Asthma

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Asthma

Definition

Asthma is a chronic inflammatory disease of the airways in which periods of relatively free breathing are punctuated by episodes in which breathing becomes difficult. During an attack, inflammation causes the airways to fill with mucus secretions and become obstructed. Asthmatics cough, gasp for air, wheeze, gag, and feel choking sensations as they struggle to breathe. Obstruction to airflow usually responds to a wide range of treatments.

Depending of the type of asthma, attacks may be triggered by environmental factors such as cold temperatures, air pollution, smoke, pollen, dust, mildew, mold, and animal hair or dander. Exercise, allergic reactions, respiratory infections, and emotional stress may also trigger attacks. Like other chronic diseases, asthma can be controlled, but not cured.

According to the American Lung Association, in 1998 there were 26 million Americans asthmatics, 10.6 of whom had had an attack during the past year. About a third of all asthmatics are children under 18. Since asthma is often undiagnosed, these statistics probably underestimate the true prevalence of the disease.

Description

The lungs of asthmatics are hypersensitive to stimuli that do not affect healthy lungs. Many patients with asthma react to allergens such as pollen, dust mites, or animal dander, but colds, viruses, and environmental irritants such as dust and pollution can also be triggers.

During an asthma attack, cells in the bronchial walls called mast cells release chemicals that force the bronchial muscle to contract in spasms These chemicals, which include histamine, acetylcholine, and a group of substances called leukotrienes, also bring white blood cells into the area, which is a key part of the inflammatory response. This process also stimulates mucus formation. The entire process creates bronchoconstriction, making it difficult for the asthmatic person to breathe.

Asthma usually begins in childhood or adolescence, but it also may first appear in adulthood. While the symptoms may be similar, certain important aspects of asthma are different in children and adults.

Child-onset asthma

When asthma begins in childhood, it often does so in an atopic child, one who is genetically predisposed to become sensitized to allergens in the environment. Atopy is present in at least one-third and as many as half of the general population. When these children are exposed to dust mites, animal proteins, fungi, or other potential allergens, they produce a type of antibody intended to engulf and destroy the foreign materials. This sensitizes the airway cells to particular allergens. Further exposure can lead rapidly to an asthmatic response.

Adult-onset asthma

Allergies may also play a role in adult-onset asthma, which can start at any age and in a wide variety of situations. Adults may begin to react to allergens such as pollen, dust mites, and pet dander; they may find themselves allergic to aspirin and other drugs; and can even trigger an asthma attack with exercise. Another major cause of adult asthma is occupational exposure (and sensitization) to animal products, certain forms of plastic, wood dust, or metals. In addition, many people have such conditions as sinusitis or nasal polyps that also make them prone to asthma attacks.

Causes and symptoms

In most cases, asthma is caused by inhaling an allergen that sets off the biochemical chain reaction, causing the tissue changes that lead to airway inflammation, bronchoconstriction, and wheezing. Since avoiding, or at least minimizing, exposure is the most effective way to treat asthma, it is vital to identify which allergen or irritant is causing symptoms in each patient. Once asthma is present, symptoms can be triggered or made worse if the patient also has rhinitis (a cold or cold-like symptoms caused by allergies), sinusitis (inflammation or infection of the sinuses), or a viral infection of the respiratory tract (such as influenza ). Gastroesophageal reflux disease (GERD), commonly referred to as acid reflux or heartburn, can also make asthma worse. Some asthmatics are free of symptoms most of the time but may occasionally be short of breath. Others spend their days (and nights) coughing and wheezing, until properly treated.

Allergens and irritants most likely to cause asthma attacks are: smoke, animal dander, dust mites, fungi and molds, cockroach allergens, pollen, and industrial chemicals, fumes, or pollution. In addition, there are three conditions that can also provoke attacks in certain asthmatic patients: inhaling cold air, breathing hard during exercise, and stress or a high anxiety level.

During moderate to severe asthma attacks wheezing may be obvious, but mild attacks can be confirmed by listening to the patient's chest with a stethoscope. Wheezing is often loudest during exhalation, when the patient tries to expel air through narrowed airways. Besides wheezing and shortness of breath, the patient may also cough and report a feeling of tightness in the chest. Children may experience itching on their back or neck. Crying or even laughing may bring on an attack. Severe episodes often occur when patients contract viral respiratory tract infections or are exposed to heavy loads of an allergen or irritant. Asthma attacks may last only a few minutes or can persist for hours or even days (a condition called status asthmaticus).

Shortness of breath may cause a patient to become very anxious, sit upright, lean forward, and use the accessory muscles of respiration to help breathe. The patient may be able to say only a few words at a time before stopping to take a breath. Confusion and a bluish tint to the skin indicate that the patient's oxygen supply is very low and emergency treatment is needed. If a severe attack lasts for some time, air sacs in the lung may rupture, trapping air within the chest. This makes it even harder to breathe in enough air. Fortunately, even patients with the most severe attacks usually recover completely.

Diagnosis

Physical examination

Apart from listening to the patient's chest, the examiner should look for maximum chest expansion while taking in air. Hunched shoulders and contracting neck muscles are other signs of narrowed airways. Nasal polyps or increased amounts of nasal secretions are often noted in asthmatic patients. Skin problems like atopic dermatitis or eczema indicate that the patient has allergic problems. A family history of asthma or allergies can be a valuable indicator. The diagnosis may be strongly suggested when typical symptoms and signs are present.

Spirometry and chest x ray

Spirometry can confirm a diagnosis of asthma by measuring lung function: how much air the lungs can hold and how much they can expel. Asthma patients typically have normal lung volumes with diminished flow rates. Repeating the test after the patient inhales a bronchodilator will show whether the airway narrowing is reversible, a finding that distinguishes asthma from other obstructive diseases like emphysema.

Often patients use a related instrument, called a peak flow meter, to monitor asthma severity at home. Because this device measures the strength with which air is exhaled, it can detect narrowed airways at the earliest stage, before an attack becomes full blown. This allows the patient to take the appropriate medication and diminish or avoid the episode.

Determining what triggers asthma attacks can be difficult. Skin testing may be helpful, although an allergic skin response does not necessarily mean that the allergen being tested is causing the asthma. Once a specific allergen is suspected, a blood test can be run to check for IgE antibodies, since the immune system always produces an antibody in response to an allergen. This will show if the patient is sensitive to a particular allergen. If the diagnosis is still in doubt, the patient can inhale a suspect allergen while using a spirometer to detect airway narrowing, a test called "allergen challenge." Spirometry may also be repeated after a bout of exercise to confirm or refute the diagnosis of exercise-induced asthma. A chest x ray may help to rule out other pulmonary disorders, or confirm findings particular to asthma.

Treatment

Patients should be examined periodically and have their pulmonary function measured by spirometry to ensure that treatment goals are being maintained. The goal is to prevent troublesome symptoms, maintain lung function as close to normal as possible, and allow patients to pursue their normal activities, including those requiring exertion. The best drug therapy is that which controls asthmatic symptoms while causing few or no side-effects.

Drugs

METHYLXANTHINES. The chief methylxanthine is theophylline. It may exert some anti-inflammatory effect, and is especially helpful in controlling nighttime asthma. When, for some reason, a patient cannot use an inhaler to maintain long-term control, sustainedrelease oral theophylline is a good alternative. The blood levels of the drug must be measured periodically, as too high a dose can cause an abnormal heart rhythm or convulsions.

BETA-RECEPTOR AGONISTS. These bronchodilators, such as albuterol, are the best choice for relieving sudden attacks of asthma and for preventing attacks triggered by exercise because they relax the smooth muscles in the lungs. This prevents bronchospasm but doesn't help the swelling that often accompanies an asthma attack. These drugs are effective within about 30 minutes, and are maximally effective for three or four hours. They may be taken by mouth, inhaled, or injected, although the oral forms often produce such side effects as jitters and sleeplessness.

STEROIDS. Steroids and corticosteroids block inflammation and are extremely effective in relieving asthma symptoms. When taken by inhalation for a long period, they reduce the airways' sensitivity to allergens, and asthma attacks become less frequent. This is the strongest medicine for asthma, and can control even severe cases over the long term. Oral or intravenous steroids taken over long periods, however, can cause numerous side effects, including gastric bleeding, loss of calcium from bones, cataracts, and diabetes. Patients on long-term steroid therapy may also have problems with wound healing and weight gain, and may develop mental problems as well. In children, growth may be slowed. Besides being inhaled, steroids may be taken by mouth or injected to control severe asthma rapidly.

LEUKOTRIENE MODIFIERS. Leukotriene modifiers, such as montelukast (Singulair), zileuton (Zyflo), and zafirlukast (Accolate) are drugs that work by counteracting leukotrienes, substances released by white blood cells in the lungs that constrict air passages and promote mucus secretion. They may reduce the need for short-acting inhalers, and may replace inhaled steroid treatment for patients with mild forms of asthma. Leukotrine modifiers may also help asthma patients recover from severe attacks more quickly, and can even help alleviate the allergic rhinitis that often accompanies allergies.

OTHER DRUGS AND TREATMENTS. Cromolyn sodium (Intal) and nedocromil (Tilade) are antiinflammatory agents that stabilize the airways and help prevent the swelling and inflammation that trigger asthma attacks. They can also prevent flareups when given before exercise or when exposure to an allergen cannot be avoided. Like most asthma medication, these drugs must be taken regularly even if there are no symptoms, and require weeks or months of use before they reach their optimum effectiveness.

Anti-cholinergic drugs, such as ipratropium bromide (Atrovent), are useful in controlling severe attacks when added to an inhaled beta-receptor agonist. They help widen the airways and suppress mucus production. The effects of anti-cholingerics usually last longer than beta-agonists, and are often given in combination with bronchodilators to improve breathing.

If a patient's asthma is caused by an allergen that cannot be avoided and has become difficult to control through drug therapy alone, immunotherapy (allergy shots) may be beneficial. In this treatment, increasing amounts of the allergen are injected over a period of three to five years, so the body can build up an effective immune response. There is a risk that this treatment may itself trigger an asthma attack or even anaphylaxis. Immunotherapy has been used since the early twentieth century to treat allergies and hayfever. New studies have indicated that it also reduces asthma symptoms caused by exposure to such allergens as dust mites, ragweed pollen, and cats.

Managing asthmatic attacks

A severe asthma attack can be a medical emergency and should be treated as quickly as possible. It is most important for a patient suffering an acute attack to be given oxygen. Rarely, it may be necessary to use a mechanical ventilator to help the patient breathe. Under a doctor's care, a beta-receptor agonist is inhaled repeatedly or continuously. If the patient does not respond promptly and completely, a steroid is given. An additional course of steroid therapy, given after the attack is over, will make a recurrence less likely.

Once asthma has been controlled for several weeks or months, the dose may be gradually tapered. The last drug added to the regimen should be the first to be reduced. Patients should be evaluated every one to six months, depending on the frequency of attacks.

Long-term treatment

Long-term asthma treatment is based on inhaled medications that are a combination of beta-receptor agonists and steroids. The drugs are delivered to the lungs via special inhalers that meter each dose. While this regimen is usually quite successful in diminishing or preventing attacks, all patients should be taught how to monitor their symptoms so they will know when an attack is starting. Those with moderate or severe asthma can use a peak flow meter to determine if inflammation is increasing.

Asthmatics should also have a written action plan to follow if symptoms suddenly worsen, including how to adjust their medication and when to seek medical care. When deciding whether a patient should be hospitalized, the past history of acute attacks, severity of symptoms, current medication, and whether good support is available at home all must be taken into account.

Referral to an asthma specialist should be considered if:

There has been a life-threatening asthma attack or severe, persistent asthma.
Treatment for three to six months has been ineffective.
Another condition, such as nasal polyps or chronic lung disease, is complicating asthma.
Special tests, such as allergy skin testing or an allergen challenge are needed.
Intensive steroid therapy has been necessary.

Special populations

INFANTS AND YOUNG CHILDREN. It is especially important to monitor the course of asthma in young patients so that treatment may be diminished or increased as necessary. The health care provider should write out an asthma treatment plan for the child's school. Although asthmatic children often need medication at school to control acute symptoms or to prevent exercise-induced attacks, proper management usually enables a child to take part in physical activities. Only as a last resort should activities be limited.

OLDER ADULTS. Side effects from beta-receptor agonist drugs (including rapid heart rate and tremor) may be more common in older patients. These patients may benefit from receiving an anti-cholinergic drug along with the beta-receptor agonist. If theophylline is given, the dose should be carefully monitored, as older patients may be less able to metabolize this drug. Asthma in older patients may also be complicated by other obstructive lung diseases such as chronic bronchitis or emphysema. It is important to know the extent the symptoms caused by the asthma. A two- to three-week course of steroids can help determine which symptoms are attributable to asthma.

Prognosis

Once the best drug or combination of drugs is found, most patients with asthma respond well and are able to lead relatively normal lives. More than half of affected children stop having attacks by the time they reach twenty-one. Many others have less frequent and less severe attacks as they grow older. In either case ongoing treatment to prevent attacks and urgent measures to control them if they occur are equally important. A small minority of patients will have progressive difficulties breathing. These patients are at risk for respiratory failure and must receive intensive treatment.

Health care team roles

Diagnosis and effective asthma management involve cooperation and collaboration between the patient, family, and an interdisciplinary team of health care professionals. These include the patient's primary health care provider, allergy and immunology specialists, nurses, laboratory technologists, respiratory therapists, pharmacists, pharmacy assistants, and health educators are involved in helping patients and families gain an understanding of how to manage this chronic disease.

Patient education

Nurses, respiratory therapists, and health educators teach patients and families how to prevent, recognize, and manage asthma attacks, including the distinction between mild episodes and those requiring immediate medical attention. They can also train them in stress management techniques that reduce anxiety to help them gain control of this chronic condition.

USING AN INHALER. Perhaps most importantly, these professionals show patients the proper technique for using inhalers and other medications, and stress the importance of compliance. Using a respiratory inhaler properly is a critical skill in asthma management and it's vitally important that patients be instructed in its proper use:

Remove the inhaler's cap.
Holding the inhaler upright, shake it thoroughly for several seconds.
Exhale as much air as possible, while tilting the head back slightly.
Hold the inhaler in the position required by the manufacturer. Some should be held an inch or two away from the mouth, others should be placed directly in the mouth.
Press the inhaler to dispense the medication.
Inhale slowly and deeply through the mouth only for several seconds.
Hold the breath for at least 10 seconds; this allows the medication to penetrate into the lungs Take only one breath for each puff.
Exhale.
Wait a minute or so between puffs (This delay allows the second dose to get even farther into the airways.)

Successful use of metered-dose inhalers requires a close degree of coordination between dispensing the drug and inhaling it. Because this is usually difficult for young children, they are often told to attach "spacers" to their inhalers. These are chambers into which the drug is sprayed before it is inhaled, allowing the medication to be ingested in one or more breaths. For the tiniest patients, masks are attached to the spacers. Many doctors recommend spacers for adult patients as well, since they decrease the chances of using the inhaler improperly, and increase the amount of medication that reaches the lungs. During a severe asthma attack, when patients may not have the ability to inhale a full dose, spacers can literally save lives by allowing patients in distress to take their medication in shorter breaths. Spacers are also usually attached to corticosteroid inhalers.

When using powder inhalers (Rotacaps), patients should close their lips around the inhaler's mouthpiece and inhale quickly. After using a corticosteroid inhaler patients should gargle or rinse their mouths with water to avoid thrush, an overgrowth of yeast in the mouth.

Pharmacists and pharmacy assistants may offer additional instruction about medication use and reiterate the importance of adhering to prescribed treatment.

Prevention

Minimizing exposure to allergens

There are a number of ways patients can reduce exposure to allergens and irritants that provoke asthmatic attacks, or to avoid them altogether:

If the patient is sensitive to the family pet, remove the animal or at least keep it out of the bedroom. Keep the pet away from carpets and upholstered furniture. Remove all feathers.
To reduce exposure to dust mites, remove wall-to-wall carpeting, keep the humidity down, and use special pillow and mattress covers. Wash bedding in hot water once a week.
Reduce the number of stuffed toys, and wash them each week in hot water as well.
Eliminate cockroaches using poison, traps, or boric acid rather than chemical pesticides.
Keep indoor air clean by vacuuming carpets once or twice a week (with the patient absent), avoid using humidifiers, and use air conditioning during warm weather so windows can remain closed.
Avoid exposure to tobacco smoke.
Do not exercise outside when air pollution levels are high.
To reduce occupational exposure, wear a mask when working with or around irritants. Some patients may find it necessary to find work in a safer environment.

KEY TERMS

Allergen— A foreign substance, such as mites in dust or animal dander which, when inhaled, causes the airways to narrow and produces asthma symptoms.

Allergen challenge— "Provocation" testing in which a patient is exposed to a suspected allergen under controlled conditions.

Atopy— An allergy (probably hereditary) that makes people react immediately to allergens they encounter. Atopic individuals are more likely to develop allergic reactions of any type, including the inflammation and airway narrowing typical of asthma.

Hypersensitivity— The state where even a tiny amount of allergen can cause the airways to constrict and bring on an asthmatic attack.

Spirometry— A test using an instrument called a spirometer that shows how well an asthmatic is breathing, the severity of the asthma, and how well it is responding to treatment.

Resources

BOOKS

American Medical Association. The Washington Manual of Medical Therapeutics, 30th ed. Philadelphia: Lippincott Williams & Wilkins, 2001, pp. 245-251.

ORGANIZATIONS

Asthma and Allergy Foundation of America. 1125 15th St. NW, Suite 502, Washington, DC 20005. 800-7ASTHMA. ?http://www.housecall.com/sponsors/nhc/1966vha/aafa.html?.

National Asthma Education Program. 4733 Bethesda Ave., Suite 350, Bethesda, MD 20814. 301-495-4484.

National Jewish Medical and Research Center. 1400 Jackson St., Denver, CO 80206. 800-222-LUNG.