A 23-year-old man presents to the clinic for assessment of a gradual but progressive increase in breathing difficulty. He mentions a long history of back pain with prolonged morning stiffness. His past medical history is also significant for an episode of iritis in the past.On physical examination, the pertinent findings are a reduced range of motion in the lumbar spine with forward flexion and pain on palpation of the sacroiliac joint and surrounding soft tissue. X-rays of the pelvis show erosions and sclerosis of the sacroiliac joint. Which of the following is the most likely pulmonary complication of this condition?