- Dr. Ladislav J. Meduna (1896-1964) from Hungary, explored the uses of Carbon Dioxide/Oxygen breathing mixture, the use of which had been described in his book Carbon Dioxide Therapy. Apparently, if one gave a psychotic patient a breathing mask and allowed him to breathe Oxygen with high percentages of Carbon Dioxide the psychotic individual became temporarily sane. Experiments were attempted where an entire room would be filled with the Oxygen/CO2 mixture and the psychotic patient would live in the room. Patients would remain sane for a period of time and then revert to their previous psychotic behavior. 
- Dr. Joseph Atkinson, a specialist in gastroenterology, created a carbon-dioxide therapy that allowed his patients to access the core issues of their personalities which he believed was the true cause of their physical ailments. Atkinson's therapy, which involved having patients inhale a carbon-dioxide mixture (called THE MEDUNA MIXTURE), triggered classic near-death experiences. Patients frequently felt that they were dying and reported moving up a tunnel and seeing a bright light. Many of Atkinson's patients also experienced the same kind of permanent changes in personality that accompany traditional near-death experiences. Although Morse claims that Atkinson was so successful that both he and his colleagues believed their therapy should be made available as an inexpensive alternative to psychotherapy, it never was accepted by the medical community at large. It was used for twenty years after World War II and then discontinued when Atkinson retired. 
- In the March 1999 issue of the "Signs of the Times" Dr. Jack Provonsha wrote an article entitled Exploring the Edges of Death. He provides a description of carbogen therapy excerpted below.
"Interestingly, an overdose of carbon dioxide elicits effects similar to those produced by NDEs and psychedelic drugs. L.J. Meduna summed up the results of the administration of thirty-percent carbon dioxide on a large number of subjects with the statement 'We definitely can see that the form-constants in Mescal [mescaline] vision...are present in the sensory alterations produced by CO2'
"Subjects on carbon dioxide report separation of the self from the body. And as with the drugs and NDEs, there were reports of caves, tunnels, intensely bright light, visions of other persons, luminaries, reliving of the past, and 'spiritual' experiences. Following an initial vision of brilliant colors and designs, one subject reported. I felt myself being separated; my soul, drawing apart from the physical being, was drawn...seemingly to leave the earth and to go upward where it reached a greater Spirit with whom there was a communion, producing a remarkable new relaxation and deep security....I seemed to receive assurance that...whatever was bothering...me...would work out all right....I felt the Greater Spirit even smiling indulgently upon me in my vain little efforts to carry on by myself, and I pressed close [to] the warmth and tender strength and felt assurance of enough power to overcome whatever lay ahead for me.
"So, altered central-nervous-system chemistry can produce illusions and hallucinations, whether that alteration is induced by extrinsic agents such as psychedelic drugs or by internal, biochemical factors.