A 24-year-old female athlete presents with recurrent episodes of dyspnea and biphasic stridor triggered by exercise and emotional stress. She has been treated for asthma for 2 years without improvement. Spirometry between episodes is normal, but during an acute episode, the flow-volume loop shows the pattern marked **A** in the diagram. Laryngoscopy during an acute episode reveals paradoxical adduction of the true vocal cords during inspiration. Which of the following is the most likely diagnosis?