OK, it’s true that I’m only scheduled to post every other week or so, but I couldn’t resist sharing this one with you (which I’ve cross-posted over at denialism blog). I promise to get back to my assigned schedule after this one. Thanks for your indulgence. –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.