Henry Dreher's superb summary of research with mind-body interventions for surgery appears in the Fetzer Institute's Advances in Mind-Body Medicine, Vol 14, no.3, Summer 1998, pp. 207-222. His discussion of Henry Bennett's placebo controlled, double blinded research with 4 audio interventions on 335 surgery patients establishes that the Health Journeys tape for Surgery was the only tape that offered statistically significant results.
The study yielded profound results on the reduction blood loss, length of hospital stay and anxiety levels, both state (the fluctuating kind) and trait anxiety (which presumably doesn't change, because it is seen as a relatively stable personality feature). In fact, the Naparstek guided imagery tape was so potent, that Dreher devotes a whole section of this article to trying to figure out why it outperformed all the others.