Abstract
Background
Short Forced Expiratory Time (FET) during spirometry is usual in children without evidence of poor cooperation.
Objectives
To determine the relationships between FET and airway obstruction (central: Forced Expiratory Volume in 1s/Forced Vital Capacity (FEV1/FVC) z-score<-1.64; peripheral: low FVC, normal FEV1/FVC and Total Lung Capacity (TLC)), FVC, FEV1 reversibility and age in asthmatic children.
Methods
A 3-year monocentre retrospective study including all spirometry for which FET was recorded in asthmatic children.
Results
We retrieved 3992 files recorded in 2623 children (973 (37.1%) females, median age 11.6 years). Median [IQR] FET was 3.0 [2.4;3.9] s for all files, with a negative, good and significant relationship between FET and FEV1/FVC z-score (r=-0.72; P<0.0001). There were significant but poor relationships between FET and age (r=0.21), and FVC z-score (r=0.11); as were relationships between age and FEV1/FVC z-score (r=-0.22); or FVC z-score (r=-0.18) (all P<0.0001). In addition, FEV1 reversibility (%baseline) was negatively related to change in FET after bronchodilation (r=-0.20; P<0.0001).
Among the 3121 files including TLC, normal baseline spirometry (68.2%) and peripheral airway obstruction (2.8%) were associated to significantly lower FET compared to central airway obstruction (25.6%)(2.9 and 2.6, respectively vs 4.3 s; P<10-5). The restrictive pattern (low TLC)(0.8%) exhibited similar FET compared to normal pattern (P=0.62) despite lower FVC z-score in the former (-1.24 vs 0.09; P<10-5).
Conclusion
FET was highly related to central airway obstruction, and poorly or not to age, FVC, or peripheral airway obstruction.