Nitrox and Type 2 DCI

[diveruk42]

I am having trouble getting my head around the idea, that nitrox reduces type 2 DCI. Here is my thinking:

At 1 bar (normal atmospheric pressure) the air we breathe is roughly 21% oxygen and 79% nitrogen. At this pressure 97% of the O2 is attached to the hemoglobin to form oxyhemoglobin and the rest is in solution (plasma) along with the nitrogen. At 1 bar the hemoglobin is saturated (4 molecules of O2 per red blood cell) and any increase in partial pressure of that oxygen, wether from higher % mix i.e. nitrox or from diving deeper, will result in all the extra diffused O2 going into solution. Once in solution (plasma), it will be carried around the tissues the same as nitrogen. Now I understand that the body can metabolize O2 at the rate of 15ml per 100ml of blood per breathing cycle, during exercise, but, at any one moment, there is still 100% of gas in the blood, be it O2 or CO2 and N2. Therefore all this extra gas will expand at roughly the same rate during a fast ascent, with the same consequences, regardless of the mix.

Now I am sure I have missed something obvious (apart from all the spelling mistakes) so someone please enlighten me.

David Wylde

[Nigel Hewitt]

(4 molecules of O2 per red blood cell)No. You mean per molecule of heamowotsit.

The big thing about O2 is that if a bubble does form and blocks things the O2 tension in the surrounding tissues drops as they consume the available oxygen so there is a net flow of gas out of the bubble and it shrinks and probably moves off. The N2 tension does not change so for a high N2 mix like air the bubble tends not to decrease as much and probably stays put.

Haldane reportedly bent goats on pure oxygen by pretty explosive decompression but they spontaneously recovered.

[Badders (Dave)]

I am having trouble getting my head around the idea, that nitrox reduces type 2 DCI. Here is my thinking:

At 1 bar (normal atmospheric pressure) the air we breathe is roughly 21% oxygen and 79% nitrogen. At this pressure 97% of the O2 is attached to the hemoglobin to form oxyhemoglobin and the rest is in solution (plasma) along with the nitrogen. At 1 bar the hemoglobin is saturated (4 molecules of O2 per red blood cell) and any increase in partial pressure of that oxygen, wether from higher % mix i.e. nitrox or from diving deeper, will result in all the extra diffused O2 going into solution. Once in solution (plasma), it will be carried around the tissues the same as nitrogen. Now I understand that the body can metabolize O2 at the rate of 15ml per 100ml of blood per breathing cycle, during exercise, but, at any one moment, there is still 100% of gas in the blood, be it O2 or CO2 and N2. Therefore all this extra gas will expand at roughly the same rate during a fast ascent, with the same consequences, regardless of the mix.

Now I am sure I have missed something obvious (apart from all the spelling mistakes) so someone please enlighten me.

David Wylde

Your spelling is fine, just forgot the H in whether and I don't know about hemowotsimacallit or oxyhemothingymajig, but they look OK:D

Badders

[PeteM]

Haldane reportedly bent goats on pure oxygen by pretty explosive decompression but they spontaneously recovered.

I have also heard reports of the WKPP having Oxygen bends but these self resolving

[Michael Purcell]

I have also heard reports of the WKPP having Oxygen bends but these self resolving

Been reading through the WKPP/DIR stuff lately and I was looking for the bit on oxygen bends. I didn't really find what I was looking for but thought this bit on 80/20 deco gas was entertaining:


Only a card-carrying stroke would do something like this, and showing up with 80/20 is no different than wearing a sign on your back saying "I am a stroke, and have the papers to prove it". It announces to all the world that you have no clue, kind of like wearing clip-on suspenders or having dog dirt on your shoes.


http://www.cisatlantic.com/trimix/diving.htm

[diveruk42]

No. You mean per molecule of heamowotsit.

The big thing about O2 is that if a bubble does form and blocks things the O2 tension in the surrounding tissues drops as they consume the available oxygen so there is a net flow of gas out of the bubble and it shrinks and probably moves off. The N2 tension does not change so for a high N2 mix like air the bubble tends not to decrease as much and probably stays put.

Haldane reportedly bent goats on pure oxygen by pretty explosive decompression but they spontaneously recovered.

Thanks for the reply Nigel.

So when metabolizing the oxygen carried on the red blood cells into CO2, the resulting pressure gradient between the tissue and the O2 in the plasma (the extra O2 in high nitrox mixes), causes diffussion of O2 from the plasma into the tissue. Therefore O2 bubbles would be constantly 'sucked' into the tissues until....... well thats another subject.

[Janos]

Thanks for the reply Nigel.

So when metabolizing the oxygen carried on the red blood cells into CO2, the resulting pressure gradient between the tissue and the O2 in the plasma (the extra O2 in high nitrox mixes), causes diffussion of O2 from the plasma into the tissue. Therefore O2 bubbles would be constantly 'sucked' into the tissues until....... well thats another subject.

The first O2 to be metabolised will be the O2 in the Plasma. Having zero O2 in the plasma will mean that the O2 bubbles have a very short lifetime - they will quickly dissolve into the plasma. The O2 in haemoglobin is last to be metabolised.

O2 bends are not really of a concern to divers. You can ignore the O2 and just concentrate on the inerts present. O2 bends are an issue for spacemen though, and there is a fair bit of research into it.

Janos

[BIGLICKER]

I am having trouble getting my head around the idea, that nitrox reduces type 2 DCI. Here is my thinking:

At 1 bar (normal atmospheric pressure) the air we breathe is roughly 21% oxygen and 79% nitrogen. At this pressure 97% of the O2 is attached to the hemoglobin to form oxyhemoglobin and the rest is in solution (plasma) along with the nitrogen. At 1 bar the hemoglobin is saturated (4 molecules of O2 per red blood cell) and any increase in partial pressure of that oxygen, wether from higher % mix i.e. nitrox or from diving deeper, will result in all the extra diffused O2 going into solution. Once in solution (plasma), it will be carried around the tissues the same as nitrogen. Now I understand that the body can metabolize O2 at the rate of 15ml per 100ml of blood per breathing cycle, during exercise, but, at any one moment, there is still 100% of gas in the blood, be it O2 or CO2 and N2. Therefore all this extra gas will expand at roughly the same rate during a fast ascent, with the same consequences, regardless of the mix.

Now I am sure I have missed something obvious (apart from all the spelling mistakes) so someone please enlighten me.

David Wylde


Wow,I thought diving would be simple.Didn't know I needed a PHd. Or am I missing something? lol. Roy :D :D :D