(This one is cross-posted over at Science-Based Medicine. FYI. –PalMD)
If you’ve been a regular reader of SBM or denialism blog, you know that plausibility plays an important part in science-based medicine. If plausibility is discounted, clinical studies of improbable medical claims can show apparently positive results. But once pre-test probability is factored in, the truth is revealed—magic water can’t treat disease, no matter what a particular study may say. So it was with great dismay that I read an email from a reader telling me about parents buying hyperbaric chambers for their autistic children. Let’s review some science.
In Breathing 101, we talked about how the oxygen delivered to your lungs depends on both the percentage of oxygen in the air, and the air pressure. We looked at how diminishing atmospheric pressure, for example at altitude, makes it harder to breathe.
Of course it is also possible to expose people to increased atmospheric pressure, which has therapeutic uses in the form of hyperbaric oxygen therapy (HBOT).
Oxygen delivery to tissue depends on several factors. We already talked about the air itself. Once air gets enters the lungs, most of the oxygen transported to your tissues is carried by the hemoglobin molecules in your red blood cells (under normal conditions). A small amount is directly dissolved in the blood. The amount dissolved in the blood is dependent on (no surprise) the percentage of oxygen and the atmospheric pressure. By increasing the atmospheric pressure from 1 atm (760 torr) to 3 atm, the amount of oxygen dissolved in the blood is enough to meet your body’s needs independent of heme-associated oxygen.
This is a good thing.
For example, up here in the Midwest, we have a lot of cases of carbon monoxide (CO) poisoning during the winter. CO binds to hemoglobin much more strongly than oxygen, so even after victims are removed to a normal environment, they are still asphyxiating.
Carbon monoxide intoxication is one of the primary uses of HBOT. Under pressure, enough oxygen is delivered to the tissues for the patient to survive. Additionally, the increased pressure helps oxygen displace CO so that heme molecules are free to go back to the work of transporting oxygen.
The original use for HBOT was of course “the bends”. When a person (for example a diver) is exposed to high pressures for a long period of time, nitrogen, which is normally not very soluble in blood, dissolves much more readily. When the diver ascends, the nitrogen bubbles are released from the blood into the tissues, causing widespread damage. HBOT can be used to help a diver “ascend” more slowly, so that the nitrogen comes out of solution in a much less damaging fashion.
HBOT can also be used to treat a variety of other conditions that are responsive to increased oxygen tension, such as anaerobic bacterial infections. But hyperbaric chambers are not without risk. Small errors can cause big problems, including death.
Strangely enough, though, you can buy your very own hyperbaric chamber for use in your own home, and parents of autistic children are doing just that.
So why does anyone think that HBOT might be appropriate for the treatment of autism? Is it even plausible? Autism spectrum disorder (ASD) is a very broad diagnostic category. Autism is a neurobehavioral disorder of inconsistent severity and unknown cause. There has been some decent research into etiology, and in some cases genetic causes have been implicated. There is no reason to suspect that autism has anything to do with decreased oxygen tension.
As you have no doubt read in this space, autism attracts a wide range of quackery, and HBOT for autism is quacks pretty loudly.
Whose idea is this, anyway?
All signs point to a guy named Dan Rossignol. Dr. Rossignol is apparently into every form of autism crankery, including mercury poisoning, mitochondrial dysfunction, and oxidative stress (although I can’t imagine that increased PaO2 is an effective treatment for “oxidative stress”). After spending a few minutes looking through is web-based material, I’m starting to think that this guy can give the Geier’s a run for their money.
True to form, Rossignol is a “pioneer” and a “maverick”. He goes where legitimate clinicians haven’t dared. Based on an implausible hypothesis, he (apparently) subjects autistic children to potentially dangerous hyperbaric oxygen therapy. He has published his ideas in the crank-magnet “Medical Hypotheses”, and in BMC Pediatrics, a journal devoted to rapid, “flexible” publication.
Even if his data were to support his nonsensical hypothesis (again, increased O2 to treat oxidative stress??), should we believe it?
Well, someone does, and that someone apparently sells hyperbaric therapy, and not just for autism. They also treat Lyme disease, multiple sclerosis, and cerebral palsy—and anything else you can spell. The site does, however, have a very small Quack Miranda Warning on the left sidebar.
There is an unbroken chain of bad medicine here. Some guy decides that a potentially dangerous treatment might help a protean syndrome. He publishes his ideas in low quality journals. Then, someone sells his treatments uncritically.
HBOT is serious medicine. Off-label use in children with autism isn’t just foolish—it’s dangerous, and should be illegal.
Rossignol DA. Hyperbaric oxygen therapy might improve certain pathophysiological findings in autism. Medical Hypotheses. 2007;68(6):1208-27. Epub 2006 Dec 4.
Rossignol DA, Rossignol LW. Hyperbaric oxygen therapy may improve symptoms in autistic children. Medical Hypotheses. 2006;67(2):216-28. Epub 2006 Mar 22.
Rossignol DA, Rossignol LW, James SJ, Melnyk S, Mumper E. The effects of hyperbaric oxygen therapy on oxidative stress, inflammation, and symptoms in children with autism: an open-label pilot study. BMC Pediatr. 2007 Nov 16;7:36.