This year, a study of 52 cardiac-arrest patients in Slovenia, published in the Journal of Critical Care, found that the 21% who had near-death experiences also had high blood levels of carbon dioxide, which has been associated with visions, bright lights and out-of-body experiences.
A study of seven dying patients at George Washington University Medical Center, published in the Journal of Palliative Medicine, noted that their brainwaves showed a spurt of electrical activity just before they were pronounced dead. Lead investigator Lakhmir Chawla, an intensive-care physician, notes that the activity started in one part of the brain and spread in a cascade and theorized that it could give patients vivid mental sensations.
The team studied 52 heart attack patients who had been admitted to three major hospitals and were eventually resuscitated. Eleven of the patients reported near-death experiences.
"We found that in those patients who experienced the phenomenon, blood carbon-dioxide levels were significantly higher than in those who did not," said team member Zalika Klemenc-Ketis, of the University of Maribor in Slovenia.
How carbon dioxide might actually interact with the brain to produce near-death sensations was beyond the scope of the study, so for now “the exact pathophysiological mechanism for this is not known,” Klemenc-Ketis said.
However, people who have inhaled excess carbon dioxide or have been at high altitudes, which can raise the blood’s CO2 concentrations, have been known to have sensations similar to near-death experiences, she said.