breathing rate and DCS

[annie]

Hi

This is probably a daft question. There is a new thread on the board about how to use less air. My question is, should divers who go through a 16l tank have a shorter NDL than someone who goes thru a 12l? Because they've breathed more air at depth, doesn't that mean that there is more nitrogen absorbed into their blood?

 

[Charlie99]

annie once bubbled...
This is probably a daft question. ...My question is, should divers who go through a 16l tank have a shorter NDL than someone who goes thru a 12l? Because they've breathed more air at depth, doesn't that mean that there is more nitrogen absorbed into their blood?

No, and No.

The only daft question is the unasked, and therefore unanswered one.


The short answer is that breathing rate has no effect on N2 absorption.

The partial pressure of nitrogen in the lungs is the same whether you are breathing fast or slow (ignoring some very, very, very minor differences in CO2 and H20 pressures). It is the partial pressure of N2 in the lungs that determines the N2 level in the blood, and then the tissues.

------

Are heavy breathers more likely to experience DCS. Yes. But only if they go out-of-air and do a rapid ascent

 

[annie]

Thanks - that makes sense!

 

[Dr Deco]

Dear annie:

Nitrogen Removal

Very little nitrogen is removed from the lungs when diving, as Charlie99 indicated. For each atmosphere of pressure, at equilibrium, the body will dissolve about 1 liter (bit more than a quart) of nitrogen. As you can see, a scuba tank holds considerably more than this. Very little nitrogen is removed.

Air Usage

In general, air usage depends on the relaxation and experience of the diver. In some cases it can reflect heavy physical exertion. When this is the case, the circulatory system will be more active to all tissues (muscles and connective tissue) and nitrogen loading will be more than anticipated in the decompression algorithm. Remember that while there are halftimes for all blood flows, these halftimes do not change from slower to faster to reflect this change in activity.

When on the surface, the circulation returns to normal and slows down. The dissolved nitrogen washout is reduced and this will promote decompression bubble growth. :boom:

Dr Deco :doctor:

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

 

[peter k]

Hi Doc,
This is probably the same kind of question just from a different angle;
Example-During the dive your 40msw max and you're finning about quite the thing, perhaps fighting a bit of current, so you're breathing a bit harder because your actually at the "doing things" part of the dive. You come up at the usual rate and hang for deco. During deco your not actually "doing things" anymore so your breathing rate slows to nearly non-existent.
I ask because I have sometimes noticed my breathing during deco dropping away dramatically and needing to make a concious effort to breath harder again to off-load. The problem is that I know that I also sometimes do not notice! :boom:
Should you try and raise your breathing during ascent + deco to off-load quicker and thus preventing a ride in the 'chopper or if you've been working harder at depth spend a good bit longer hanging about during deco?

Peter

 

[MonkSeal]

peter k once bubbled...
Should you try and raise your breathing during ascent + deco to off-load quicker and thus preventing a ride in the 'chopper or if you've been working harder at depth spend a good bit longer hanging about during deco?

I keep some activity during deco/safety stop (fining, swiming in circles etc.)

 

[Dr Deco]

Dear peter:

Activity

There are now papers beginning to appear in the literature based on the original research of the Air Force (Brooks) and my work (at NASA) with reduction of prebreathe duration that indicates that better results come with some light exercise following decompression. Therefore, it will behoove you to perform some kicks or bicycle movements with your arms and legs. Monkseal mentioned this previously.

You are correct in believe that exercise, and increased breathing rate, will result in more nitrogen uptake. It is not the breathing rate, per se that is the culprit, but rather what it represents. The increased activity leads to increased tissue blood flow and the production of carbon dioxide. This in turn will result in the increase in breathing rate. One should be careful that there is not excessive breathing rate at depth and a slow rate near the surface. That indicates that tissue perfusion is maximizing at depth and being reduced during the decompression phase. :boom: A time bomb in the making.

Dr Deco :doctor:

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