Pulmonary fibrosis means a build-up of scar tissue (fibrosis) in your lungs. The scar tissue restricts the transfer of oxygen from the tiny air sacs in your lungs into your bloodstream. See the leaflet called The respiratory system for more information about the lungs.
This is a companion discussion topic for the original article at https://patient.info/signs-symptoms/breathlessness-and-breathing-difficulties-dyspnoea/pulmonary-fibrosis