I’m not sure what you are saying Seb. I think it has been fairly well established that blood flow to the brain increases by a small amount during both BH dives and prolonged apnea. The assumption is rising carbon dioxide levels cause cerebral artery vasodilation. That’s why I said the diving response doesn’t protect the brain from DCS. This considers only the perfusion aspect.
If you lower brain temperature more than 4 or 5 degrees you will have significant cognitive decline. Nitrogen solubility increases with cooling by about 0.7 to 0.9 percent per degree (1), which translates to maybe about 5 percent change. Not a very big effect over that temperature range. How this difference might influence bubble nucleation or growth and translate to DCS risk is not clear, but I wouldn’t anticipate a big difference.
Regardless, I don’t see how you could significantly change brain temperature over the course of a dive of 3 to 4 minutes. I would be interested to hear more. Do you have some data?
Reference:
(1) Weathersby PK, Homer LD. Solubility of inert gases in biological fluids and tissues: a review. Undersea Biomed Res. 7(4):277-96;1980
If you lower brain temperature more than 4 or 5 degrees you will have significant cognitive decline. Nitrogen solubility increases with cooling by about 0.7 to 0.9 percent per degree (1), which translates to maybe about 5 percent change. Not a very big effect over that temperature range. How this difference might influence bubble nucleation or growth and translate to DCS risk is not clear, but I wouldn’t anticipate a big difference.
Regardless, I don’t see how you could significantly change brain temperature over the course of a dive of 3 to 4 minutes. I would be interested to hear more. Do you have some data?
Reference:
(1) Weathersby PK, Homer LD. Solubility of inert gases in biological fluids and tissues: a review. Undersea Biomed Res. 7(4):277-96;1980