You may be entitled to a Blue Badge if you find walking difficult or are caring for a child who cannot walk far because of their lung condition.  There is useful information here :-

www.citizensadvice.org.uk/benefits/sick-or-disabled-people-and-carers/help-for-disabled-travellers1/blue-badge-scheme/applying-for-a-blue-badge/

There are also some Department of Transport notes about people with  lung/heart conditions. The sentence referring to lung conditions is on page 22. It may be useful to quote this when completing the application.

www.gov.uk/government/uploads/system/uploads/attachment_data/file/519091/blue-badge-scheme-local-authority-guidance-paper.pdf