Bohr Effect

[blueface]

To my knowledge, a lower PH and increasing CO2 triggers the release of O2 from the oxyhemoglobin wherever metabolism occurs in the body. How does freediving affect the saturation curve?

Does decreased hemoglobin saturation mean less O2 is available to the tissues?

I know... use the search funtion.. I have.

Can some one help me out? Trux?

 

[trux]

The purpose of easier releasing O2 at high low pH (high CO2), is the facilitation of discharging of oxygen in tissue that is in need of it. And of course it also makes it more difficult to bind new oxygen, so at the end of a breath-hold it gets more and more difficult to use the oxygen remaining in the lungs. That's also why the exhaled air after a BH still contains quite high concentration of O2. However, you need to keep on mind that there is certain gradient of CO2 concentration - it is highest in the hypoxic tissue, and little lower in alveolar blood.

 

[cdavis]

"Does decreased hemoglobin saturation mean less O2 is available to the tissues?"

not necessarily

As Trux's reply suggests, it is more than a little complicated, but looking just at 02 release from blood cells to the tissues, it is possible to have relatively high hemoglobin saturation and poor transfer from blood to tissue, if co2 is low. That is part of the "hyperventilation" effect. Transversely, you can have relatively low saturation and good transfer if co2 is high. All this is dependent on just how high and/or low the various gas levels in the blood and in the tissues actually are. Eventually, if 02 saturation gets low enough, you are toast even with high co2 levels.

Bottom line: dive with as much co2 as you can handle and don't stay down too long.

Connor

 

[blueface]

Thanks Trux and Connor! Nice to hear from you guys.

I have started diving again after a few months off. On one of my deeper dives I felt a lot of lactic acid in my legs so I started reading some old threads. I am guessing that my reflex is just working normally but to be safe I cut my times short. 1 45 was the longest and 29 meters.

 

[hteas]

Thank you guys,
I think we could all use a refresher from time to time.

 

[blueface]

If I understand this correctly, the low ph, high cO2 is good for releasing the O2 from the hemoglobin but at the some time it makes them (hemoglobins) less able to get O2 when they pass through the alveoli/capillary beds in the lungs.

What conditions contribute to this lack of affinity between the hemoglobin and O2 in the later stages of the dive? Is it the ambient pressure or the just the CO2? both?

Sorry if I sound like a broken record.

 

[Anders]

Towards the end of a dive blood pH is lowered due to CO2 release from tissues. The lowered pH of the blood will reduce hemoglobin O2 affinity and enable the blood to release more O2 to the tissues. This effect will be most prominent at the tissues due to their continuing release of CO2, thereby lowering pH and reducing hemoglobin O2 affinity, and causing more O2 to discharge from hemaoglobin and be taken up at the tissues. This means that even though blood pH drops in the entire circulation during a freedive, it is always lowest at the tissues, which is beneficial for O2 release to tissues.

In a normal situation (continuous breathing) the opposite would happen in the lungs: CO2 release to alveolar air and consequent increased pH, meaning increased hemoglobin O2 affinity and increased O2 uptake from alveolar air. I suppose this happens also while freediving since there is some air left in the lungs, but to a lesser extent than during continuous breathing as CO2 is bound to build up in the lungs during a freedive.

 

[blueface]

Thanks for the response. I have a lot to learn. I found a pretty good thread from some time ago. It seems you guys have to answer the same questions over and over. Thanks for being patient.

http://forums.deeperblue.com/freediving-science/78976-some-iscience-swb.html

 

[trux]

The build-up of CO2 in lungs during a breath-hold is quite limited, so after reaching certain threshold, the CO2 practically does not diffuse into the lungs anymore (or at very limited pace), but instead remains in the blood and body liquids in three different forms - bind to the hemoglobin, dissolved (primarily as bicarbonate), and mostly in form of H2CO3.

When ascending from depth, the change of ambient pressure, and hence the change of PaO2 has also impact on the reduced intake of the remaining oxygen in the lungs.

So to answer you question, both effects (the pH and the pressure change) have influence.

 

[blueface]

Thanks Trux!