What is asthma?

1.0 What is asthma?

1.0.1 What is chronic asthmatic bronchitis?
1.0.2 What is status asthmaticus?
1.0.3 What is anaphylactic shock?
1.0.4 What is COPD?
1.0.5 What is emphysema?
1.0.6 What is bronchitis?
1.0.7 What is pneumonia?
1.0.8 What is cystic fibrosis?

1.0 What is asthma?
Asthma is best described by its technical name: Reversible Obstructive Airway Disease (ROAD). In other words, asthma is a condition in which the airways of the lungs become either narrowed or completely blocked, impeding normal breathing. However, in asthma, this obstruction of the lungs is reversible, either spontaneously or with medication.

Quickly reviewing the structure of the lung: air reaches the lung by passing through the windpipe (trachea), which divides into two large tubes (bronchi), one for each lung. Each bronchi further divides into many little tubes (bronchioles), which eventually lead to tiny air sacs (alveoli), in which oxygen from the air is transferred to the bloodstream, and carbon dioxide from the bloodstream is transferred to the air. Asthma involves only the airways (bronchi and bronchioles), and not the air sacs. The airways are cleaned by trapping stray particles in a thin layer of mucus which covers the surface of the airways. This mucus is produced by glands inside the lung, and is constantly being renewed. The mucus is then either coughed up or swept up to the windpipe (trachea) by cilia, tiny hairs on the lining of the airways. Once the mucus reaches the throat, it can again be coughed up or, alternatively, swallowed.

Although everyone's airways have the potential for constricting in response to allergens or irritants, the asthmatic's airways are oversensitive, or hyperreactive. In response to stimuli, the airways may become obstructed by one of the following:

* constriction of the muscles surrounding the airway;
* inflammation and swelling of the airway; or
* increased mucus production which clogs the airway.

Once the airways have become obstructed, it takes more effort to force air through them, so that breathing becomes laboured. This forcing of air through constricted airways can make a whistling or rattling sound, called wheezing. Irritation of the airways by excessive mucus may also provoke coughing.

Because exhaling through the obstructed airways is difficult, too much stale air remains in the lungs after each breath. This decreases the amount of fresh air which can be taken in with each new breath, so not only is there less oxygen available for the whole body, but more importantly, the high concentration of carbon dioxide in the lungs causes the blood supply to become acidic. This acidity in the blood may rise to toxic levels if the asthma remains untreated.
1.0.1 What is chronic asthmatic bronchitis?
f Chronic asthmatic bronchitis is the condition in which the airways in the lungs are obstructed due to both persistent asthma and chronic bronchitis (see sections 1.0 and 1.0.6). People with this disease generally also have a persistent cough which brings up mucus. Chronic asthmatic bronchitis which also involves emphysema is usually classified under the more general category of COPD.
1.0.2 What is status asthmaticus?
Status asthmaticus is defined as a severe asthma attack that fails to respond to routine treatment, such as inhaled bronchodilators, injected epinephrine (adrenalin), or intravenous theophylline.
1.0.3 What is anaphylactic shock?
Anaphylactic shock is defined as a severe and potentially life-threatening allergic reaction throughout the entire body. It occurs when an allergen, instead of provoking a localized reaction, enters the bloodstream and circulates through the entire body, causing a systemic reaction. (There may also be an intrinsic trigger, as some cases of exercise-induced anaphylaxis have been reported.)

The symptoms of anaphylactic shock begin with a rapid heartrate, flushing, swelling of the throat, nausea, coughing, and chest tightness. Severe wheezing (asthma), cramping, and a rapid drop in blood pressure follow, which may lead to cardiac arrest. Hives and vomiting are also common features. The treatment for anaphylaxis is intravenous epinephrine (adrenalin), with antihistamines and steroids also being used in selected cases. Aminophylline may also be given for pronounced asthmatic reactions that do not respond to epinephrine.
1.0.4 What is COPD?
COPD is chronic obstructive pulmonary disease, also known as either COAD, for chronic obstructive airway disease, or COLD, for chronic obstructive lung disease. COPD is a disease in which the airways are obstructed due to a combination of asthma, emphysema, and chronic bronchitis. The 1987 Merck Manual notes that "the term COPD was introduced because these conditions often coexist, and it may be difficult in an individual case to decide which is the major one producing the obstruction."

[Maintainer's note: the entries for COPD, emphysema, bronchitis, pneumonia, and cystic fibrosis have been included because of common confusion between the various diseases which can affect the lungs.]
1.0.5 What is emphysema?
Emphysema is the disease in which the air sacs themselves, rather than the airways, are either damaged or destroyed. This is an irreversible condition, leading to poor exchange of oxygen and carbon dioxide between the air in the lungs and the bloodstream.
1.0.6 What is bronchitis?
Bronchitis is an inflammation of the bronchi, the large airways inside the lungs. (Bronchiolitis is the inflammation of the bronchioles, the small airways.) This inflammation often leads to increased mucus production in the airways.

Bronchitis is generally caused either by a virus or by exposure to irritants such as dust, fumes, or cigarette smoke. If caused by a virus, the bronchitis will likely be only temporary. In the case of prolonged exposure to irritants, particularly cigarette smoking, if there is permanent damage to the bronchi, bronchitis may become chronic.
1.0.7 What is pneumonia?
Pneumonia is an infection of the lung tissue. In adults, it is generally caused by bacterial infections, though viruses, fungi, and protozoa may also be culprits. The latter microorganisms have become very common as causes of pneumonia in immunosuppressed persons, such as those with HIV infection. However, for those with chronic illnesses, especially cardiac or respiratory diseases, or those at increased risk for pneumonia, there is a pneumococcal pneumonia vaccination available as a preventive measure for the most common of these bacterial infections, streptococcus pneumoniae. In children, pneumonia is most commonly caused by viruses.
1.0.8 What is cystic fibrosis?
Cystic fibrosis is a disease in which excessive amounts of unusually thick mucus are produced throughout the body. Because this mucus production also occurs in the lungs, people with cystic fibrosis are extraordinarily prone to bacterial infections which result in progressive lung damage. Cystic fibrosis can be diagnosed by a "sweat test" as people with cystic fibrosis have elevated chloride levels in their perspiration. This condition often resembles asthma in children.