Childhood Asthma Pre/Post Bronchodilator Reversibility

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?