I think it is related to amalgam fillings. Of course the lungs are also affected by other toxins in the air we breathe too.

I always get a spate of coughs when chelating, doesn't last long, maybe 3-4 minutes about 20-30 minutes after a chelator, whether DMSA, IV EDTA, a big dose of cilantro, anything. I don't swallow what gets pushed up (ever, anytime of day anymore, if I can help it), I spit it out.