Restrictive lung disease - reduced residual volume

Why does residual volume decrease in restrictive lung disease?
Thank you

Restrictive lung disease literally decreases the volume of the lungs. Pulmonary fibrosis replaces the sponge-like, air-holding lung tissue with scarring, reducing volume. This reduces all lung function numbers.

I'm not sure whether other diseases sometimes classified as restrictive (or with restrictive pictures) like musculoskeletal problems would reduce residual volume, but pulmonary fibrosis is the big, common, important one.

Thanks so much.
I just thought elasicity was affected so was confused

Thinking about it some more I'm not sure residual volume would be reduced - are you sure it is? I mean, it will be very slightly, but compared to the changes to FEV1 and FVC I wouldn't expect it to be particularly noticeable myself - I'm with you in your confusion.

But if your lecturers/textbooks are telling you that then what I've said before is the reason I'd go with.