Why dont you breath less at depth?

[wedivebc]

H2Andy's link says pretty much the same thing, but here are my two references (no links, sorry)

ANDI International Recreational Diving with Closed Circuit Rebreathers: ISC Megalodon Rebreather is where I got my information.

Chapter 2 Page 13:


,

Thanks for that. Andy's reference was a little vague on the cause but vasodilation makes sense.
Funnily enough I had already ordered the manual you quoted and it should be here "any day now"

 

[boulderjohn]

This is one of those posts, that when he looks back 2 years later, realise what a dumb***** question it was

I would really hate to have that kind of thought go through someone's head before posting. It is a good question, and the answer is not at all easy to find or intuitive. I bet a lot of people reading this thread learned a lot from the throughtful and informative responses.

I have seen posts in other threads where people asked a question and got thrashed by a couple of posters. I spoke with another person recently whose question was received so harshly by a couple of people that she said she would never post a question again. People should never be made to feel that way.

 

[MookieMoose]

Breathing compressed air doesn't cause you to breath less because the added pressure does very little to increase the amount of oxygen in your blood.

The vast majority of oxygen in the blood stream is carried by hemoglobin in the red blood cells. A typical healthy diver usually has 99% of the hemoglobin saturated with oxygen on room air at sea level. Increasing air pressure does very little to increase the amount of oxygen bound to hemoglobin. There is about 20 milliliters of oxygen carried by hemoglobin per 100 milliliters of blood.

A small amount of oxygen is dissolved in the plasma. Increasing the air pressure significantly increases the amount of oxygen dissolved in the plasma. However, in the big picture, this dissolved oxygen in the plasma is really insignificant in terms of the entire oxygen load. There is only 0.3 milliliters of dissolved oxygen per 100 milliliters of blood.

Although your explanation is technically correct, many of us in the gas transport physiology realm are beginning to believe that O2 content as you have described it is not as important as once believed. It is starting to look like the level of hemoglobin in our blood evolved to buffer the vasoactive effects of nitric oxide, not to carry oxygen, and that the oxygen dislolved in plasma, although it is much smaller, is the part that we actually use to sustain life. O2 bound to hemoglobin appears to act as a reservoir to replenish the disolved plasma O2.

For example, if we take a patient to the OR for coronary bypass grafting, and while they are on the bypass machine, hemodilute them we can take hemoglobin levels down as low as 7 mg/dl (approx 50% of normal) and see no detrimental effects of their arterial O2 content being cut nearly in half. On the other hand, if we take somebody with normal blood at normal atmospheric pressure and make them breathe a gas which is only 15% O2, they will die from hypoxia even though their arterial O2 content has only decreased by less than 10%.

That small fraction of O2 disolved in plasma looks like it is much more important than once believed. Hyperbaric exposure greatly increases this amount, but alas, as mentioned by many others above it will have no impact on the fact that you need to fill your lungs with a breath, and that CO2 is normally the dominant player in determining when you need to take a breath

Cam

 

[RJP]

I dont think there is such a thing as a dumb question.

But there is such thing as dumb people asking questions.

 

[beautybelow]

ugh...

 

[rawls]

But there is such thing as dumb people asking questions.

And then there are dumb statements...

 

[RJP]

And then there are dumb statements...

And then there's sarcasm, which apparently doesn't travel well on the internet.

There's also "smilies" which apparently don't display on all monitors.

And then there's sarcasm, which we've already covered.

Didn't intend comment to be directed at original poster, or any poster. Just a statement of fact.

 

[frankc420]

And then there's sarcasm, which apparently doesn't travel well on the internet.

There's also "smilies" which apparently don't display on all monitors.

And then there's sarcasm, which we've already covered.

Didn't intend comment to be directed at original poster, or any poster. Just a statement of fact.

 

[dhampton82]

But there is such thing as dumb people asking questions.

Woah, hold on. This is supposed to mean what? Please explain....

 

[ScottB]

Hey fellow SBers.. can't we keep this nice and civil =)

Sorry about the thread dying in civility dhampton.....

Best wishes everyone,
Scott