This is one of the articles I have seen explaining how gaseous reflux gets into the lungs. https://breathe.ersjournals.com/content/9/4/256 It does not mention NTM or MAC specifically but I have read other articles that do. Also Dr Jamie Koufman is an expert on LPR here is one of her articles http://www.voiceinstituteofnewyork.com/patient-services/treatments/diagnosis-treatment-of-chronic-cough/ She also has a book called The Chronic Cough Enigma you can find on Amazon.