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 one second (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)s, not detected by FEV1. The aim was to test the
diagnosis ability 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 asthmatic children and
twenty-nine controls aged 8 to 11 years 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≤0.04) and higher
BD reversibility, significant for Δ%FEF50/PEF (p=0.02) 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.