Reactive Airways Dysfunction Syndrome

A 44-year-old previously healthy warehouse foreman with no history of asthma or atopy is acutely exposed to a large chlorine gas cloud from a ruptured containment tank. He develops immediate severe cough, chest burning, wheezing, and dyspnea. After emergency treatment with oxygen, bronchodilators, and corticosteroids, he is discharged but continues to have daily wheezing, exercise-induced dyspnea, and nocturnal cough at 6-week follow-up despite inhaled fluticasone/salmeterol. Spirometry at 8 weeks and methacholine challenge at 12 weeks are performed. The spirometric pattern marked **A** in the diagram is most consistent with this patient's diagnosis. Which of the following best characterizes the spirometric findings in this case?