Inhalation...Exhalation

[TexasMike]

One for the docs here....

All divers are aware of the oxygen content of standard air is 21%. Which means that when we are diving on air, or sitting at our computers reading this post, we are inhaling 21% oxygen.

My question is, when we are at rest (reading this post) how much oxygen are we exhaling with a normal breath?

How much when we are diving?

I'm hoping to gain a better grasp on general lung efficiency.

Thanks!

 

[miked]

TM,
First, I'm not a doctor, and I am sorry that I can't remember the source of the information, but I recall reading that under "normal" diving circumstances(whatever that means), the oxygen content of our exhaled air is in the 15-17 % range, and that number was the same as while breathing on land (i.e while not diving.)
Hope we can find a more verifiable numberfrom our MD board members.
Miked

 

[Liquid]

Texas-
Great question!

First of all, I think, though I'm not sure, it's 18% oxigen in normal EXHALED air.

While diving, though, It will change becouse the body gets more and more air. It's a known fact that Saturation divers while working very deep are using mixtures that hold about 3-4% of oxigen. So the deeper you get with normal air, the bigger percent of oxigen you exhale. Seems like a waste eh?

 

[TexasMike]

Liquid....

Are you sure the percentage changes???

Let's keep the question simple by diving with a typical AL80 to 40 meters. This means that the "mix" of the gas stays the same throughout the dive.

From what I remember in my OW class, while the "amount" of air we are breathing (density) is 4 times that of when we are on the surface (IOW, 4 times the oxygen molecues), the percentage of what we inhale is stay the same.

Right?

And even as we ascend to shallower depths and consume less air, the intake is still 21%...yes?

 

[Liquid]

That's obviouse mike, you keep INHALING air with 21% oxigen. Your body, though, keeps using the same amount of oxigen molecules, so it results in EXHALING air with a larger percent of oxigen, since you used a smaller portion of the inhaled oxigen. So if on surface you exhale 18%, at 40 meters deep it may be you will exhale 20%.

At least, it seems the most logical thing. Divers that use mixtures of 4% oxigen at 600 feet will use the same amount of molecules as you and me on the surface but their exhaled percentage will be differnt. BTW- For some reason the mixture should have a minimal percentage of 3% oxigen, below that the body has problems using the oxigen, though the partial pressure may be more than on surface.

 

[miked]

Help!!
Where are the doctors with the medical facts??
miked

 

[BillP]

Hi TexasMike:

A complex question without an easy answer. The best answer is the catch-all..."Depends".

The numbers you've been given of 15-18% O2 in exhaled air at rest are good. How much oxygen you exhale when diving depends on how much oxygen you inhale in the breath and how much of the oxygen in the breath you use. When studying oxygen use at depth, researchers report "oxygen consumption" measured in liters per minute (and sometimes in ml/kg/min) rather than %O2 in the exhaled gas. Oxygen consumption depends on activity level, conditioning, etc. To get the %O2 exhaled you would need to figure the amount of O2 inhaled and subtract out the O2 that is consumed. There are just too many variables to give you a number.

The US Navy has done some research on oxygen consumption in divers at various workloads. You can find the results of their research in the US Navy Diving Manual. You can download the manual in PDF format at http://diverlink.com/library/usn/ . Go to Volume 1 Chapter 3 and look at figure 6 "Oxygen Consumption and RMV at Different Work Rates".

HTH,

Bill

 

[TexasMike]

Bill....

Thanks for the answer and the link...I'll check that out.

BTW, since I know you haunt around North Texas, are you gonna make the Halloween Dive at Lake Travis?

 

[BillP]

Thanks for the invite, but it looks like that is going to be a working weekend for me. Y'all have fun!

Bill