Target Workload For Exercise Challenge Tests Exceeds Achievable Workload In Children With Mild Asthma

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PURPOSE: Exercise challenge tests are bronchoprovocation tests used to diagnose exercise induced bronchoconstriction. The American Thoracic Society (ATS) recommends calculating the target workload for exercise challenge tests using predicted forced expiratory volume in 1s (FEV1). The goal is for patients to achieve a minute ventilation between 40 to 60% of predicted maximum voluntary ventilation (PMVV) during the exercise challenge test. The purpose of this study was to compare predicted workload with actual workload achieved during an exercise challenge test in 8 to 12-year-old children with mild asthma. METHODS: Eleven children (3 girls, 10.3 ± 0.9 yr, 142.6 ± 8.1 cm, 40.7 ± 9.6 kg) completed pulmonary function testing and also completed maximal exercise tests and exercise challenge tests on a stationary bike. PMVV was calculated as 35 x measured FEV1. The test was completed at a target workload calculated using measured FEV1 (53.76 x measured FEV1 - 11.07). Our goal was to increase workload every minute as follows: 60%, 75%, 90%, and 100% target. However, if the child was unable to maintain cadence or expressed inability to complete 6 minutes of cycling, the workload was maintained or reduced to an achievable workload. RESULTS: 27% of children were below 40% PMVV, 36% were between 40 - 60% of PMVV, and 36% exceeded 60% of PMVV during the fifth minute of the exercise challenge test. After excluding the 3 children who did not achieve minute ventilation of at least 40% of PMVV, measured workload during the exercise challenge test (64 ± 18W; 66 ± 9%, Range: 49 - 78% of predicted target workload) was significantly lower than predicted target workload (96 ± 18W; P<0.001). Workload during the exercise challenge test was 67 ± 8% (Range: 60 - 80%) of maximum workload from the maximal exercise test. In the current project, we used measured FEV1 to calculate target workload for exercise challenge tests. However, even when predicted FEV1 was used to calculate target workload, measured workload during the exercise challenge test was below target and ranged from 43 - 112% (66 ± 22%) of target workload. CONCLUSIONS: The predicted workload for exercise challenge tests based on ATS guidelines may be difficult to achieve for children with mild asthma. However, target ventilation can be achieved at a workload that is between 60 - 80% of maximum workload.