To comment, Alfonso was correct. I have been accepted by black belt magazine for publication of an article on the topic-still don't have a date yet. The article is focused on aikido striking of pressure points.
However, it is not a common aspect of aikido and is seldom taught. It is a particular interest of mine, my friend Gary Chase, and a few others practicing aikido. A few of us feel this is a lost aspect of the art. A very good book to explain the medical aspects is Dr. Michael Kelly's book: Death Touch. It explains medically what happens (vagovasal faint for example). He is not an aikido practitioner though. Causing people to black out is not a recommended practice for aikidoka or others for that matter since it has serious health implications for someone with heart disease.