A 7-year-old boy presents with a 6-month history of episodic wheeze, nocturnal cough, and dyspnea triggered by play and upper respiratory infections. Spirometry shows a baseline FEV1/FVC ratio of 0.78 (below the lower limit of normal). The flow-volume loop demonstrates a scooped expiratory curve. After inhalation of 400 mcg salbutamol via spacer, spirometry is repeated 10–15 minutes later. The curve marked **B** in the diagram shows the post-bronchodilator response. Which of the following findings in the post-bronchodilator curve would be MOST consistent with a positive bronchodilator reversibility test and support a diagnosis of childhood asthma in this clinical context?
A. An increase in FEV1 of >12% from baseline, with normalization of the expiratory limb from scooped to linear
B. An increase in FEV1 of 8–10% from baseline with persistent scooping of the expiratory limb
C. A decrease in FEV1 by 5% from baseline due to bronchial hyperresponsiveness to the bronchodilator
D. No change in FEV1 or flow-volume loop morphology, indicating fixed airway obstruction
Explanation
Why An increase in FEV1 of >12% from baseline, with normalization of the expiratory limb from scooped to linear is right
The SME anchor defines a POSITIVE bronchodilator reversibility test as an INCREASE IN FEV1 of >12% from baseline in children ≥5 years (ATS/ERS 2022 criteria). The flow-volume loop classically shows a SCOOPED (concave) expiratory limb pre-bronchodilator that NORMALIZES post-bronchodilator. This combination—>12% FEV1 improvement AND morphologic normalization of the expiratory curve (marked B)—is the hallmark of reversible airflow obstruction and is diagnostic of asthma in a child with compatible clinical history (episodic wheeze, cough, nocturnal symptoms, trigger-induced dyspnea). GINA 2024 and Nelson Pediatrics 22e emphasize that objective demonstration of variable expiratory airflow limitation via spirometry is essential for asthma diagnosis in children ≥5 years, and the bronchodilator reversibility test is the cornerstone confirmatory test.
Why each distractor is wrong
An increase in FEV1 of 8–10% from baseline with persistent scooping of the expiratory limb: An 8–10% improvement falls below the >12% threshold required for a positive response. Persistent scooping indicates incomplete reversal and does not meet diagnostic criteria for asthma; this pattern may suggest other obstructive conditions or inadequate bronchodilator response.
A decrease in FEV1 by 5% from baseline due to bronchial hyperresponsiveness to the bronchodilator: A paradoxical decrease in FEV1 after salbutamol is extremely rare in asthma and would suggest either measurement error, poor technique, or an alternative diagnosis (e.g., vocal cord dysfunction). Bronchial hyperresponsiveness is a feature of asthma but does not cause FEV1 to fall after a bronchodilator.
No change in FEV1 or flow-volume loop morphology, indicating fixed airway obstruction: Absence of reversibility argues against asthma and suggests fixed obstruction (e.g., bronchiectasis, tracheomalacia, or other structural disease). This finding would not support an asthma diagnosis and would prompt investigation for alternative diagnoses.
High-YieldNEET PG
Childhood asthma diagnosis requires BOTH compatible clinical history (episodic wheeze, cough, dyspnea) AND objective spirometry showing >12% FEV1 reversibility with post-bronchodilator normalization of the expiratory flow-volume loop.
GINA Global Strategy 2024; Nelson Textbook of Pediatrics 22e; ATS/ERS 2022 Spirometry Guidelines
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