander
body parts from house mites (microscopic creatures found in all houses)
house dust
mold spores
cigarette smoke
solvents
cleaners
Common food allergens include the following:
The following types of drugs commonly cause allergic reactions:
penicillin or other antibiotics
flu vaccines
tetanus toxoid vaccine
gamma globulin
Common causes of contact dermatitis include the following:
poison ivy, oak, and sumac
nickel or nickel alloys
latex
Insects and other arthropods whose bites or stings typically cause allergy include the following:
bees, wasps, and hornets
mosquitoes
fleas
scabies

Symptoms depend on the specific type of allergic reaction. Allergic rhinitis is characterized by an itchy, runny nose, often with a scratchy or irritated throat due to post-nasal drip. Inflammation of the thin membrane covering the eye (allergic conjunctivitis) causes redness, irritation, and increased tearing in the eyes. Asthma causes wheezing, coughing, and shortness of breath. Symptoms of food allergies depend on the tissues most sensitive to the allergen and whether the allergen was spread systemically by the circulatory system. Gastrointestinal symptoms may include swelling and tingling in the lips, tongue, palate or throat; nausea; cramping; diarrhea; and gas. Contact dermatitis is marked by reddened, itchy, weepy skin blisters, and an eczema that is slow to heal. It sometimes has a characteritic man-made pattern, such as a glove allergy with clear demarkation on the hands, wrist, and arms where the gloves are worn, or on the earlobes by wearing earrings.
Whole body or systemic reactions may occur from any type of allergen, but are more common following ingestion or injection of an allergen. Skin reactions include the raised, reddened, and itchy patches called hives that characteristically blanch with pressure and resolve within twenty-four hours. A deeper and more extensive skin reaction, involving more extensive fluid collection and pain, is called angioedema. This usually occurs on the extremities, fingers, toes, and parts of the head, neck, and face. Anaphylaxis is marked by airway constriction, blood pressure drop, widespread tissue swelling, heart rhythm abnormalities, and in some cases, loss of consciousness. Other syptoms may include, dizziness, weakness, seizures, coughing, flushing, or cramping. The symptoms may begin within five minutes after exposure to the allergen up to one hour or more later. Mast cells in the tissues and basophils in the blood release mediators that give rise to the clinical symptoms of this IgE-mediated hypersensitivity reaction. Commonly, this is associated with allergies to medications, foods, and insect venoms. In some individuals, anaphylaxis can occur with exercise, plasma exchange, hemodialysis, reaction to insulin, contrast media used in certain types of medical tests, and rarely during the administration of local anesthetics.

Diagnosis
Allergies can often be diagnosed by a careful medical history, matching the onset of symptoms to the exposure to possible allergens. Allergy is suspected if the symptoms presented are characteristic of an allergic reaction and this occurs repeatedly upon exposure to the suspected allergen. Allergy tests can be used to identify potential allergens, but these must be supported by eveidence of allergic responses in the patient's clinical history.

Skin tests
Skin tests are performed by administering a tiny dose of the suspected allergen by pricking, scratching, puncturing or injecting the skin. The allergen is applied to the skin as an auqeous extract, usually on the back, forearms, or top of the thighs. Once in the skin, the allergen may produce a classic immune wheal and flare response (a skin lesion with a raised, white, compressible area surrounded by a red flare). The tests usually begin with prick tests or patch tests that expose the skin to small amounts of allergen to observe the response. A positive reaction will occur on the skin even if the allergen is at levels normally encountered in food or in the airways. Reactions are usually evaluated approximately fifteen minutes after exposure. Intradermal skin tests involved injection of the allergen into the dermis of the skin. These tests are more sensitive and are used for allergies associated with risk of death, such as allergies to antibiotics.

Allergen-Specific IgE Measurement
Tests that measure allergen-specific IgE antibodies generally follow a basic method. The allergen is bound to a solid support, either in the form of a cellulose sponge, microtiter plate, or paper disk. The patient's serum is prepared from a blood sample and is incubated with the solid phase. If allergen specific IgE antibodies are present, they will bind to the solid phase and be retained there when the rest of the serum is washed away. Next, an labeled antibody against the IgE is added and will bind to any IgE on the solid phase. The excess is washed away and the levels of IgE are determined. The commonly used RAST test (radio allergo sorbent test) employed radio-labeled Anti-IgE antibodies. Updated methods now incorporate the use of enyzme-labeled antibodies in ELISA assays (enzyme-linked immunosorbent assays).

Total Serum IgE
The total level of IgE in the serum is commonly measured with a two-site immunometric assay. Some research indicates that there is a higher level of total serum IgE in allergic as compared to non-allergic people. However, this may not always be the case as there is considerable overlap between the two groups. This test is useful for the diagnosis of allergic fungal sinusitis and bronchopulmonary aspergillosis. Other conditions that are not allergic in nature may give rise to higher IgE levels such as smoking, AIDS, infection with parasites, and IgE myeloma.

Provocation tests
These tests involve the administration of allergen to elicit an immune response. Provocation tests, most commonly done with airborne allergens, present the allergen directly through the route normally involved. Delayed allergic contact dermatitis diagnosis involves similar methods by application of a skin patch with allergen to induce an allergic skin reaction. Food allergen provocation tests require abstinence from the suspect allergen for two weeks or more, followed by ingestion of a measured amount of the test substance administered as an opaque capsule along with a placebo control. Provocation tests are not used if anaphylaxis is is a concern due to the patient's medical history.

Future diagnostic methods
Attempts have been made for direct measurement of immune mediators such as histamine, eosinophil cationic protein (ECP), and mast cell tryptase. Another, somewhat controversial,test is electrodermal testing or electro-acupuncture allergy testing. This test has been used in Europe and is under investigation in the United States, though not approved by the Food and Drug Administration. An electric potential is applied to the skin, the allergen presented, and the electrical resistance observed for changes. This method has not been verified.

Treatment
Avoiding allergens is the first line of defense to reduce the possibility of an allergic attack. It is helpful to avoid environmental irritants such as tobacco smoke, perfumes, household cleaning agents, paints, glues, air fresheners, and potpourri. Nitrogen dioxide from poorly vented gas stoves, woodburning stoves, and artificial fireplaces has also been linked to poor asthma control. Dust mite control is particularly important in the bedroom areas by use of allergen-impermeable covers on mattress and pillows, frequent washing of bedding in hot water, and removal of items that collect dust such as stuffed toys. Mold growth may be reduced by lowering indoor humidity, repair of house foundations to reduce indoor leaks and seepage, and installing exhaust systems to ventilate areas where steam is generated such as the bathroom or kitchen. Allergic individuals should avoid pet allergens such as saliva, body excretions, pelts, urine, or feces. For those who insist on keeping a pet, restriction of the animal's activity to certain areas of the home may be beneficial.
Complete environmental control is often difficult to accomplish, hence therapuetic interventions may become necessary. A large number of prescription and over-the-counter drugs are available for treatment of immediate hypersensitivity reactions. Most of these work by decreasing the ability of histamine to provoke symptoms. Other drugs counteract the effects of histamine by stimulating other systems or reducing immune responses in general.

Antihistamines
Antihistamines block the histamine receptors on nasal tissue, decreasing the effect of histamine released by mast cells. They may be used after symptoms appear, though they may be even more effective when used preventively, before symptoms appear. Antihistamines help reduce sneezing, itching, and rhinorrhea. A wide variety of antihistamines are available.
Older, first generation antihistamines often produce drowsiness as a major side effect, as well as dry mouth, tachycardia, blurred vision, constipation, and lower the threshold for seizures. These medications also have similar effects to a alcohol and care should be taken when operating motor vehicles, as individuals may not be aware that they are impaired. Such antihistamines include the following:
diphenhydramine (Benadryl and generics)
chlorpheniramine (Chlor-trimeton and generics)
brompheniramine (Dimetane and generics)
clemastine (Tavist and generics)
Newer antihistamines that do not cause drowsiness or pass the blood-brain barrier are available by prescription and include the following:
loratidine (Claritin)
cetirizine (Zyrtec)
fexofenadine (Allegra)
Desloratadine (Clarinex) was approved in 2004 in syrup form for children two years and older for seasonal allergies and for hives of unknown cause in children as young as six months. It is the only nonsedating antihistamine approved as of 2004 for children as young as six months.
Hismanal has the potential to cause serious heart arrhythmias when taken with the antibiotic erythromycin, the antifungal drugs ketoconazole and itraconazole, or the antimalarial drug quinine. Taking more than the recommended dose of Hismanal can also cause arrhythimas. Seldane (terfenadine), the original non-drowsy antihistamine, was voluntarily withdrawn from the market by its manufacturers in early 1998 because of this potential and because of the availability of an equally effective, safer alternative drug, fexofenadine.

Decongestants
Decongestants constrict blood vessels to the mucosa to counteract the effects of histamine. This decreases the amount of blood in the nasopahryngeal and sinus mucosa and reduces swelling. Nasal sprays are available that can be applied directly to the nasal lining and oral systematic preparations are available. Decongestants are stimulants and may cause increased heart rate and blood pressure, headaches, insomnia, agitation, and difficulty emptying the bladder. Use of topical decongestants for longer than several days can cause loss of effectiveness and rebound congestion, in which nasal passages become more severely swollen than before treatment.

Topical corticosteroids
Topical corticosteroids reduce mucous membrane inflammation by decreasing the amount of fluid moved from the vascular spaces into the tissues. These medications reduce the recruitment of inflammatory cells as well as the synthesis of cytokines. They are available by prescription. Allergies tend to become worse as the season progresses because the immune system becomes sensitized to particular antigens and can produce a faster, stronger response. Topical corticosteroids are especially effective at reducing this seasonal sensitization because they work more slowly and last longer than most other medication types. As a result, they are best started before allergy season begins. Side effects are usually mild, but may include headaches, nosebleeds, and unpleasant taste sensations.

Bronchodilators or metered-dose inhalers (MDI)
Because allergic reactions involving the lungs cause the airways or bronchial tubes to narrow, as in asthma, bronchodilators, which cause the smooth muscle lining the airways to open or dilate, can be very effective. When inhalers are used, it is important that the patient be educated in the proper use of these medications. The inhaler should be shaken, and the patient should breathe out to expel air from the lungs. The inhaler should be placed at least two fingerbreadths in front of the mouth. The medication should be aimed at the back of the throat, and the inhaler activated while breathing in quite slowly 3-4 seconds. The breath should be held for at least ten seconds, and then expelled. At least thirty to sixty seconds should pass before the inhaler is used again. Care should be taken to properly wash out the mouth and brush the teeth following use, as residual medication remains in this area with only a small amount actually reaching the lungs. Some bronchodilators used to treat acute asthma attacks include adrenaline, albuterol, Maxair, Proventil, or other "adrenoceptor stimulants," most often administered as aerosols. Successfully managing asthma and allergies can reduce the use of inhalers. This is done through good communication between the physician and patient, self-management with written action plans, avoiding allergy triggers, and through the use of preventive medications such as montelukast.

Anticholinergics
Ipratropium bromide (atrovent) and atropine sulfate are achticholinergic drugs used for the treatment of asthma. Ipratropium is used for treating asthmatics in emergency situations with a nebulizer.

Nonsteroidal drugs
MAST CELL STABILIZERS
Cromolyn sodium prevents the release of mast cell granules, thereby preventing the release of histamine and other chemicals contained in them. It acts as a preventive treatment if it is begun several weeks before the onset of the allergy season. It can also be used for year round allergy prevention. Cromolyn sodium is available as a nasal spray for allergic rhinitis and in aerosol (a suspension of particles in gas) form for asthma.

LEUKOTRIENE MODIFIERS
These medications are useful for individuals with aspirin sensitivity, sinusitis, polposis, urticaria. Examples include zafirlukast (Accolate), montelukast (Singulair), and zileuton (Zyflo). When zileuton is used, care must be taken to measure liver enzymes.

Immunotherapy
In this form of therapy, allergen is injected into the skin in increasing doses over a specific period of time. This may be helpful for patients who do not respond to medications or avoidance of allergens in the environment. This type of therapy may reduce the need for medications. A 2004 study recommended that children who have severe reactions to insect sting receive immunotherapy to protect them against future stings.

Treatment of contact dermatitis
An individual suffering from contact dermatitis should initially take steps to avoid possible sources of exposure to the offending agent. Calamine lotion applied to affected skin can reduce irritation somewhat, as can cold water compresses. Side effects of topical agents may include over-drying of the skin. In the case of acute contact dermatitis, short-term oral corticosteroid therapy may be appropriate. Moderately strong coricosteroids can also be applied as a wrap for twenty-four hours. Health care workers are especially at risk for hand eruptions due to glove use.

Treatment of anaphylaxis
The emergency condition of anaphylaxis is treated with injection of adrenaline, also known as epinephrine. People who are prone to anaphylaxis because of food or insect allergies often carry an "Epi-pen" containing adrenaline in a hypodermic needle. Other medications may be given to aid the action of the epi-pen. Prompt injection can prevent a more serious reaction from developing. Particular care should be taken to assess the affected individual's airway status, and he or she should be placed in a recumbent pose and vital signs determined. If a reaction resulted from insect sting or an injection, a tourniquet may need to be placed proximal to the area where the agent penetrated the skin. This should then be released at intervals of ten minutes at a time, for one to two minutes duration. If the individual does not respond to such interventions, then emergency treatment is appropriate.

Alternative treatment
Any alternative treatment for allergies begins with finding the cause and then helping the patient to avoid or eliminate the allergen, although this is not always possible. As with any alternative therapy, a physician should be consulted before initiating a new form of treatment. Education on the use of alternative agents is critical, as they are still "drugs" even though they are derived from natural sources. Various categories of alternative remedies may be helpful in allergy treatment, including:
antihistamines: vitamin C and the bioflavonoid hesperidin act as natural anithistamines.
decongestants: vitamin C, the homeopathic remedies Ferrum phosphoricum and Kali muriaticum (used alternately), and the dietary supplement N-acetylcysteine are believed to have decongestant effects.
mast cell stabilizers: the bioflavonoids quercetin and hesperidin may help stabilize mast cells.
immunotherapy: the herbs echinacea (Echinacea spp.) and astragalus or milk-vetch root (Astragalus membranaceus) may possibly help to strengthen the immune system.
bronchodilators: the herbal remedies ephedra (Ephedra sinica, also known as ma huang in traditional Chinese medicine), khellin (Ammi visnaga) and cramp bark (Viburnum opulus) are believed to help open the airways.

Treatment of contact dermatitis
A variety of herbal remedies, either applied topically or taken internally, may possibly assist in the treatment of contact dermatitis. A poultice (crushed herbs applied directly to the affected area) made of jewelweed (Impatiens spp.) or chickweed (Stellaria media) may soothe the skin. A cream or wash containing calendula (Calendula officinalis), a natural antiseptic and anti-inflammatory agent, may help heal the rash when applied topically. Homeopathic treatment may include such remedies as Rhus toxicodendron, Apis mellifica, or Anacardium taken internally. A qualified homeopathic practitioner should be consulted to match the symptoms with the correct remedy. Care should be taken with any agent taken internally.

Prognosis
Allergies can improve over time, although they often worsen. While anaphylaxis and severe asthma are life-threatening, other allergic reactions are not. Learning to recognize and avoid allergy-provoking situations allows most people with allergies to lead normal lives.

Prevention
Avoiding allergens is the best means of limiting allergic reactions. For food allergies, there is no effective treatment except avoidance. By determining the allergens that are causing reactions, most people can learn to avoid allergic reactions from food, drugs, and contact allergens such as poison ivy or latex. The government will help now, since passing the Food Allergen Labeling and Consumer Protection Act in 2004. Beginning January 1, 2006, food manufacturers will be required to clearly state if a product contains any of the eight major food allergens that are responsible for more than 90% of allergic reactions to foods. These are milk, eggs, peanuts, tree nuts, fish, shellfish, wheat, and soy.
Airborne allergens are more difficult to avoid, although keeping dust and animal dander from collecting in the house may limit exposure. Cromolyn sodium can prevent mast cell degranulation, thereby limiting the allergic response.
Immunotherapy, also known as desensitization or allergy shots, alters the balance of antibody types in the body, thereby reducing the ability of IgE to cause allergic reactions. Immunotherapy is preceded by allergy testing to determine the precise allergens responsible. Injections involve very small but gradually increasing amounts of allergen, over several weeks or months, with periodic boosters. Full benefits may take up to several years to achieve and are not seen at all in about one in five patients. Individuals receiving all shots will be monitored closely following each shot because of the small risk of anaphylaxis, a condition that can result in difficulty breathing and a sharp drop in blood pressure.
Other drugs, such as leukotriene modifiers, are used to prevent asthma attacks and in the long-term management of allergies and asthma.

Key Terms
Allergen
A substance that provokes an allergic response.
Allergic rhinitis
Inflammation of the mucous membranes of the nose and eyes in response to an allergen.
Anaphylaxis
Increased sensitivity caused by previous exposure to an allergen that can result in blood vessel dilation and smooth muscle contraction. Anaphylaxis can result in sharp blood pressure drops and difficulty breathing.
Angioedema
Severe non-inflammatory swelling of the skin, organs, and brain that can also be accompanied by fever and muscle pain.
Antibody
A specific protein produced by the immune system in response to a specific foreign protein or particle called an antigen.
Antigen
A foreign protein to which the body reacts by making antibodies.
Asthma
A lung condition in which the airways become narrow due to smooth muscle contraction, causing wheezing, coughing, and shortness of breath.
Atopic dermatitis
Infection of the skin as a result of exposure to airborne or food allergens.
Conjunctivitis
Inflammation of the thin lining of the eye called the conjunctiva.
Contact dermatitis
Inflammation of the skin as a result of contact with a substance.
Delayed hypersensitivity reactions
Allergic reactions mediated by T cells that occur hours to days after exposure.
Granules
Small packets of reactive chemicals stored within cells.
Histamine
A chemical released by mast cells that activates pain receptors and causes cells to become leaky.
Immune hypersensitivity reaction
Allergic reactions that are mediated by mast cells and occur within minutes of allergen contact.
Mast cells
A type of immune system cell that is found in the lining of the nasal passages and eyelids, displays a type of antibody called immunoglobulin type E (IgE) on its cell surface, and participates in the allergic response by releasing histamine from intracellular granules.
T cells
Immune system cells or more specifically, white blood cells, that stimulate cells to create and release antibodies.

For Your Information
Resources/Books

Hans-Uwe, Simon, editor. CRC Desk Reference for Allergy and Asthma. Boca Raton: CRC Press, 2000.
Kemp, Stephen F., and Richard Lockey, editors. Diagnostic Testing of Allergic Disease. New York: Marcel Dekker, Inc., 2000.
Lieberman, Phil, and Johh Anderson, editors. Allergic Diseases: Diagnosis and Treatment. 2nd ed. Totowa: Humana Press, Inc., 2000.
Periodicals
"Children With Serious Insect-sting Allergies Should Get Shots." Drug Week (September 3, 2004): 19.
"FDA Approves Clarinex Syrup for Allergies and Hives in Children." Biotech Week (September 29, 2004): 617.
"President Bush Signs Bill that Will Benefit Millions With Food Allergies." Immunotherapy Weekly (September 1, 2004): 50.
"What's New in: Asthma and Allergic Rhinitis." Pulse (September 20, 2004): 50.

Gale Encyclopedia of Medicine, Published December, 2002 by the Gale Group The Essay Author is Richard Robinson.
More Information
Like clockwork, the sneezing and sniffling hits you every spring. Or maybe it's every fall. But chances are it's not a cold. You have allergies. So what are allergies? They are exaggerated reactions of the immune system to substances that in most people don't cause problems. Symptoms may be caused by different exposures such as a certain chemical affecting the skin, dust or pollen particles affecting the respiratory system, or particular foods affecting the stomach and intestines.
As many as 40 million to 50 million Americans may have allergies, according to the American Academy of Allergy, Asthma and Immunology. Allergies affect more than 20 percent of the U.S. population and allergic diseases are the sixth leading cause of chronic disease in the United States. And at least 35 million have seasonal allergic rhinitis, also known as hay fever.
Common allergens are pollen, molds, dust mites, animal dander, certain foods and medications, and latex.
Allergic rhinitis (AR), or hay fever, happens when an allergen is inhaled through the mouth or nose. Sometimes symptoms are year-round, meaning it could be triggered by dust mites, cockroaches, animal dander, pollen or mold spores. AR is the most common allergy and is considered a risk in developing asthma. Nearly 80 percent of people with asthma also have AR. Sinusitis is a common disease often triggered by AR. The condition is an acute or chronic inflammation of the nasal sinuses, the hollow cavities around the eyes and behind the nose. More than 15 percent of the U.S. population has this condition.
Eczema (atopic dermatitis). Eczema often happens when the allergen such as animal dander touches the skin. For 80 percent of people with the condition, symptoms started in childhood. More than 50 percent of sufferers develop asthma.
Hives (uritcaria) are caused by allergens such as foods, dust mites, pollens and animals. Medications include penicillin, sulfa, anti-seizure drugs, phenobarbital and aspirin.
Contact dermatitis. When skin contacts certain substances, usually a chemical, this condition may happen. Reaction may take hours or days to develop, as with poison ivy.
Allergic conjunctivitis is the most common eye allergy, occurring when airborne allergens get into the eye, irritating thin membranes covering the eyelids and the exposed surface of the eyes. Allergic conjunctivitis is in two forms: seasonal and perennial. The seasonal version is much more common, and is related to exposure to grass, tree and weed pollens and molds. The perennial form lasts throughout the year and can be triggered by dust mites, feathers or animal dander.
Food allergies may have severe and possibly life-threatening reactions, although this is not true for all people with food allergies. The most common triggers are cow's milk, eggs, peanuts, wheat, soy, fish, shellfish and tree nuts. Food allergies are more common in children and are increasing in prevalence. However, many children may outgrow certain allergies.
Anaphylaxis. Anaphylaxis is a rare, potentially fatal allergic reaction affecting many parts of the body at once. A trigger may be an insect sting, a food, such as nuts or shellfish, or medications. Usually the reaction is immediate and progresses within minutes. You must get to a hospital right away. About 150 to 200 people in the United States die each year from food-related anaphylaxis, the Food Allergy & Anaphylaxis Network reports.

Prognosis
Allergies do not have a cure, but they can be controlled effectively with good prevention, awareness of your triggers and knowing how to manage symptoms if they happen. If you cannot deal effectively with allergies on your own, a doctor can help.s

Do You Have Hay Fever?
If you have the following symptoms and they seem to come every spring or fall, you may have hay fever:
Congestion.
Sneezing.
Itching and dripping nose.
Itchy, watery eyes.

Allergic rhinitis

Definition
Allergic rhinitis, more commonly referred to as hay fever, is an inflammation of the nasal passages caused by allergic reaction to airborne substances.

Description
Allergic rhinitis (AR) is the most common allergic condition and one of the most common of all minor afflictions. It affects between 10-20% of all people in the United States, and is responsible for 2.5% of all doctor visits. Antihistamines and other drugs used to treat allergic rhinitis make up a significant fraction of both prescription and over-the-counter drug sales each year.
There are two types of allergic rhinitis: seasonal and perennial. Seasonal AR occurs in the spring, summer, and early fall, when airborne plant pollens are at their highest levels. In fact, the term hay fever is really a misnomer, since allergy to grass pollen is only one cause of symptoms for most people. Perennial AR occurs all year and is usually caused by home or workplace airborne pollutants. A person can be affected by one or both types. Symptoms of seasonal AR are worst after being outdoors, while symptoms of perennial AR are worst after spending time indoors.
Both types of allergies can develop at any age, although onset in childhood through early adulthood is most common. Although allergy to a particular substance is not inherited, increased allergic sensitivity may "run in the family." While allergies can improve on their own over time, they can also become worse over time.

Causes and symptoms
Causes

Allergic rhinitis is a type of immune reaction. Normally, the immune system responds to foreign microorganisms, or particles, like pollen or dust, by producing specific proteins, called antibodies, that are capable of binding to identifying molecules, or antigens, on the foreign particle. This reaction between antibody and antigen sets off a series of reactions designed to protect the body from infection. Sometimes, this same series of reactions is triggered by harmless, everyday substances. This is the condition known as allergy, and the offending substance is called an allergen.
Like all allergic reactions, AR involves a special set of cells in the immune system known as mast cells. Mast cells, found in the lining of the nasal passages and eyelids, display a special type of antibody, called immunoglobulin type E (IgE), on their surface. Inside, mast cells store reactive chemicals in small packets, called granules. When the antibodies encounter allergens, they trigger release of the granules, which spill out their chemicals onto neighboring cells, including blood vessels and nerve cells. One of these chemicals, histamine, binds to the surfaces of these other cells, through special proteins called histamine receptors. Interaction of histamine with receptors on blood vessels causes neighboring cells to become leaky, leading to the fluid collection, swelling, and increased redness characteristic of a runny nose and red, irritated eyes. Histamine also stimulates pain receptors, causing the itchy, scratchy nose, eyes, and throat common in allergic rhinitis.
The number of possible airborne allergens is enormous. Seasonal AR is most commonly caused by grass and tree pollens, since their pollen is produced in large amounts and is dispersed by the wind. Showy flowers, like roses or lilacs, that attract insects produce a sticky pollen that is less likely to become airborne. Different plants release their pollen at different times of the year, so seasonal AR sufferers may be most affected in spring, summer, or fall, depending on which plants provoke a response. The amount of pollen in the air is reflected in the pollen count, often broadcast on the daily news during allergy season. Pollen counts tend to be lower after a good rain that washes the pollen out of the air and higher on warm, dry, windy days.
Virtually any type of tree or grass may cause AR. A few types of weeds that tend to cause the most trouble for people include the following:

ragweed
sagebrush
lamb's-quarters
plantain
pigweed
dock/sorrel
tumbleweed

Perennial AR is often triggered by house dust, a complicated mixture of airborne particles, many of which are potent allergens. House dust contains some or all of the following:
house mite body parts. All houses contain large numbers of microscopic insects called house mites. These harmless insects feed on fibers, fur, and skin shed by the house's larger occupants. Their tiny body parts easily become airborne.
animal dander. Animals constantly shed fur, skin flakes, and dried saliva. Carried in the air, or transferred from pet to owner by direct contact, dander can cause allergy in many sensitive people.
mold spores. Molds live in damp spots throughout the house, including basements, bathrooms, air ducts, air conditioners, refrigerator drains, damp windowsills, mattresses, and stuffed furniture. Mildew and other molds release airborne spores that circulate throughout the house.

Other potential causes of perennial allergic rhinitis include the following:
cigarette smoke
perfume
cosmetics
cleansers
copier chemicals
industrial chemicals
construction material gases
Symptoms

Inflammation of the nose, or rhinitis, is the major symptom of AR. Inflammation causes itching, sneezing, runny nose, redness, and tenderness. Sinus swelling can constrict the eustachian tube that connects the inner ear to the throat, causing a congested feeling and "ear popping." The drip of mucus from the sinuses down the back of the throat, combined with increased sensitivity, can also lead to throat irritation and redness. AR usually also causes redness, itching, and watery eyes. Fatigue and headache are also common.

Diagnosis
Diagnosing seasonal AR is usually easy and can often be done without a medical specialist. When symptoms appear in spring or summer and disappear with the onset of cold weather, seasonal AR is almost certainly the culprit. Other causes of rhinitis, including infection, can usually be ruled out by a physical examination and a nasal smear, in which a sample of mucus is taken on a swab for examination.
Allergy tests, including skin testing and provocation testing, can help identify the precise culprit, but may not be done unless a single source is suspected and subsequent avoidance is possible. Skin testing involves placing a small amount of liquid containing a specific allergen on the skin and then either poking, scratching, or injecting it into the skin surface to observe whether redness and swellings occurs. Provocation testing involves challenging an individual with either a small amount of an inhalable or ingestable allergen to see if a response is elicited.
Perennial AR can also usually be diagnosed by careful questioning about the timing of exposure and the onset of symptoms. Specific allergens can be identified through allergy skin testing.

Treatment
Avoidance of the allergens is the best treatment, but this is often not possible. When it is not possible to avoid one or more allergens, there are two major forms of medical treatment, drugs and immunotherapy.

Drugs
ANTIHISTAMINES

Antihistamines block the histamine receptors on nasal tissue, decreasing the effect of histamine release by mast cells. They may be used after symptoms appear, though they may be even more effective when used preventively, before symptoms appear. A wide variety of antihistamines are available.
Older antihistamines often produce drowsiness as a major side effect. Such antihistamines include the following:
diphenhydramine (Benadryl and generics)
chlorpheniramine (Chlor-trimeton and generics)
brompheniramine (Dimetane and generics)
clemastine (Tavist and generics).
Newer antihistamines that do not cause drowsiness are available by prescription and include the following:
astemizole (Hismanal)
fexofenadine (Allegra)
cetirizine (Zyrtec)
azelastin HCl (Astelin).
Loratidine (Claritin) was available only by prescription but was released to over-the-counter status by the FDA.
Hismanal has the potential to cause serious heart arrhythmias when taken with the antibiotic erythromycin, the antifungal drugs ketoconazole and itraconazole, or the antimalarial drug quinine. Taking more than the recommended dose of Hismanal can also cause arrhythimas. Seldane (terfenadine), the original non-drowsy antihistamine, was voluntarily withdrawn from the market by its manufacturers in early 1998 because of this potential and because of the availability of an equally effective, safer alternative drug, fexofenadine.

LEUKOTRIENE RECEPTOR ANTAGONISTS
Leukotriene receptor antagonists (montelukast or Singulair and zafirlukast or Accolate) are a newer class of drugs used daily to help prevent asthma. They've also become approved in the United States to treat allergic rhinitis.

DECONGESTANTS
Decongestants constrict blood vessels to counteract the effects of histamine. This decreases the amount of blood in the nasopahryngeal and sinus mucosa and reduces swelling. Nasal sprays are available that can be applied directly to the nasal lining and oral systemic preparations are available. Decongestants are stimulants and may cause increased heart rate and blood pressure, headaches, isomnia, agitation and difficulty emptying the bladder. Use of topical decongestants for longer than several days can cause loss of effectiveness and rebound congestion, in which nasal passages become more severely swollen than before treatment.

TOPICAL CORTICOSTEROIDS
Topical corticosteroids reduce mucous membrane inflammation and are available by prescription. Allergies tend to become worse as the season progresses because the immune system becomes sensitized to particular antigens and can produce a faster, stronger response. Topical corticosteroids are especially effective at reducing this seasonal sensitization because they work more slowly and last longer than most other medication types. As a result, they are best started before allergy season begins. Side effects are usually mild, but may include headaches, nosebleeds, and unpleasant taste sensations.

MAST CELL STABILIZERS
Cromolyn sodium prevents the release of mast cell granules, thereby preventing release of histamine and the other chemicals contained in them. It acts as a preventive treatment if it is begun several weeks before the onset of the allergy season. It can be used for perennial AR as well.

Immunotherapy
Immunotherapy, also known as desensitization or allergy shots, alters the balance of antibody types in the body, thereby reducing the ability of IgE to cause allergic reactions. Immunotherapy is preceded by allergy testing to determine the precise allergens responsible. Injections involve very small but gradually increasing amounts of allergen, over several weeks or months, with periodic boosters. Full benefits may take up to several years to achieve and are not seen at all in about one in five patients. Individuals receiving all shots will be monitored closely following each shot because of the small risk of anaphylaxis, a condition that can result in difficulty breathing and a sharp drop in blood pressure.

Alternative treatment
Alternative treatments for AR often focus on modulation of the body's immune response, and frequently center around diet and lifestyle adjustments. Chinese herbal medicine can help rebalance a person's system, as can both acute and constitutional homeopathic treatment. Vitamin C in substantial amounts can help stabilize the mucous membrane response. For symptom relief, western herbal remedies including eyebright (Euphrasia officinalis) and nettle (Urtica dioica) may be helpful. Bee pollen may also be effective in alleviating or eliminating AR symptoms. A 2004 report said that phototherapy (treatment with a combination of ultraviolet and visible light) decreased the symptoms of allergic rhinitis in a majority of patients who did not respond well to traditional drug treatment.

Prognosis
Most people with AR can achieve adequate relief with a combination of preventive strategies and treatment. While allergies may improve over time, they may also get worse or expand to include new allergens. Early treatment can help prevent an increased sensitization to other allergens.

Prevention
Reducing exposure to pollen may improve symptoms of seasonal AR. Strategies include the following:
stay indoors with windows closed during the morning hours, when pollen levels are highest
keep car windows up while driving
use a surgical face mask when outside
avoid uncut fields
learn which trees are producing pollen in which seasons, and avoid forests at the height of pollen season
wash clothes and hair after being outside
clean air conditioner filters in the home regularly
use electrostatic filters for central air conditioning
Moving to a region with lower pollen levels is rarely effective, since new allergies often develop
Preventing perennial AR requires identification of the responsible allergens.
Mold spores:
keep the house dry through ventilation and use of dehumidifiers
use a disinfectant such as dilute bleach to clean surfaces such as bathroom floors and walls
have ducts cleaned and disinfected
clean and disinfect air conditioners and coolers
throw out moldy or mildewed books, shoes, pillows, or furniture

House dust:
vacuum frequently, and change the bag regularly. Use a bag with small pores to catch extra-fine particles
clean floors and walls with a damp mop
install electrostatic filters in heating and cooling ducts, and change all filters regularly

Animal dander:
avoid contact if possible
wash hands after contact
vacuum frequently
keep pets out of the bedroom, and off furniture, rugs, and other dander-catching surfaces
have your pets bathed and groomed frequently

Key Terms
Allergen
A substance that provokes an allergic response.
Anaphylaxis
Increased sensitivity caused by previous exposure to an allergen1 that can result in blood vessel dilation (swelling) and smooth muscle contraction. Anaphylaxis can result in sharp blood pressure drops and difficulty breathing.
Antibody
A specific protein produced by the immune system in response to a specific foreign protein or particle called an antigen.
Antigen
A foreign protein to which the body reacts by making antibodies.
Granules
Small packets of reactive chemicals stored within cells.
Histamine
A chemical released by mast cells that activates pain receptors and causes cells to become leaky.
Mast cells
A type of immune system cell that is found in the lining of the nasal passages and eyelids, displays a type of antibody called immunoglobulin type E (IgE) on its cell surface, and participates in the allergic response by releasing histamine from intracellular granules.

For Your Information
Resources
Finn, Robert. "Rhinoohototherapy Targets Allergic Rhinitis." Skin & Allergy News (July 2004): 62.
"What's New in: Asthma and Allergic Rhinitis." Pulse (September 20, 2004): 50.

Gale Encyclopedia of Medicine, Published December, 2002 by the Gale Group The Essay Author is Richard Robinson.

Adult respiratory distress syndrome

Definition
Adult respiratory distress syndrome (ARDS), also called acute respiratory distress syndrome, is a type of lung (pulmonary) failure that may result from any disease that causes large amounts of fluid to collect in the lungs. ARDS is not itself a specific disease, but a syndrome, a group of symptoms and signs that make up one of the most important forms of lung or respiratory failure. It can develop quite suddenly in persons whose lungs have been perfectly normal. Very often ARDS is a true medical emergency. The basic fault is a breakdown of the barrier, or membrane, that normally keeps fluid from leaking out of the small blood vessels of the lung into the breathing sacs (the alveoli).

Description
Another name for ARDS is shock lung. Its formal name is misleading, because children, as well as adults, may be affected. In the lungs the smallest blood vessels, or capillaries, make contact with the alveoli, tiny air sacs at the tips of the smallest breathing tubes (the bronchi). This is the all-important site where oxygen passes from air that is inhaled to the blood, which carries it to all parts of the body. Any form of lung injury that damages this point of contact, called the alveolo-capillary junction, will allow blood and tissue fluid to leak into the alveoli, eventually filling them so that air cannot enter. The result is the type of breathing distress called ARDS. ARDS is one of the major causes of excess fluid in the lungs, the other being heart failure.

Along with fluid there is a marked increase in inflamed cells in the lungs. There also is debris left over from damaged lung cells, and fibrin, a semi-solid material derived from blood in the tissues. Typically these materials join together with large molecules in the blood (proteins), to form hyaline membranes. (These membranes are very prominent in premature infants who develop respiratory distress syndrome; it is often called hyaline membrane disease.) If ARDS is very severe or lasts a long time, the lungs do not heal, but rather become scarred, a process known as fibrosis. The lack of a normal amount of oxygen causes the blood vessels of the lung to become narrower, and in time they, too, may become scarred and filled with clotted blood. The lungs as a whole become very "stiff," and it becomes much harder for the patient to breathe.

Causes and symptoms
A very wide range of diseases or toxic substances, including some drugs, can cause ARDS. They include:

Breathing in (aspiration) of the stomach contents when regurgitated, or salt water or fresh water from nearly drowning.

Inhaling smoke, as in a fire; toxic materials in the air, such as ammonia or hydrocarbons; or too much oxygen, which itself can injure the lungs.

Infection by a virus or bacterium, or sepsis, a widespread infection that gets into the blood.

Massive trauma, with severe injury to any part of the body.

Shock with persistently low blood pressure may not in itself cause ARDS, but it can be an important factor.

A blood clotting disorder called disseminated intravascular coagulation, in which blood clots form in vessels throughout the body, including the lungs.

A large amount of fat entering the circulation and traveling to the lungs, where it lodges in small blood vessels, injuring the cells lining the vessel walls.

An overdose of a narcotic drug, a sedative, or, rarely, aspirin.

Inflammation of the pancreas (pancreatitis), when blood proteins, called enzymes, pass to the lungs and injure lung cells.

Severe burn injury.

Injury of the brain, or bleeding into the brain, from any cause may be a factor in ARDS for reasons that are not clear. Convulsions also may cause some cases.

Usually ARDS develops within one to two days of the original illness or injury. The person begins to take rapid but shallow breaths. The doctor who listens to the patient's chest with a stethoscope may hear "crackling" or wheezing sounds. The low blood oxygen content may cause the skin to appear mottled or even blue. As fluid continues to fill the breathing sacs, the patient may have great trouble breathing, take very rapid breaths, and gasp for air.

Diagnosis
A simple test using a device applied to the ear will show whether the blood is carrying too little oxygen, and this can be confirmed by analyzing blood taken from an artery. The chest x ray may be normal in the early stages, but, in a short time, fluid will be seen where it does not belong. The two lungs are about equally affected. A heart of normal size indicates that the problem actually is ARDS and not heart failure. Another way a physician can distinguish between these two possibilities is to place a catheter into a vein and advance it into the main artery of the lung. In this way, the pressure within the pulmonary capillaries can be measured. Pressure within the pulmonary capillaries is elevated in heart failure, but normal in ARDS.

Treatment
The three main goals in treating patients with ARDS are:

To treat whatever injury or disease has caused ARDS. Examples are: to treat septic infection with the proper antibiotics, and to reduce the level of oxygen therapy if ARDS has resulted from a toxic level of oxygen.

To control the process in the lungs that allows fluid to leak out of the blood vessels. At present there is no certain way to achieve this. Certain steroid hormones have been tried because they can combat inflammation, but the actual results have been disappointing.

To make sure the patient gets enough oxygen until the lung injury has had time to heal. If oxygen delivered by a face mask is not enough, the patient is placed on a ventilator, which takes over breathing, and, through a tube placed in the nose or mouth (or an incision in the windpipe), forces oxygen into the lungs. This treatment must be closely supervised, and the pressure adjusted so that too much oxygen is not delivered.

Patients with ARDS should be cared for in an intensive care unit, where experienced staff and all needed equipment are available. Enough fluid must be provided, by vein if necessary, to prevent dehydration. Also, the patient's nutritional state must be maintained, again by vein, if oral intake is not sufficient.

Prognosis
If the patient's lung injury does not soon begin to heal, the lack of sufficient oxygen can injure other organs, such as the kidneys. There always is a risk that bacterial pneumonia will develop at some point. Without prompt treatment, as many as 90% of patients with ARDS can be expected to die. With modern treatment, however, about half of all patients will survive. Those who do live usually recover completely, with little or no long-term breathing difficulty. Lung scarring is a risk after a long period on a ventilator, but it may improve in the months after the patient is taken off ventilation. Whether a particular patient will recover depends to a great extent on whether the primary disease that caused ARDS to develop in the first place can be effectively treated.

Prevention
The only way to prevent ARDS is to avoid those diseases and harmful conditions that damage the lung. For instance, the danger of aspirating stomach contents into the lungs can be avoided by making sure a patient does not eat shortly before receiving general anesthesia. If a patient needs oxygen therapy, as low a level as possible should be given. Any form of lung infection, or infection anywhere in the body that gets into the blood, must be treated promptly to avoid the lung injury that causes ARDS.

Key Terms
Alveoli
The tiny air sacs at the ends of the breathing tubes of the lung where oxygen normally is taken up by the capillaries to enter the circulation.

Aspiration
The process in which solid food, liquids, or secretions that normally are swallowed are, instead, breathed into the lungs.

Capillaries
The smallest arteries which, in the lung, are located next to the alveoli so that they can pick up oxygen from inhaled air.

Face mask
The simplest way of delivering a high level of oxygen to patients with ARDS or other low-oxygen conditions.

Steroids
A class of drugs resembling normal body substances that often help control inflammation in the body tissues.

Ventilator
A mechanical device that can take over the work of breathing for a patient whose lungs are injured or are starting to heal.
For Your Information

Resources
Books
Smolley, Lawrence A., and Debra F. Bryse. Breathe RightNow: A Comprehensive Guide to Understanding and Treating the Most Common Breathing Disorders. New York: W. W. Norton & Co., 1998.

Organizations
National Heart, Lung and Blood Institute. P.O. Box 30105, Bethesda, MD 20824-0105. (301) 251-1222.

National Respiratory Distress Syndrome Foundation. P.O. Box 723, Montgomeryville, PA 18936.
Gale Encyclopedia of Medicine, Published December, 2002 by the Gale Group The Essay Author is David A. Cramer, MD.

Allergic bronchopulmonary aspergillosis

Definition
Allergic bronchopulmonary aspergillosis, or ABPA, is one of four major types of infections in humans caused by Aspergillus fungi. ABPA is a hypersensitivity reaction that occurs in asthma patients who are allergic to this specific fungus.

Description
ABPA is an allergic reaction to a species of Aspergillus called Aspergillus fumigatus. It is sometimes grouped together with other lung disorders characterized by eosinophilia--an abnormal increase of a certain type of white blood cell in the blood--under the heading of eosinophilic pneumonia. These disorders are also called hypersensitivity lung diseases.
ABPA appears to be increasing in frequency in the United States, although the reasons for the increase are not clear. The disorder is most likely to occur in adult asthmatics aged 20-40. It affects males and females equally.

Causes and symptoms
ABPA develops when the patient breathes air containing Aspergillus spores. These spores are found worldwide, especially around riverbanks, marshes, bogs, forests, and wherever there is wet or decaying vegetation. They are also found on wet paint, construction materials, and in air conditioning systems. ABPA is a nosocomial infection, which means that a patient can get it in a hospital. When Aspergillus spores reach the bronchi, which are the branches of the windpipe that lead into the lungs, the bronchi react by contracting spasmodically. So the patient has difficulty breathing and usually wheezes or coughs. Many patients with ABPA also run a low-grade fever and lose their appetites.

Complications
Patients with ABPA sometimes cough up large amounts of blood, a condition that is called hemoptysis. They may also develop a serious long-term form of bronchiectasis, the formation of fibrous tissue in the lungs. Bronchiectasis is a chronic bronchial disorder caused by repeated inflammation of the airway, and marked by the abnormal enlargement of, or damage to, the bronchial walls. ABPA sometimes occurs as a complication of cystic fibrosis.

Diagnosis
The diagnosis of ABPA is based on a combination of the patient's history and the results of blood tests, sputum tests, skin tests, and diagnostic imaging. The doctor will be concerned to distinguish between ABPA and a worsening of the patient's asthma, cystic fibrosis, or other lung disorders. There are seven major criteria for a diagnosis of allergic bronchopulmonary aspergillosis:
a history of asthma.
an accumulation of fluid in the lung that is visible on a chest x ray.
bronchiectasis (abnormal stretching, enlarging, or destruction of the walls of the bronchial tubes).
skin reaction to Aspergillus antigen.
eosinophilia in the patient's blood and sputum.
Aspergillus precipitins in the patient's blood. Precipitins are antibodies that react with the antigen to form a solid that separates from the rest of the solution in the test tube.
a high level of IgE in the patient's blood. IgE refers to a class of antibodies in blood plasma that activate allergic reactions to foreign particles.
Other criteria that may be used to support the diagnosis include the presence of Aspergillus in samples of the patient's sputum, the coughing up of plugs of brown mucus, or a late skin reaction to the Aspergillus antigen.

Laboratory tests
The laboratory tests that are done to obtain this information include a complete blood count (CBC), a sputum culture, a blood serum test of IgE levels, and a skin test for the Aspergillus antigen. In the skin test, a small amount of antigen is injected into the upper layer of skin on the patient's forearm about four inches below the elbow. If the patient has a high level of IgE antibodies in the tissue, he or she will develop what is called a "wheal and flare" reaction in about 15-20 minutes. A "wheal and flare" reaction is characterized by the eruption of a reddened, itching spot on the skin. Some patients with ABPA will develop the so-called late reaction to the skin test, in which a red, sore, swollen area develops about six to eight hours after the initial reaction.

Diagnostic imaging
Chest x rays and CT scans are used to check for the presence of fluid accumulation in the lungs and signs of bronchiectasis.

Treatment
ABPA is usually treated with prednisone (Meticorten) or other corticosteroids taken by mouth, and with bronchodilators.
Antifungal drugs are not used to treat ABPA because it is caused by an allergic reaction to Aspergillus rather than by direct infection of tissue.

Follow-up care
Patients with ABPA should be given periodic checkups with chest x rays and a spirometer test. A spirometer is an instrument that evaluates the patient's lung capacity.

Prognosis
Most patients with ABPA respond well to corticosteroid treatment. Others have a chronic course with gradual improvement over time. The best indicator of a good prognosis is a long-term fall in the patient's IgE level. Patients with lung complications from ABPA may develop severe airway obstruction.

Prevention
ABPA is difficult to prevent because Aspergillus is a common fungus; it can be found in the saliva and sputum of most healthy individuals. Patients with ABPA can protect themselves somewhat by avoiding haystacks, compost piles, bogs, marshes, and other locations with wet or rotting vegetation; by avoiding construction sites or newly painted surfaces; and by having their air conditioners cleaned regularly. Some patients may be helped by air filtration systems for their bedrooms or offices.

Key Terms
Antifungal
A medicine used to treat infections caused by a fungus.
Antigen
A substance that stimulates the production of antibodies.
Bronchiectasis
A disorder of the bronchial tubes marked by abnormal stretching, enlargement, or destruction of the walls. Bronchiectasis is usually caused by recurrent inflammation of the airway and is a diagnostic criterion of ABPA.
Bronchodilator
A medicine used to open up the bronchial tubes (air passages) of the lungs.
Eosinophil
A type of white blood cell containing granules that can be stained by eosin (a chemical that produces a red stain).
Eosinophilia
An abnormal increase in the number of eosinophils in the blood.
Hemoptysis
The coughing up of large amounts of blood. Hemoptysis can occur as a complication of ABPA.
Hypersensitivity
An excessive response by the body to a foreign substance.
Immunoglobulin E (IgE)
A type of protein in blood plasma that acts as an antibody to activate allergic reactions. About 50% of patients with allergic disorders have increased IgE levels in their blood serum.
Nosocomial infection
An infection that can be acquired in a hospital. ABPA is a nosocomial infection.
Precipitin
An antibody in blood that combines with an antigen to form a solid that separates from the rest of the blood.
Spirometer
An instrument used to test a patient's lung capacity.
"Wheal and flare" reaction
A rapid response to a skin allergy test characterized by the development of a red, itching spot in the area where the allergen was injected.
Wheezing
A whistling or musical sound caused by tightening of the air passages inside the patient's chest.

For Your Information
Resources/Books

Stauffer, John L. "Lung." In Current Medical Diagnosis and Treatment, 1998, edited by Stephen McPhee, et al., 37th ed. Stamford: Appleton & Lange,1997.

Organizations
Centers for Disease Control and Prevention. 1600 Clifton Rd., NE, Atlanta, GA 30333. (800) 311-3435, (404) 639-3311.

National Institute of Allergy and Infectious Disease. Building 31, Room 7A-50, 31 Center Drive MSC 2520, Bethesda, MD 20892-2520. (301) 496-5717.

National Organization for Rare Disorders. P.O. Box 8923, New Fairfield, CT 06812-8923. (800) 999-6673.

Gale Encyclopedia of Medicine, Published December, 2002 by the Gale Group The Essay Author is Rebecca J. Frey, PhD.

Antiarrhythmic Drugs

Definition
Antiarrhythmic drugs are medicines that correct irregular heartbeats and slow down hearts that beat too fast.

Purpose
Normally, the heart beats at a steady, even pace. The pace is controlled by electrical signals that begin in one part of the heart and quickly spread through the whole heart. If something goes wrong with this control system, the result may be an irregular heartbeat, or an arrhythmia. Antiarrhythmic drugs correct irregular heartbeats, restoring the normal rhythm. If the heart is beating too fast, these drugs will slow it down. By correcting these problems, antiarrhythmic drugs help the heart work more efficiently.

Description
Antiarrhythmic drugs are available only with a physician's prescription and are sold in capsule (regular and extended release), tablet (regular and extended-release), and injectable forms. Commonly used antiarrhythmic drugs are disopyramide (Norpace, Norpace CR), procainamide (Procan SR, Pronestyl, Pronestyl-SR), and quinidine (Cardioquin, Duraquin, Quinidex, and other brands). Do not confuse quinidine with quinine, which is a related medicine with different uses, such as relieving leg cramps.

Recommended dosage
The recommended dosage depends on the type of antiarrhythmic drug and other factors. Doses may be different for different patients. Check with the physician who prescribed the drug or the pharmacist who filled the prescription for the correct dosage.
Always take antiarrhythmic drugs exactly as directed. Never take larger or more frequent doses.
Do not stop taking this medicine without checking with the physician who prescribed it. Stopping it suddenly could lead to a serious change in heart function.
Antiarrhythmic drugs work best when they are at constant levels in the blood. To help keep levels constant, take the medicine in doses spaced evenly through the day and night. Do not miss any doses. If taking medicine at night interferes with sleep, or if it is difficult to remember to take the medicine during the day, check with a health care professional for suggestions.

Precautions
Persons who take these drugs should see their physician regularly. The physician will check to make sure the medicine is working as it should and will note any unwanted side effects.
Some people feel dizzy, lightheaded, or faint when using these drugs. This medicine may cause blurred vision or other vision problems. Because of these possible problems, anyone who takes these drugs should not drive, use machines or do anything else that might be dangerous until they have found out how the drugs affect them. If the medicine does cause vision problems, wait until vision is clear before driving or engaging in other activities that require normal vision.
Antiarrhythmic drugs make some people feel lightheaded, dizzy, or faint when they get up after sitting or lying down. To lessen the problem, get up gradually and hold onto something for support if possible.
Anyone taking this medicine should not drink alcohol without his or her physician's approval.
Some antiarrhythmic drugs may change the results of certain medical tests. Before having medical tests, anyone taking this medicine should alert the health care professional in charge.
Anyone who is taking antiarrhythmic drugs should be sure to tell the health care professional in charge before having any surgical or dental procedures or receiving emergency treatment.
Antiarrhythmic drugs may cause low blood sugar in some people. Anyone who experiences symptoms of low blood sugar should eat or drink a food that contains sugar and call a physician immediately.
Signs of low blood sugar are:

anxiety
confusion
nervousness
shakiness
unsteady walk
extreme hunger
headache
nausea
drowsiness
unusual tiredness or weakness
fast heartbeat
pale, cool skin
chills
cold sweats

Antiarrhythmic drugs may cause dry mouth. To temporarily relieve the discomfort, chew sugarless gum, suck on sugarless candy or ice chips, or use saliva substitutes, which come in liquid and tablet forms and are available without a prescription. If the problem continues for more than 2 weeks, check with a physician or dentist. Mouth dryness that continues over a long time may contribute to tooth decay and other dental problems.
People taking antiarrhythmic drugs may sweat less, which can cause the body temperature to rise. Anyone who takes this medicine should be careful not to become overheated during exercise or hot weather and should avoid hot baths, hot tubs, and saunas. Overheating could lead to heat stroke.
Older people may be especially sensitive to the effects of antiarrhythmic drugs. This may increase the risk of certain side effects, such as dry mouth, difficult urination, and dizziness or lightheadedness.
The antiarrhythmic drug procainamide can cause serious blood disorders. Anyone taking this medicine should have regular blood counts and should check with a physician if any of the following symptoms occur:

joint or muscle pain
muscle weakness
pain in the chest or abdomen
tremors
wheezing
cough
palpitations
rash, sores, or pain in the mouth
sore throat
fever and chills
loss of appetite
diarrhea
dark urine
yellow skin or eyes
unusual bleeding or bruising
dizziness
hallucinations
depression

Special conditions
People with certain medical conditions or who are taking certain other medicines may have problems if they take antiarrhythmic drugs. Before taking these drugs, be sure to let the physician know about any of these conditions:

ALLERGIES
Anyone who has had unusual reactions to an antiarrhythmic drug in the past should let his or her physician know before taking this type of medicine again. Patients taking procainamide should let their physicians know if they have ever had an unusual or allergic reaction to procaine or any other "caine-type" medicine, such as xylocaine or lidocaine. Patients taking quinidine should mention any previous reactions to quinine. The physician should also be told about any allergies to foods, dyes, preservatives, or other substances.

CONGESTIVE HEART DISEASE
Antiarrhythmic drugs may cause low blood sugar, which can be a particular problem for people with congestive heart disease. Anyone with congestive heart disease should be familiar with the signs of low blood sugar (listed above) and should check with his or her physician about what to do if such symptoms occur.

DIABETES
Antiarrhythmic drugs may cause low blood sugar, which can be a particular problem for people with diabetes. Anyone with diabetes should be familiar with the signs of low blood sugar (listed above) and should check with his or her physician about what to do if such symptoms occur.

PREGNANCY
The effects of taking antiarrhythmic drugs in pregnancy have not been studied in humans. In studies of laboratory animals, this medicine increased the risk of miscarriage. In addition, some women who have taken these drugs while pregnant have had contractions of the uterus (womb). Women who are pregnant or who may become pregnant should check with their physicians before taking this medicine. Women who become pregnant while taking this medicine should let their physicians know right away.

BREASTFEEDING
Antiarrhythmic drugs pass into breast milk. Women who are breastfeeding should check with their physicians before taking this medicine.

OTHER MEDICAL CONDITIONS
Before using antiarrhythmic drugs, people with any of these medical problems should make sure their physicians are aware of their conditions:

heart disorders such as structural heart disease or inflammation of the heart muscle
congestive heart failure
kidney disease
liver disease
diseases of the blood
asthma or emphysema
enlarged prostate or difficulty urinating
overactive thyroid
low blood sugar
psoriasis
glaucoma
myasthenia gravis
systemic lupus erythematosus

USE OF CERTAIN MEDICINES
Taking antiarrhythmic drugs with certain other drugs may affect the way the drugs work or may increase the chance of side effects.
Side effects
The most common side effects are dry mouth and throat, diarrhea, and loss of appetite. These problems usually go away as the body adjusts to the drug and do not require medical treatment. Less common side effects, such as dizziness, lightheadedness, blurred vision, dry eyes and nose, frequent urge to urinate, bloating, constipation, stomach pain, and decreased sexual ability, also may occur and do not need medical attention unless they do not go away or they interfere with normal activities.
More serious side effects are not common, but may occur. If any of the following side effects occur, check with the physician who prescribed the medicine as soon as possible:

fever and chills
difficult urination
swollen or painful joints
pain when breathing
skin rash or itching

People who are especially sensitive to quinidine may have a reaction to the first dose or doses. If any of these side effects occur after taking quinidine, check with a physician immediately:

dizziness
ringing in the ears
breathing problems
vision changes
fever
headache
skin rash

Other rare side effects may occur with any antiarrhythmic drug. Anyone who has unusual symptoms after taking antiarrhythmic drugs should get in touch with his or her physician.

Interactions
Antiarrhythmic drugs may interact with other medicines. When this happens, the effects of one or both of the drugs may change or the risk of side effects may be greater. Anyone who takes antiarrhythmic drugs should let the physician know all other medicines he or she is taking. Among the drugs that may interact with antiarrhythmic drugs are:

other heart medicines, including other antiarrhythmic drugs
blood pressure medicine
blood thinners
pimozide (Orap), used to treat Tourette's syndrome

The list above does not include every drug that may interact with antiarrhythmic drugs. Be sure to check with a physician or pharmacist before combining antiarrhythmic drugs with any other prescription or nonprescription (over-the-counter) medicine.

Key Terms
Anxiety
Worry or tension in response to real or imagined stress, danger, or dreaded situations. Physical reactions, such as fast pulse, sweating, trembling, fatigue, and weakness may accompany anxiety.
Arrhythmia
Abnormal heart rhythm.
Asthma
A disease in which the air passages of the lungs become inflamed and narrowed.
Emphysema
A lung disease in which breathing becomes difficult.
Glaucoma
A condition in which pressure in the eye is abnormally high. If not treated, glaucoma may lead to blindness.
Hallucination

A false or distorted perception of objects, sounds, or events that seems real. Hallucinations usually result from drugs or mental disorders.

Heat stroke
A severe condition caused by prolonged exposure to high heat. Heat stroke interferes with the body's temperature regulating abilities and can lead to collapse and coma.

Inflammation
Pain, redness, swelling, and heat that usually develop in response to injury or illness.

Myasthenia gravis
A chronic disease with symptoms that include muscle weakness and sometimes paralysis.

Palpitation
Rapid, forceful, throbbing, or fluttering heartbeat.

Prostate
A donut-shaped gland below the bladder in men that contributes to the production of semen.

Psoriasis
A skin disease in which people have itchy, scaly, red patches on the skin.

Systemic lupus erythematosus (SLE)
A chronic disease that affects the skin, joints, and certain internal organs.

Tourette syndrome
A condition in which a person has tics and other involuntary behavior, such as barking, sniffing, swearing, grunting, and making uncontrollable movements.

Tremor
Shakiness or trembling.

Bibliography
Gale Encyclopedia of Medicine, Published December, 2002 by the Gale Group The Essay Author is Nancy Ross-Flanigan.