RMV Spinoff from Accident & Incident Discussion - Northernone - aka Cameron Donaldson

[Pedro Burrito]

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A ScubaBoard Staff Message...

The very interesting subject about RMV has been moved from the Accident & Incident Discussion - Northernone - aka Cameron Donaldson

Please continue the RMV discussion here.

Thank you!

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[tursiops]

In no way am I advocating changing decompression practice or changing a dive schedule by bottom gas usage. I’m talking about loading the dice in your favor by practicing good breathing techniques ,improving your fitness level and oxygen efficiency. I may have some controversial ideas but I wouldn’t stick my neck out that far.

Why does your oxygen efficiency matter if nitrogen is the culprit in DCS?

 

[Celt]

The odds of a diver who is breathing 21% oxygen at depth in an open circuit suffering CO2 retention has to be very small no matter how light they are breathing. But the opposite where a diver over breathing oxygen reduces CO2 to the point of hyperventilating can very easily happen. Has there ever been a case of CO2 poisoning in a healthy diver using air.

 

[Celt]

Why does your oxygen efficiency matter if nitrogen is the culprit in DCS?

Why does your oxygen efficiency matter if nitrogen is the culprit in DCS?

Less stress, far better focus, much better at coping during a dive, are all benefits from a slow light breathing rate. The more stressful the dive the greater the chance of a DCS incident.

 

[tursiops]

Less stress, far better focus, much better at coping during a dive, are all benefits from a slow light breathing rate. The more stressful the dive the greater the chance of a DCS incident.

Nothing you suggest is really related to oxygen efficiency. I think you are confusing facts with non-scientific opinions.

 

[kelemvor]

It seems as if science disagrees with you: Does higher RMV cause higher DCS risk?

Those threads where rossh gets destroyed by actual scientists are always good for a chuckle.

As I mentioned earlier, the galileo DC's do use SAC rate in deco calculations (ZHL8 ADT MB). They also use heart rate, if you have the add-on heart rate sensor. It seems like an odd computer to put those things into. As far as I can tell, the galileo is tailored exclusively for rec diving and isn't well suited to tech diving at all... which is where things like that would matter more.

 

[Compressor]

Most oxygen in the body is transported in the blood by binding heavily to Hb. Only a small amount is dissolved in the blood.

Mathematically here is the equation: CaO2 = (Hb x 1.39 x SaO2) + (PaO2 x 0.003).
CaO2 is arterial content of oxygen
Hb= Is your Hb levels
SaO2 is your oxygen situation
PaO2 is partial pressure of oxygen

Oxygen is transported by 2 different mechanisms: convection and diffusion

Convection process is a process by which O2 is transported by the blood using hemoglobin as a carrier (i.e. DO2). Oxygen delivery may be calculated as follows:

DO2 = CO x CaO2 x 10. (the number is 10 is used to make the units right).

CO= cardiac output

So you see that Oxygen delivery is dependent on how well your heart pumps (CO) and by the arterial content of oxygen.
The normal CI is 2.5 to 4.0 L/min/m2. The normal oxygen transport 0.6 to 14 L/min.

Now convection is related to VO2 by Fick's law of convection:
More physiology now about the second method of oxygen transport: Diffusion:
Oxygen diffusion from capillary (blood vessels at the end of the arterial system) to cell may be related to VO2 by the Fick law of diffusion:

VO2 = CO x (CaO2 - CvO2) = CO x CaO2. [(CaO2 - CvO2)/CaO2].

VO2I = CI x (CaO2 - CvO2).

where CvO2 is the venous O2 content:

CvO2 = (Hb x 1.39 x SvO2) + (PvO2 x 0.003).


We are getting towards the end:
Oxygen diffusion from capillary to cell is related to VO2 by you guessed it: Fick law of diffusion

VO2 = KO2 x (PcO2 - PmitO2)

where KO2 is a variable which takes into account the capillary surface area, path length from the capillaries to the mitochondria (which uses oxygen to make energy), PcO2 is the mean capillary PO2 and PmitO2 is the PO2 in the tissue surrounding mitochondria. Mitochondria is the structure in the cell that takes oxygen and make energy aerobically (hopefully) with the glucose.You can see then that the greater the pressure gradient and the capillary surface area, the higher will be the total number of molecules to diffuse. The diffusion distance is inversely related to the rate of diffusion.

So now, mathematically I am proving to the inquiring mind how oxygen is transported to where it's needed and why shallow breathing is detrimental to diving.

So in conclusion (take home message): Convection and diffusion are the limiting factors of 0xygen uptake. These are in turn effected by blood flow, and blood oxygenation parameters including oxygen content, arterial oxygen partial pressure and hemoglobin's affinity for its buddy; oxygen. Similarly, factors effecting oxygen convection include blood flow and arterial oxygen content.


I tried to keep things simple. @rsingler gave an excellent synopsis above and here is my contribution to the discussion for those interested.

 

[Storker]

I’m talking about loading the dice in your favor by practicing good breathing techniques ,improving your fitness level and oxygen efficiency.

Improving one's fitness level is totally uncontroversial. And physiologically, I'd expect that to reduce heart rate, thus reducing perfusion and thus - again - reducing N2 loading.

The odds of a diver who is breathing 21% oxygen at depth in an open circuit suffering CO2 retention has to be very small no matter how light they are breathing.

While the proper hyperbaric scientists of course are extremely careful and reluctant about drawing conclusion they aren't more than reasonably sure about, nobody have been able to point at anything indicating that the effects of gas density and dead volume in the airways should be different on OC compared to CC.

And what, exactly, do you mean with "light breathing"?

 

[cerich]

The odds of a diver who is breathing 21% oxygen at depth in an open circuit suffering CO2 retention has to be very small no matter how light they are breathing. But the opposite where a diver over breathing oxygen reduces CO2 to the point of hyperventilating can very easily happen. Has there ever been a case of CO2 poisoning in a healthy diver using air.

actually regulator second stage design can be a huge factor, and was very much an issue in reg design 25+ years ago

 

[cerich]

While the proper hyperbaric scientists of course are extremely careful and reluctant about drawing conclusion they aren't more than reasonably sure about, nobody have been able to point at anything indicating that the effects of gas density and dead volume in the airways should be different on OC compared to CC.

CC the loop, can and counterlungs are in effect part of the divers airways