Asthma is common in industrialized countries, affecting about 334 million people worldwide. The disease is most prevalent in Australia, New Zealand, Brazil, and northwestern Europe. Although asthma prevalence in the United Kingdom has been stable since the 1990s, rates there for asthma are higher than in other European countries, and on average three deaths occur each day from asthma.
In the United States, asthma prevalence in 2017 was about 8.7% of the population, or 25.7 million people, including over 6 million children and 18.5 million adults. Among these individuals, the prevalence of asthma is highest in children aged 5–14 years; young adults 22–29 years; and adults 35–64 years. The Centers for Disease Control and Prevention (CDC) reports that 46% of individuals with current asthma report having one or more asthma attacks a year, accounting for 1.8 million emergency department visits annually. The majority of asthma attacks treated as emergencies occur in adult asthma patients. Asthma is responsible for about 3,400 deaths annually, representing a steady decline since 2001. More women than men are diagnosed with adult-onset asthma. Prevalence is greater in non-Hispanic white U.S. residents than in non-Hispanic blacks and Hispanics. Although similar symptoms are present in all asthmatic individuals, certain important aspects of asthma differ between children and adults.
During an asthma attack, or asthma exacerbation, a fairly rapid sequence of changes unfolds; airways in an asthmatic individual become inflamed and swollen, usually in response to a specific trigger. Muscles in the airways contract, extra mucus is produced, the bronchial tubes narrow, and symptoms such as coughing, chest tightness, wheezing, and difficulty breathing follow. Asthma attacks also may occur at night (nocturnal asthma) during sleep. Since individuals who work at night may have attacks during daytime sleeping hours, experts suggest that an internal trigger associated with sleep is responsible for these attacks. Attacks occurring at any time can be either mild with symptoms that respond to home treatment or severe needing immediate emergency treatment. In individuals with asthma, the inflamed airways may be hyper-responsive to stimuli such as cold air, exercise, dust mites, airborne pollutants (smoke, industrial dusts, and particulate matter), and stress and anxiety. However, although any of these stimuli may cause asthma attacks in some individuals, not all people with asthma are affected by them.
Hypersensitivity to known allergens is a major risk factor for asthma. Allergies are present in about 75% of asthmatic individuals and allergy-induced asthma may be triggered by airborne dusts, vapors, and particulate matter, including pollen, industrial pollutants, mold spores, cockroach waste, and pet dander, among many others. Those who work in occupations that involve exposure to inhaled dusts or fumes are at higher risk of asthma than those who are not exposed.
The most common inhaled allergens that trigger asthma attacks are:
Approximately 20% of asthma cases begin in the first year of life. When asthma begins in childhood, it often does so in children who are likely, for genetic reasons, to become sensitized to common allergens in the environment (atopic individuals). When these children are exposed to dust mites, animal proteins (i.e., animal hair, dander), mold, or other potential allergens, their immune systems produce an antibody that is intended to engulf and destroy the foreign materials. The presence of the antibody has the effect of making the airway cells sensitive to specific types of materials. Further exposure can lead rapidly to an asthmatic response. This condition, called atopy, is present in at least one-third and as many as one-half of the general population.
Individuals who do not have allergies may still develop a form of asthma triggered by aerobic exercise. These exercise-induced episodes can last for several minutes and leave the individual gasping for breath. About 12%–15% of Americans who do not have allergies are estimated to be susceptible to exercise-induced asthma; rates as high as 40%–90% have been reported among individuals who do have allergies. Inhaling cold air, aerobic exercise lasting more than ten minutes or shorter periods of very heavy aerobic exercise tend to trigger an exercise-induced asthma attack in susceptible individuals. Exposure to airborne pollutants and certain chemicals (e.g., chlorine in pools, herbicides on a playing field) appear to increase the likelihood of asthma episodes in sensitive individuals.
Causes and symptoms vary between individuals. Not every person with asthma has the same symptoms and even common symptoms may manifest in response to different triggers. Some children have an asthma attack when running or playing hard, especially in cold weather. Upper respiratory infections, laughing, and crying hard can all cause an asthma attack. Periods of time pass without symptoms in some individuals, whereas others may have symptoms daily. Mild asthma attacks are more common than severe attacks, which last longer and require immediate medical care.
In most cases, asthma is caused by inhaling an allergen to which individuals are hypersensitive. This sets off the chain of biochemical and tissue changes leading to airway inflammation, bronchoconstriction, and wheezing. Avoiding or minimizing exposure to asthma triggers is the most effective way of treating asthma, so identifying the specific allergen or irritant that triggers symptoms is especially helpful in determining a treatment strategy. Once asthma is present, symptoms may be triggered or exacerbated if individuals also have rhinitis (inflammation of the lining of the nose such as from allergies) or sinusitis (inflammation of the sinuses). For individuals with gastroesophageal reflux (GERD), a condition in which stomach contents and hydrochloric acid move up into the esophagus, this condition may exacerbate asthma symptoms. A viral infection of the respiratory tract (e.g., a cold) also may trigger or exacerbate an asthmatic reaction. Exacerbations of asthma may also occur in response to taking aspirin, NSAIDs, and beta-blocker drugs, especially in adults.
Inhaling tobacco smoke, either from smoking or being around people who are smoking, can irritate the airways and trigger an asthmatic attack. Air pollutants such as wood smoke can have a similar effect. In addition, three factors regularly produce attacks in certain asthmatic individuals and may sometimes be the sole cause of symptoms:
Asthma attacks are usually accompanied by warning signs and rarely happen without them. The most common warning signs are:
Wheezing is often obvious, but mild asthma attacks may be confirmed only when the physician listens to the chest with a stethoscope. Besides wheezing and being short of breath, individuals may cough and/or may report a feeling of tightness in the chest. Wheezing is often loudest when individuals breathe out (exhale) in an attempt to expel air through the narrowed airways. Some people with asthma are free of symptoms most of the time but occasionally may have episodes of shortness of breath. Others spend much of their time wheezing or have frequent bouts of shortness of breath until properly treated. Crying or laughing may bring on an attack. Severe episodes often develop when individuals have a viral respiratory tract infection or are exposed to a heavy load of an allergen or irritant (e.g., breathing in smoke from a campfire). Asthma attacks may last only a few minutes or continue for hours or even days (a condition called status asthmaticus).
The physician will ask about personal and family history regardomg asthma or allergies. A diagnosis of asthma may be strongly suggested by typical signs and symptoms such as coughing, wheezing, and shortness of breath. The examining physician will listen to the individual's chest sounds and look for maximum chest expansion while enhaling. Hunched shoulders and contracted neck muscles are prominent signs of narrowed airways. Nasal polyps or increased amounts of nasal secretions are noted frequently in asthmatic individuals. Skin changes, such as atopic dermatitis or eczema, are indications that the individual is likely to have allergies.
A test called spirometry is used to evaluate breathing by measuring how rapidly air is exhaled and how much air is retained in the lungs. The test is performed to estimate the extent of narrowing of the airways, an indicator of severity of the disease. Repeating the test after the individual inhales a bronchodilator drug that widens the airways helps determine whether the airway narrowing is reversible. A related instrument called a peak flow meter measures how hard the individual can breathe air out and allows individuals to keep track of asthma severity when at home.
It often is difficult to determine what is triggering asthma attacks in some individuals. Allergy skin testing may be used, although an allergic skin response does not always mean that the allergen being tested is responsible for exacerbating asthma. Sputum eosinophils may be identified by staining a sputum sample (mixture of saliva and mucus from coughing) pink to highlight the cells produced in allergic reactions. The body's immune system produces specific antibodies targeted toward each allergen. Measuring the amount of a specific antibody in the blood may indicate how sensitive the individual is to a particular allergen. If the diagnosis is still in doubt, the individual can inhale a suspect allergen while using a spirometer to detect airway narrowing. Spirometry also can be repeated after a bout of exercise when exercise-induced asthma is suspected. A chest x-ray may be done to help rule out other lung disorders.
Other tests may include scans of the lungs and sinuses using chest x ray and high-resolution computed tomography (CT) to identify structural abnormalities that may aggravate breathing. Nitric oxide may be measured in the breath to evaluate inflammation in the airways; asthma produces higher than normal levels of the nitric oxide gas.
Asthma has no definitive cure but can be managed by controlling symptoms. Modern asthma management guidelines include four components of asthma care:
The goals of asthma treatment are to prevent troublesome symptoms, maintain lung function as close to normal as possible, and allow individuals to pursue their normal activities, including those requiring exertion. Individuals are advised to be examined periodically and undergo spirometry to measure lung function and ensure that treatment goals are being met. The most effective drug therapies control asthmatic symptoms with minimal or no side effects. Many people with asthma are treated with a combination of long-acting drugs that help prevent asthma attacks and short-acting (quick relief) drugs given by an inhaler to reduce the immediate symptoms of an attack.
The choice of initial drug treatment often depends on whether the asthma is classified as intermittent, mildly persistent, moderately persistent, or severely persistent. Other factors such as the age of the individual, other medical conditions that may be present, and other drugs the patient may be taking may also influence medication choices. Several attempts may be needed to find the best combination of drugs to control an individual's asthma.
BETA-RECEPTOR AGONISTS (BRONCHODILATORS). Bronchodilators relax airway walls and open the airway lumen. They are often the first and best choice for relieving sudden attacks of asthma and for preventing attacks of exercise-induced asthma. Some bronchodilators, such as albuterol (Ventolin, Proventil) and levalbuterol (Xopenex), act mainly on lung cells and have little effect on other organs. Bronchodilators may be taken orally (i.e., tablets, capsules, or liquids), but typically they are administered through inhalers. The inhaled drugs go directly into the lungs and are associated with fewer systemic side effects. These drugs generally start acting within minutes, but the beneficial effects last only four to six hours.
Long-acting beta agonists (LABAs) have been developed with effects lasting up to 12 hours. These include salmeterol (Severent), fluticasone/salmeterol (Advair), formoterol (Perforomist, Foradil), and budesonide/formoterol (Symbacort). Although the U.S. Food and Drug Administration (FDA) issued a warning in December 2008 that LABAs may increase the chance of severe asthma episodes and asthma-induced death, these drugs have been investigated but not banned. Research results indicate that they should only be used in combination with an inhaled corticosteroid. Some are not recommended as a first-line treatment for asthma or for use alone (i.e., without inhaled steroids) as an asthma treatment. The FDA strongly recommends that people taking LABAs discuss the risks and benefits with their physician in light of emerging information about their safety.
INHALED CORTICOSTEROIDS. Inhaled corticosteroids (steroids) are anti-inflammatory drugs resembling natural body hormones. They are long-term asthma control medications that are still considered the cornerstone of treatment. Regular use relieves symptoms of chronic asthma and prevents asthma episodes. However, they are not used to treat acute asthma attacks once they have begun. Examples of inhaled corticosteroids include fluticasone (Flovent), flunisolide (Aerospan), triamcinolone (Azmacort), and beclomethasone (Vanceril, Beclovent, QVAR), among others. Long-term use of inhaled corticosteroids reduces sensitivity to allergens, thereby reducing the frequency of asthma attacks. Prednisone (Deltasone, Orasone, Meticorten) is given by mouth (i.e., tablets or capsules) to speed recovery after treatment of initial symptoms of an asthma attack and sometimes to treat chronic asthma.
Corticosteroids usually can provide long-term control of even severe cases of asthma and help to maintain good lung function. However, long-term use of corticosteroids is noted for causing numerous side effects, including bleeding in the stomach, reduction of bone stores of calcium, cataracts in the eye, and a metabolic condition that mimics diabetes. Individuals using corticosteroids for lengthy periods also may have problems with wound healing, weight gain, and may experience psychological problems. In children, growth may be slowed.
LEUKOTRIENE RECEPTOR ANTAGONISTS. Leukotriene receptor antagonists are anti-inflammatory drugs that block the action of leukotrienes, which are the pro-inflammatory cytokines in the blood that produce inflammation in the airways characteristic of asthma. Commonly used drugs in this category include montelukast (Singulair), zafirlukast (Accolate), and zileuton (Zyflo). These drugs are prepared as tablets to be taken by mouth regularly to treat or prevent symptoms of asthma, especially exercise-induced asthma. Some are available as extended-release tablets to be taken twice a day with morning and evening meals.
OTHER DRUGS. Cromolyn (Intal) and nedocromil (Tilade) are anti-inflammatory drugs that affect mast cell production. They may be used as initial treatment to prevent asthma attacks. They may also prevent attacks when given before exercise or when exposure to an allergen cannot be avoided. To be effective, these drugs must be taken regularly even if no asthma symptoms are present. Anticholinergic drugs, such as atropine, may be useful in controlling severe attacks when added to an inhaled beta-receptor agonist. These drugs suppress mucus production and help to open the airways.
FUTURE DRUG THERAPIES. Targeted cytokine therapy is a drug therapy that has been shown in some studies to decrease blood eosinophils, a type of white cell activated in allergic reactions. After comprehensive clinical trials are completed, cytokine therapy was expected to become an integral part of asthma management.
A severe asthma attack requires immediate treatment. Emergency medical assistance may be needed, as an individual experiencing an acute attack may need to be given extra oxygen. Rarely is it necessary to use a mechanical ventilator to help the individual breathe. An inhaler, usually containing a beta-receptor agonist, is inhaled repeatedly or continuously. If the individual does not respond promptly and completely, a corticosteroid may be given, but usually corticosteroids are not given once an attack has begun. Instead, a course of corticosteroid therapy given when the attack is over may make recurrence less likely.
Many asthma experts recommend a device called a spacer to be used along with metered-dose inhalers. The spacer is a tube or bellows-like device held in or around the mouth into which the metered-dose inhaler is puffed. This device enables more medication from a metered-dose inhaler to reach the lungs.
Long-term asthma treatment is based on inhaling appropriate drugs using a special inhaler that meters the dose. Individuals must be instructed in proper use of an inhaler to be sure that it will deliver the right amount of drug. Once asthma has been controlled for several weeks or months, a physician may recommend that the patient gradually cut down on drug treatment. The last drug added usually is the first to be reduced. Individuals should be seen by their physician every one to six months, or as needed, depending on the frequency of asthma episodes.
Peak flow meters may be prescribed for school-age and older children, allowing parents to monitor asthma severity. With home peak-flow monitoring, many children with asthma are able to discern at an early stage if a flare-up is just beginning and adjust their medications appropriately.
Individuals with asthma do best when they have a written action plan that addresses how to adjust their medication and when to seek medical help. Individuals with self-management written action plans have been found to have fewer hospitalizations, fewer emergency department visits, improved lung function, and lower mortality rate.
Referral to an asthma specialist should be considered if any of the following occurs:
INFANTS AND YOUNG CHILDREN. The course of asthma must be closely monitored in infants and young children, particularly to tailor treatment to levels of asthma severity. Asthmatic children often need medication at school to control acute symptoms or to prevent exercise-induced attacks. Parents or guardians of these children are advised to consult with the school district on school drug policies in order to assure that children are permitted to carry an inhaler. Healthcare providers are urged to write an asthma treatment plan that can be presented to a child's school. Proper management will usually allow a child to take part in play activities.
OLDER ADULTS. Older adults with asthma often have other types of lung disease such as chronic obstructive pulmonary disease (COPD) in which both chronic bronchitis and emphysema are present. Chronic bronchitis, bronchiectasis, or emphysema may also be present as a single entity. Such chronic lung conditions must be taken into account when treating asthma symptoms. Side effects from beta-receptor agonist drugs, including a speeding heart and tremor, may be more common in older individuals.
Alternative and complementary medicine tends to view asthma as the body's protective reaction to environmental agents and pollutants. As such, the treatment goal is to restore balance to and strengthen the entire body and provide specific support to the lungs and to the immune and hormonal systems. Individuals with asthma can help by keeping a diary of asthma attacks in order to determine environmental and emotional factors that may be contributing to their condition.
Alternative treatments such as acupuncture, herbal aromatherapy, and food-based or herbal medicines have minimal side effects, are generally inexpensive, and are convenient forms of self-treatment. They also can be used alongside allopathic (conventional drug treatments) treatments (integrative approach) to improve their effectiveness and reduce side effects.
DIETARY AND NUTRITIONAL THERAPIES. Some physicians recommend minimizing or eliminating dairy products from the diet, as these increase mucus secretion in the lungs and are sources of food allergies.
Other recommendations are to avoid processed foods, refined starches and sugars, and foods with artificial additives and sulfites. Beneficial plant-based diets that are high in fresh fruits, vegetables, and whole grains, and low in salt are less apt to provoke allergies. Individuals with asthma can experiment with their diets to determine if food allergies are triggering asthma. Some studies have shown that a sustained vegan diet can be effective in controlling asthma.
Individuals with asthma are also advised to stay well hydrated by drinking plenty of water to help maintain moisture in the lungs. Onions and garlic contain quercetin, a flavonoid (a chemical compound/biological response modifier) that inhibits the release of histamine and may be effective in this regard if added to an asthmatic individual's diet. Quercetin is also available as a supplement and can be taken with a digestive enzyme to increase its absorption.
Vitamins A, C, and E are known as important nutritional support for asthma. Also, the B complex vitamins, particularly B6 and B12, may be helpful for individuals with asthma, as well as magnesium, selenium, and an omega-3 fatty acid supplement such as flaxseed oil. A good multivitamin supplement also is recommended.
Traditional Chinese Medicine (TCM) uses ma huang to help treat symptoms during asthma attacks. Ma huang contains ephedrine, a bronchodilator that was once used in many drugs. However, in the United States, the FDA banned the sale of ephedra in April 2004 after several reports of high blood pressure and circulatory system distress were published and some users had heart attacks and strokes. Although manufacturers of ephedra raised legal challenges to this decision and the U.S. Supreme Court refused to hear these challenges in 2007, the ban on ephedra became permanent.
Mind/body medicine has demonstrated that psychological factors play a complex role in asthma. Emotional stress can trigger asthma attacks. Mind/body techniques strive to reduce stress and help asthma sufferers manage the psychological component of their condition. Biofeedback is a treatment method that uses monitors to reveal physiological information to patients and to teach relaxation and deep breathing techniques that may help people with asthma. Specific mind/body techniques used for asthma include relaxation methods, meditation, hypnotherapy, mental imaging, psychotherapy, and visualization.
Some studies have shown that yoga significantly helps people with asthma by teaching exercises specifically designed to expand the lungs, promote deep breathing, and reduce stress. Pranayama is the yogic science of breathing, which includes hundreds of deep breathing techniques. These breathing exercises may be done daily as part of any treatment program for asthma, as they are an effective and inexpensive measure that can be done anywhere.
Many people, including parents of children with asthma, believe that people with asthma should not exercise. Many parents believe it is dangerous for their asthmatic children to participate in sports or physical exercise, but physical activity has been shown to benefit all children, including those with asthma. Parents are advised to work with their children's healthcare providers and any coach or organized sport leader to help plan and then carefully monitor their children's physical activities.
Acupuncture can be an effective treatment for asthma. It is used in TCM along with dietary changes. Acupressure also can be used as a self-treatment and prevention for asthma attacks. The Lung 1 points in acupuncture, used to stimulate breathing, can be found on the chest easily. These are sensitive, often knotted spots on the muscles that run horizontally about an inch below the collarbone and about two inches from the center of the chest. The points can be pressed in a circular manner with the thumbs, while the head is allowed to hang forward and the individual takes slow, deep breaths. Reflexology also uses specific acupressure points on the hands and feet to stimulate the lungs.
Aromatherapists recommend eucalyptus, lavender, rosemary, and chamomile as fragrances that promote free breathing. In Japan, cold baths are a common treatment for asthma as a form of hydrotherapy that opens constricted air passages. Massage therapies such as Rolfing may help individuals with asthma as well by opening the bronchioles and increasing circulation in the chest area. Homeopathic treatment for asthma uses the remedies Arsenicum album, Kali carbonicum, Natrum sulphuricum, and Aconite.
More than half of all asthma cases in children resolve by young adulthood, but in some children with chronic infection and/or exposure to environmental pollution, cigarette smoke, and allergens, resolution may be less likely. Infants and toddlers who have persistent wheezing even without viral infections and those who have a family history of allergies are most likely to continue to have asthma into the school-age years.
Most individuals with asthma respond well once the proper drug or combination of drugs is found and are able to lead relatively normal, active lives. A relatively few individuals will have progressive breathing difficulties and run the risk of respiratory failure requiring intensive treatment. About 3,400 individuals in the United States die from asthma each year.
Exposure to the common allergens and irritants that provoke asthmatic attacks often can be reduced or avoided by implementing the following preventive measures:
See also Chronic obstructive pulmonary disease .
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Allergy and Asthma Network: Mothers of Asthmatics (AANMA), 2751 Prosperity Ave., Ste. 150, Fairfax, VA, 22031, (800) 878-4403, Fax: (703) 573-7794, http://www.aanma.org .
American Academy of Allergy Asthma & Immunology (AAAAI), 555 E. Wells St., Ste. 1100, Milwaukee, WI, 53202-3823, (414) 272-6071, http://www.aaaai.org .
American College of Allergy, Asthma, and Immunology, 85 W. Algonquin Rd., Ste. 550, Arlington Heights, IL, 60005, (847) 427-1200, firstname.lastname@example.org, http://www.acaai.org .
Asthma and Allergy Foundation of America, 8201 Corporate Dr., Ste. 1000, Landover, MD, 20785, (800) 727-8462, email@example.com, http://www.aafa.org .
National Institute of Allergy and Infectious Diseases, 6610 Rockledge Dr., MSC 6612, Bethesda, MD, 20892-6612, (301) 496-5717, (866) 284-4107, Fax: (301) 402-3573, http://www.niaid.nih.gov .
David A. Cramer, MD
Revised by L. Lee Culvert