I don't know if this can be done this way. I know that by using GPDL, one can create any variable, I just don't know how to associate it with a particular PC.
However, if you wanted to have the even occur if a specific race, class or gender were in the party and that character had at least 10% of her hit points, I think that can be done. If there was only one dwarf, you could have an event fire where he said, "The tunnel seems to be sloping down."
How to do this? It's using the Logic Block. (You may need to call on a GPDL function from within the logic block.)