This damned nodeshell has taunted me since the day I first set foot in E2. Well, enough is enough. I'm mad as hell, and I'm not going to take it anymore!

Dr. Sandor Gardos provides us with this bit of official debunking:

While it is indeed a theoretical danger, I have never been able to locate a confirmed case in the medical literature, except in cases of pregnancy.

If you were to blow air very strongly into the vagina, with your lips pressed tightly against the vulva (thus preventing escape of the air), it is theoretically possible that you could create what is known as an air embolus. This is a form of embolism, where an air bubble blocks the passage of blood in an artery or vein. In severe cases, if blood flow is completely obstructed, the tissue in that area would die. If the embolus were to travel up to the heart or lungs, it would indeed be possible to die. You should know that when a woman is pregnant, and her cervix begins to dilate, she is more likely to suffer an embolism. In extremely rare cases, this has even been reported to occur from intercourse.

In the days before abortion was legal, many women used to die each year from embolisms created by the insertion of instruments into the uterus. So, yes, you can definitely die from an air embolus, but the question is how likely one is to be created from blowing air into the vagina.

I think it is pretty clear that normal, run-of-the-mill oral sex carries no risk. Even blowing lightly onto the vagina is perfectly fine. I would, however, avoid blowing strongly into the vagina, especially if your partner is pregnant. Otherwise, there is really nothing to worry about.

And Dr. Patti Britton has this to add:

Yes, there is a very slight chance that an embolism — a gas bubble in the blood stream, which can be deadly — could occur if a guy were to blow extremely hard into your vagina. However, it would probably take a hefty, determined, hard, ceaseless blow into that ‘sealed’ opening to create such an impact. Imagine blowing hard into a balloon with a tiny opening, with your mouth straining. That's the kind of blowing required to even tease out the possibility of such an occurrence. Heavy breathing is just not that kind of action.

Most oral sex performed on women includes gentle stroking with the tongue, licking and sucking, but not intense blowing. Some men and women report that blowing gently into the woman's vulva region is a way to create a pleasant sensation. That's about the only way that sending air on to or into your private parts usually occurs. So, let go of your worries about being blown away.