Breathing Theory

[Tobagoman]

The amount of available oxygen in a breath has limits on the upper and lower ends. Oxygen toxicity can begin to set in at roughly 1.6 ata or at the surface at concentrations of 100% over protracted periods. At a lower concentrations where hypoxia sets in (may be enough molecules available to sustain life at depth i.e. higher partial pressure, but when surfacing the concentration will drop allowing hypoxia to set in) I can't remember the bottom limit. Even though at depth, more oxygen molecules are available in each breath, the limiting factor is the binding sites on the hemoglobin proteins within the red blood cells. These receptors have a finite limit to the amount of oxygen that can be carried. With more oxygen molecules (e.g. a higher oxygen partial pressure), more oxygen can diffuse into the blood, but only so much of it can be carried to the cells by the hemoglobin.

People who live in higher altitudes have acclimated to the lower available oxygen by having higher hemoglobin counts.

Hypoxia with non-acclimated people at altitude occurs because less oxygen (concentration) is available with each breath and the receptors are not filled, so less oxygen is available for metabolism.

Higher concentrations of oxygen are given to DCS victims when they are treated do to the affect of dropping the nitrogen partial pressure and therefor allowing it to diffuse out of the cellular tissue and blood to be outgassed by the lungs.

That was your Biology 101 lesson for today.

 

[pete340]

1 ATA is simply one atmosphere, or 10m/33 feet of seawater.

At the risk of sounding hypertechnical, ATA stands for ATmosphere Absolute, that is, the pressure relative to a vacuum. At sea level you're under 1 ATA. 10m down you're under 2 ATA. Descending through 10m of sea water gives you a pressure increase of 1 ATM (stands for ATMosphere), not 1 ATA.

 

[Andy Hipkiss]

FWIW, the urge to breathe is totally controlled by the pH of the blood (i.e. the effect of CO2 forming carbonic acid). You can have NO oxygen in your system at all and if the pH of your blood is above the body's set limit, you just won't bother breathing.

One of the reasons you can pass out thru hyperventilation (which lowers the CO2 concentration).


Bottom line, the act of breathing has NOTHING to do with oxygen.

HTH

 

[cornfed]

Bottom line, the act of breathing has NOTHING to do with oxygen.

Unless you have COPD.

 

[wedivebc]

Ok, I know that the deeper you go, the more air you consume with each breath (@33 feet your consumption is twice as much as at the surface), because the air is regulated to the same pressure as the water around you. Thus, the deeper you go, the more dense the air is that you are breathing, correct? Now, if the air is twice as dense, wouldn't that mean that there are twice as many oxygen molecules in the same volume of air? If thats true than it seems like we would only need to breathe half as often at this depth to have the same amount of oxygen supplied to our lungs as at the surface. I guess this does not hold true for some reason, because I feel the need to breathe just as often at depth as at the surface. Although the reverse seems to be true: At very high altitudes you are more likely to become "out of breath" due to the low air density. Am I missing something?

Good job WQFTruckster, you've just invented the rebreather. Oh wait, it's been done. Actually you have just stumbled on the magic behind the rebreather. The issue is the CO2 which the body senses and triggers a breathing response. It is the fraction of co2 not the partial pressure of co2 that causes the breathing response. If there was a way to eliminate co2 in our lungs your theory just might work. Otherwise the RB is the way to go.

 

[Andy Hipkiss]

duplicate post

 

[Andy Hipkiss]

Unless you have COPD.

Nope, nothing to do with pulmonary disease (per se although that does affect the ability to exhaust CO2 from the blood). Purely and simply it's to do with the pH. Now a lot can affect the pH, O2 however is not one of them.

 

[jdcrouch]

Also remember that the same principal of pressure at depth is working on your lung's volume. At surface you may have a lung capacity of 4 liters but at 1 atmo. it is cut to half or 2 liters. In math terms, twice the desity of air pressure in half the volume of space is the same volume of air at sea level.

James

 

[jbd]

Also remember that the same principal of pressure at depth is working on your lung's volume. At surface you may have a lung capacity of 4 liters but at 1 atmo. it is cut to half or 2 liters. In math terms, twice the desity of air pressure in half the volume of space is the same volume of air at sea level.

James

Maybe in regards to ideal gas laws but I think the rib cage has some affect on the real volume of lungs underwater.

 

[miketsp]

Also remember that the same principal of pressure at depth is working on your lung's volume. At surface you may have a lung capacity of 4 liters but at 1 atmo. it is cut to half or 2 liters. In math terms, twice the desity of air pressure in half the volume of space is the same volume of air at sea level.

James

Sounds like you're well on your way to confusing freediving and scuba diving.
Scuba divers keep breathing and lung volume doesn't change from the surface to 10m.