Asthma occurs because the airways in the lungs overreact tvarious stimuli, resulting in narrowing with obstruction tairflow. This results in one or more of the following symptoms:
- Tightness in the chest
- Labored breathing
- Noises in the chest heard particularly during a prolonged forced expiration (wheezing). As a result of these symptoms, asthmatics may not tolerate exertion. They may be awakened frequently at night. More severe symptoms may result in requirements for urgent medical care and hospitalization. For a very few with particularly severe asthma, there is a risk of fatality.
Asthma affects the airways, which begin just below the throat as a single tube called the trachea. The trachea is situated immediately in front of the esophagus, the passageway that connects the throat with the stomach. The trachea divides inttwslightly narrower tubes called the main bronchi (singular = bronchus). Each main bronchus then divides intprogressively smaller tubes – the smallest are called “bronchioles” – tcarry air tand from microscopic air spaces called alveoli (singular = alveolus). It is in the alveoli that the important work of the lung occurs, exchanging oxygen in the air for carbon dioxide in the blood. The airways (trachea, bronchi, bronchioles) are surrounded by a type of involuntary muscle known as smooth muscle. The airways are lined with a mucus membrane that secretes a fine layer of mucus and fluid. This mucus washes the airways tremove any bacteria, dirt, or other foreign material that might get intthe lungs.
The overreaction or hyper-responsiveness of the airways results in bronchospasm, which is excessive contraction or spasm of the bronchial smooth muscle. The airways alsbecome inflamed with swelling of the bronchial mucous membrane (mucosa) and secretion of excessive thick mucus that is difficult texpel. It is part of the evaluation process tidentify the role of each of these physiologic components in asthma. This is important because bronchospasm (constriction of the muscle surrounding the airways) and inflammation respond tdifferent medications.
The airway hyper-responsiveness leading tobstruction of the airways occurs from one or more of various stimuli that vary with the individual patient. These include:
- Viral (but not bacterial) respiratory infections (common colds)
- Inhaled irritants (cigarette smoke, wood burning stoves and fireplaces, strong odors, chemical fumes)
- Inhaled allergens (pollens, dusts, molds, animal danders)
- Cold air
- Occasional ingested substances (aspirin, sulfite preservatives, specific foods)
The obstruction of the airways decreases the rate at which air can flow. This is felt as tightness in the chest and labored breathing (dyspnea – pronounced dissp-nee-uh). The obstruction and inflammation causes coughing. Obstruction tair flow can be measured with pulmonary function tests, which can detect even degrees of airway obstruction not yet causing symptoms.
The increased mucus in the airways stimulates coughing as the body attempts tclear the airways. The unusually thick (viscous) mucus is difficult texpel, however, resulting in continued coughing that fails tadequately expel the mucus. General irritability of the airways alscauses coughing. The coughing and mucus production may cause some physicians tdiagnose bronchitis. However, the term “bronchitis” simply means “inflammation of the airways,” and asthma causes airway inflammation. Consequently, anti-asthmatic medication, and not antibiotics, is the appropriate treatment.
Narrowing of the airway causes noise when air passes through it with sufficient speed. This typical high-pitched noise is called wheezing. Mucus in the airway causes a rattling sound. Complete obstruction of some airways can cause absorption of air from the alveoli (air sacs at the end of the airways in the lungs). This causes portions of the lung tappear more dense and cast more of a shadow on a chest x-ray (this is called “atelectasis” – at-til-eck-tuh-sis). The rattling sounds or increased shadows on the x-ray are often misinterpreted as indicating pneumonia. The inappropriate diagnoses of bronchitis and pneumonia cause much unnecessary use of antibiotics, which are ineffective both for asthma in general and for most of the infections, such as the common cold viruses, that trigger asthma.
DISCLAIMER: The information provided here is for general informational purposes only, and is provided as a supplement for students enrolled in Meditec’s medical career training courses. The information should NOT be used for actual diagnostic or treatment purposes or in lieu of diagnosis or treatment by a licensed physician.