The most common subtype of asthma is allergic asthma or extrinsic asthma. Having this means you have a double whammy of allergies and asthma, and controlling one means controlling the other. Here is what is presently known about this asthma subtype.
Statistics. About 75% of the 334 million asthmatics worldwide have allergic asthma. This includes about 90% of child asthmatics, and 50% of adult asthmatics.
Immune system. It’s designed to help protect you from foreign invaders such as viruses or bacteria. Nose hairs and the sneeze and cough reflexes are meant to keep them out.
Bone marrow makes white blood cells to attack invaders when they get in. More on this in a bit.
Allergens. These are substances that are harmless to people without allergies. Common allergens include dust mites, cockroach urine, animal dander, pollen, and mold spores. Also included are certain foods, like peanuts, nuts, eggs, milk, wheat, soy, fish and shellfish.
Abnormal Immune Response. In those of us with a genetic predisposition to developing asthma, our immune systems think allergens are harmful. Let’s say, for example, you’re exposed to a cat, and inhale cat dander (flakes of cat skin). Your immune system responds. The following events occur:
- Your immune system recognizes cat dander as harmful, and releases chemicals into your bloodstream.
- These chemicals trigger the release of special white blood cells called T-Cells. They in turn release chemicals into your bloodstream to instruct another type of white blood cell called B-Cells to produce antibodies, in this case cat dander IgE antibodies.
- IgE antibodies are specially trained to recognize cat dander. They can remain in your body for many years. Some stay in the bloodstream, while others attach to another special type of white blood cells called Mast Cells. For this reason, allergic asthma is sometimes referred to as IgE mediated asthma.
- Mast cells are randomly scattered throughout connective tissue, including your skin, conjunctiva of your eyes, and respiratory tract (nose, throat, and airways).
Sensitization. Your body is now armed and ready for battle should you ever inhale cat dander again. You are sensitized to cat dander. Allergic asthmatics have elevated IgE blood levels, so allergy testing can show if you’re sensitized.
Allergies. During subsequent exposures, cat dander IgE antibodies recognize and immediately bind to them. Mast cells now release their contents into the bloodstream. They are called the mediators of inflammation because they cause inflammation of certain cells to trap harmful substances, in this case cat dander. Along with viral infections (colds), allergies are the most common asthma triggers.
Allergy Symptoms. They are caused by the mediators of inflammation.
- Histamine: It causes tiny blood vessels around cells lining your skin, eyes, and respiratory tract to leak fluid, causing these cells to become inflamed. This causes allergy symptoms such as itchy skin, itchy and watery eyes, nasal congestion, runny nose, sneezing, and coughing.
- Leukotrienes: These cause fluid to leak from tiny blood vessels around cells lining airways, resulting in inflammation. This can cause asthma symptoms such as chest tightness, wheezing, coughing, and shortness of breath. Leukotriene antagonists like Singulair are meant to block this response.
- Cytokines: These substances also communicate with other cells to induce a response. One is interleukin, a substance responsible for the growth, activation and survival of eosinophils, which control mast cells and the asthma and allergic responses. Those with elevated eosinophil levels are said to have eosinophilic asthma.
Asthma. The mediators of inflammation may also cause asthma. This is mainly the result of chronic exposure to anything that may cause the inflammatory response, such as allergens. Asthma is basically defined as chronic underlying airway inflammation, thereby making airways hypersensitive to asthma triggers, which include allergens, strong smells, strong emotions, smoke, pollution, and other substances inside and outside your body. Asthmatics also produce an excessive amount of goblet cells, which produce mucus to trap harmful substances (or, in our case, innocuous substances).
Asthma Attacks. Exposure to asthma triggers causes smooth muscles (bronchial muscles) that spiral around airways (bronchial airways) to spasm and constrict (bronchospasm), thereby squeezing airways (bronchial obstruction). This, along with excessive mucus production, causes airway obstruction, airflow limitation, and asthma symptoms, such as chest tightness, coughing, wheezing, and shortness of breath. Asthma symptoms are completely reversible with either time or treatment (to be discussed in my next post).
Asthma can be controlled and prevented. Periods between attacks can be prolonged by working with a physician to obtain ideal allergy and asthma control. This can be accomplished by identifying your allergens and other asthma triggers, and developing methods of controlling them. This may also be accomplished by a daily regime of asthma controller medicines and, if necessary, allergy medicines.