This has a good rundown of helpful COPD supplements, with study references at the end:
https://www.lifeextension.com/protocols/respiratory/copd
The Vitamin C study showing it counters some iNOS activity (supports BH4):
https://www.ahajournals.org/doi/pdf/10.1161/01.res.0000049166.33035.62
A study describing superoxide dismutase (SOD) helping (along with a ton of other information):
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2248324/
Another resource that appears to have collected various studies and doctor’s protocols:
http://www.medicalinsider.com/cardiac3.html
THX
Thank you ... good information, some I missed.