Asthma

What is Asthma?

Asthma is a chronic inflammation of the bronchial tubes (airways) that cause swelling and narrowing (constriction) of the airways. The result is difficulty breathing.

Bronchial tubes that are chronically inflamed may become overly sensitive to allergens (specific triggers) or irritants (non-specific 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 non-asthmatic and non-allergic 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

Normal bronchial tubes

Before we can appreciate how asthma affects the bronchial airways, we should first take a quick look at the structure and function of normal bronchial tubes.

The air we breathe in through our nose and mouth passes through the vocal cords (larynx) and into the windpipe (trachea). The air then enters the lungs by way of two large air passages (bronchi), one for each lung. The bronchi divide within each lung into smaller and smaller air tubes (bronchioles), just like branches of an inverted tree. Inhaled air is brought through these airways to the millions of tiny air sacs (alveoli) that are contained in the lungs. Oxygen (O2) passes from the air sacs into the blood stream through numerous tiny blood vessels called capillaries. Similarly, the body’s waste product, carbon dioxide (CO2), is returned to the air sacs and then eliminated upon each exhalation.

Normal bronchial tubes allow rapid passage of air in and out of the lungs to ensure that the levels of O2 and CO2 remain constant in the blood stream. The outer walls of the bronchial tubes are surrounded by smooth muscles that contract and relax automatically with each breath. This allows the required amount of air to enter and exit the lungs to achieve this normal exchange of O2 and CO2. The contraction and relaxation of the bronchial smooth muscles are controlled by two different nervous systems that work in harmony to keep the airways open.

The inner lining of the bronchial tubes, called the bronchial mucosa, contains: (1) mucus glands that produce just enough mucus to properly lubricate the airways; and (2) a variety of so called inflammatory cells, such as eosinophils, lymphocytes, and mast cells. These cells are designed to protect the bronchial mucosa from the inhaled microorganisms, allergens, and irritants we inhale, and which can cause the bronchial tissue to swell. Remember, however, that these inflammatory cells are also important players in the allergic reaction. Therefore, the presence of these cells in the bronchial tubes causes them to be a prime target for allergic inflammation.

How does asthma affect breathing?

Asthma causes a narrowing of the breathing airways, which interferes with the normal movement of air in and out of the lungs. Asthma involves only the bronchial tubes and does not affect the air sacs or the lung tissue. The narrowing that occurs in asthma is caused by three major factors; inflammation, bronchospasm, and hyper-reactivity.

Inflammation: The first and most important factor causing narrowing of the bronchial tubes is inflammation. The bronchial tubes become red, irritated, and swollen. The inflammation occurs in response to an allergen or irritant and results from the action of chemical mediators (histamine, leukotrienes, and others). The inflamed tissues produce an excess amount of “sticky” mucus into the tubes. The mucus can clump together and form “plugs” that can clog the smaller airways. Eosinophils and other cells, which accumulate at the site, cause tissue damage. These damaged cells are shed into the airways, thereby contributing to the narrowing.
Bronchospasm: The muscles around the bronchial tubes tighten during an attack of asthma. This muscle constriction of the airways is called bronchospasm. Bronchospasm causes the airway to narrow further. Chemical mediators and nerves in the bronchial tubes cause the muscles to constrict.
Hyper-reactivity (Hypersensitivity): In patients with asthma, the chronically inflamed and constricted airways become highly sensitive, or reactive, to triggers such as allergens, irritants, and infections. Exposure to these triggers may result in progressively more inflammation and narrowing

The combination of these three factors results in difficulty with breathing out, or exhaling. As a result, the air needs to be forcefully exhaled to overcome the narrowing, thereby causing the typical “wheezing” sound. People with asthma also frequently “cough” in an attempt to expel the thick mucus plugs. Reducing the flow of air may result in less oxygen passing into the blood stream and if very severe, carbon dioxide may dangerously accumulate in the blood.

Asthma triggers

Asthma symptoms may be activated or aggravated by many agents. Not all asthmatics react to the same triggers. Additionally, the effect that each trigger has on the lungs varies from one individual to another. In general, the severity of your asthma depends on how many agents activate your symptoms and how sensitive your lungs are to them. Most of these triggers can also worsen nasal or eye symptoms.
Triggers fall into two categories:

Allergens (“specific”)
Non-allergens – mostly irritants (non-“specific”)

Once your bronchial tubes (nose and eyes) become inflamed from an allergic exposure, a re-exposure to the offending allergens will often activate symptoms. These “reactive” bronchial tubes might also respond to other triggers, such as exercise, infections, and other irritants. The following is a simple checklist.

Common Asthma Triggers:

Allergens

“Seasonal” pollens.
Year-round dust mites, molds, pets, and insect parts.
Foods, such as fish, egg, peanuts, nuts, cow’s milk, and soy
Additives, such as sulfites.
Work-related agents, such as latex.

Irritants

Respiratory infections, such as those caused by viral “colds,” bronchitis, and sinusitis.
Drugs, such as aspirin, other NSAIDs (nonsteroidal anti-inflammatory drugs), and Beta Blockers (used to treat blood pressure and other heart conditions).
Tobacco smoke.
Outdoor factors, such as smog, weather changes, and diesel fumes.
Indoor factors, such as paint, detergents, deodorants, chemicals, and perfumes.
Nighttime
GERD (gastro-esophageal reflux disorder)
Exercise, especially under cold dry conditions
Work-related factors, such as chemicals, dusts, gases, and metals
Emotional factors, such as laughing, crying, yelling, and distress
Hormonal factors, such as in premenstrual syndrome

Typical symptoms of asthma

The symptoms of asthma vary from person to person and in any individual from time to time. It is important to remember that many of these symptoms can be subtle and similar to those seen in other conditions. All of the symptoms mentioned below can be present in other respiratory, and sometimes, in heart conditions. This potential confusion makes identifying the settings in which the symptoms occur and diagnostic testing very important in recognizing this disorder.

The 4 Major Recognized Symptoms:

Shortness of breath – especially with exertion or at night
Wheezing – a whistling or hissing sound when breathing out
Coughing – may be chronic; usually worse at night and early morning. May occur after exercise or when exposed to cold, dry air
Chest tightness – may occur with or without the above symptoms