The temporary damage thing could be quite cool. In the AMX version of the Gas Grenade plugin they have incorporated a gas mask icon for when you are damaged. Maybe it's a similar thing.
Hopefully the answer will come to you in a blinding flash
Here that post again for AMX. Seems it has sounds for "gasps" and uses an icon...
http://djeyl.net/forum/index.php?showtopic=22220&st=180
Cheers for now