"Carbon Dioxide Therapy is a seminal monograph documenting the use of carbogen in psychiatry as a treatment for neurosis. Carbogen is a psychoactive mixture of carbon dioxide and oxygen that exerts anesthetic and visionary effects. The book's author administered a blend called "Meduna's Mixture", consisting of 30% carbon dioxide and 70% oxygen, to hundreds of patients, and the results of his research are copiously document in this engaging monograph. Exposure to increased levels of carbon dioxide can be dangerous or even be fatal, but Meduna encountered no serious problems in administering his 70/30 blend in sessions of up to 50 breaths in length.
Meduna concludes that carbogen was effective in generating improvement in 68% of the subjects he evaluated in this book"
http://www.erowid.org/library/review/review.php?p=250
hmm huffing carbon dioxide..