Holding your breath at depth ???

[the_dumper]

Here's a question one of my Open Water students came out with last night, what do you lot think?

Ok, for the purpose of this question we are going to ignore the holding your breathe underwater rule , because otherwise the thread is just going to get full of "you shouldn't be holding your breath underwater anyway" replies.

I hold my breath at the surface and time how long I can hold it and say for a nice round number I can hold it for a minute.
If I then decsend to 40m / 132ft and do the same thing again, can I now hold my breath for five minutes because the surrounding pressure is 5 bar/ata, and the air that I am now breathing is five times as dense and contains five times the O2 molecules.
It sounds logical that you can but i'm not sure for certain.

 

[nickjb]

As I understood it the trigger to breathe is partial pressure of carbon dioxide. When it hits a particular figure you need to breathe. This is independant of depth or percentage of O2.

HTH
Nick

 

[adder70]

You could hold your breath for much longer without passing out, but the CO2 triggered breathing reflex would cause immense head pain.

 

[dwright]

You can hold your breathe longer at depth but to some extent you have to be careful of shallow water blackout..a point where expanding, oxygen-hungry lungs literally suck oxygen from the divers blood. This would be somewhat extreme and is assuming you have no air source (free diving) but I thought it was worth mentioning.

Dale
:scuba:

 

[String]

As mentioned the (main) breathing trigger is CO2 production NOT oxygen limit - in fact when you exhale you are breathing out a lot of unused oxygen.

Even at 40m the chemical reactions take place, producing CO2 which needs to be removed. This is what causes the burning "need for air" feeling when you are nearing the end of a breath hold.

Speculating here a bit but id suspect that as increased pressure can speed up chemical reactions there maybe faster CO2 production (slightly) at depth so decreasing the time.
I havent tried the maths to work it out though so unsure of that.

 

[Karl_in_Calif]

NAUI offers a publication called Breathhold Diving which discusses these issues and more, all related to freediving. All their analyses are extended to a depth of 10 ATAs (100 meters / 330 ft). Its written by expert freedivers, and contains detailed scientific and medical explanations.

 

[quimby]

297 ft 10 ATAAAAAAAA's

 

[Karl_in_Calif]

quimby once bubbled...
297 ft 10 ATAAAAAAAA's

Thanks. My mistake.

 

[Uncle Pug]

the_dumper once bubbled...

If I then decsend to 40m / 132ft and do the same thing again, can I now hold my breath for five minutes because the surrounding pressure is 5 bar/ata, and the air that I am now breathing is five times as dense and contains five times the O2 molecules.

As has been mention blood gas level of CO2 is the trigger for breathing. A build up of CO2 in the blood due to breath holding can result in more than a headache. CO2 is far more narcotic than nitrogen but high levels of CO2 can also exacerbate nitrogen narcosis itself. A CO2 narc is not a pleasant warm feeling... it carries with it a sense of impending doom... the *dark narc*.

Bottom line... not a good idea... especially at 132'.

 

[bwerb]

Uncle Pug once bubbled...

A CO2 narc is not a pleasant warm feeling... it carries with it a sense of impending doom... the *dark narc*.

I'll second that...no thanks...when all you can hear is your heart...and your head is arguing with itself about you being alright or not...it's time to turn it around. I wouldn't wish that feeling on anyone.