Breathe in sharply when embraced by doctor (4)
I believe the answer is:
gasp
'breathe in sharply' is the definition.
(to gasp is to take a breath suddenly)
'when embraced by doctor' is the wordplay.
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'embraced by' means one lot of letters goes inside another.
'doctor' becomes 'gp' (general practitioner).
'as' inserted into 'gp' is 'GASP'.
(Other definitions for gasp that I've seen before include "Fight for breath" , "Show amazement" , "Puff, struggle for breath" , "Inhale sharply with astonishment" , "Pant" .)