Interprétation et utilisation de la courbe débit-volume chez l'enfant asthmatique

The flow-volume loop is the most common lung function test performed in children with asthma or suspected of having asthma. To correctly perform this test, the child must control and coordinate breathing, which is achieved between 3 and 8 years of age, usually round 6 years. This test is required in every child with asthma or suspected of having asthma in order to confirm the diagnosis and assess the future risk. It is recommended to repeat the test after the onset of anti-asthma medication or after a change in anti-asthma medication and it is mandatory to control lung function a few months after treatment cessation. Quality control of the flow-volume loop must use age-specific criteria. Interpretation of the result is based on comparison of measured values to reference values adapted to the child's age, sex, height and ethnic origin. The most frequently encountered central airway obstruction is defined as the decrease in forced expiratory volume in 1 s (FEV1)/vital capacity (VC) ratio under the lower limit of normal (z-score, < −1.64). A significant reversibility after bronchodilator administration is characterized by a 12% increase in FEV1 and/or VC. An alternative peripheral airway obstruction pattern is described when there is a simultaneous decrease in VC (due to early airway closure) and in FEV1, resulting in no decrease in the FEV1/VC ratio. In this case and in the absence of significant reversibility, further tests are warranted to untangle the mechanism of lung function impairment.