There’s an interesting article at the International Herald Tribune about Doctor Gary Hartstein, originally from Staten Island, New York and now living and working in Belgium. He is the FIA’s medical rescue coordinator and rides in the Mercedes response car, the one following the field on the first lap. He took over from (the legendary) Professor Sid Watkins a few years ago when Watkins went off to found the FIA Institute.
The article is written by Hartstein and he explains his role at race weekends, you should check it out (there are two pages).
I also recommend clicking the author’s name when done to see some of Brad Spurgeon’s words on the subject, particularly the 2002 article.