Course Advice and Breath-Up issues

[baiyoke]

How do you know your readings were inaccurate and unrealistically high unless you were also sampling core blood?

Because of the picture I get is the same as the video I posted of Gorans static: After vasoconstriction it pretty much flattens out, but then after re-breathing and release of vasoconstriction it takes a huge drop, before going up. So for me, the readings are useless. They are probably accurate at the very beginning, but from there on, there's no way of telling how wrong the measure is, if it's progressively wrong, or fluctuating in measurement, or wrong from a certain point....

I can see that the way you use it, you can get ideas of where you are in the dive as you describe... But so could the bodily sensations in combinations with a watch, as far as I can tell...

 

[growingupninja]

Because of the picture I get is the same as the video I posted of Gorans static: After vasoconstriction it pretty much flattens out, but then after re-breathing and release of vasoconstriction it takes a huge drop, before going up. So for me, the readings are useless. They are probably accurate at the very beginning, but from there on, there's no way of telling how wrong the measure is, if it's progressively wrong, or fluctuating in measurement, or wrong from a certain point....

I am sorry if I am not quite understanding your English. You mean to say, your readings were similar to the video of Goran's, and you believe them to be incorrect because it flattened out, and then dropped again when you started breathing? The drop is normal. I have read that it drops because of the Bohr shift, and I believe it because I have witnessed that drop in my own holds, regardless of vasoconstriction. For instance, if I do a medium hold with no vasoconstriction to 85%, when I start to breath again it will dip to perhaps 76-79% for a moment. In this case it cannot be because low O2 blood was collecting in my core since there was no vasoconstriction during the hold. I know there was no vasoconstriction because I can find a wrist pulse and the meter itself shows a steady pulse. As far as 'flattening out', this too seems to be normal--drop in O2 seems to slow down for many people after a certain point, but it will continue to drop if given time.

I can see that the way you use it, you can get ideas of where you are in the dive as you describe... But so could the bodily sensations in combinations with a watch, as far as I can tell...

Not exactly, because in my case at least, when dive response is strongly activated I feel certain sensations. When O2 is truly low I also feel certain sensations, in addition to the dive response sensations. But sometimes dive response is activated when O2 is still very high, maybe 30 seconds into a hold, which we can agree is a good thing. Training in a controlled, mostly dry environment with a meter was an effective way for me to separate the feeling of low O2 from the feeling of dive response. I always train with watches but I don't spear with a watch, so I am relying on physical cues.

It was also helpful in checking to see where my psychological apnea tolerance is, which is important from a safety perspective since I am spearfishing often, and my tolerance changes depending on the kind of spearing and/or training I am doing--what FEELS comfortable can mean that I pushing into my safety margin if my tolerance happens to be very high. Related to this, it can useful for understanding CO2 response and sensations. I can train exertion (high CO2) vs static and see what my absolute O2 numbers are even though the urge to breath will be very different between the two.

It is no substitute for a buddy and too technical for many recreational freedivers, but I found it incredibly helpful. I also think that in the context of safety it would take more than a week of use to get much out of it....

 

[baiyoke]

The drop is normal. I have read that it drops because of the Bohr shift, and I believe it because I have witnessed that drop in my own holds, regardless of vasoconstriction. .

The drop is normal because a finger oximeter is faulty... I'm 99,9 % sure (until otherwise convinced9 that it has nothing to do with the Bohr effect. I am be no means knowledgable in these things, but since the Bohr effect is a change of how easily O2 is released from blood, as an effect of blood ph when looking at THE SAME O2 SAT, it would make no sense at all to attribute a drop like that to the Bohr effect as I can see... (take a look, the y-axis is O2 SAT http://classconnection.s3.amazonaws.com/86/flashcards/468086/jpg/bohr_effect.jpg) AND it is a steep sudden drop that is DEFINATELY NOT an actual effect of O2 consumption... It is something else = vasoconstriction. Wich has been confirmed to me at least in this thread: http://forums.deeperblue.com/freediving-science/96804-time-lowest-o2-level-bo-risk.html#post900595

For now I truly believe it is really faulty because of vasoconstriction... And to me that makes it is useless, especially because it is for the final minutes I really want to use it.

For instance, if I do a medium hold with no vasoconstriction to 85%, when I start to breath again it will dip to perhaps 76-79% for a moment. In this case it cannot be because low O2 blood was collecting in my core since there was no vasoconstriction during the hold. I know there was no vasoconstriction because I can find a wrist pulse and the meter itself shows a steady pulse. As far as 'flattening out', this too seems to be normal--drop in O2 seems to slow down for many people after a certain point, but it will continue to drop if given time.

- To you the example is backing up your experience, to me it is showing me, that even on shorter holds it is faulty...
- You seem to think of vasoconstriction as something happening at one point. I believe it to be partly gradual, since that is how the body works everyday regardless of apnes. But for sure, at one point during apnea it kicks in much harder, but it seems to exeist early on also.
- I would expect you to have a puls reading, especially if it's a good meter. I would expect the pulse to exist, allthough I must admit I don't know exactly how puls is measured, but if wiki is correct (wiki: "puls oximetry"), it would suggest that puls and O2 measurement allways go hand in hand:

The monitored signal fluctuates in time with the heart beat because the arterial blood vessels expand and contract with each heartbeat. By examining only the varying part of the absorption spectrum (essentially, subtracting minimum absorption from peak absorption), a monitor can ignore other tissues or nail polish, (though black nail polish tends to distort readings)[34] and discern only the absorption caused by arterial blood. Thus, detecting a pulse is essential to the operation of a pulse oximeter and it will not function if there is none.

So this kind of also strongly suggest that 1) it is faulty during vasoconstriction, and/or 2) puls is no indication of vasoconstriction and/or 3) vasoconstriction is not 100%. Probably all the above apply...

I don't think I need to experiment with a faulty device for more than a week, to move on and exclude it in my training. But on the other hand, I won't say that it can't help others... Up to you, but I left it for the above reasons...

It was also helpful in checking to see where my psychological apnea tolerance is, which is important from a safety perspective since I am spearfishing often, and my tolerance changes depending on the kind of spearing and/or training I am doing--what FEELS comfortable can mean that I pushing into my safety margin if my tolerance happens to be very high. Related to this, it can useful for understanding CO2 response and sensations. I can train exertion (high CO2) vs static and see what my absolute O2 numbers are even though the urge to breath will be very different between the two.

Again I have to say, that I don't understand how relating subjective feelings, that change from time to time, with an instrument that also isn't reliable, can help you, but if it works for you that's fine with me... I just don't get it

 

[growingupninja]

Baiyoke-- Yes, mine works fine for my purposes, and I found it a useful and reliable tool for gaining a better understanding of my particular dive response, which in turn can increase safety.

I have nothing more to add except one thing that you may not be considering, which has not been tested or discussed much (indeed I am not sure if it is even possible to non-invasively test with existing technology), which I believe could account for fluctuations in blood O2 saturation when deep in apnea is spleenic contraction. The spleen has been proven to release oxygenated blood when in apnea, so to me it makes sense that a device which measures O2 in the blood would show a flattening in the drop and possibly even a slight rise when the diver's spleen releases oxygenated blood during an apnea event. Spleenic contraction is very likely influenced by training and--same as something like lung capacity--by genetics.