Descending too fast??

[miguel sanz]

I thought the main reason to recommend slow descent (other than ears and the "non tested" issue, was to observe sign of narcosis on you or you buddy (eventhough I think it´s also related to time exposure, ´cause doesn´t pressuriced O2 +/- CO2 affect the deggree of narcosis, and isn´tb this related to time?).
And another question, other than the fact that it´s not tested, is there any physiologic explenation for the hipothesis that faster descent means higher on-gasing?

 

[Dr Deco]

Hello Miguel:

Fast Descents

I would say that the main reason for the increased gas loads during fast descents would be that you would need to work vigorously to be able to go down quickly.

While it is not classical decompression theory, there exists evidence from my studies at NASA that half times can and do change. They are not fixed. While it would be generally conceded that increased activity will increase gas loading, it must also be recognized that classical barophysiology uses fixed halftimes in the models. It is either one or the other, not a fuzzy in between.

When one kicks to descend, the muscle pump is in activity and the heart rate is increased. When you reach bottom, the blood flow continues at a high level for several minutes (“post exercise excess oxygen consumption”). This will increase the gas loading beyond what would be expected from the algorithm. A later gentle, slow ascent to the surface will slow the circulatory system and the off loading will not be equal to the on gassing.

This wording is different than would be used by professional barophysiologists, but they would probably agree with the concept.

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology :grad:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[Remy B.]

Bringing this to light again.

I Was told by experienced divers that the tables didn't have safety factors build in them, I didn't argue because I really don't know, I just assumed that they had because it make sense.

As well I understood that N2 narcosis is related to time of exposure, so if someone makes a fast descent for a touch and go dive to 50m on air is less likely to get the effects of N2 narcosis, but after reading all the interventions it seems there are opposing opinions and as well some contradictions.

This is a 11 year old thread, I guess by now their will more to say regarding N2 narcosis.

 

[Saturation]

Nothing scientific has been added to the literature beyond what is posted here. I descend quickly to spend most time at the bottom, it did take some time for me to learn rapid ear equalization. I descend over 100fpm and will slow down only if my buddy cannot follow, and I dive open circuit.

 

[Taliena]

I did some fast decends. If I use a trimix with an END around 45m, and go fast to 100m, I feel some norcosis. After 1-2 minutes it dissapears again. The more narcosis in the first minutes is due to the big pressure difference between your bodytissues and the ambient pressure under water.