The changes to CPR over the years have been dramatic. I first learned how to preform it in the late 80's, at that time survival rate were abysmal. Now that has all changed for the better. To help understanding you need to remember that the body's circulatory system is a closed pumping system, for blood to actual flow you need to bring the system up to working pressure. In the past we never did that, we would get up to pressure and than stop. This is why you want as minimal interruptions as possible! Get the pressure up and keep it up for the blood to circulate, this is why you are performing 200 compressions. The New York website and video is good but I prefer this one from the crew in Florida , https://www.youtube.com/watch?v=4u69rGzWmcQ [url=https://www.youtube.com/watch?v=4u69rGzWmcQ][/url]