Limitations of forced spirometry in the detection of bronchodilator response in asthmatic children

Abstract

The diagnostic value of FEV₁ for assessing functional impairment in asthma has been debated, primarily because forced expiratory manoeuvres may alter bronchial tone. The forced oscillation technique (FOT) does not affect the baseline tone, thus may be a more appropriate tool to evaluate the bronchodilator response (BDR) in children.

FOT and spirometry were performed before and after administration of 400 ug salbutamol in school-aged children with stable asthma. Mean R at 6 Hz (R₆) was calculated for several breaths and the end-expiratory (ReE) and end-inspiratory (ReI) values at 10 Hz were also determined. Positive BDR was defined according to the guidelines.

Four children had positive BDR with both the FOT and spirometry (Group 1, Table 1), 6 had positive BDR with FOT but not with FEV₁ (Group 2) and 15 did not have a BDR with either technique (Group 3). Baseline ReE was elevated in Groups 1 and 2 as compared to Group 3 (p<0.05); however, ReI was significantly lower in Group 2 than in Group 1, suggesting that these children can dilate their airways during tidal breathing.The different patterns in the volume dependence suggest that the baseline airway tone in asthmatics can be reduced by the deep inspiration associated with the FEV₁ test and hence remain hidden in children who exhibit positive BDR.