A 68-year-old man is referred to the respiratory clinic by his GP due to progressive shortness of breath over the past 6 months. He reports increasing difficulty climbing stairs and walking uphill. He also has a dry cough that’s been persistent for several months. He denies chest pain, haemoptysis, or recent infections. His past medical history includes rheumatoid arthritis diagnosed 12 years ago. He is a retired builder with a 40-pack-year smoking history. Medications include methotrexate and a salbutamol inhaler.