An obese, 13-year-old, neutered male Pomeranian is brought to the veterinarian because of a cough that has worsened over the last 3 to 4 months. His owner reports that the cough sounds like a “goose honk,” occurs when the dog is excited (e.g., when the doorbell rings), and is unproductive of sputum. The dog then appears to have trouble breathing after coughing. On physical examination, auscultation of the heart and lungs is normal, and the veterinarian is unable to stimulate the cough. The owner declines thoracic x-rays due to financial concerns. Which of the following is the most likely diagnosis?