I remember hearing or reading somewhere that diving with Helium can be more dangerous to people with PFOs since it's a lighter and faster gas, so the bubbles can more easily pass to the left atrium.
Has this been proven or is it just speculation? Any research about this?
Thanks
Interesting question. A physiologist with expertise in gas/blood dynamics might be able to tell you whether helium bubbles would be more likely to arterialize through a PFO than nitrogen bubbles of an equivalent size and quantity.
The practicalities of experimentally comparing the behaviors of different gases in situ are difficult. You could look at the rate of occurrence of sudden-onset severe neurological DCS, inner ear DCS, and/or cutis marmorata in heliox or trimix divers compared to that in compressed air divers, but the other potential influences are the depths of the dives, the environment, and the characteristics of the different decompression algorithms. You could also look at doppler studies using different breathing gases, but even going to the same depth, the decompression algorithms would be a confounding factor. In order to make a direct comparison between gases you have to eliminate all of those influences, which means compressing live test subjects on different breathing gases to a specified depth in an environmentally-controlled hyperbaric chamber, leaving them there long enough to accumulate a high inert gas load, then bringing them straight to the surface without decompression stops. You can't do that with human subjects, so you're left with animal models. The only diving-related literature I could find was a
paper from 1974 published by Dr. Mike Powell, our own now-retired Dr. Deco, comparing air, helium and neon venous gas emboli in pigs. I've requested a copy from the Duke Medical Center library since it's not available electronically (if anyone has it please share!). I'll post when I have the article.
@Dr Simon Mitchell might know of more work on this.
There are some studies that suggest that the solubility of a gas in blood is a factor in venous gas embolus lethality, which makes intuitive sense. These are exploring the use of helium for insufflation during laparoscopic surgery vs. CO2:
Gas embolism: helium is more lethal than carbon dioxide - PubMed
Venous gas embolism--a comparison of carbon dioxide and helium in pigs - PubMed
Best regards,
DDM
