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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.
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I currently have three pulse oximeters set up at the same time:
- Ohmeda 3900P with ear-clip sensor OR finger sensor
- Masimo Radical with finger sensor
- Quartz Q400 with finger sensor

All three have data logged to PC's.

When I finish the breath-hold, I can measure the 'response' time (delay), by checking to see how long it takes for the SaO2 to reach a minimum.

For example:

4'00" static
Minimum SaO2 occurs at 4'25" on the oximeter
This implies a delay of 25 seconds.

The delay also strongly depends upon your 'perfusion', i.e. how much blood is flowing to your fingers/ears etc.

If you have cold hands, the delay is much longer.

With WARM hands, I have found that my finger sensors have a delay/response time of 23-30 seconds, and the ear-clip sensor has an astonishing response time of 10 seconds.

Also, the ear-clip sensor catches brief transient desaturations much better than the finger sensor. This means that on inhale statics, all three oximeters drop to about the same SaO2, but on exhale statics, where the drop is much faster and shorter, the ear clip sensor consistently drops to 4-6% lower SaO2 than the finger sensors.

Masimo now makes a forehead transflectance sensor, but it costs $430. I was hoping to get one but I have other expenses.

I also have a transcutaneous O2/CO2 monitor. This is very interesting because it measures your PO2 and PCO2, not your SaO2. Your PO2 decreases linearly with apnea, unlike the SaO2 which changes at strange rates (seems to accelerate at the end because of the shape of the Hb-O2 curve).

Eric Fattah
BC, Canada
Eric & Tyler,

Thanks guys I've got it working now, it seems that I've done something to the com port by installing a utility to run USB ports on Win NT machines. If I find some time I'll write an interface that shows the same info as on the unit but also graphs it in realtime. I'll send you a copy when it's done. It will work just fine but please don't look at the code as it will be kindergarten standard:)


Here is a static I did this evening without any breath-up. Noticeable difference in heart rate. Contractions started at 2:30, static ended at 5:38 with 100 contractions. Could have gone longer and should have to see the output.

Interesting was during the period after the static from 6:30 to 7:15 when my heart rate plummeted 10 beats lower than my resting heart-rate.

Maybe that was the point where you were supposed to do a second attempt? :)

Should be interesting to see how consecutive statics affect O2 consumption and heart-rate.
Does warm-up holds (for those who do them) really increase the potential of the next static? or just makes it easier for us?
Very interesting Tyler. I printed out your two graphs and although your hr was lower with the no breathup, SaO2% fell much faster. At 5:30 it was only 55% where with your normal breathup it was in the low 80’s. I doubt you could have gone much further on your no breathup with how fast you SaO2% was falling. The only time I did a no-breathup I believe I made it to 4:30, my SaO2 was actually better than normal, but the pain was outrageous!

The first thing I noticed when I started using a pulse/oximeter is that my SaO2% was not any better in later holds than the first ones, except maybe toward the end of a hold if the contractions were difficult. For me it appears the only advantage of warm-up holds are an increase in CO2 tolerance and thus less pain in the later holds. The exception is like I said earlier with hard contractions. If the contractions are hard and causing my body to jerk a lot, than I do seem to burn O2 faster and can benefit from more warm-ups.

Too many warm-ups seem to drop my SaO2%. If I have done dynamic walking within the last few days, I can handle just one warmup and prefer that. Its painful, but I prefer getting it over with quicker than having to do another one.

Kirk Krack said at the PFD clinic that the earlier holds help shift the hemoglobin release curve which means your hemoglobin will release more O2 and you can keep from blacking out at lower SaO2%. I don’t know about this, because I have no data from blacking out with a pulse/oximeter. The only two times I have blacked out were with wet statics. I have a lot more pain with dry statics, plus I stop if my SaO2% gets really low on the meter. My gut feeling is that 5+ minutes in one static is enough to dilate the blood vessels in the brain and cause some acidity from CO2 buildup to shift the release curve.
Yes I should have done another static after that one, but it was 1:30am and I was still working. So I really just wanted to sleep! ;) Anyhow I will do the same test soon again, but follow it with another static afterwards.

As well I have been extremely active lately so that probably accounts for the rapid decrease. I often do a no-breath-up test of 3:30 and usually end with an SaO2 of 90-95%. So I didn't even notice last night in my dreary state, that this static I was at 85% already at 3:30. This is normally a sign that my metabolism is working away, due to intense exercise during the day or not eating right. I did not do a lot of physical activities this day but for the past week I have been doing much more than normal.

So I would say disregard this one, but actually it still provides valuable comparison information for being in such a state. I look forward to comparing to when my body has calmed down.
I have not confirmed the difference in SaO2 between my first holds and second since normally I only do one static, but on those days that I do two, the first is a 3:30 without packing and the max static is with packing usually. So, the times that I was comparing SaO2 between the two statics, it is possible that the higher SaO2 for longer in the max was due to the packing (increase in O2 and pressure). Although, until now I believed it was due to the hyperventilating, causing a drop in CO2 and the increase of Haemoglobin's resistance to releasing oxygen. Which technically could cause the same effect? As well the spleen release more blood into the circulation which provides a greater amount of oxygen.

I do not understand the idea that earlier holds help shift the Haemoglobin release curve and that this is a good thing. It would not seem to assist in preventing blackout. To me it would seem it would assist a blackout. During any max hold you are going to reach a state of high CO2, which will shift the curve, make the Haemoglobin release O2 easily. But you would think this effect would be highly preferable to occur in the later part of the static only. So, shifting the curve for the beginning of the static would seem counter productive, since you would be releasing O2 to the extremeties easily. They would eat up this O2 and thereby give you less reserves once blood shunting occurs.

So, shifting the curve for the beginning of the static would seem counter productive
That is my line of reasoning too. Shifting the curve to release more O2 through out the body would be good in most sports where the athlete is breathing, but in statics, you want to decrease O2 consumption in all non-vital tissues. Maybe the real benefit from acidity caused by earlier holds is the quicker the body develops Bradycardia and blood shunting. Shifting the release curve might be a side effect, but not a positive one?

It's all speculation until somebody does a study that measures the SaO2 at black out at different ph levels. Any volunteers? I think I would pass on that one! :D
I have measured SaO2 at blackout for different ph levels via different breathe-ups (and different CO2 levels). There is no doubt that you black out at a higher SaO2 if you hyperventilate.

For inhale statics, it has been well established that you want a left shifted hemoglobin curve, which shifts far to the right under higher acidity. (i.e. high bohr effect).

For exhale statics, a right shifted curve which shifts further to the right is needed.

The examples come from marine mammals who inhale (i.e. penguins) and those who exhale (seals, whales etc.)

Eric Fattah
BC, Canada
Niacin Flush

Tyler, can you tell something about the effect of Niacin on your statics please?
This flush is an interesting phenomenon by the way. I had them after drinking a certain kind of sports drink and thought it was some kind of allergic reaction to it, but after reading the article and checking the contents of the drink I realised that the reaction must have been caused by the large amounts of niacin in it.

Fred S.
What kind of difference have you seen in your SaO2% at black out point when you have hyperventilated to make yourself more alkaline and when you have not?
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Samba at 60% SaO2

Today I did 6:00, which was the first time I ever made it to 6 mins with my pulse/oximeter and with writing down the SaO2% and heart rates at different intervals. It was also the first time I ever had a massive Samba with a dry static. I got my SaO2 written down before the Samba started, but not the hr. My SaO2 was 60%. I have been down to 58 and 60% in the past and not had Sambas. It’s also significantly higher than what you other guys with pulse/oximeter are reporting for the end of your statics. I did 3 purges and it was my second hold.

Any comments as to why I Sambaed at 60% SaO2?
Checking the SaO2 of a samba has several issues:

- You need to make sure you record the minimum SaO2, which will occur 15-30 seconds after you finish the static (usually when you are waking up from the samba)

- If you do an exhale static, you will reach a much lower SaO2 than with an inhale static, but, because of the averaging interval of the oximeter, instead it may appear as though you reached a lower SaO2 on the inhale static, unless you use an earclip or forehead sensor. During exhale statics, the SaO2 can drop below a level compatible with life, yet you remain conscious due to the creatine phosphate and ATP stored in your brain. These allow for about 10 seconds of consciousness regardless of your SaO2 level. So, if the SaO2 drops extremely fast, it can reach an arbitrarily low value. On an inhale static, your brain energy stores cannot save you because the drop is much more gradual.

- The blood flow to your hands will strongly influence the minimum SaO2 found by the oximeter, possibly confusing your results.

- Even taking into account all these factors, I have found that I samba at dramatically different SaO2 levels on different days. The effect could be due to many things, including sleep, ingestion of pro-convulsants such as chocolate, caffeine, etc., the ingestion of alcohol, your hydration & blood pressure, ingestion of garlic, onions or spicy foods, body temperature, etc...

I have had shakes at SaO2 = 68%, and I have gone to 37% without shakes, on the same oximeter under similar conditions, on different days.

Eric Fattah
BC, Canada
Those numbers, by the way, are on the state-of-the-art oximeters. On my old Ohmeda 3700, the numbers were always too low (as proven by studies). The numbers were shown to be 25% or more too low. I once got that oximeter down to 11% without a samba, but now I know that it was probably more like 48%.

Eric Fattah
BC, Canada
Technical advice?

Don, I'de imagine that writing your own data will not give you the max benefit of your pulse oximeter. I guess that your pulse-oximeter doesn't have a computer output... Do you have a webcam? you could capture the data while doing statics, and extract the information afterwards...
Some webcams/programs has the possibility (mine has) to take still photos at specified interval, so you wouldn't even have to watch the whole movie, just a bunch of stills...
Webcams should cost 20$ nowdays I guess... much cheaper than a new pulse oximeter...
Fred S,

Every time so far that I have taken Niacin I find my resting SaO2 drops and that my statics resemble the statics after a day of diving, which for me are generally horrible. SaO2 drops very rapidly and contractions come early.
You are correct, mine doesn’t have an interface. It’s an all-in-one finger unit. I tried the web cam, but the camera would not capture the red LED display of pulse/oximeter very well. I tried several different settings, but it just didn’t like a bright red numbers and I could not read it when viewing it later.

I have gotten quite used to writing the numbers down. To me the amount of mental and physical energy it takes is similar to the response necessary in signaling and focusing in a wet static toward the end. For the first 3 minutes though it does take me out of the nice relax zone so I am starting to skip those data intervals more often.

Thanks for the suggestion.
That is interesting what you have said about niacin use being similar to a day of diving for you. On good days my SaO2 will read 100% resting and I can keep it at 100% for the first 2 ½ minutes. These days usually happen after a few days of rest from no apnea activity and good sleep the night before. They also tend to happen in the first 2 days after being in the water for a long time, but if I didn’t push it hard; like it’s a delayed dive reflex.

On so-so days it will read 99% and reach 100% during the breath up. Sometimes it will read 99% at the start of static, be back to 100% at about 20 seconds and fall back to 99% at 2:00. These days seem to be after doing some apnea in the previous days or being a little tired.

On bad days it will be 97-98% at rest and I can only get it up to 99% with the breath up. It may reach 100% after 20 seconds in the hold, but it falls back to 99% soon and will be 98% by 1 minute. From there its down hill fast! These days happened after 3 to 4 days of apnea and poor sleep, or the start of an infection. There have been days where I slept well the night before and think everything is in place to do a good static that day, only to find my resting SaO2 is low. By the end of that day the tale-tale signs of a sickness are usually apparent.

Good thread!

When looking at resting saturation, you must be careful to interpret the numbers properly.

The hemoglobin SaO2 curve shows that a saturation of more than 98% is virtually impossible without either excessive hyperventilation or breathing pure O2. In fact, I read somewhere that a saturation of 100% is impossible without pure O2 or hyperbaric pressure.

There are two types of SaO2's that oximeters can display: relative or fractional. In fractional mode, the oximeter displays your true % saturation, where 100% is truly 100% saturation.

In relative mode, the oximeter scales your saturation so that it is based on an assumed maximum of 98%. So, the actual saturation displayed would be:
[SaO2]/98 * 100

So, if you are at 98%, it would display 100%. If you are at 96%, it would display 96/98 = 97.9% or 98%.

I think this is sometimes the reason why people report 100% saturations; their oximeters are showing relative saturation.

In particular, with my three modern oximeters, it is very difficult to even reach 98% saturation. Two of my oximeters allow me to switch between relative and fractional mode as well. In relative mode it is quite easy to reach 100%.

In general, my (fractional) saturation is around 95-96%, until I take a few deep breaths, then it goes to 97-98%. After excessive hyperventilation I might hit 99% for a second or two.

Eric Fattah
BC, Canada

Does your Ohmeda 3700 measure relative or fractional SaO2? I have the same one and have been assuming that it measures fractional saturations.


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