Similar to above commenter, I'm just flinging poo, but

Those who are trained in the tougher situations are, I imagine, more desensitized and therefore don't do the egads! sort of gasp. I imagine they probably don't necessarily need to rely on that burst of air because they'll take a purposeful deep breath before heading into the fray.

That being said, I think professionals do still gasp. It's probably just not something one's brain really catches onto. But it is a startle reflex - so if a surgeon is squirted in the face with blood, if there's a close call with a firefighter, if a cop walks up to a car and has a gun out under their chin.... I imagine each of these will get a little gasp at the very least.