Due to the negative intrapleural pressure, the pleural sac must remain airtight. If the pleural sac were broken, as in a piercing wound, which of the following would happen? Due to the negative intrapleural pressure, the pleural sac must remain airtight. If the pleural sac were broken, as in a piercing wound, which of the following would happen? 1. The lungs would burst. 2. The lungs would remain the same. 3. The lungs would expand outward. 4. The lungs would collapse.