physiological model on oxygenation

[Waterenthusiast]

Hello there,
I was wondering if someone tried to design a physiological model caracterizing the oxygen release by hemoglobin while freediving. Mainly i was wondering how the parameters pressure, cold and blood pH are juggling with one another and if someone succesfully integrated those into one model.
Any ideas?

Christophe

 

[Mullins]

If you do a google search for "oxyhemoglobin dissociation curve" you'll get a few results. Temperature and pH are often both shown as variables. However I haven't seen pH integrated with Temp and, not really being much of a geek, I'm not sure how that could be expressed simply.

 

[Waterenthusiast]

Thanks Mullins,
I know the dissociation curves related to single parameters, but i was wondering if any research group or geek had tried to integrate the main freediving related parameters into one model. My idea was that in this way we could (at least based on these variables, and mainly ignoring narcosis effects) try to define "optimal" conditions for a dive, or at least try to discern less optimal configurations related to equipment and dive strategy.
Just a thought running through my mind...

 

[Mullins]

Well reduced pH and increased temperature both shift the curve to the right, so assuming they don't interact in any weird ways you could assume a diver is better off moving from cold to hot as the dive progresses, just like they are better off moving from high to low pH.

Of course that's just from looking at the dissociation curve, not taking into account other effects of temperature change like vasoconstriction.

Edit: though they might have a complicated relationship because as Eric pointed out a while back there is a larger temperature gradient from core to extremities in cold water, which affects the solubility of CO2 and the pH in each location.

 

[blueface]

Here's the curve. You can click on Right, normal, or left to see the shift.
Google Image Result for http://www.rnceus.com/oxydiscrv.gif

 

[Waterenthusiast]

Thanks blueface!

 

[Fitz-Clarke]

To answer your original question, I have a computer model that simulates physiology of the breath-hold diver. It accounts for immersion effects, cardiac contractility, circulation redistribution, vasoconstriction, pressures, blood flows, chest and abdomen compliances, thoracic blood shifts, pulmonary circulation, lung packing, lung compression, alveolar collapse and reopening, gas exchange kinetics, muscle metabolism, lactate production, control loops, dive responses, etc. It is the most advanced model of its type presently in existence, having been developed over several years. I have used it to explore many issues pertaining to freediving. Feel free to contact me if you would like copies of the papers, although they are fairly technical.

I am not sure what you mean by "optimal conditions for a dive". If you have specific questions on diving physiology that a model might help answer, let me know. Sometimes the best use of a model is simply to help sharpen the questions. I don't think blood temperature is a big factor in humans. Elevated blood carbon dioxide level and respiratory/metabolic acidosis both shift the oxygen dissociation curve for hemoglobin to the right, as stated above. This helps unload a bit more oxygen from the blood to the tissues at low partial pressures. Cold blood counteracts this effect slightly, but I don't believe central circulating blood gets cold enough to have a significant effect, and the change in gas solubility with temperature is negligible. Cold blood returning to the core could have a small effect on reducing oxygen unloading to tissues after the dive by shifting the curve a bit to the left, but the opposing effect of high CO2, the Bohr effect, is more significant. In addition, the low oxygen level in the tissues helps blood carry more CO2 back to the lungs by the Haldane effect. But there are many far more important phenomena than these pertaining to blood redistribution and changes in perfusion and diffusion gas exchange that serve to help optimize physiology in breath-hold diving.