Playing with Oximeter...

[ShallowGuy]

Recently I've bought oximeter to monitor O2 level in my body during some dry breath-holds.

Now I'm thinking how to get the best use out of it. So far I limit myself to simply keeping it on my finger watching how levels drop during the hold. How can I estimate maximum hold before the blackout knowing O2 level after let say 3 minutes? Is that kind of calculation/estimation possible? I assume I would need to know the black out level. Is the blackout level individual or is there some general level (or range) which might be consider "near black out"?

Are oximeters effective during apnea walk training? I tried it once, did around 70% of my max with apnea walk but the O2 level was at 98%, but I already had strong breathing urge. Could that mean my potential is greater than I thought (based on this new data) or perhaps I shouldn't rely on oximeter data for apnea walks.

Is there any other use for oximeter which might be beneficial for training? I did some research but caould find clear answers for these questions so sorry if that was already discussed.

 

[Apneaddict]

It's funny when moving (apnea walks / biking, etc) or doing CO2 holds when you feel like you're just about to die because you need to breathe so badly... Then look down and you're 97% or 98% O2 saturated.

Happens to me too from time to time.

Just means that your CO2 tolerance isn't where it could be. Work on that with more CO2 work.

Now I use it during CO2 tables as a "suck-it-up" self pep-talk. "Come on - you have plenty of oxygen left, quit being such a suck!"

Do a maximum breath hold and see how low you can get the O2 level.

For me, once it gets to 95%, it drops pretty linearly to about 80% over time and it's hard to push much beyond that... But once I breathe normally again it plummets - likely because the vasoconstriction isn't as severe and I get a more accurate reading.

At some point in the near future ill really give it a go and see how low we can take it!

I don't do dry training to the point of samba (intentionally).

 

[MarcinB]

ShallowGuy, its difficult to estimate max breath hold time from oximeter readings during a sub-maximal hold due to a nonlinear relationship between hemoglobin saturation and blood oxygen partial pressure. However, if it's below 70% there is not much time left till blackout.
Most people would black out at around 50% saturation (top freedivers probably at around 40%) but it can vary from individual to individual. The problem is that most oximeters are accurate only down to 70%. Moreover, fingertip probes overestimate blood saturation during breath hold due to vasoconstriction. When you start breathing saturation continues to drop for about 10s with finger probe. You should take the lowest value reached at that time and take 6% away. This way you would get an estimate of oxygen saturation of blood going to your brain (according to one study comparing finger and ear probes).
IMHO oximeter can be useful for monitoring progress in static breath hold or to test different types of preparation/breath up. If you observe higher saturation (the minimal value after breathing was resumed) after breath hold of the same duration it means that oxygen consumption rate was lower.

 

[Erki]

My oximeter freezes after the first contraction and saturation number do not decrease anymore. This is probable because of some algorithm that trust read out only when regular blood flow oscillation is detected. Temporal taking off from the finger helps, but I still do not trust my oximeter results during contractions. I believe that most of the devices do not have this problem, but I suggest you to control if saturation read-out decreases by using empty lung holds, that allows to go further hypoxia before contractions.

 

[growingupninja]

Moreover, fingertip probes overestimate blood saturation during breath hold due to vasoconstriction. When you start breathing saturation continues to drop for about 10s with finger probe. You should take the lowest value reached at that time and take 6% away. This way you would get an estimate of oxygen saturation of blood going to your brain (according to one study comparing finger and ear probes)..

Can you please provide a link to this study of finger and ear probes, and how you arrived at this formula? Thank you.

Most of the studies that come up on Google search which compare ear probes to fingertip probes, where they actually sampled blood to get 'real' O2 levels report the fingertip probe to be more reliable, even in patients with 'poor peripheral perfusion' which would basically mean poor circulation--which is also a pretty good description of vasoconstriction. Other studies which compare them also report the value of ear meters to be HIGHER. This supports everything we understand about dive response--the body works to keep its most oxygenated blood going to torso and head, where it is most necessary.

I know it is much discussed on here, and many cheap O2 sat meters are NOT accurate at the lower levels of pulse and O2 sat which trained freedivers achieve, but I do not think vasoconstriction is entirely responsible for post-apnea O2 drop. I have been told it has to do with Bohr shift, which has to do with the blood's affinity for O2. I do not 'get' all the chemistry, but if Bohr shift causes a sudden change in the blood's O2 affinity, it makes perfect sense to me that we could see a sudden drop in arterial O2 as hemoglobin loses its affinity for O2, and the O2 is quickly diffused into hungry tissues.

Furthermore, I have trained extensively with a meter that shows pulse strength, so I can see vasoconstriction happening (or not, as the case may be). I can prep in such a way that I get little or no vasoconstriction during a hold, as shown by my meter, and I am also able to check the meter's report manually, in that I can find a wrist pulse (when vasoconstriction is strong I can't find a wrist pulse). Even with no vasoconstriction, the meter shows a brief O2 dip when I start to breathe. For long holds the O2 dip is markedly higher, but once my O2 reaches a certain level (low eighties), vasoconstriction is extremely strong and unavoidable. By doing dry holds in repetition I can pretty easily blunt my response so I get no vasoconstriction even in to the low 90's. But I will still see an O2 dip when I start to breathe.

 

[MarcinB]

Here's the link to the paper by Peter Lindholm which I mentioned previously:
ingentaconnect Pulse Oximetry to Detect Hypoxemia During Apnea: Comparison of Fi...

This is the only study that compares two types of probes during apnea. According to this study the lowest saturation showed by finger probe is on the average 6% higher compared to the ear one. The ear probe should give a much better estimate of true blood saturation during apnea because its readings are much less affected by vasoconstriction.
Saturation always continues to decrease during the first few seconds after breath hold because it takes some time before oxygenated blood is transported to tissues. It takes much longer for finger than for ear which was clearly shown in the above study.

 

[Apneaddict]

The real question is:

Does anyone here have a large ear / long enough ear lobe to be able to test the difference in readings at both locations with the same fingertip oximiter?

Mine doesn't reach - it just says "finger out".

 

[growingupninja]

Here's the link to the paper by Peter Lindholm which I mentioned previously:
ingentaconnect Pulse Oximetry to Detect Hypoxemia During Apnea: Comparison of Fi...

This is the only study that compares two types of probes during apnea. According to this study the lowest saturation showed by finger probe is on the average 6% higher compared to the ear one. The ear probe should give a much better estimate of true blood saturation during apnea because its readings are much less affected by vasoconstriction.
Saturation always continues to decrease during the first few seconds after breath hold because it takes some time before oxygenated blood is transported to tissues. It takes much longer for finger than for ear which was clearly shown in the above study.

From what I got of the abstract, the fingertip meter just seems to have a delay of about 15 secs but readings were not necessarily inaccurate? I am not sure that a 15 second delay is particularly significant for even advanced divers; I have not personally tested O2 sat multiple times to BO/samba, but of tests I have seen, this threshhold fluctuates as much as 5-10% in the same diver, plus there is likely a daily variance. In my case, 15 secs is never enough for my O2 sat to fall as much as 5-10%. Although the Lindholm study measured only 60 sec dynamic holds--I know in myself 60 secs of dry dynamic would cause vasoconstriction, but it would not be anywhere near as severe as it would be with longer holds so the delay could be longer in deeper apnea.

To train to even within 10% BO or samba is not particularly easy, especially if you are doing full lung, dynamic training.

Thanks for the link. I would prefer to see a more conclusive study that measured actual arterial blood saturation.. there seems to be a fair bit of variance between readings of both fingertip and ear models: Pulse oximeter probes. A comparison between fing... [Anaesthesia. 1991] - PubMed - NCBI

 

[MarcinB]

Read the whole paper (it's free), there is much more information there compared to abstract.

 

[growingupninja]

Ah, thank you. Very good information there...

 

[kierandiver]

Hi guys, I recently attended a seminar by Patrick McKeown, a leading specialist on breathing. We used fingertip oximiter to measure our SP02 levels during our breath holding exercises. I found I was able to get my levels down to 60-70% compared to the rest of the class who were up around the high 80s, low 90s..I'm a little concerned whether or not this is a good thing? Apparetnly thats the same o2 saturation levels you would hit at the top of mount everest..! Curious what you folks think ?

 

[MarcinB]

I depends on duration of the breath hold. If it was considerably longer compared to the rest of the class it simply means that your CO2 tolerance is higher than average. If the duration was more or less the same it implies that your body consumes oxygen faster.