My mom had a triple bypass 9 months ago and now has a persistent cough, but the chest x-ray is normal. what could it be?

?Intubated?: Was she on a mechanical ventilator via an endotracheal tube after her surgery for any length of time? If so, perhaps her vocal cords should be examined as injury to the vocal cords and/or surrounding structures (is she also hoarse? This could mean a nerve injury..) if no other etiology for the cough is found, an ENT doctor could put a small scope in her upper airway and examine her cords in office.