Asthma - Breathing Tests

By editor | September 8, 2007

Based on family medical history and your child’s medical history and symptoms, the doctor may strongly suspect your child has asthma. The doctor may want your child to have other tests to be certain of the diagnosis and to determine how severe the asthma is and what treatment steps to take. One of these is a special breathing test known as pulmonary function testing (PFTs) or spirometry.

Spirometry measures how much the airways are blocked by the swelling and squeezing of asthma. The test is a bit complicated and needs some special equipment, but it’s not at all painful and doesn’t take very long. Not every physician has a spirometer machine in the office, so you may need to go to an asthma specialist or hospital clinic to have the test done.

To take this test, your child will sit up straight in a chair, breathe in as deeply as she can, and then breathe out as hard as she can into a special mouthpiece. To make sure that all the exhaled air goes into the mouthpiece, the doctor or respiratory therapist will gently pinch the child’s nose closed with special soft clips. You can prepare your child for spirometry by explaining that it’s very much like blowing out candles on a birthday cake.

The air goes from the mouthpiece through a tube and into a machine that measures how much air she breathed out, and how fast it came out. The measurements look at three things:

Your child will repeat the “maneuver,” as this process is called, at least three times in a row to be sure the reading is accurate. Each maneuver only takes about six seconds. The results are compared to a table of typical results for your child’s gender, age, ethnicity, and height. Your child’s readings will be a percentage of normal based on the tables.

After the first round of maneuvers is over, the doctor may give your child a dose of an inhaled bronchodilator, a drug that opens up the breathing tubes. After giving the drug about fifteen to twenty minutes to work, your child will repeat the breathing maneuvers another three times. If your child has asthma, the results should be noticeably better this time because the bronchodilator will have opened the airways, allowing more air to move in and out. If that happens, the doctor will say that the airflow obstruction is reversible in other words, medicines help reduce the bronchospasm/squeezing that blocks the airways. This is extremely important in determining that the problem is asthma.

By comparing the FEV 1 before and after use of the bronchodilator, a physician can get a clear idea of the reversibility of the airway obstruction. This information helps the doctor decide which medicines are needed and what the starting doses should be.

Is this test necessary? Spirometry is a very good way to confirm that a child has asthma, even if a doctor is already quite certain. Spirometry is also important for helping a physician decide how severe the asthma is and what the best treatment would be. Once the treatment has started and your child’s asthma has been under control for a few months, the doctor will want your child to repeat the test. This will help make sure the airways are as open and near normal as possible. After these initial tests, your child should have spirometry at least once a year simply to be sure the airways are staying at or near normal. If a child has a change in treatment for example, a change in the dosage of her medicine she may need spirometry again to be sure that the new treatment is working well.

If your child is younger than four or five, you’re probably wondering how a spirometry maneuver can ever be done with a baby, a toddler, or even a preschooler. It can’t. But doctors can do specialized breathing tests on babies and young children. These tests are more complex and require special equipment. If your doctor feels these tests are needed, you’ll probably have to go to a specialist based at a large hospital.

Sometimes older children can’t manage the spirometry maneuver either. When a child can’t do it for some reason, doctors may suggest a “therapeutic trial,” which means trying an inhaled bronchodilator or steroid pills for a short time. Seeing if one of these medicines helps reduce wheezing and other symptoms is a way to help determine whether the child has asthma.

Some children have asthma symptoms, but their spirometry results are normal. In that case, a doctor may recommend a different type of spirometry test called bronchoprovocation. In this test, a child inhales a small, safe amount of a substance called methacholine. If the child has asthma, the methacholine will make her airways constrict or squeeze just as if she were having mild asthma symptoms. When she does the spirometry maneuvers after taking the medicine, her readings will be lower. If she doesn’t have asthma, the methacholine will have little effect, and the spirometry readings will be nearly the same as before. A similar test can be done using another medication called histamine. In a third test, a child breathes cold dry air or gets on a bicycle or treadmill and does vigorous exercise. All of these tests may cause bronchoconstriction in children with asthma and are useful in confirming the diagnosis.

Other tests, such as a chest X-ray, a sweat test, barium swallow exam, or allergy testing, may be done to help rule out other causes of the symptoms or to identify factors that might complicate your child’s asthma.


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