Popcorn lung is a serious and irreversible condition in which the tiny air sacs in the lungs become scarred and constricted, which results in no air movement or O2 – CO2 exchange in the lungs. Other names for popcorn lung are bronchiolitis obliterans and obliterative bronchiolitis.

https://www.medicinenet.com/popcorn_lung_bronchiolitis_obliterans/article.htm