CO2 'theory' question

[OceanAfrica]

Hey everyone,

I've got a question about levels of CO2 before and during a dive. I think I'm doing my constant weight dives (and pool dives, for that matter) with way too little C02.

Am I correct in saying:

Above average C02 levels prior to a dive will ensure a heightened dive reflex - but will make the dive 'harder' with earlier contractions?

And...

Below average C02 levels prior to a dive will ensure an easier dive for about two-thirds of the total dive, but with earlier samba's and blackout?

If anyone could explian the basic theory behind this - or direct me to a thread that does, that would be great.

For my constant weight dives right now, I think my breathe-ups leave me with too little C02, and I'm having sambas on quite a few of my dives...:duh

 

[trux]

Above average C02 levels prior to a dive will ensure a heightened dive reflex - but will make the dive 'harder' with earlier contractions?

Well, the scientists claim tha CO2 has little or no impact on diving reflex. See for example the following post of Dr. thread
http://forums.deeperblue.com/beginn...-technique-diving-environment.html#post837626
or the document Arterial blood gas changes and the d... [Aust J Exp Biol Med Sci. 1971] - PubMed - NCBI

However, that claim contradicts the expereince of many freedivers, and especially FRC divers, so personally I'd like to see a more detailed study on it before really believing it.

Below average C02 levels prior to a dive will ensure an easier dive for about two-thirds of the total dive, but with earlier samba's and blackout?

Yes, more or less. All depends on the level of hyperventilation. There are many different factors involved, so a very light hyperventilation may increase oxygen stores (primarily in venous blood), but with the level increasing the negative effects take over and the hypoxic threashold becomes more and more critical, meaning you will indeed suffer samba/BO earlier than you otherwise would. You will find many details here in several threads here on DB - just type "hyperventilation" into the search box. Even better may be searching in the Science subforum, or using the advanced search and searchin in thread titles only.

 

[efattah]

Am I correct in saying:

Above average C02 levels prior to a dive will ensure a heightened dive reflex - but will make the dive 'harder' with earlier contractions?

And...

Below average C02 levels prior to a dive will ensure an easier dive for about two-thirds of the total dive, but with earlier samba's and blackout?

I would say you are exactly correct-- you should try to keep reducing the amount of breathing until you are unable to complete the dive due to overwhelming urge to breathe. In order to do this, keep the depth the same and gradually with each dive reduce your pre-dive breathing until you cannot anymore.

With proper (low) breathing, most divers get a significant urge to breathe at 30m on the descent, which fades from 40-50m then starts to get worse and worse after 60m. If you reach the bottom with no urge to breathe, then you breathed way too much and a blackout is likely.

You should also get contractions for the entire ascent.

 

[OceanAfrica]

Hey guys thanks for the response and info!

Really going to focus on breathing up for more C02 on my next dives. I feel a lot of potential dive is being 'wasted' with the way I breath up...and its as if I'm developing a habit of samba'ing on every dive. So looking forward to experimenting.

Cheers,
Paul

 

[watts]

Eric how much of a difference do you think snorkel breathing prevents the lowering of to much co2. You still breathup through snorkel dont you?

 

[Tommy_R]

Eric,

you never had problems with cold water and contractions at depth ?
I already get squeezed when i get contractions at 40m ( 4 degree water at that depth ) ..... but have no problem at all when my BU prevents the contractions down there ...


Tommy

 

[Dan Evans]

Your body's respiratory drive is governed by a) increasing levels of co2 and b) hypoxia.

Your body is very sensitive to co2 drive, but nowhere near as sensitive to hypoxia. This is -apparently- why after expelling a large amount of c02 via hyperventilation, you fail to realise that you are running out of o2, hence, blackout.

 

[Lauri_A]

There's actually quite a lot happening with CO2

1. Bohr effect: https://en.wikipedia.org/wiki/Bohr_effect

2. Chemical receptors that affect the dive reflex in your arteries (debatable as stated above, but at least these affect to the breathing reflex causing the urge to breathe)

All in all, CO2 is your friend, breathe as little of it out as possible.

 

[Sorandril]

Hypercapnia Suppresses the HIF-dependent Adaptive Response to Hypoxia - PubMed

Molecular oxygen and carbon dioxide are the primary gaseous substrate and product of oxidative metabolism, respectively. Hypoxia (low oxygen) and hypercapnia (high carbon dioxide) are co-incidental features of the tissue microenvironment in a range of pathophysiologic states, including acute and...

pubmed.ncbi.nlm.nih.gov

Kinda bad news.