Poor Alex, he'd expelled air (7)
I believe the answer is:
exhaled
'expelled air' is the definition.
('exhale' can be a synonym of 'expel air')
'poor alex he'd' is the wordplay.
'poor' indicates anagramming the letters.
'alex'+'hed'='alexhed'
'alexhed' anagrammed gives 'EXHALED'.
(Other definitions for exhaled that I've seen before include "blown out" , "Sent out" , "Gave off" , "Breathed out" .)