How doctors test for asthma with management guidelines
Pulmonary Function Tests
Breathing tests can help establish a diagnosis of asthma as well as measure its severity. The amount of air that can be rapidly forced out of the child’s lungs each second (the one-second forced expired volume or FEV1) is reduced in proportion to the narrowing of the air passages. The laboratory instrument most commonly used to measure how well your child’s lungs are working is called a spirometer. When your child breathes in as deeply as possible and then exhales rapidly into the mouthpiece, a computer measures how much air is blown out within one-second. The narrower the air passages, the smaller the FEV1. The total amount of air breathed out until the lungs are empty is also measured (the forced vital capacity or FVC1 this can also be reduced in asthma because of trapped air. When this test is repeated after administering a bronchodilator to open up the airways, a considerable improvement usually occurs in children with asthma. This simple and painless test can be done in most children over the age of 5. In specialized centers, a similar test can be done in sedated infants less than 2 years of age.
Peak Flow Meters and Chart
An even simpler breathing test, which can be done at home with an inexpensive device, is peak flow measurement. A peak flow meter reliably measures airway narrowing, and can easily be carried around. The measurement takes only a minute. This test is even better for diagnosing asthma than a single spirometer test done in a clinic, because asthma is variable and a test may be normal when the measurement is made in the doctor’s office. Since asthma symptoms are generally worse at night or first thing in the morning having a peak flow meter at home allows you to measure the severity at the time the symptoms are present. Also, the response to treatment can be measured and so provide a long-term perspective of the problem for you and your doctor. The peak flow meter measures the maximum speed with which air can be blown out of the lungs after a full breath has been taken in. The test is usually repeated three times, and the best result can be read directly from the scale on the instrument. Usually you will be asked to measure the peak flow in the morning and at night and record it on a chart. The chart can be used to record medications and symptoms and allows you to see how your child responds to various treatments. The chart that we have developed for use at the Brenner Children’s Hospital and Wake Forest University School of Medicine in Winston-Salem, North Carolina, is reproduced on page 33. Make as many copies of this chart as you need.
An exercise test in a laboratory may be helpful in children who only get asthma with exercise, but otherwise have normal lung function tests. This test is performed by having the child exercise as much as possible, while measuring breathing and heart rate. Lung function testing is repeated after exercise to see if it has decreased during the test. Exercise testing can help your doctor tell the difference between breathing problems, heart problems, or poor muscle conditioning as the cause of breathlessness with exercise.
ALLERGY SKIN TESTS
To confirm that allergy is present, skin testing may be recommended for your child. The tests consist of skin scratch tests; allergens from different classes (molds, pollens, house-hold pets, house dust mites, and sometimes food in very young children) are used. A drop of allergen is placed on the
skin, which is then pricked with a small needle. Positive reactions produce itching after 5 minutes, formation of a small blister (wheal) and reddening of the surrounding area (flare), which last an hour or two. Some reactions may be greater than others, but this does not necessarily relate to the severity of the allergy. About 20% of people without symptoms of allergy. About 20% of people without symptoms of allergy can have positive skin tests. The things that you have observed to produce asthma symptoms in your child (eg., cats) are most important in establishing the cause of asthma, and skin tests can confirm this. Skin tests may also lead to consideration of factors not previously thought of some people with asthma do not have skin reactions, since asthma is also triggered by some non allergic factors.
In asthma, unless the problem is severe or complicated, a chest x-ray is rarely needed. Shadows may show up on x-ray, however, because of plugs of mucus blocking the air passages. During an attack, the lungs are usually over inflated.
with trapped air. A mold called Aspergillus can also cause severe asthma and permanent inflammatory
changes in the airways. In this situation, damaged distended airways, full of secretions may show up on the x-ray and assist with the diagnosis. Occasionally, the over inflation of the lungs becomes so severe that air may pass through ruptured air sacs and spread into the pleural space around the lungs. This may cause one, or very rarely both, lungs to collapse (Pneumothorax).
Pneumothorax can sometimes lead to large amounts of air collecting in the pleural space and build up such high levels of air pressure that the heart can no longer pump the blood effectively. Death can result unless the problem is quickly treated by inserting a needle into the chest to let the air escape.