I have found some interesting articles through a normal google search on breath control, but there is one at the deviant's dictionary that is especially informative on different techniques (I'd post the link but am unable). With the carotid artery technique she can get the same benefits (blackness, fading, head rush, heightened awareness) with less pressure and little contact directly on the most fragile areas of the neck. Personally, I prefer this method, while my Master remains focused on the windpipe.