Forced expiratory decay in asthmatic preschool children – Is it adult type?

Abstract

The forced expiratory decay in healthy preschool children portrays a convex shape that differs from the linear decay in the older healthy population. The "adult-type" expiratory decay during airway obstruction is concave. The study objective was to determine if the expiratory decay in young asthmatic children is "adult-type". Among 245 children (age 3-7yrs), 178 had asthma (asthmatics) and 67 were non-asthmatic (controls). The expiratory flow decay was inspected by FEF25-75/FVC ratio (=1.0 when linear). Values were compared to those of our formerly studied (n=108) healthy children. A meaningful obstruction in FEF25-75/FVC ratio was defined as 2-zScores from healthy. A meaningful response to bronchodilators was related to non-asthmatics. In healthy subjects FEF25-75/FVC ratio declined with age from 1.73±0.17 to 1.28±0.11. Non-asthmatics portrayed ratio values similar to those of healthy subjects. In asthmatics, 118/178 displayed a convex to linear expiratory decay (FEF25-75/FVC=1.33±0.22). Sixty/178 asthmatics portrayed concavity (FEF25-75/FVC-0.79±0.16) that appeared when FEF50 was 43.4±12%healthy. Concavity appearance was also age-dependent (30.4% of 3-4y old and 59.1% of 6-7y). Vital-Capacity decreased in either decays, forming a visually petit curve. Most asthmatic children respond to bronchodilators by a meaningful elevation in FEF25-75/FVC values and by a visual change in the shape of the curve. Other common spirometry indices also increased meaningfully. Most asthmatic preschool children portray convex to linear expiratory decay with diminished vital-capacity, resulting in a visually smaller than healthy curve, with seemingly normal expiratory decay. These curves may be misinterpreted as "normal" or as "no-cooperation" and may lead to misinterpretation. In response to bronchodilators, FEF25-75/FVC value increases in asthmatics and the curve changes from concave to linear or from linear to convex contour.