Final answer:
Acquired tracheal stenosis is a narrowing of the trachea from inflammation or injury, often requiring surgery, while saber sheath trachea, associated with COPD, is a tracheal deformity that usually does not require treatment.
Step-by-step explanation:
The question is asking to distinguish between acquired tracheal stenosis and saber sheath trachea, both of which can be associated with chronic obstructive pulmonary disease (COPD). Acquired tracheal stenosis is a condition where there is a narrowing of the trachea usually due to inflammation, injury, or previous medical procedures. It can lead to difficulty breathing and may require surgical intervention. On the other hand, saber sheath trachea is specifically associated with COPD and is characterized by a marked narrowing of the intrathoracic trachea, particularly in the coronal plane, while the sagittal diameter remains normal. It is called 'saber sheath' due to its resemblance to the sheath of a saber sword. This condition does not typically require treatment unless it causes significant airflow limitation.