Bronchodilation Increases Estimated Ventilatory Capacity In Children With Mild Asthma

Abstract

PURPOSE: Children with asthma experience reduced maximal expiratory flows, which can decrease ventilatory capacity and increase ventilatory limitations during exercise; however, the effects of mid-flow bronchodilation on these variables are underappreciated. The purpose of this study was to examine the effect of bronchodilation on ventilatory capacity and ventilatory limitations during a maximal exercise test. METHODS: Nine children with mild asthma (7 boys, 10±1 yr, BMI percentile: 66±30, forced expiratory volume in 1s, FEV1: 106±24 %predicted, Range 78-144) completed spirometry before and after 360μg of albuterol. On a separate visit, they completed an incremental exercise test to exhaustion. Estimated ventilatory capacity was calculated using the volume time curve from estimated maximal tidal volume (FVC/2) and estimated maximal total respiratory cycle time (2×FET25-75%) both before and after bronchodilator. Ventilatory limitation was defined as <10% of breathing reserve (Estimated ventilatory capacity - maximum minute ventilation). RESULTS: Estimated ventilatory capacity increased by 16% after bronchodilator (60±23 vs. 69±27 L/min; p=0.013). Measured maximal tidal volume was lower than estimated (1.12±0.32 vs. 1.33±0.25, p=0.002) but measured maximal total respiratory cycle time (TTot) was not different from estimated (1.41±0.36 vs. 1.47±0.46, p=0.792). In a subset of seven children who received 180μg albuterol before the incremental test, five would have been ventilatory limited (i.e., <10%breathing reserve) at maximal exercise using “before bronchodilator” estimated ventilatory capacity (breathing reserve range: -61 to +9%). However, only one child was ventilatory limited at maximal exercise using “after bronchodilator” estimated ventilatory capacity. CONCLUSIONS: Bronchodilator administration prior to maximal exercise testing may be necessary to increase estimated ventilatory capacity and reduce ventilatory limitations even in children with mild asthma.