Asthma is a chronic inflammation of the bronchial tubes (airways) that causes swelling and narrowing (constriction) of the airways. The result is difficulty breathing. The bronchial narrowing is usually either totally or at least partially reversible with treatments.

Bronchial tubes that are chronically inflamed may become overly sensitive to allergens (specific triggers) or irritants (nonspecific triggers). The airways may become "twitchy" and remain in a state of heightened sensitivity. This is called "bronchial hyperreactivity" (BHR). It is likely that there is a spectrum of bronchial hyperreactivity in all individuals. However, it is clear that asthmatics and allergic individuals (without apparent asthma) have a greater degree of bronchial hyperreactivity than nonasthmatic and nonallergic people. In sensitive individuals, the bronchial tubes are more likely to swell and constrict when exposed to triggers such as allergens, tobacco smoke, or exercise. Amongst asthmatics, some may have mild BHR and no symptoms while others may have severe BHR and chronic symptoms.

Asthma affects people differently. Each individual is unique in their degree of reactivity to environmental triggers. This naturally influences the type and dose of medication prescribed, which may vary from one individual to another.

Asthma is caused by environmental and genetic factors, which can influence how severe asthma is and how well it responds to medication. Some environmental and genetic factors have been confirmed by further research, while others have not been. Underlying both environmental and genetic factors is the role of the upper airway in recognizing the perceived dangers and protecting the more vulnerable lungs by shutting down the airway. Profet has argued that allergens look to our immune systems like significant threats. Asthma, in this view, is seen as an evolutionary defense. This view also suggests that removing or reducing airborne pollutants should be successful at reducing the problem.

Because of the spectrum of severity within the asthma, some people with asthma only rarely experience symptoms, usually in response to triggers, where as other more severe cases may have marked airflow obstruction at all times.

Asthma exists in two states: the steady-state of chronic asthma, and the acute state of an acute asthma exacerbation. The symptoms are different depending on what state the patient is in.

Common symptoms of asthma in a steady-state include: nighttime coughing, shortness of breath with exertion but no dyspnea at rest, a chronic 'throat-clearing' type cough, and complaints of a tight feeling in the chest. Severity often correlates to an increase in symptoms. Symptoms can worsen gradually and rather insidiously, up to the point of an acute exacerbation of asthma. It is a common misconception that all people with asthma wheeze—some never wheeze, and their disease may be confused with another chronic obstructive pulmonary disease such as emphysema or chronic bronchitis.

An acute exacerbation of asthma is commonly referred to as an asthma attack. The cardinal symptoms of an attack are shortness of breath (dyspnea), wheezing, and chest tightness. Although the former is often regarded as the primary symptom of asthma, some patients present primarily with coughing, and in the late stages of an attack, air motion may be so impaired that no wheezing may be heard. When present the cough may sometimes produce clear sputum. The onset may be sudden, with a sense of constriction in the chest, as breathing becomes difficult and wheezing occurs (primarily upon expiration, but sometimes in both respiratory phases). It is important to note inspiratory stridor without expiratory wheeze however, as an upper airway obstruction may manifest with symptoms similar to an acute exacerbation of asthma, with stridor instead of wheezing, and will remain unresponsive to bronchodilators.

Signs of an asthmatic episode include wheezing, prolonged expiration, a rapid heart rate (tachycardia), and rhonchous lung sounds (audible through a stethoscope). During a serious asthma attack, the accessory muscles of respiration (sternocleidomastoid and scalene muscles of the neck) may be used, shown as in-drawing of tissues between the ribs and above the sternum and clavicles, and there may be the presence of a paradoxical pulse (a pulse that is weaker during inhalation and stronger during exhalation), and over-inflation of the chest.

During very severe attacks, an asthma sufferer can turn blue from lack of oxygen and can experience chest pain or even loss of consciousness. Just before loss of consciousness, there is a chance that the patient will feel numbness in the limbs and palms may start to sweat. The person's feet may become cold. Severe asthma attacks which are not responsive to standard treatments, called status asthmaticus, are life-threatening and may lead to respiratory arrest and death.

Though symptoms may be very severe during an acute exacerbation, between attacks a patient may show few or even no signs of the disease.

Asthma is defined simply as reversible airway obstruction. Reversibility occurs either spontaneously or with treatment. The basic measurement is peak flow rates and the following diagnostic criteria are used by the British Thoracic Society:

* ≥20% difference on at least three days in a week for at least two weeks;
* ≥20% improvement of peak flow following treatment, for example:
•    10 minutes of inhaled β-agonist (e.g., salbutamol);
•    six weeks of inhaled corticosteroid (e.g., beclometasone);
•    14 days of 30 mg prednisolone.
* ≥20% decrease in peak flow following exposure to a trigger (e.g., exercise).

In many cases, a physician can diagnose asthma on the basis of typical findings in a patient's clinical history and examination. Asthma is strongly suspected if a patient suffers from eczema or other allergic conditions—suggesting a general atopic constitution—or has a family history of asthma. While measurement of airway function is possible for adults, most new cases are diagnosed in children who are unable to perform such tests.

In children, the key to asthma diagnosis is the sound of wheezing or a high-pitched sound upon exhalation. Other clues are recurrent wheezing, breathing difficulty, or chest tightness, or a history of coughing that is worse at night. The doctor should also know if the child's symptoms are worse with exercise, colds, or exposure to certain irritants such as smoke, emotional stress, or changes in the weather.

Other information important to diagnosis is the age at which symptoms began and how they progressed, the timing and pattern of wheezing, when and how often a child had to visit a clinic or hospital emergency department because of symptoms, whether the child ever took bronchodilator medication for the symptoms and the nature of the response to medication.

Although pediatricians may tend to ask parents for information about their children's symptoms, studies suggest that children themselves are reliable sources as early as age 7 and perhaps even as early as age 6.

In adults and older children, diagnosis can be made with spirometry or a peak flow meter (which tests airway restriction), looking at both the diurnal variation and any reversibility following inhaled bronchodilator medication. The latest guidelines from the U.S. National Asthma Education and Prevention Program (NAEPP) recommend spirometry at the time of initial diagnosis, after treatment is initiated and symptoms are stabilized, whenever control of symptoms deteriorates, and every 1 or 2 years on a regular basis.

In the Emergency Department, doctors may use a capnography which measures the amount of exhaled carbon dioxide, along with pulse oximetry which shows the percentage of hemoglobin that is carrying oxygen, to determine the severity of an asthma attack as well as the response to treatment.

More recently, exhaled nitric oxide has been studied as a breath test indicative of airway inflammation in asthma.

• Develop a written asthma plan. With your doctor and health care team, write a detailed plan for taking maintenance medications and managing an acute attack. Then be sure to follow your plan. Asthma is an ongoing condition that needs regular monitoring and treatment. Taking control of your treatment can make you feel more in control of your life in general.

• Identify and avoid asthma triggers. A number of outdoor allergens and irritants — ranging from pollen and mold to cold air and air pollution — can trigger asthma attacks. Find out what causes or worsens your asthma, and take steps to avoid those triggers.

• Monitor your breathing. You may learn to recognize warning signs of an impending attack, such as slight coughing, wheezing or shortness of breath. But because your lung function may decrease before you notice any signs or symptoms, regularly measure your peak airflow with a home peak flow meter.

• Identify and treat attacks early. If you act quickly, you're less likely to have a severe attack. You also won't need as much medication to control your symptoms. When your peak flow measurements decrease and alert you to an impending attack, take your medication as instructed and immediately stop any activity that may have triggered the attack. If your symptoms don't improve, get medical help as directed in your action plan.

• Don't let up on your medication program. Just because your asthma seems to be improving, don't change anything without first talking to your doctor. It's a good idea to bring your medications with you to each doctor visit, so your doctor can double-check that you're using your medications correctly and taking the right dose.

Treatment for asthma generally involves avoiding the things that trigger your asthma attacks and taking one or more asthma medications. Treatment varies from person to person.

• Most people with persistent asthma use a combination of long-term control medications and quick-relief medications, taken with a hand-held inhaler.
• If your asthma symptoms are triggered by airborne allergens, such as pollen or pet dander, you may also need allergy treatment.
• You may need to try a few different medications before you find what works best.
• Because asthma changes over time, you will need to work with your doctor to monitor your symptoms and learn how to make needed adjustments.

Medications used to treat asthma include long-term control medications, quick-relief (rescue) medications and medications to treat allergies. The right medication for you depends on your age and symptoms, and what seems to work best to keep your asthma under control.

Long-term control medications
In most cases, these medications need to be taken every day. Types of long-term control medications include:

• Inhaled corticosteroids such as fluticasone, budesonide, triamcinolone, flunisolide, beclomethasone and others. These medications reduce airway inflammation and are the most commonly used long-term asthma medication. Unlike oral corticosteroids, these medications are considered relatively low risk for long-term corticosteroid side effects. You may need to use these medications for several days to weeks before they reach their maximum benefit.
• Long-acting beta-2 agonists (LABAs) such as salmeterol and formoterol. These inhaled medications, called long-acting bronchodilators, open the airways and reduce inflammation. They are often used to treat persistent asthma in combination with inhaled corticosteroids. Long-acting bronchodilators should not be used for quick relief of asthma symptoms.
• Leukotriene modifiers such as montelukast, zafirlukast and zileuton. These inhaled medications work by opening airways, reducing inflammation and decreasing mucus production.
• Cromolyn and nedocromil. These inhaled medications reduce asthma signs and symptoms by decreasing allergic reactions. They're considered a second choice to inhaled corticosteroids, and need to be taken three or four times a day.
• Theophylline, a daily pill that opens your airways (bronchodilator). It relaxes the muscles around the airways.

Quick-relief medications

Also called rescue medications, you use quick-relief medications as needed for rapid, short-term relief of symptoms during an asthma attack, or before exercise, if your doctor recommends it. Only use these medications as often as your doctor tells you to. If you need to use these medications too often, you probably need to adjust your long-term control medication. Keep a record of how many puffs you use each day. Types of quick-relief medications include:

• Short-acting beta-2 agonists, such as Salbutamol. These inhaled medications, called bronchodilators, ease breathing by temporarily relaxing airway muscles. They act within minutes, and effects last four to six hours.

• Ipratropium. Your doctor might prescribe this inhaled anticholinergic for the immediate relief of your symptoms. Like other bronchodilators, ipratropium relaxes the airways, making it easier to breathe. Ipratropium is mostly used for emphysema and chronic bronchitis.

• Oral and intravenous corticosteroids to treat acute asthma attacks or very severe asthma. Examples include prednisone and methylprednisolone. These medications relieve airway inflammation. They may cause serious side effects when used long term, so they're only used to treat severe asthma symptoms.

Medications for allergy-induced asthma. These decrease your body's sensitivity to a particular allergen or prevent your immune system from reacting to allergens. Allergy treatments for asthma include:

• Immunotherapy. Allergy-desensitization shots (immunotherapy) are generally given once a week for a few months, then once a month for a period of three to five years. Over time, they gradually reduce your immune system reaction to specific allergens.

• Anti-IgE monoclonal antibodies, such as omalizumab. This medication reduces your immune system's reaction to allergens. It is delivered by injection every two to four weeks.

Salbutamol inhaler changes: Know what to expect
The Food and Drug Administration (FDA) has required that metered-dose Salbutamol inhalers that use chlorofluorocarbon (CFC) propellent be replaced with hydrofluoroalkane (HFA) inhalers by the end of 2008. HFA inhalers work as well as CFC inhalers and are as safe, but they don't harm the ozone layer. If you're used to using a CFC inhaler, talk to your doctor about making the switch to an HFA inhaler. There are a few differences you should know about:

Your HFA inhaler may have a different taste and feel from your older CFC inhaler.

• HFA inhalers have a less forceful spray than the older CFC inhalers. Make sure you know how to use your inhaler correctly - otherwise, you may not get the full dose of medication with each spray.
• HFA inhalers are more costly than the older, generic Salbutamol CFC inhalers.
• HFA inhalers should be cleaned with water every week.

Treatment by severity for better control: A stepwise approach
Treatment based on asthma control can help you manage your asthma. Asthma treatment should be flexible and based on changes in symptoms, which should be assessed thoroughly each time you see your doctor. Then, treatment can be adjusted accordingly.

For example, if your asthma is well controlled, your doctor may prescribe less medicine. If your asthma is not well controlled or getting worse, your doctor may increase your medication and recommend more frequent visits.

Asthma may cause a number of complications, including:
•    Emergency room visits and hospitalizations for severe asthma attacks
•    Permanent narrowing of the bronchial tubes (airway remodeling)
•    Side effects from long-term use of some medications used to stabilize severe asthma