tips on practice
Therapists Routinely Treat Atopic Asthma
By Michael P. Hahn, RRT
Respiratory care practitioners see patients with allergic (atopic or extrinsic) asthma on a regular basis. We can help these people manage their asthma by educating them about allergy types, treatments and, most importantly, allergen avoidance measures.
FYI: About 20-30 percent of the U.S. population is allergic to something. Their allergies are generally traced to plant pollen, animal or human skin dander, dust mites, cockroach feces or their exoskeletons, rodent urine, insect venom, foods, and fungal spores (molds).
Some unfortunate people are sensitive to all of the above. Immunologic disorders caused by allergens include allergic rhinitis (hay fever), bronchial asthma, atopic dermatitis, food allergies, urticaria, non-hereditary angioedema, allergic conjunctivitis and systemic anaphylaxis.
A WORD ABOUT ATOPHY
The word atopy refers to a strong hereditary predisposition to becoming sensitized to an antigen (allergen), typically a foreign protein. For this reason, caregivers find it important to document a familial history of atopy. Children under the age of two years do not usually exhibit a sensitization to an allergen. By the time they are eight, however, they may, because sensitization occurs only after individuals are chronically exposed to a sufficient amount of an allergen so their bodies produce high quantities of immunoglobulin E (IgE) antibodies. The normal IgE concentration is 300 ng/ml, with a half-life of about two days.
By contrast, the IgE level of an allergic individual may be as much as 1,000 to 10,000-fold higher than in the norm. In about 60 percent of allergen-induced asthma cases, the individual has an elevated IgE level. The IgE response initially helped the individual rid itself of the allergen.
When the immune system combats bacteria, it utilizes other antibodies. The initial immune response usually does not produce symptoms, but it primes the body against future exposure to the allergen. As a result, the body produces an increasing number of allergen-specific IgE antibodies which attach themselves to mast and basophil cells and can be detected for months after the initial exposure.
ALLERGIC RESPONSE
Mast cells contain histamine granules, which are released (degranulated) during an allergic response. Histamine can cause itching, coughing, lacrimation, mucus production, airway congestion and smooth muscle constriction in addition to dilation and increased permeability of capillaries with resultant redness and swelling.
Other key mediators involved in the immune response include slow-reacting substance of anaphylaxis (SRS-A), various kinins, serotonin, eosinophils, macro-phages, lymphocytes, prostaglandins, leukotrienes, platelet-activating factor, and cytokines.
Basically, any allergic reaction opens a huge can of worms.
In the upper airways, the allergic response produces sneezing and nasal congestion (rhinitis). In the lower airways the reactions include bronchoconstriction, swelling, congestion, wheezing, and ciliostasis.
In the case of food allergies, the allergic response in the G.I. tract causes nausea, vomiting, cramps, and diarrhea. Incidentally, food allergies rarely trigger asthma. On the other hand, bee stings or systemic reactions to some parenteral drugs can.
In addition to triggering asthma attacks, allergens may cause inflammation, late reactions and bronchial hyperresponsiveness (BHR). Once individuals develop BHR, their airways remain sensitive and will illicit an allergic response at much lower levels of exposure to an allergen.
The initial exposure to an allergen causes an early (acute phase) reaction of symptoms, such as sneezing, congestion, wheezing or shortness of breath. These symptoms generally subside or disappear within an hour but can return with a vengeance hours later. This is the reason caregivers treating asthmatics in an emergency room usually administer a dose of corticosteroids to patients before releasing them with instructions they should return for further treatments if their symptoms reappear.
ALLERGY TESTING
One of the most common, simple and safe in vivo investigations for allergies is the skin scratch test which involves the application of a drop of aqueous extract of an antigen on the forearm and than scratching or pricking the skin below the extract. Mold, pollen, house dust, feathers, food, or dander are among the most commonly used extracts.
If the individual is sensitive to the substance, histamine will move to the area and typically produce a 3 mm wheal and flare reaction peak within 20 to 30 minutes. Results of the skin test may show anything from erythema but no wheal to erythema with a large wheal (up to 15-mm). Saline injections are done concurrently as controls.
Chronic inflammatory skin conditions like dermatographism and ectopic eczema make skin testing difficult to interpret. Individuals using antihistimines are subject to false-negative skin test results, so caregivers should be careful in compiling a complete clinical history.
Bronchial provocation testing with aeroallergen extracts is largely restricted to use in occupational exposure testing and research purposes. Well-performed skin tests coupled with accurate medical histories generally provide enough useful information so the patient can avoid being subjected to an inhaled allergen test.
Bronchial aeroallergen provacation testing may be indicated, however, when there is a negative skin test but a strong clinical history of atopic asthma.
The radioallergoabsorbent test (RAST) is used as an in vitro test to measure specific IgE levels. RAST appears to correlate with skin test reactivity and leukocyte histamine release.
There are some other important considerations in diagnosing allergic diseases too. For exmple, IgE levels can be elevated due to cigarette smoking, parasitic infection, malignancies, and immune deficiencies.
Michael Hahn, a California therapist, is the author of Life Support: A Family Clinical Guide.
References
Duff AL, Platts-Mills TAE. Allergens and asthma. Ped Clin N Am (1992;39:1277-90).
Hoover GE, Platts-Mills TAE. What the pulmonologist needs to know about allergy. Clin Chest Med (1995; 16:603-20).
Lichenstein LM. Allergy and the immune system. Sci American (1993; 269:
117-24).
Netter FH. Respiratory system, section 7. Diseases and Pathology. CIBA Publishing: Summit, NJ, 1979.
