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Compare our outputs from Pulse Oximeters

Thread Status: Hello , There was no answer in this thread for more than 60 days.
It can take a long time to get an up-to-date response or contact with relevant users.
Eric, I kind of figured that 100% didn’t really mean 100% SaO2. Your explanation of relative verses fractional helps. The importance of that to me is that even if my reading is showing 100% in the breathup, I may still be able to oxygenate myself a little more by continuing the breathup a longer rather than just start the static because of the reading.

What I have found interesting with using the pulse/oximeter regardless if 100% means 98% or 100%, is that how sleep the night before and apnea activity in the preceding days (and sickness) can change my resting SaO2% by 2-3 points which almost always translates into even larger differences at later intervals in the static.

To me this is good info because it verifies the importance sleep and other things have on my physical ability to hold my breath. Although I am still a little confused as to why if resting SaO2 is low for one or more reasons the body just doesn’t regulated the breathing to increase it, like it normally does. For example it seems that if someone were at 95% true SaO2% due to infection, wouldn’t the body be better able to fight the infection at 98%? So why doesn’t the body increase the frequency and depth of breaths to achieve this?
don :confused:
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It has no need to increase the SaO2% before some threshold is reached, since the blood acidity/alkalinity is as the body expects and the return supply of oxygen in the blood is high enough to feed the body's needs at that point.

Which brings up an interesting idea, if you use sensors in different locations (ear, forehead, finger) then would it not be expected to have different SaO2% in general, even at resting? Since the blood path to the different extremities will have different requirements upon O2. As well your body metabolism along your arms, could be in a more active state than the metabolism leading to your ear, no?

As a metaphor, if you are driving 100km to work, you need 10 litres of fuel, if you are driving 1000km to a friend's cabin, you need 100 litres. Not a perfect comparison but I hope you get the idea.

One other question that comes to my mind because of this, since the blood that reaches the sensor, is actually blood that has directly flowed to the, let's say, finger, where did it actually release a % of its O2? I thought O2 was only released at the capillaries and then they return through the veins. Meaning the blood cells arriving at the finger should never have arrived at a capillary, therefore they have not had a chance to release O2? Therefore if the sensor detects a lower % of O2 in the blood, what was the source and the how of this decrease? I obviously missed something in my studies here.
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To clear things up:

After blood passes the lungs, and is oxygenated, it flows through the arteries, which feed the capillaries, which feed the cells; then the blood goes into the veins.

So, in the arteries, the blood should be fully oxygenated...?

The oximeter, passing light through a sensor site, must deal with a problem; there is both venous and arterial blood at that location. The 'dumb' oximeter just uses the net result of that. The 'smart' oximeter uses a complicated algorithm to 'separate' the venous signal from the arterial signal, and then it shows your arterial oxygen saturation.

Keep in mind that the blood in your veins will be very poorly saturated, SvO2 = 30-70%, or even less at the end of a breath hold. This is where Lindholm's theory comes in; when you hyperventilate, your ARTERIAL O2 saturation (SaO2) will never go over 99%, but your VENOUS O2 saturation (SvO2) can increase dramatically from perhaps 50% to 80% or more. So, given that perhaps 1/2 of your blood is in your veins, there is a huge gain in O2 storage capacity by oxygenating your venous blood.

For that purpose, I wish my damn oximeter would display SvO2!! For me that is a much more important number than SaO2! The dumb thing is that the oximeter KNOWS SvO2 (it had to calculate it to get SaO2), but it won't display it, because it is not considered important in healthcare!

Eric Fattah
BC, Canada
Then would it be correct to say that if the SaO2 % is lowering upon rest, then the blood is not being fully reloaded as it passes the alveoli at the lungs? Which if correct would most likely imply that your SvO2% was very low due to high metabolism somewhere in the body? This would also account for why sensors at different locations should get results NOT dependent upon the location of the sensor, other than characteristics hindering the sensors accuracy in general.
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The 'smart' oximeter uses a complicated algorithm to 'separate' the venous signal from the arterial signal, and then it shows your arterial oxygen saturation.

To add to that, part of how it figures the arterial O2% is by taking readings between and during the pulse. The idea is that the difference between these two readings is going to be the extra blood in the artery from the pulse, which it can use to help estimate what part of the readings is from SaO2% rather than a net of arteries, veins and tissue.

This is also the difference between a plain oximeter and a pulse/oximeter. It’s also the reason why they don’t display a different SaO2% until a pulse beat.

Great explanation on why SaO2 is constant in the arteries regardless of the location. :)
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I was doing a search for oximetry related information and discovered this thread.

I have just released an online application for the trending of data gathered from pulse oximeters. The solution is called Etrending and is available at www.etrending.com. I am making the service available for free during the development and validation period.

We developed etrending to diagnose obstructive sleep apnea in children but the graphical interface will easily display the data described in this thread. It will also be very interesting to see what kind of numbers our expert system gives out when it looks at data derived from a free dive.

Register at www.etrending.com to enter the service. You will need to update the version of Java on your computer to view the demo study and a couple of other applications on the New Study page to upload data. Etrending is currently only compatible with the Masimo Radical, Rad-8, Rad-9 and Nellcor’s N-395, N-595 but if you send me the hyperterminal info and the keywords to initiate the dump I can add new oximeters relatively easily.

Thanks for reading and good luck with your dives.
What would be interesting would be to compare SaO2 graphs of a person new to the sport, and compare graphs after they have trained for several weeks/months/years and see how the results compare. This could give an indication on how effective different types of training are for BH's.
Does anyone happen to have a collection of any such SaO2 graphs?

John :)
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