As you evaluate diaphragmatic excursion and note asymmetry, which could explain this finding?

• A. Lower airway obstruction
• B. C6 fracture and spinal cord disruption
• C. Paralyzed phrenic nerve
• D. C2 fracture and cord disruption

Answer: (C)

Diaphragmatic excursion relies on the diaphragm’s ability to contract on both sides. The diaphragm is innervated by the phrenic nerve, which arises from C3–C5. If the phrenic nerve on one side is injured or paralyzed, that side’s diaphragm cannot contract effectively, leading to reduced (or absent) excursion on that side and thus asymmetry when you assess movement.

That’s why a paralyzed phrenic nerve best explains unilateral diaphragmatic asymmetry. Lower airway obstruction affects airflow and lung volumes rather than causing one-sided diaphragmatic paralysis. Higher cervical injuries like C6 or C2 can cause broader respiratory weakness, but they wouldn’t typically produce isolated, unilateral diaphragmatic excursion asymmetry.