X-ray — Tension Pneumothorax with Mediastinal Shift

A 28-year-old male with COPD on home non-invasive positive pressure ventilation (NIPPV) is brought to the emergency department in severe respiratory distress following a sudden episode of acute dyspnea and agitation. On examination, he is cyanotic, tachycardic (HR 130/min), hypotensive (BP 85/50 mmHg), with distended neck veins and absent breath sounds on the left side. A portable chest X-ray is obtained and shows the finding marked **B** in the diagram. Which of the following pathophysiological mechanisms DIRECTLY explains the hemodynamic collapse observed in this patient?