Ah, nothing like daytime television when it comes to sober presentations of science. “The Oprah Winfrey Show” is promoting David Blaine’s appearance this Wednesday as a death-defying feat, which is not quite the way scientists (or Mr. Blaine) see his attempt to break the world record for breath-holding. Underwater breath-holding can lead to fatal blackouts if you do it without proper supervision, but Mr. Blaine will be carefully observed. Experts like Ralph Potkin, the pulmonologist who monitored Mr. Blaine during his training (which I described in my Findings column), say that prolonged breath-holds don’t appear to cause harm to the body — at least not in the short term.

But what about the long term effects on the brain? I’m afraid there’s no clear answer yet from Dr. Potkin and other scientists who have studied veteran free divers, the competitors who regularly practice holding their breath underwater and sometimes suffer blackouts. The research results so far have been mixed.

In an Australian study, researchers looked for evidence of “brain insults” by administering tests to 21 free divers. Here’s the summary of the results from the researchers, Lynne “Ridgway and Ken McFarland of the University of Queensland, as reported in 2006 in the Clinical Neuropsychologist:

Standard neuropsychological tests, with known sensitivity to mild brain insults, included speed of visuo-motor responding, speed of language comprehension, response inhibition, and visual and verbal attention and recall tasks. Results indicated that the breath-hold divers performed tasks within the average range compared to norms on all tests, suggesting that 1-20 years of repeated exposure to hypoxemia [an abnormally low level of oxygen in the arterial blood] including multiple adverse neurological events did not impact on performance on standard neuropsychological tasks.

In another study, Dr. Potkin and Michael Uszler conducted brain scans of five people who had done at least 1,000 breath-hold dives over a five-year period. One kind of scan, the well-known M.R.I., revealed no abnormalities in the structure of their brains, Dr. Potkin reports. But another kind of brain can, called S.P.E.C.T. (single photon emission computed tomography anatomy), revealed abnormalities in their metabolism of the frontal and temporal lobes of the brain, according to the study, which was published in 2006 in the Proceedings of the Proceedings of the Undersea and Hyperbaric Medical Society.

Dr. Potkin calls these abnormalities “troubling” but says it’s not clear whether or not they indicate a problem, particularly in light of the Australian study that found no apparent damage to the divers’ mental abilities.

“This was a preliminary study and we did not have the benefit of pre-dive scans for comparison,” says Dr. Potkin, who is the physician for the United States free-diving team. “The issue of long term brain damage is not yet settled and will require further investigation.”

Several readers asked for specific tips on how to prolong breath-holding, but I’m not going to try to answer their questions. To repeat the advice of Dr. Potkin and other authorities: Don’t try underwater apnea unless you’re being monitored by an expert — the way David Blaine will be on Wednesday. source

A comment from the source:
obstructive sleep apnea is indeed the perfect model of humans who breath-hold frequently and to extreme degrees, with significant desaturations. It is not uncommon to find those who have apneic episodes over 100 times per hour for each hour of sleep for years, and with concomitant desaturations into levels we would have thought twenty years ago to be fatal.

Recovery from many of the effects of these episodes with treatment is total except in those with significant desaturations, where persistent performance deficits on testing of intellectual function are found. This research finding has been repeated and found consistent.

Perhaps then it is the frequency of the desaturation events, not just their severity, that can cause permanent damage. One might conclude, facetiously, that the deep-divers should be discouraged from doing their dives more than 800 times in each 24 hour period.

— Posted by Walter James MD