A 72-year-old woman with a history of lung cancer presents with progressive dyspnea over 2 weeks. On examination, breath sounds are diminished on the left side. Chest X-ray shows complete opacification of the left hemithorax with the mediastinum and trachea shifted to the left, and the left hemidiaphragm is elevated. The left hilum appears elevated and small. Which of the following mechanisms best explains these radiological findings?