afaik: aero bars can indeed constrict your breathing if you have a standard road frame. that's why tri / TT bikes have a 2-3° smaller angle (a more forward position). it opens up your upper body when your crouched in that aero position.
however: bikesetups are extremely individual.

imho (unless it's a super long du) i would not mess around with your bike setup on such short notice. (people have after all also done IMs w/o aerobars).

if you want to do tris and/or dus regularly i would then consider experimenting with your bike setup so that it works (aerobars, forward seatpost...)