When a dog is staying cool by panting, why doesn't it pass out.?

Panting does not expand the lungs very much so less carbon dioxide is exhaled.When humans try it they hyperventilate and get dizzy

It does happen with dogs along with other mammals without sweat glands, but not as easily. They have an ability to breathe like this for short durations, or very lightly for a long duration.

Most of the time, they are able to stop cool off, and then continue. However, if they are running from a predator, and do this for to long, they'll pass out, and the predator gets lunch.

Well, dog's have no sweat glands. They perspire from the pads on their feet and by panting. It's a way of getting rid of excess body heat. For them it's not hyperventilating, but cooling.

Because thats how dogs are designed they pant instead of sweat!

DOgs are not people.

i think you need a video game to play buddy...keep your mind of these unimportant things :P

Because... dogs are not people! Duh! They are a different species altogether.