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A phrenic nerve injury primarily affects the diaphragm, which is the principal muscle involved in respiration. When the phrenic nerve is damaged, it can lead to unilateral diaphragm paralysis. This means that one side of the diaphragm cannot contract effectively, inhibiting the normal mechanism of inhalation on that side. As a result, when a patient breathes in, the affected side of the chest may not rise as high, leading to impaired ventilation and reduced lung capacity on the paralyzed side.

While complete respiratory arrest may occur in severe cases of respiratory failure, this usually involves more extensive damage to multiple aspects of the respiratory system, rather than being solely a consequence of phrenic nerve injury. Asymmetrical lung expansion can be a part of the manifestations of unilateral diaphragm paralysis, but it is not a specific diagnosis in itself. Chronic respiratory distress typically refers to prolonged difficulties in breathing associated with ongoing lung conditions and would not be directly attributed to a phrenic nerve injury. The vital understanding of the phrenic nerve's role in diaphragm function clarifies that unilateral diaphragm paralysis is the most relevant consequence of this type of injury.