Hi, my mother is facing persistent cough problem, its a dry cough most of the times. We have tested tb which is negative, also cough syrup is not helping, we have consulted with general physician and ent specialist, it is not helping. She is using cpap machine as she has sleep apnoea. Her bp is normal, blood sugar is normal. Could you please advice on what to do, what may be the probable cause of this cough.