Vestibular DCI and Counterdiffusion

[Kendall Raine]

Mike;

Would you please discuss causes/mechanics of vestibular bends, particularly as pertains to helium based dives, and how inert gas counterdiffusion relates to this.

Many thanks,


Kendall

 

[cudachaser]

Are you talking PFO's?

 

[PaulChristenson]

http://www.scuba-equipment-usa.com/forums/data/73.html
http://www.inspired-training.com/As...using a combined decompression model V1_6.pdf
https://www.daneurope.org/eng/faq117.htm

You probably should contact DAN directly...

 

[Dr Deco]

Hello readers:

As I understand the current thinking, during a deep helium dive, helium gas wall be present in the middle ear. When the switch is made QUICKLY to nitrogen, this will dissolve in the vestibular tissue. However, added to this is the he=gaseous helium in the middle ear that will diffuse into the vestibular tissue. Helium will diffuse very rapidly , resulting in an actual supersaturation.

Dr Deco :doctor:

 

[Kendall Raine]

OK. If I get this, several mechanisms are at work. First, pressure gradiant is driving He from middle to inner ear? Presumably perfusion in two chambers is not the same. Maybe solubility differentials as well? Second, introduction of increased levels of N2 create positive isobaric diffusion of N2 into existing bubbles creating supersaturation. Is that right?

Are gas switches from He dominant mixes to N2 dominant mixes necessary for the supersaturation or can you get a vestibular hit breathing heliox all the way to the surface?

Would lowering the FN2 in the switch gas (e. g. 50/50 nitrox to 50/25/25 trimix) lower the liklihood of counterdiffusion all things equal?


Many thanks,