Exercise Challenge Test

Written by Dr Fred Nagel

Asthma in childhood is common. The prevalence of asthma has previously been shown to be 3.17% in black children in Guguletu⁽¹⁾. A prevalence of 5% has recently been reported in white Cape Town school children⁽²⁾. In Cardiff, Wales, the prevalence of current asthma in 1989 was 9%⁽³⁾. Exercise induced bronchospasm is characteristic of asthma and any child with post-exercise wheezing or cough is considered to have asthma⁽⁴⁾. An exercise challenge is therefore a valuable diagnostic test of asthma especially if doubt exists about the diagnosis. The test is easy to perform, non-invasive, reproducible and inexpensive. In addition, the exercise challenge test can be used to determine the prevalence of asthma in a given population^(1,3).

Indications:
the exercise challenge test is indicated in all patients in whom any doubt exists about a diagnosis of asthma. They must be able to run and to use a peak flow meter.

Method:
the exercise challenge test for asthma is performed as follows:

1. Explain the test to the patient.
2. Then perform a forced expiratory volume in one second (FEV1) or a peak expiratory flow rate (PEFR) with the patient at rest before the exercise. The FEV1 is more accurate but Vitalograph equipment is not always readily available. Both the FEV1 and the PEFR are acceptable.
3. Request that he or she run on the level for six minutes. Circular running on a patch of lawn, up and down a quiet corridor or in a hall are all suitable. Most children prefer to remove warm clothing and run in shorts or a skirt and a thin shirt.
4. A simple digital wrist watch is ideal for time keeping.
5. Ask the patient to start running. Patients may select their own pace but should run briskly for exactly six minutes. Children running too fast can be slowed down and those moving too slowly asked to speed up. In practice, the self selected pace is usually adequate.
6. After exactly six minutes the patient is stopped and the heart rate is counted immediately. Post exercise, the heart rate in children invariably slows down very rapidly and so it is advisable to count the rate for 15 seconds and multiply the result by four. A heart rate of 170 or more beats/min after exercise is generally accepted as evidence of adequate exertion (Ref. 1).
7. The patient then rests for exactly five minutes.
8. At five minutes post-exercise the FEV1 or PEFR measurements are repeated.
9. The percentage fall in FEV1 or PEFR is calculated as follows:
   
   E0 – E5 X 100
   E0

   Where E = pre-exercise reading and E5 = the reading five minutes post exercise.

Interpretation:
A fall in post-exercise FEV1 or PEFR of 15% or greater is diagnostic of exercise induced asthma.

However, some allergists believe a reduction of even 10% or greater to be sufficient for the diagnosis (Ref. 5). A fall of 25% or more in the FEV1 or PEFR usually necessitates prophylactic therapy (Ref. 5). Children with pre-exercise FEV1 or PEFR values that are less than 30% of predicted for height should not be allowed to run and the test should be postponed. In children who have positive exercise tests, the broncho-constriction can be rapidly and safely reversed using one or two puffs of a beta-2-stimulant inhaler. However, treatment is not essential as the bronchoconstriction will reverse spontaneously within 20-30 minutes.

The exercise test will identify between 70-80% of patients with clinically recognisable asthma (Ref. 5). Exercise may fail to induce bronchospasm in patients who have asthma, for the following reasons:

1. Inadequate exercise (as judged by failure to achieve a post-exercise heart rate of 170 beats/min or more).
2. Recent asthma medication blocking the broncho-constrictive effects of exercise.
3. Some patients do not respond for reasons which are unclear.

False positive broncho-constrictive responses to exercise are exceptionally rare.

References:

1. Van Niekerk CH, Weinberg EG, Shore SC, de V Heese H and van Schalkwyk DJ. Prevalence of asthma: a comparative study of urban and rural Xhosa children. Clinical Allergy, 1979(9): 319-324.
2. Nagel FO, Weinberg EG, Benatar SR, Burr ML. Asthma prevalence in primary school children. Unpublished.
3. Burr ML, Butland BK, King S, Vaughan-Williams E. Changes in asthma prevalence: two surveys 15 years apart. Arch Dis Child, 1989(64): 1452-1456.
4. Godfrey S. Exercise induced asthma. Arch Dis Child, 1983(53): 1-2.
5. Anderson SA. Current concepts of exercise induced asthma. Allergy, 1983(38): 289-302.

NOTE: This article was published in Current Allergy & Clinical Immunology, vol. 3 (no.1). February 1990, page 17.