> Forwarded by:   FIS1@op*.up*.ac*.za*
> Forwarded to:   fis1@sh*.up*.ac*.za*
> Date forwarded: Sat, 15 Jul 95 22:12:44 GMT+2
> Date sent:      Sat, 15 Jul 1995 12:05:47 -0400 (EDT)
> From:           Clifford Sumbler <csumbler@fr*.ni*.co*>
> Subject:        Re: Breath holding
> To:             Jason Rogers <gasdive@sy*.DI*.oz*.au*>
> Copies to:      Robert Favorite <rwfavorite@uc*.ed*>, techdiver@terra.net

> > > On Thu, 13 Jul 1995, Jason Rogers wrote:
> > >
> > > > PS I don't trigger breathing on raised CO2, I trigger on depressed O2
> > > > (dispite what the text books say)
> > > > Cheers Jason :)
> Sorry but unless you have an extraterestrial body chemistry your 
> breathing is triggered by CO2.

Yes, but people who are exposed long-term to high levels of CO2 
become desensitized (see Bennet & Elliot "Underwater Medicine" for 
references), with the relevant risks attached.

> 
> > > --
> > When I hold my breath on air, I find that a horrible sense of impending
> > doom forces me to breathe at about 3 minutes.  If I don't, I pass out.
> 
> As it should, when the level of CO2 reaches a threshold level, reflex to 
> breath.
> 
> > When I take a couple of breaths of pure O2 first, I have no trouble
> > Holding on for 7 minutes.  I feel fine!  Though I find that I have
> > these rather alarming diaphram spasams that cause me to jiggle about
> > in a most amusing fashion.  I get the feeling that this isn't really
> > first class, top notch way of looking after your body, so I've only
> > done it once, just to see.  It does however make me *very* sure that
> 
> By breathing O2 you have flushed the CO2 from your system.  The result is 
> as the O2 in your lungs is metabolised and converted into CO2 the 
> resulting Patrial Pressure of CO2 is to low to trigger breathing.

At the risk of being pedantic, please note that the O2 you breathe is 
NOT converted to CO2.  The CO2 comes from the metabolism of molecules 
like glucose, free fatty acids, etc.  The O2 is changed to H2O by the 
process of oxidative phosphorylation (making ATP).
You are, however, partially correct in that the lowered pCO2 will 
extend his "bottom time" even further.  Anyone who is acclimated to 
CO2 is anyway at great risk when breath-hold diving.

> > I could dive down 20m or so, feel no pain, then pass out on ascent.
> > Hence I free dive *very* carefully.
> 
> Ever heard of underwater blackout.  By prugeing the CO2 from you system 
> by hyperventalating with O2 you have effectively overriden your natural 
> breathing response.   You will swim merrily along with no desire to 
> breath until you blackout for lack of O2.  With potential letheal result.
> 
> 
> 
> 
> --
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> Greetings

Prof JG van der Walt
Head: Dept. Physiology
Veterinary Science
University of Pretoria
Onderstepoort 0110
Republic of South Africa

Tel # + 27 12 529-8025
Fax # + 27 12 529-8305

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