Assessment of bronchial obstruction and its reversibility by shape indexes of the flow‐volume loop in asthmatic children

Abstract

Asthma assessment by spirometry is challenging in children as forced expiratory volume in 1 s (FEV1) is frequently normal at baseline. Bronchodilator (BD) reversibility testing may reinforce asthma diagnosis but FEV1 sensitivity in children is controversial. Ventilation inhomogeneity, an early sign of airway obstruction, is described by the upward concavity of the descending limb of the forced expiratory flow-volume loop (FVL), not detected by FEV1. The aim was to test the sensitivity and specificity of FVL shape indexes as β-angle and forced expiratory flow at 50% of the forced vital capacity (FEF50)/peak expiratory flow (PEF) ratio, to identify asthmatics from healthy children in comparison to "usual" spirometric parameters. Seventy-two school-aged asthmatic children and 29 controls were prospectively included. Children performed forced spirometry at baseline and after BD inhalation. Parameters were expressed at baseline as z-scores and BD reversibility as percentage of change reported to baseline value (Δ%). Receiver operating characteristic curves were generated and sensitivity and specificity at respective thresholds reported. Asthmatics presented significantly smaller zβ-angle, zFEF50/PEF and zFEV1 (p ≤ .04) and higher BD reversibility, significant for Δ%FEF50/PEF (p = .02) with no difference for Δ%FEV1. zβ-angle and zFEF50/PEF exhibited better sensitivity (0.58, respectively 0.60) than zFEV1 (0.50), and similar specificity (0.72). Δ%β-angle showed higher sensitivity compared to Δ%FEV1 (0.72 vs. 0.42), but low specificity (0.52 vs. 0.86). Quantitative and qualitative assessment of FVL by adding shape indexes to spirometry interpretation may improve the ability to detect an airway obstruction, FEV1 reflecting more proximal while shape indexes peripheral bronchial obstruction.

It is high time we standardize the interpretation of bronchodilator responsiveness in children

“…On the one hand, the Δ %Pred expression mode permits the comparison of subjects regardless of age and height (in the French study, 1 heights' interquartile were huge in both controls [130-143 cm] and asthmatics [129-138 cm]). 1 On the other hand, the Δ A expression mode correlates with age and height, and changes in FEV 1 (i.e., ΔFEV 1 ) are smaller in short children than in tall ones. 5 The third point implicates the evaluation of BDR via only flows (i.e., FEV 1 and peak expiratory flow).…”

“…The second point involves the expression mode of the BDR, where the authors considered the percentage change reported to initial value (Δ %Init ). 1 Despite its huge use in clinical practice, the aforementioned expression' mode presents two main weaknesses. 5 First, Δ %Init exhibits size-and sex-bias in evaluating BDR.…”

“…5 The third point implicates the evaluation of BDR via only flows (i.e., FEV 1 and peak expiratory flow). 1 In children, some scholarly societies still recommend the inclusion of an interesting volume (i.e., forced vital capacity [FVC]) to interpret BDR. 3 It is true that the distinction between the flow and the volume effects is not completely understood in the literature.…”

“…7 Furthermore, an increase in FVC is linked to a reduction in air trapping. 7 Finally, the approach of Berrier et al 1…”