Asthma Medicines

As a rule, all patients with bronchial asthma should have an allergy evaluation. In children, allergy clearly plays a significant role in the severity of the disease and the frequency of attacks. In adults, the role of allergy is less important although most patients, when tested, are found to be allergic.

Allergy Skin Tests

Although useful as a screening test, the IgE level by itself is not sufficient to determine the presence of allergy (also called atopy). Additional evaluation may include allergy skin testing for specific substances known as allergens that may trigger asthma attacks. This method has been used for more than 100 years and represents an extremely reliable way of determining the presence of allergy to a specific substance. Skin testing is performed by pricking, scratching, or injecting the skin with a small amount of allergen. Positive reactions, which resemble hives, are noted in twenty to thirty minutes. But skin testing is time consuming and may cause total body reactions in highly sensitive individuals.

Allergy Blood Tests

Evidence for allergy may also be obtained through blood testing that detects the presence of specific antibodies to various allergens. One technique is known as RAST (Radioallergosorbent test). This test utilizes radioactive material and detects the presence of a specific IgE antibody that has been produced against a certain allergen. This method is thought to be less accurate than skin testing, however, although it may prove useful in selected individuals. Other drawbacks include greater cost when compared to skin testing as well as a delay of up to three weeks in obtaining results.

A relatively new technique known as MAST (Multiple Antigen Simultaneous Testing) has been developed for measuring allergen specific IgE antibodies. This technique is faster and less expensive than RAST and provides accurate results when compared to RAST and skin prick tests. Results may be obtained in one week.

Allergic Reaction

A positive allergy test does not always identify a significant allergy, so the patients history becomes an extremely important factor in correlating allergy test results with true triggers of asthma attacks.

Immediate and “Late” Reactions

Allergy reactions are often immediate and severe as in the patient who is allergic to bee venom, but an allergic reaction may not always be immediately apparent. Recently, it has been demonstrated that a “late phase” response may occur several hours after exposure to an offending substance. In the late phase reaction, inflammation plays a significant role, and it is essential that effective therapy be directed at this component as well as to bronchial obstruction. If not treated, this late phase reaction may form the basis of recurrent and increasingly severe asthma attacks.

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Peak Flow Meter

In bronchial asthma it is extremely important to recognize the presence of an attack before it becomes severe and requires emergency measures. Each patient should have a means of assessing the degree of asthma that is present from day to day. In this manner severe episodes and often the use of oral or injectable corticosteroids necessary for such emergencies can be avoided. As an extension of this home monitoring the patient should be instructed how to respond to the presence of increased asthma. In this way a contingency plan can be in place and ready before severe attacks occur and require emergency room care. The cornerstone of this home monitoring is the peak flow meter. In essence it is an “early warning” device for individuals with asthma.

What the Peak Flow Meter Measures

The peak flow meter is a simple and inexpensive device that can be used in and out of the home to monitor bronchial asthma and similar conditions. This compact device determines the maximal expiratory flow rate that the patient is capable of producing. Similar to the office spirometry, the patient inhales fully and then exhales fully and forcefully into the flow meter device. A simple scale registers the peak flow. If done as instructed this flow rate correlates well with other measurement of airflow through the large airways of the lung. With a diary to record readings the patient can maintain an accurate assessment of the degree of asthma from day to day. This is not unlike the diabetic who records blood sugar readings. This information can be invaluable to the physician in managing patients with bronchial asthma since it gives an objective measurement to go by instead of trying to assess asthma by the degree of shortness of breath or wheezing. Communication with the physician can be much more meaningful with a record of the patient’s peak flows, resulting in earlier and better treatment. With earlier recognition of an attack through peak flow measurements, severe and potentially fatal asthma attacks may be avoided.

An electronic peak flow meter is now available in the form of Air-Watch which is made by Enact. This more sophisticated and expensive device is capable of storing several hundred peak flow measurements. Patients may also download their readings by phone to a central computer which then faxes the results to the physician.

Asthma with Normal Peak Flows

Remember that peak flow measurements reflect primarily large airways and therefore do not totally assess the asthmatic condition. Normal peak flows may occur in the presence of significant small airway disease that requires continued and effective treatment. This explains why patients may continue to be symptomatic even with normal peak flow rates.

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Cromolyn sodium, a derivative of khellin, an Egyptian herbal remedy, is a useful anti-inflammatory agent that may be used as an alternative to inhaled corticosteroids. In severe patients, cromolyn sodium (Intal) may be used in conjunction with steroids. Like the inhaled corticosteroids, cromolyn is also underused. This underutilization does not result from fear of adverse effects but rather from a misunderstanding of its application. Since its introduction, cromolyn has been the drug of choice for childhood asthmatics. From this early application it has been incorrectly assumed that it was a poor drug for adults, particularly those without allergic characteristics. Many studies, however, have documented that cromolyn may be an effective drug for asthmatics of all ages, even in patients with “intrinsic” asthma. It is also clear that cromolyn does not work for all patients. Like the inhaled corticosteroids, it is slow acting and therefore requires a trial of three to six weeks to assess response. Because of this, many patients abandon this drug before it has had an adequate trial.

How Does Cromolyn Work?

It is not clear how cromolyn sodium reduces inflammation. Some evidence has pointed to an action on inflammatory and allergy cells that prevents release of irritating chemicals that cause inflammation. There may also be an antagonistic action on nervous stimulation that prevents bronchoconstriction and reflex cough. Cromolyn has been demonstrated to prevent both the immediate and late reactions of asthma as well as exercise induced asthma in many patients.

How Cromolyn Is Supplied and Used

Cromolyn sodium was initially made available as a powder for inhalation. Unfortunately, this produced considerable coughing and wheezing. It is currently also available as an aerosol for metered-dose inhalers and in solution for nebulization. When used for nebulization it may be combined with a B2-adrenergic agonist. The recommended dosage is two puffs four times a day from an MDI or 20 mg in solution via a nebulizer, also four times a day.

Cromolyn is not an effective drug for acute asthmatic attacks and, like the inhaled corticosteroids, must be used as a preventive maintenance drug. For this reason cromolyn is best not started during an acute attack. It can be introduced toward the end of an oral steroid taper similar to the way that the inhaled corticosteroids are started. Also, like the inhaled corticosteroids, cromolyn can be used alone and does not necessarily require premedication with a B-adrenergic agonist.

Adverse Effects of Cromolyn

Besides being an effective drug, cromolyn has an extremely low incidence of side effects, which explains its first-line use in children where high-dose inhaled corticosteroids have been shown to slow bone development. In adults the inhaled corticosteroids are considered more effective, making cromolyn a second line agent. In those patients with adverse steroid effects cromolyn is an excellent alternative anti­inflammatory. There are few adverse effects to speak of. Occasionally, cough and wheezing may result from its inhalation. This can often be prevented with the use of a B-adrenergic agonist sprayed five to ten minutes before use or given in solution with cromolyn via nebulization. Rarely have total body effects been noted. An extremely small number of patients have noted joint pains and rash. These effects have resolved completely on discontinuation.

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Although there are differences from patient to patient, the asthma attack is typically characterized by shortness of breath and wheezing. Cough and mucus production may be prominent symptoms. In some patients wheezing may not occur and a cough may be the dominant symptom. The patient demonstrates a rapid rate of breathing, often with heaving of the chest and use of neck muscles to assist each breath. During an attack the patient is totally disabled. Even speech may be impossible due to severe breathlessness. The patient may be totally consumed by the effort to breathe and unable to eat or dress. The patient is often restless and unable to lie flat. Severe attacks may end in exhaustion, with ominous slowing of the respiratory rate and arrest of breathing.

Depending on the severity of the patient’s disease the attack may be totally or partially reversible, allowing the patient to assume normal activities between episodes. Patients with severe asthma, however, may remain to some degree symptomatic at all times.

It should be noted that the degree of wheezing can be misleading. The severity of the asthmatic attack should never be judged on this basis alone. Some patients who are capable of moving large amounts of air may produce more turbulence and audible wheezing than others who are so severely obstructed that their breaths are shallow and incapable of producing much sound.

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The Medical History

All diagnosis begins with a thorough medical history. The physician looks for the age at onset of symptoms and associated allergies. Evidence of air-way obstruction may be suggested by a report of wheezing and shortness of breath. Coughing may be a prominent symptom and the physician will inquire as to the character of phlegm produced. The physician will also ask about the presence of nasal symptoms or sinus pain or infection as well as the presence of allergic skin problems such as rash ( eczema) or hives (urticaria). A diminished sense of smell or taste may suggest the presence of nasal polyps. Common questions include: “What seems to trigger your attack?” “What are your attacks like?” Asthma often worsens at night and the patient may be asked,”Do you ever awaken with an attack?” The timing of attacks other than at night is also important. A relationship between asthma and hormonal influences should be explored. Many women note increased asthmatic symptoms before their period, as well as changes during pregnancy. The physician will ask about the effect of exercise on the patient’s symptoms since asthma may occasionally occur only with exercise. Emotional factors will also be investigated as potential triggers: “Are you under more stress?” A thorough family history will also be obtained since the presence of asthma or allergy in closely related family members will support the diagnosis. The physician will also ask about occupation and possible exposures to irritating chemicals, dust, or fumes. To help establish the hyperresponsiveness evident in asthma the physician will ask how the patient reacts to changes in temperature, humidity, air pollution, or the presence of cigarette smoke, fumes, or odors. Reaction to foods containing sulfites as well as to drugs (especially aspirin and penicillin) are also important historical factors.

Looking For Asthma Triggers

When obtaining the initial history the physician must be like a detective, especially in examining sources of irritation that may have precipitated or irritated an underlying asthmatic condition. Both the home and workplace must be reviewed in that context. Many patients are aware of the “sick building syndrome” in which asthma may be produced by a particular contaminant, and thus are able to give important information. The type of heating and cooling system in place should be known. Although the patient may be a nonsmoker, sources of secondhand smoke should be investigated. “Have you recently moved or renovated?”Do you have pets?”How often do you clean your humidifier?” If attacks occur frequently at night the bedroom should be singled out for review. “Do you have a mattress cover?” “What type of floor covering do you have?”

It is not unusual for a patient to supply information that may identify a specific source of irritation and asthma attacks. A thirty-four-year-old man was referred to me for asthma that was extremely difficult to control. He had had many severe attacks and was receiving several asthma medications. Corticosteroids had been prescribed several times and he had noted side effects of weight gain and stomach upset. The patient noted that he was often well during the day but worsened at night, especially after returning to his apartment. The patient often worked in his bedroom where he spent a great deal of time when he was home. He was often awakened during the night by wheezing and shortness of breath and noted that he was “worse in the morning.” Asthma attacks often occurred whenever he attempted to clean his apartment. I suspected he was allergic to dust mites and that was confirmed by allergy testing. The patient acquired a mattress cover and began following several recommendations. He returned for a visit after six weeks and noted he was now sleeping through the night and awakening without wheezing. His medications were sharply reduced and he has not required further corticosteroids. I often remind him that the credit for his improvement belongs to his mattress cover.

Participating in Your Care

Patients can be extremely helpful by detailing that type of specific information for the physician. Write down the important facts in your history that you want to present to your physician. If this narrative is lengthy, send the material ahead of you with other medical records so our physician can review it in detail before your visit. You can be anctive participant in your care. Start at the initial interview with your physician. The more detailed information you can supply, particularly in the areas noted above, the more accurate the diagnosis will be. It is also helpful to describe to your physician how your symptoms have affected your life at home and at work. It is extremely helpful for your physician to know what kind of support you as a patient can rely on as well as whether there are any adverse influences in your life, either environmental or emotional. Reviewing this material is time consuming and addressing the relief of asthma may take precedent, so tell your physician you want to discuss certain topics at another time. Use a portion of each office visit to discuss a specific topic.

Tho often patients are treated only when severe asthmatic symptoms emerge, often requiring emergency room care. While this is essential and often life saving the “quick fix” of ER treatment is not designed for the careful historical review needed to make the correct diagnosis of asthma.

The Physical Examination

The next step in the diagnosis of asthma is the physical examination, where your physician seeks to correlate the historical information you have provided. For example, the skin and nasal passages are examined for allergic manifestations such as eczema and rhinitis. In the nose, the finding of nasal polyps identifies the patient as someone who may have severe asthma or allergy.

Examination of the chest is extremely important. The physician will note the quality of the breath sounds as air is inhaled and exhaled. When there is airway obstruction the flow of air through the bronchial tubes is turbulent and often creates wheezing, which is more commonly noted upon exhaling. In addition, the narrowed passages prolong the time it takes for air to be exhaled and the physician will note a prolonged expiratory phase. Although the patient’s breathing may be quiet at rest, when asked to take a deep breath and exhale, wheezing and cough may then occur. This maneuver enables a physician to discover an airway obstruction.

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Besides simple spirometry, the physician may perform other pulmonary function tests to better assess and define a patient’s condition. Patients with a variety of illnesses may have reduced capacities and flow rates and further testing may be needed. These tests include measurement of lung volume in which the different divisions or “compartments” of the lungs are measured. These divisions represent quantities of air that are distributed throughout the lung. One example would be the quantity of air that remains in the lung at all times to keep it expanded.

Measuring of lung volumes may be performed by two methods. A common technique requires inhaling a special gas mixture containing helium that the patient breathes for several minutes. Analyzing the amount of helium exhaled allows the physician to calculate how the air was distributed in the different air divisions of the lung. Another technique for measuring lung volumes requires an airtight box called a body plethysmograph. In this technique the patient sits in a clear box that resembles a phone booth and breathes against a mouthpiece. By analyzing pressure changes in the box as the patient breathes it is possible to determine the volume of gas in the lungs.

Another important pulmonary function test is known as a diffusion capacity. This is a sensitive test for the loss of gas exchanging units of the lung as in emphysema. In this test the patient again breathes a special gas mixture and an amount of exhaled gas is collected. By determining how fast the inhaled gas has disappeared, it is possible to determine whether the air sacs are exchanging gases normally.

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Following the careful review of the patient’s history and physical examination the physician will proceed to several commonly used laboratory tests to complete the diagnostic evaluation. There is no universal”checklist” of tests for every patient since there is great variation in each case. Physicians may also have differences in their laboratory evaluations.

Blood Tests

In the laboratory evaluation of asthma it would be common to evaluate the patient’s blood count looking for “allergy cells” called eosinophils. The physician may also obtain a level of IgE, the immunoglobulin in the blood that is often elevated in allergic patients. .

X-rays

A chest x-ray is often necessary to exclude many of the entities discussed above that can mimic asthma. It does not serve to confirm the diagnosis since the features of asthma occurring within the bronchial tubes cannot be seen on a chest x-ray.

Occasionally, the chest x-ray may show that the lungs are greatly expanded and appear larger than normal or hyperinflated. This occurs in asthma because air may enter the bronchial tubes but have difficulty being exhaled, also known as “air-trapping.” This x-ray finding cannot be used as a diagnostic tool for asthma since the same finding may occur in emphysema and in some cases of bronchitis.

Often the physician will order sinus x-rays as part of the laboratory evaluation. Evidence of sinusitis or nasal polyps would identify patients as high-risk candidates for asthma. In addition, the sinusitis may be viewed as a potential aggravating factor in asthmatic attacks and thus become a focus of treatment of individual patients. There is a recent trend toward using the more detailed CAT scan for this exam because of the increased information it provides.

Sputum Exam

Examination of swabs of nasal mucus or chest phlegm (sputum) may be helpful in diagnosing asthma. Microscopic examination may identify abundant eosinophils that would be characteristic of allergy and asthma. The presence of pus cells called neutrophils would suggest an infectious process; for example, bronchitis or sinusitis. The physician may request a culture of the coughed sputum if pus cells are seen under the microscope.

Pulmonary Function Testing

Forced Expiratory Maneuver

The most important laboratory test the physician performs in the diagnosis of asthma is pulmonary function testing. Before the testing begins the patient’s age, race, sex, height, and weight are recorded. From these statistics the expected normal values are determined. These are called the predicted normals and they are determined from statistical analysis of large groups of normal subjects.

The most common test involves a device known as a spirometer, which measures the amount of air (volume) expelled by the patient as well as its speed as the air is exhaled forcefully. In this simple but extremely important maneuver the patient is asked to take a full deep breath in, then exhale fully and forcefully this is called a maximum forced expiratory maneuver. In tracing this maneuver the physician determines the maximum amount of air the patient can expel after the deepest inhalation. This amount is called the vital capacity.

As air is expelled the airflow is measured throughout the maneuver until the patient is unable to exhale further. One extremely useful measurement is of the greatest flow that can be obtained after the patient has inhaled fully and forcefully exhaled. This is termed peak expiratory flow rate or “peak flow.” This important and easily performed. Flow rates are recorded at the beginning, middle, and end of the forced exhalation maneuver and so is the amount of air expelled each second. As air is exhaled by the lungs it is the large bronchial tubes (large airways) that empty first with the smaller passages (small airways) contributing a greater share as exhalation continues and ends. In one second a certain amount of air should normally be exhaled with an expected increase as time increases. The one-second measurement is often a good reflector of the large airways and measurements toward the middle and end of the breath usually determine the condition of smaller air passages.

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In the last several years it has become clear that a group of patients with all the characteristics of asthma (airway obstruction, inflammation, and hyperresponsiveness) may never manifest wheezing. In these patients a persistent cough is the main symptom. Although the physical exam may be unremarkable these patients often have typical histories of cough attacks at night or triggered by exposure to allergens. Laboratory evaluation will often demonstrate all the features of asthma. This syndrome is often identified as the “asthma equivalent syndrome” or “cough asthma.” In the past too much weight has been put on the presence of wheezing in the diagnosis of asthma.

Wheezing Without Asthma

Just as the absence of wheezing has often led to patients being misdiagnosed as nonasthmatic, the presence of wheezing also may lead to the erroneous diagnosis of asthma. It has been said that “all that wheezes is not asthma” since many illnesses may produce turbulent airflow through the airways. Tho often patients are “diagnosed” simply on this one physical finding.

Wheezing may occur in a variety of illnesses, such as when lesions produce a fixed blockage or obstruction in an air passage. In a child or an adult this may be as simple as a foreign body that has been aspirated. In these cases wheezing may be localized to one area or one lung, which should alert the physician to such a possibility. The history of onset may have been sudden, following a “choking spell.” In an adult with a history of smoking a lung tumor that may be benign or malignant may also produce wheezing by growing within the bronchial tube and blocking the air flow. In these and similar cases, chest x-rays and diagnostic techniques such as bronchoscopy often produce the correct diagnosis.

Emphysema and Chronic Bronchitis

Many respiratory illnesses are characterized by wheezing and may be mistaken for asthma. Emphysema is a disease in which the elasticity of the lung is reduced, often resulting in closure of the airways. The term “floppy airways” is often used in this disease to describe how easily the bronchial tubes may close and produce wheezing. Chronic bronchitis is a disease in which there is chronic cough and mucus production. Wheezing is often produced by the clogged and inflamed airways of these patients.

Cystic Fibrosis and Bronchiectasis

Patients with cystic fibrosis, a genetic deficiency disease occurring in children and young adults, often have wheezing due to the clogging of their bronchial tubes by an abnormally viscous mucus. A similar mechanism explains the wheezing found in patients with bronchiectasis, an illness in which infections have permanently damaged the bronchial tubes, leading to plugging and inflammation.

Heart Failure (”Cardiac Asthma”)

In patients with heart failure fluid may collect in the lungs around or within the bronchial tubes. These patients often complain of wheezing, especially at night, mimicking the asthma patient. Due to these similar features this has been called “cardiac asthma” although it is a heart syndrome that often resolves with mobilization of the lung fluid by specific medication. The diagnosis is often made by additional physical findings of heart disease as well as by the chest x-ray and other tests of heart function.

Laryngeal Asthma

A rare but increasingly reported illness that produces wheezing and may be misdiagnosed as asthma is vocal cord dysfunction syndrome. This syndrome is also known as “laryngeal asthma” since in this illness wheezing is produced at the voice box by an abnormal closure of the vocal cords when the patient breathes in (inspiration). Normally, the vocal cords separate on inspiration allowing more air to flow into the lungs. In these patients the sounds of turbulent flow are transmitted over the lung fields, mimicking the wheezing of asthma. The cause of this disorder is unknown. It is thought to be involuntary and often responds to voice therapy. The diagnosis may only be made by direct visualization of the vocal cords by the physician. This is increasingly done with a fiberoptic scope.

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Asthma is often divided into either an allergic or “extrinsic” type that commonly has its onset in childhood, and an adult onset or “intrinsic”type. Although there is considerable overlap between these groups, it is helpful to classify patients according to several features that distinguish them.

Extrinsic Asthma

Extrinsic patients are younger and have attacks clearly triggered by exposure to allergens such as pollens, dust, animal dander, foods, and molds. These patients often have strong family histories of relatives with allergies or asthma. Allergy treatment known as desensitization has often been helpful in these patients. For many years it has been thought that the majority of these patients “outgrew” their asthma by age thirty, but recent evidence suggests that 75 percent remain asthmatic for life. These patients may have long symptom free periods.

Intrinsic Asthma

Intrinsic group patients often develop asthma as adults, and at any age. Often the trigger for these attacks is infection with involvement of the lower respiratory tract as in bronchitis or pneumonia. Some of the most severe infections of this type are viral but they may also be bacterial. Patients in the intrinsic group usually do not have histories of allergies and produce negative allergy tests. Once the diagnosis is evident, further attacks are often triggered by less severe infections. There are fewer symptom free periods in this group and these patients usually require medication for life.

Should This Classification Be Used

Many practitioners no longer use this older classification of the types of bronchial asthma. When discussing the future outlook of the disease as well as treatment options, I find it helpful to use these two general classes of asthma to provide simple guidelines that can be followed. In the younger, highly allergic, or extrinsic asthmatic, for example, emphasis on avoidance of allergens will be extremely important.

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Although asthma may be defined by the factors noted above, its cause remains uncertain. At this time it appears several factors are involved.

Heredity

Heredity certainly plays a major role: asthma and allergy often occur in families. Geneticists have located a gene on chromosome 11 that is strongly associated with allergy and speculate that several other genes may also be involved. One study suggests that a variant gene may direct the immune system to “overreact” to allergic stimuli by allowing a protein known as Immunoglobulin E (IgE) to “lock on&” to the surface of allergy cells called mast cells. When IgE reacts with allergy substances known as allergens, the mast cell disintegrates, releasing irritating chemicals that cause inflammation. These chemicals are the asthma mediators. Further research will undoubtedly produce a more detailed explanation for the genetic basis of asthma.

The Immune System

The immune system also plays a major role in the development of asthma. The immune system has two basic branches: cellular and humoral. Cellular immunity involves white blood cells called lymphocytes that can be provoked or “sensitized.” An example of this would be the body’s rejection process against a transplanted organ. Humoral immunity involves production of substances called antibodies that circulate in the blood. An example would be how the body reacts to a vaccination by producing antibodies. An antigen (may be called an allergen) is a substance capable of provoking the immune response.

Lymphocytes, Mast Cells, and Eosinophils

In asthma, the immune system is provoked in two ways. First, the cellular elements are mobilized and activated. Microscopic studies of the lining of the bronchial tubes in asthma have revealed increased numbers of lymphocytes. These cells produce substances that result in an increase in the number of mast cells that are known to store and release many irritating chemicals involved in production of the asthmatic reaction. These chemical substances or mediators of asthma produce inflammation. Another active cell that is “recruited” by lymphocytes found in the inflamed bronchial lining is the eosinophil. Large numbers of these cells may also be found in the blood of allergic and asthmatic individuals.

Immunoglobulin E

The second major immune response in asthma is the production of antibodies known as immunoglobulins, which is stimulated by substances released by the activated lymphocytes. One type, Immunoglobulin E or IgE, may be produced by inhaling a specific foreign substance such as ragweed. When the IgE attaches to the surface of the mast cell, a process is initiated that leads to release of the “asthma chemicals” and an ensuing asthmatic reaction.

Allergy

Allergy is the leading cause of asthma. In many patients allergens, activated lymphocytes, mast cells, eosinophils, and IgE all play major roles in the immune response that produces the asthmatic reaction. However, asthma may also occur without allergy. In nonallergic patients doctors believe the immune response may be triggered by infection.

Viruses

Viral infections in susceptible individuals have been thought to be potent triggers for the development of asthma. Researchers have recently demonstrated that viruses may cause human immune system cells to produce IgE. Animal research has shown that viruses are capable of altering the nervous impulses that stimulate the bronchial tubes. The altered nerve impulses may then produce constriction in the bronchial tubes. Susceptible patients with viral bronchial infections may become “sensitized” and display all the features noted in the definition of asthma.

The Environment

Environmental irritants, such as cigarette smoker pollutants (ozone, particulates), dust, and chemicals and proteins found in the home and the workplace are also considered capable of provoking the asthmatic response. These irritants may account for large numbers of asthmatic attacks each year and may also, in part, explain an increase in the number of asthma cases.

The Nervous System

Another possible cause of asthma is a dysfunction of nerve receptors or endings in the muscle surrounding the bronchial tubes that produces constriction of the air passage. Research has shown that an imbalance may exist in the nervous system that supplies the bronchial tubes of asthmatic individuals. This inborn error may shift the balance of forces toward those nerve signals that promote narrowing of the bronchial passages.

The Future

At this time the specific causes of asthma and the signals that are involved in starting the chain reaction that produces the disease are unknown. In the last five years promising research has shown that asthma is an inflammatory disease with features similar to other illnesses such as arthritis. This breakthrough is likely to lead to a further understanding of the causes of asthma and will likely form the basis for greater advances in treatment.

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