Doctors do not have to prescribe. You blow into it and it creates a positive pressure in your lungs to help break up the phlem from the walls and expectorate is easier. I tried to post a link for you. I will try again. In a pinch, take saran wrap...pull tight across your mouth and blow against it...it will create positive pressure in your lungs and help also.
I use a flutter valve after morning meds and anytime I have a bronchial infection. It makes it much easier to bring up the phlem/mucus/sputum. Mine looks like a pipe and has the steel ball bearing in it. I have tried the others that attach to my nebulizer but find I do not get as good a result. Baxter manufacturs the one I have.
NAC - N-Acetyl Cysteine (1000mg a day) You can get it at Amazon or most vitamin/supplement sites.