Oxygen window

[Seabear70]

No, imagine it like this...

The closed container has a semi-permiable lid, and is full of blood. If you increase the pressure outside the container, you'll get a corresponding increase inside, but it will occur much more slowly.

As you reverse the change in pressure, lower it outside the container, you will get a drop in pressure inside, but much more slowly.

If you start to get bubbles either in the container or on the membrane, then you've just bent the container of blood.

At least that's how I understand it.

 

[lamont]

No, imagine it like this...

The closed container has a semi-permiable lid, and is full of blood. If you increase the pressure outside the container, you'll get a corresponding increase inside, but it will occur much more slowly.

As you reverse the change in pressure, lower it outside the container, you will get a drop in pressure inside, but much more slowly.

If you start to get bubbles either in the container or on the membrane, then you've just bent the container of blood.

At least that's how I understand it.

Isn't that semi-permiable lid just the surface of the blood itself? I mean if you just take a container filled with H2O (or, maybe, beer) and pressurize it with CO2, the ppCO2 in the H2O/beer will take awhile to increase. So, if you immediately depressure the container you shouldn't see any bubbles -- but if you leave it awhile so that the CO2 dissolves and then let the pressure off the container you'll see bubbles and now you've got a carbonated beverage (or if this is blood and air, now you're bent...).

 

[Seabear70]

Actually in the thought experiment, I was tryingto simulate the body by using a semi-permiable membrane

 

[DepartureDiver]

Let's see if we can simplify this some. Gasses move independent of each other. In other words, nitrogen or helium will in-gas or off-gas only depending on the nitrogen or helium levels or pressures. Oxygen has no role in the in-gassing or off-gassing. Oxygen levels do of course change the levels of nitrogen or helium in the mix. Oxygen is ignored because it is either metabolized or being held on the red blood cell. If the oxygen levels are too high (i.e. not being metabolized and in the plasma), then oxygen would play a role since it would then be a “free gas” that could lead to a gas build up just like helium and nitrogen. This is known as oxygen bends and I believe it has been shown in laboratory animals, but only at very high oxygen levels that divers simply do not use. Back to the oxygen window/metabolism part. When more oxygen is used in a mix, any increase in CO2 from metabolism is less than the initial amount of oxygen that was metabolized. In other words, it is not a one to one ratio and more oxygen is removed than CO2 is built up. But to put it in simple terms, the oxygen and CO2 are bound to the red blood cell and can basically be ignored. While the window or partial pressure vacancy deals with oxygen metabolism, it simply plays no role in off-gassing. The window does play a role in calculations of how to ascend through decompression stops. But it simply does not affect inert gas exchange other than oxygen “removing” other gases being breathed … but that is not the “window”.

 

[Dr Deco]

Hello Readers:

“Oxygen Window” :umnik:

Haldane recognized that oxygen consumption would result in a decreased pressure of gases at the tissues level. Momsen (calculated tables for the US Navy), in 1942, referred to this as the “partial pressure vacuum,” Brian Hills called it “inherent unsaturation” and Al Behnke termed it the “oxygen window.”

Basically it states that oxygen is consumed by living tissue and replaced by carbon dioxide. The carbon dioxide is not replaced molecule for molecule, however, since some oxygen is used in metabolic processes that do not include carbon dioxide as the end product. [In addition, considerable amounts of carbon dioxide are combined with water to form carbonic acid and some is removed by the buffering mechanisms of the body.]

If oxygen were not consumed [e.g., the tissue was metabolically inactive or dead], then oxygen would now be considered an inert gas - - surprising as that might sound. In such a case, oxygen would form gas bubbles just as any other gas such as nitrogen or helium.

”Inherent Unsaturation”

Often in this usage of the term, a change in pressure is not considered, and one looks at the stability of a gas bubble in tissue. The sum of the partial pressures of dissolved gases in tissue does not add up to ambient pressure [760 mm]. Again, this is because of the metabolism of oxygen and its replacement by carbon dioxideis not one to one. Because of this, the pressure in a microbubble will be greater than the pressures in the tissue because the Laplace pressure from surface tension will continually try to shrink the bubble. Nuclei will fade away in time if there is not some method of stabilization or regeneration. In my cosmological view, these nuclei are generated in living creatures by their physical activity. :11:

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology :1book:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[HolgerS]

Dear DrDeco,

I agree on what you wrote. My only question is:

Does the total gas tension in tissue have any impact on bubble generation or growth in case of constant physical activity?

Regards
HolgerS

 

[Dr Deco]

Hello Holger:

With or without physical activity, the total gas tension plays a role in the growth of a micronucleus. This is especially true in depress to altitude. In this case, we must factor in the partial pressures of water vapor (47 torr), carbon dioxide (40 torr), and oxygen (40 torr). When the external (ambient) pressure is low, these are big players. And is known by many, at 63,000 feet, the Armstrong limit, the ambient pressure is low that blood will actually boil at body temperature. Ugh!

Physical activity plays a bigger role in the generation of micronuclei, I believe.

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology :1book:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[Seabear70]

Hello Holger:

With or without physical activity, the total gas tension plays a role in the growth of a micronucleus. This is especially true in depress to altitude. In this case, we must factor in the partial pressures of water vapor (47 torr), carbon dioxide (40 torr), and oxygen (40 torr). When the external (ambient) pressure is low, these are big players. And is known by many, at 63,000 feet, the Armstrong limit, the ambient pressure is low that blood will actually boil at body temperature. Ugh!

Physical activity plays a bigger role in the generation of micronuclei, I believe.

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology :1book:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

Seems that I had been told that the micronuclei were the result of cavitation in the legs. Was I taught wrong?

 

[Dr Deco]

The cavitation can occur from "stress-assisted nucleation" wherever there is physical activity. That would include the legs, arms, and spinal column when it is flexed (eg, when bending over).

Dr D.

 

[Mako Mark]

If the arterial and venous pressure of nitrogen stays the same then it is this the gradient between the arterial/venous blood and the tissues that determines the release of nitrogen from the tissues.

If the argument above is true then it seems the oxygen window doesn't help offgassing. What am I missing here?

simply put it is the relationship between disolved gas tension and alviolar partial pressure.

by reducing the partial pressure of the nitrogen in the lungs (by breathing O2) you increase the pressure gradient and this speeds up off gassing.

I think the Oxygen window is something that is over complicated and mis understood, it can be seen in its simple form as where your EAD (equivalent air depth) while decompressing is above the surface.