Asthma

DEFINITION: A chronic inflammatory obstructive pulmonary disease that obstructs the airways to the lungs and makes it difficult or, in severe attacks, nearly impossible to breathe

ANATOMY OR SYSTEM AFFECTED: Chest, immune system, lungs, respiratory system

CAUSES: Environmental factors, allergens, viral infections

SYMPTOMS: Tightening of the chest, sudden breathlessness, wheezing, coughing, chest pain

DURATION: Chronic, with acute episodes

TREATMENTS: Medications such as short-acting beta agonists (SABA), inhaled corticosteroids (ICS), long-acting beta-2 agonists (LABA), and omalizumab; subcutaneous allergen immunotherapy; lifestyle modification to avoid triggers

Causes and Symptoms

Asthma is a Greek word meaning “gasping” or “panting.” It is a chronic obstructive pulmonary (lung) disease that involves repeated attacks in which the airways in the lungs are suddenly blocked. Asthma attacks cause the affected person to experience tightening of the chest, sudden breathlessness, wheezing, and coughing. Death by asphyxiation is rare but possible. Fortunately, the effects can be controlled with proper medication.

The severity of asthma symptoms and attacks varies greatly among individuals, and those living with the disease can be categorized in one of four classes: intermittent, mild persistent, moderate persistent, and severe persistent. Mild persistent asthma is characterized by fewer than six minimal attacks per year, no symptoms between attacks, and no hospitalizations and little or no medication between attacks. Severe persistent asthma is characterized by more than six serious attacks each year, symptoms between attacks, more than ten missed school days or workdays, and two or more hospitalizations per year. Attacks are typically spaced with symptom-free intervals but may also occur continuously. Rather than focusing only on the specific attacks, one should view and treat asthma as a chronic disease that persists over a long period of time.

A review of the path of air into the body during normal breathing helps in understanding asthma. During inhalation, air travels into the nose and mouth and then into the trachea (windpipe); it then divides into the two tubes called bronchi and enters the lungs. Inside each lung, the tubes become smaller and continue to divide. The air finally moves into the smallest tubes, called bronchioles, and then flows into the millions of small, thin-walled sacs called alveoli. Vital gas exchange occurs in the alveoli.

This gas exchange involves two gases in particular, oxygen and carbon dioxide. Oxygen must cross the membrane of the alveoli into the blood and then travel to all the cells of the body. Within the cells, it is used in chemical reactions that produce energy. These same reactions produce carbon dioxide as a by-product that is returned by the blood to the alveoli. This gas is removed from the body through the same pathway that brings oxygen into the lungs.

The parts of this airway that are involved in asthma are the bronchioles. These tubes are wrapped with smooth, involuntary muscles that adjust the amount of air that enters. The lining of the bronchioles also contains many cells that secrete a substance called mucus. Mucus is a thick, clear, slimy fluid produced in many parts of the body. Normal production of mucus in the lungs catches foreign material and lubricates the pathway to allow smooth airflow. People living with asthma have very sensitive bronchioles.

Three pathological processes in the bronchioles contribute to an asthma attack. One is an abnormal sensitivity and constriction of the involuntary muscles surrounding the airway, which narrows the diameter of the airway. Another is an inflammation and swelling of the tissues that make up the bronchioles themselves. The third is an increased production of mucus, which then blocks the airways. These three mechanisms may work in combination and are largely caused by the activation of mast cells in the airways. The result can be extreme difficulty in taking air into the lungs until the attack subsides. The characteristic “wheeze” of asthma is caused by efforts to exhale, which is more difficult than inhaling. In the most serious attacks, the airways may close down to the point of suffocating the patient if medical help is not given.

Attacks can vary in severity at different times because of variations in tension within the bronchiole muscles. Although there is still debate about the general function of these muscles, they probably help to distribute the air entering the alveoli evenly. Control of the tension in these smooth muscles is involuntary and follows a circadian (twenty-four-hour) rhythm influenced by neurohormonal control.

Following a given asthma attack, patients are sometimes susceptible to additional, more severe attacks. This period of high risk, called a "late-phase response," occurs five or six hours after the initial symptoms pass and may last as long as several days.

The initial cause and mechanism of an asthma attack can vary from person to person. Accordingly, asthma is usually divided into two types. One type is extrinsic—that is, caused by external triggers that bring about an allergic response. Allergic reactions involve the immune system. Normal functioning of the immune system guards the body against harmful substances. With an allergy, the body incorrectly identifies a harmless substance as harmful and reacts against it. This substance is then called an allergen. If the symptoms of this reaction occur in the lungs, the person has extrinsic or allergic asthma.

Researchers have discovered that many people with asthma have elevated levels of immunoglobulin E (IgE), a substance that indicates an allergic reaction within the body. Allergic triggers for asthma include dust, pollens, mold, animal dander, and other substances. Infants may have an IgE response to respiratory syncytial virus. Improved asthma treatments may lie in substances that interfere with interleukin-4 (IL-4), which promotes IgE production in the body.

When allergens enter the body, the white blood cells make specific IgE antibodies that can bond with the invaders. Next, the IgE antibodies attach to the surfaces of mast cells; these cells are found all over the body and are numerous in the lungs. The allergens attach to the IgE antibodies located on the mast cells, and the mast cells are stimulated to produce and release chemicals called mediators, such as histamine, prostaglandin D₂, and leukotrienes. These mediators cause sneezing, tighten the muscles in the bronchioles, swell the surrounding tissues, and increase mucus production.

The second type of asthma is intrinsic and does not involve allergies. People with intrinsic asthma have hyperactive airways that overreact to irritating factors. The mechanism for this form is not clearly understood, but no IgE antibodies for the irritant are placed on the mast cells. Examples of such nonallergic stimuli are cigarette smoke, house dust, artificial coloring, aspirin, ozone, or cold air. Insecticides, cleaning fluids, cooking foods, and perfume can also trigger attacks. Also included in this category are attacks that are caused by viral infections (including colds and flu), stress, and exercise. Asthma can be triggered by many different substances and events in different people. While the symptoms are the same whether the asthma is intrinsic or extrinsic, individuals with asthma need to identify what substances or events trigger their attacks in order to gain control of the disease.

In addition to tightening of the chest, sudden breathlessness, wheezing, coughing, and chest pain common to an asthma attack, symptoms of a severe attack include rapid pulse, blue lips or skin, perspiration, anxiety, or extreme fatigue.

Why people develop asthma is not well understood. Asthma can begin at any age, but it is more likely to arise in childhood. While it is known that heredity predisposes an individual to asthma, the pattern of inheritance is not a simple one. Most geneticists now regard allergies as polygenic, which means that more than one pair of genes is involved. Exposure to particular external conditions may also be important. Boys who develop asthma are more likely to display symptoms in childhood, while girls are more likely to show signs of the disease at puberty (about age twelve). Childhood asthma is also most likely to disappear or to be “outgrown” at puberty; about half of the cases of childhood asthma eventually disappear.

Early exposures to some triggers may be a key in the development of asthma. Increasingly, studies indicate that air pollution is an important risk factor for developing asthma, especially in children. Smoking by mothers during and after pregnancy can cause children who have a genetic disposition to develop asthma, as early exposure to secondhand smoke can cause an allergy to develop. Early studies in this area were confusing until the data were sorted by level of education. Lung specialist Fernando Martinez of the University of Arizona believes that less-educated women who smoke are more likely to cause this effect because their homes tend to be smaller and therefore expose the children to more concentrated levels of smoke. Early exposure by genetically susceptible children to dust and dust mites may also cause some to develop asthma. Exposure to chemicals in utero is also a risk factor for developing asthma. Lower respiratory infections early in life are also associated with an increased risk for asthma. Being overweight or obese also increases the risk of developing asthma.

While attacks can cause complications, there is no permanent damage to the lungs themselves. Complications include possible lung collapse, infections, chronic dilation, rib fracture, a permanently enlarged chest cavity, and respiratory failure. However, millions of days of work and school are lost as individuals recuperate from attacks; asthma is the leading cause of missed school days. Even though attacks can be controlled by medication, fatalities do occur. In the United States, there are more than three thousand deaths due to asthma each year, although asthma death rates have declined since the late 1990s.

Treatment and Therapy

The key to gaining control of asthma is discovering the particular factors that act as triggers for an attack in a given individual. These factors vary and at times can be surprising; for example, one person found that a mint flavoring in a particular toothpaste was a trigger for his asthma. Nevertheless, most common triggers fall in the following groups: allergies; irritants, including dust, fumes, odors, vapors, molds, mildew, and red tide; air pollution, weather and temperature changes, and dryness; colds, flu, and other viral infections; and stress. Even types of food may be important. Diets low in vitamin C, fish, or a zinc-to-copper ratio, as well as diets with a high sodium-to-potassium ratio, may increase the risk of asthma attacks and bronchitis. There have also been correlations between low niacin levels in the diet and tight airways and wheezing. Food allergies and sulfites, chemical preservatives found in wine and dried fruits, may also act as triggers.

Diagnosis of asthma is based on medical history, a physical examination, and spirometry. Some doctors supplement their diagnosis of asthma with a tool called the "peak flow meter," which measures peak expiratory flow rate. The meter can also be used by patients at home to predict impending attacks. This inexpensive device measures how quickly air can be moved out of the lungs. Therefore, it can be discovered that airways are beginning to tighten before other symptoms occur. The early warning allows time to adjust medications to head off attacks. This tool can help individuals with asthma take charge of their disease.

Various medications are available to keep the airways open and to lower their sensitivity. In an emergency, drugs may be injected, but medications are usually either inhaled or taken orally as pills. Because inhalation transports the medication directly to the lungs, lower doses can be used. Individuals with asthma should carry inhalers, which allow them to breathe in medication such as short-acting beta agonists (SABA) during an attack. Because this action requires a person to coordinate inhaling with the release of the spray, young children are sometimes better off with a device that requires them to wear a mask. The choice and dosage of medicine vary with the patient, and physicians need to determine what is safest and most effective for each individual.

The treatment of asthma is based on a stepwise management approach. The National Heart, Lung, and Blood Institute recommends individuals with intermittent asthma to use SABA as needed; for exacerbations due to viral infections, individuals with intermittent asthma may need to use SABA every four to six hours. Oral systemic corticosteroids may also be prescribed to treat moderate to severe exacerbations. For individuals with persistent asthma, the recommended treatment begins with low-dose inhaled corticosteroids (ICS); subcutaneous or sublingual immunotherapy may be considered for individuals with allergic asthma. Low-dose ICS plus long-acting beta-2 agonists (LABAs) or medium-dose ICS alone may be used if low-dose ICS is insufficient. High-dose ICS and LABA may be used to treat more severe cases of asthma.

Some of the common prescribed drugs are bronchodilators, inflammation reducers, and trigger-sensitivity reducers. The bronchodilators include albuterol. These are beta-agonists that mimic the way in which the body’s nervous system relaxes or dilates the airways. (Any drug that functions as a beta-blocker should be avoided by people with asthma because of its opposite effects.)

The use of inflammation reducers known as corticosteroids plays an important role in the treatment of asthma. Whether administered orally or via an inhaler, these medications can both prevent and treat the airway inflammation that leads to asthma attacks. Their anti-inflammatory effects mean fewer symptoms and attacks, better airflow, and airways that are less likely to react to triggers in an exaggerated or hyperresponsive manner. Inhaled steroids are preferred for long-term management of asthma. Inhalation delivers the medication directly to the site of inflammation and is associated with fewer side effects, which can include osteoporosis, thinning and easily bruised skin, cataracts, and suppression of the adrenal glands. However, oral steroids may also be used in the treatment of moderate to severe persistent asthma, and short courses of oral corticosteroids may be used during periods of sudden, life-threatening symptoms. To minimize possible side effects, oral steroids are given every other day or in decreasing dosage over a limited period of time. Calcium and vitamin D supplements are used to prevent bone loss in these patients.

Individuals should not exceed their prescribed dosage when using an inhaler. An individual who feels the need to use an inhaler more often to obtain adequate relief should see a doctor. The increased need is a sign of worsening asthma, and a doctor needs to investigate and perhaps change the treatment.

With a doctor’s approval, regular sports and exercise may be pursued. Furthermore, exercise may be helpful in reducing the frequency and severity of attacks. Many athletes compete at high levels in spite of their asthma. Sports that do not require continuous activity or exposure to cold, dry air are preferred. Swimming is considered ideal. Doctors can help the athlete with a pre-exercise medication plan and a backup plan if symptoms occur during or after the exercise.

Individuals with asthma are advised to avoid allergens and other asthma triggers and to consider installing air conditioning and HEPA air filtering units. Breathing techniques and written emotional disclosure may also offer relief.

Perspective and Prospects

In the United States, about one in twelve people have asthma, according to the Asthma and Allergy Foundation of America. An estimated 27 million persons had asthma in the United States in 2023. Asthma prevalence is higher among individuals with family incomes that are below the poverty level. Despite the rising incidence of asthma, asthma death rates per one thousand persons with asthma have declined significantly since their peak in the 1980s; nevertheless, asthma deaths rates per one thousand persons with asthma were higher for women, black persons, and the elderly.

According to the World Health Organization (WHO), an estimated 262 million people worldwide were living with asthma in 2019. The majority of asthma deaths occur in low- and lower-middle-income countries, where asthma is often underdiagnosed and undertreated.

Bibliography

American Medical Association. Essential Guide to Asthma. Pocket, 2000.

"Asthma." MedlinePlus Medical Encyclopedia, US National Library of Medicine, 1 Jan. 2023, medlineplus.gov/ency/article/000141.htm. Accessed 28 Jan. 2024.

"Asthma." World Health Organization, 6 May 2024, www.who.int/news-room/fact-sheets/detail/asthma. Accessed 2 Aug. 2024.

"Asthma Facts." Asthma and Allergy Foundation of America, Sept. 2023, www.aafa.org/asthma-facts/. Accessed 28 Mar. 2024.

"Asthma Overview." American Academy of Allergy, Asthma, and Immunology, Sept. 2023, www.aaaai.org/conditions-and-treatments/asthma. Accessed 28 Mar. 2024.

Bernstein, Jonathan A., and Mark L. Levy, eds. Clinical Asthma: Theory and Practice. CRC, 2014.

Bislimi, Adelina H., and Lulezime C. Tolka, eds. Asthma: Causes, Complications, and Treatment. Nova Science, 2012.

Currie, Graeme P., and John F. W. Baker.Asthma. 2nd ed. Oxford UP, 2012.

Judd, Sandra J. Asthma Sourcebook. 3rd ed. Omnigraphics, 2012.

Lockey, Richard F., and Dennis K. Ledford. Asthma: Comorbidities, Coexisting Conditions, and Differential Diagnosis. Oxford UP, 2014.

Lotvall, Jan, ed. Advances in Combination Therapy for Asthma and COPD. Wiley, 2012.

"Most Recent National Asthma Data." Centers for Disease Control and Prevention, 10 May 2023, www.cdc.gov/asthma/most‗recent‗national‗asthma‗data.htm. Accessed 28 Mar. 2024.

Parker, James M., and Philip M. Parker, eds. The Official Patient’s Sourcebook on Asthma. Rev. ed. Icon Health, 2005.

Welch, Michael J., and the American Academy of Pediatrics. American Academy of Pediatrics Guide to Your Child’s Asthma and Allergies: Breathing Easy and Bringing Up Healthy, Active Children. Random, 2000.