Asthma is a chronic illness involving the respiratory system in which the airway occasionally constricts, becomes inflamed, and is lined with excessive amounts of mucus, often in response to one or more triggers. These episodes may be triggered by such things as exposure to an environmental stimulant (or allergen)such as cold air, warm air, moist air, exercise or exertion, or emotional stress. In children, the most common triggers are viral illnesses such as those that cause the common cold. This airway narrowing causes symptoms such as wheezing, shortness of breath, chest tightness, and coughing. The airway constriction responds to bronchodilators. Between episodes, most patients feel well but can have mild symptoms and they may remain short of breath after exercise for longer periods of time than the unaffected individual.

The symptoms of asthma, which can range from mild to life threatening, can usually be controlled with a combination of drugs and environmental changes.

Public attention in the developed world has recently focused on asthma because of its rapidly increasing prevalence, affecting up to one in four urban children.

Signs and symptoms

In some individuals asthma is characterized by chronic respiratory impairment. In others it is an intermittent illness marked by episodic symptoms that may result from a number of triggering events, including upper respiratory infection, stress, airborne allergens, air pollutants (such as smoke or traffic fumes), or exercise. Some or all of the following symptoms may be present in those with asthma: dyspnea, wheezing, stridor, coughing, an inability for physical exertion. Some asthmatics that have severe shortness of breath and tightening of the lungs never wheeze or have stridor and their symptoms may be confused with a COPD-type disease.

An acute exacerbation of asthma is referred to as an asthma attack. The clinical hallmarks of an attack are shortness of breath (dyspnea) and either wheezing or stridor. Although the former is "often regarded as the sine qua non 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, breathing becomes difficult, and wheezing occurs (primarily upon expiration, but can be in both respiratory phases).

Signs of an asthmatic episode include wheezing, rapid breathing (tachypnea), prolonged expiration, a rapid heart rate (tachycardia), rhonchous lung sounds (audible through a stethoscope), and over-inflation of the chest. 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 the presence of a paradoxical pulse (a pulse that is weaker during inhalation and stronger during exhalation).

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. Feet may become icy cold. Severe asthma attacks, which may not be responsive to standard treatments (status asthmaticus), are life-threatening and may lead to respiratory arrest and death. Despite the severity of symptoms during an asthmatic episode, between attacks an asthmatic may show few or even no signs of the disease.

Diagnosis

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 week of inhaled corticosteroid (e.g., beclometasone);
  • 14 days of 30mg 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. Diagnosis in children is based on a careful compilation and analysis of the patient's medical history and subsequent improvement with an inhaled bronchodilator medication. In adults, diagnosis can be made with a peak flow meter (which tests airway restriction), looking at both the diurnal variation and any reversibility following inhaled bronchodilator medication.

Testing peak flow at rest (or baseline) and after exercise can be helpful, especially in young asthmatics who may experience only exercise-induced asthma. If the diagnosis is in doubt, a more formal lung function test may be conducted. Once a diagnosis of asthma is made, a patient can use peak flow meter testing to monitor the severity of the disease.

In the Emergency Department doctors may use a capnography PMID 16187465 which measures the amount of exhaled carbon dioxide along with pulse oximetry which shows the amount of oxygen dissolved in the blood, to determine the severity of an asthma attack as well as the response to treatment.

Treatment

The most effective treatment for asthma is identifying triggers, such as pets or aspirin, and limiting or eliminating exposure to them. Desensitization to allergens has been shown to be a treatment option for certain patients.

As is common with respiratory disease, smoking is believed to adversely affect asthmatics in several ways, including an increased severity of symptoms, a more rapid decline of lung function, and decreased response to preventive medications. Automobile emissions are considered an even more significant cause and aggravating factor. Asthmatics who smoke or who live near traffic typically require additional medications to help control their disease. Furthermore, exposure of both non-smokers and smokers to wood smoke, gas stove fumes and second-hand smoke is detrimental, resulting in more severe asthma, more emergency room visits, and more asthma-related hospital admissions. Smoking cessation and avoidance of second-hand smoke is strongly encouraged in asthmatics.

The specific medical treatment recommended to patients with asthma depends on the severity of their illness and the frequency of their symptoms. Specific treatments for asthma are broadly classified as relievers, preventers and emergency treatment. The Expert Panel Report 2: Guidelines for the Diagnosis and Management of Asthma (EPR-2) of the U.S. National Asthma Education and Prevention Program, and the British Guideline on the Management of Asthma are broadly used and supported by many doctors. On August 29, 2007 the final Expert Panel Report 3: Guidelines for the Diagnosis and Management of Asthma was officially released. Bronchodilators are recommended for short-term relief in all patients. For those who experience occasional attacks, no other medication is needed. For those with mild persistent disease (more than two attacks a week), low-dose inhaled glucocorticoids or alternatively, an oral leukotriene modifier, a mast-cell stabilizer, or theophylline may be administered. For those who suffer daily attacks, a higher dose of glucocorticoid in conjunction with a long-acting inhaled β-2 agonist may be prescribed; alternatively, a leukotriene modifier or theophylline may substitute for the β-2 agonist. In severe asthmatics, oral glucocorticoids may be added to these treatments during severe attacks.

For those in whom exercise can trigger an asthma attack (exercise-induced asthma), higher levels of ventilation and cold, dry air tend to exacerbate attacks. For this reason, activities in which a patient breathes large amounts of cold air, such as skiing and running, tend to be worse for asthmatics, whereas swimming in an indoor, heated pool, with warm, humid air, is less likely to provoke a response.

Researchers at Harvard Medical School (HMS) have come up with convincing evidence that the answer to what causes asthma lies in a special type of natural "killer" cell. This finding means that physicians may not be treating asthma sufferers with the right kinds of drugs. For example, natural killer T cells seem to be resistant to the corticosteroids in widely used inhalers.

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