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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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Well-Known Member
Jun 19, 2002
Not sure how many people out there have access to pulse oximeters and also have the ability to acquire the complete log of the oximeter during their static. However, if there are some people out there maybe we can share output results.

Here is one from the other night where I did a slow breath-up for the first time in half a year. I over venitlated due to a pee-break part way through. So actually I did 7:30 breath-up then took my break and came back to do 4:30 breath-up.


Hope to see other results.



Great idea.
Maybe it's easier to read if you drop it into Excell and create a simple graph of it. Makes it easier to compare etc.
Here is my 7 min static

about 5 minutes slow breathing followed by a ~1 min deep faster breathing to hyperventilation. Then 1 minute very slow breathing to bring back down the HR , 2 big final breaths + little packing and go.

Also check out Sebastian Naslund's recent 7'04'' at:
and the great and extensive "samba" experiments with a pulseoxymeter : http://www.webvideo.nu/freediving/features/samba.html
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Could you tell when the contractions started on these statics?
Another thing that would be interesting to see is a max static without breathup and compare that to the other. My gues is that the O2 will start to drop erlier...

I've been meaning to post my data since I stuffed up an bought the exact one Eric told me to avoid! ....speaking of which, does anyone know how to hook a laptop up to the 25pin serial plug on the back of a Ohmeda 3700 pulse oximeter. I've been thinking of trying to write a VB app and find a relevant comms port control object but it's been about 5 years since I cut any code so was hoping someone might have already solved this and would be willing to share some code???

To connect your pulse oximeter to your computer, just get the appropriate serial cable (DB9 to DB9 or DB25 to DB9), plug it into your PC, and then run an application like hyperterminal, and set the serial port options to what your oximeter uses (i.e. 9600 baud, 1 stop bit, etc..)

No programming required. Tyler is also using the 3700 Ohmeda (he's borrowing mine!)

Eric Fattah
BC, Canada

My contractions began at 4:27. I will eventually get the output of a no breath-up static and put it up, but I as well would expect the O2 to be lower at the beginning, but towards the end I expect the O2 to be relatively the same. In general the more hyperventilating one does, I think the sharper the curve drop-off of O2 saturation. That is the O2 saturation is dropping faster at the end of the static, even though it was higher for longer at the beginning when compared to a no breath-up static.

Regarding oximeter output:

I couldn't find any online documentation on the Ohmeda 3700, but through trial an error, I found it works with 1200 baud, 8 bits, parity none, 1 stop bit, flow control hardware. Find a serial cable with one end being a female 25-pin connector and the other end begin the opposite of whatever connector is on your computer, generally a 9-ping male connector would be required on the other end.


Thanks Eric and Tyler I can't wait to get home and try it.

I feel better about my purchase already...if Eric's old Ohmeda 3700 is good enough for Tyler then it is easily good enough for my novice needs :)

;) Well, "beggers can't be choosers", so I make the most of what I can. Even though it may be inaccurate to some degree, the most beneficial aspects may be the comparisons over successive outputs and the overall trend of the output curve, as opposed to the accuracy of any given instantaneous sample. It definately gives accurate heart-rate readings for me, unless I am having heavy contractions as you can see at the end of my output.

It also is brilliant at noticing metabolic changes in my body which is useful to see what helps or hinders your body's consumption of oxygen. The other day I took Niacin (B3) and later on my resting O2 saturation had plummeted as I expected.
Why should B3 have such a result?
I take vitamin supplemnts (centrum) after my daily morning statics, so I don't exepct it to interfere with the statics the day after.
In anyway I didn't expect general supplements to make any effect at all. What quantity of B3 did you take? how long before the static?
I have been taking 500mg tablets, not multi-vitamins.
See the article here:

To summarize these cause the small capillaries to expand, thereby allowing more blood flow to the whole of the body near the skin surface. One is subjected to a "flush", where some (me at this dose) can see your whole body go red and you get itchy to some degree from released histamine. Nourishment of cells at these locations is increased and more oxygen I expect would be consumed. The effect probably only occurs with a dosage over 100mg, but depends on the person.
Thanks Tyler
it seems that the contractions start about the same time as the O2 starts to drop and the pulse start to drop at the same time...
Another interesting thing is that the O2 drop seems to accelerate. I thought the body would try to save O2 as it gets lower...shouldn't the lowered puls save O2...? :confused:

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During a static your pO2 decreases somewhat constantly, but it is the SaO2 which 'appears' to decrease faster, because of the sigmoidal shape of the SaO2-pO2 curve (Hb-O2 affinity curve).

My experiments lead me to believe that the lowest rate of O2 consumption occurs while you resist contractions, and during the first, weak contractions. When contractions go into body-buckling mode, the muscular effort increases O2 consumption somewhat (at least in me).

Eric Fattah
BC, Canada
10x for the link and info Tyler. I'll check it out.

SaO2 is in your blood and PO2 is in your lungs:confused:?
I'm really in the dark as to the difference between the 2.
I always assumed that Sao2 is amount of O2 saturated in your blood - linked to hemoglobin. Was I wrong?
What's PO2?

(I'll start learning chemistry only in October/November I think, sorry.)
Eric & Tyler,

I had the cable at home and connected it up and ran hyperterminal with the properties set as listed, but couldn't get anything across to hyperterminal. Does the Ohmeda unit send/stream data continuosly to the port on the back when your connected to it or do you need to do something to get it to send a dump of what's in it's memory?


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It dumps continuously. Possible problems:

1. The cable is the wrong type but with the correct connectors. There are two types of serial cables. One is what is known as a straight-through or just standard serial cable and the other is known as null-modem or cross over serial cable. Another possibility is that it is a printer/parallel cable, which use the same connectors for extensions or other things, but I am not sure if it is different as far as wiring than a standard serial.

2. You have hyperterminal using the wrong COM port. How many connectors do you have at the back of your computer that are male and 9-pin or 25-pin? You could be plugged into the wrong port and possibly even into the printer port. You could have hyperterminal using COM 1 instead of 2 or vis-a-vera.

3. Your computer has the COM port required, disabled in bios.

4. There is a conflict between a device in your computer at the COM port.

To ensure you are getting data from the ohmeda you can probably put an LED between the ground pin and the rx pin. However I am not sure if the Ohmeda supplies power in the connection or only the computer. In which case I think it is 5V which you could supply technically if your inclined.

Well hope something here helps you troubleshoot it.
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There is another possibility for problem with the cable that almost drove me mad while testing my home cooked cable. (for the nellcor, but can be the case for other brands as well)
Normaly there are only 3 wires involved for a simple no brainer serial connection without flow control.
- recieve data
- send data
- ground

For a so called 0-modem cable recieve and send should be cross connected between the two devices.
Sounds simple enough. Well it did'nt work. Resoldered the cable about 20 times , still no signal.
After some more thinking and reading a service manual i found out the freaking thing has 2 types of ground (2 physically separated ground cirquits), which has to do with the fact that these things are used i hospital environments.
There is signal ground and device ground. Only when i connected both of these together on the side of the O2 meter it worked, flawless with a continuos stream of data.
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Pulse Oximeters are relatively new for most freedivers. Information about a particular pulse oximeter and its usability for freedive training is hard to find. Therefore a comparison of output and usability might be very handy, both for users and potential users.

There is already information posted on the forum about pulse oximeters, a lot of which comes from Eric fattah. From the posts I conclude that there is a huge difference among reported (low) O2 saturation values due to the generation (age) of the equipment, newer equipment being more accurate. Besides accuracy of low O2 saturation measurements there is also mention of the delay factor. The speed of the rise and fall of O2 is supposed to give quite different measurements depending on the model of pulse oximeter used, regardless of the recorded samplng rate. Furthermore there is also the difference in measurements caused by different types of sensors (for example: finger sensor, ear sensor, sensor on the forehead, reusable sensors versus disposable sensors, waterproof sensors?). All of these factors can produce different measurements, only caused by different equipent, which must be taken into account when comparing output or choosing equipment. Can there also be a difference caused by ambient temperature or the way the equipment is used (most will not be trained in the use of a pulse oximeter)?

Quote from erik fattah post in http://forums.deeperblue.net/showthread.php?threadid=41519
Of the 1st generation, the Ohmeda is very inaccurate, and the Physio-control Lifestat 1600 is by far the most accurate. Of the 2nd generation, the most accurate are the Nellcor N-395, Nellcor N-595, Masimo Radical, and Ohmeda 3800 & 3900. The Masimo Radical with the earclip sensor is the most accurate of all oximeters, followed closely by the Nellcor N-595 with the forehead sensor.

A question that might be interesting is which difference there is between equipment for freediving use and how much effect this has on measurements caused by for example:
1 generation/ age of the equipment
2 inconsistency of readings (same equipment, same test, different readings)
3 delay factor in displaying changes in O2 saturation
4 sensor type
5 ambient influences like temperature, improper use of equipment, ...

I hope it is posible to say something about which equipment might be best suited and, when comparing output, how much gathered data can differ caused by different equipment.

Another question I would like to ask is if you think the differences between equipment are relevant when you always use the same machine for training? And for comparisons with others?
I have been studying the data from everyone who has posted on this subject for quite a while, and Tyler has the slowest drop of SaO2% I have seen yet. I’m jealous! :vangry

But I am happy to report that my O2% has been doing better. Some of my numbers lately are: 98% for 3 minutes, 91% for 4 minutes, 86% for 4:30, and 70% for 5:30. This is a significant increase in SaO2% for me, which I contribute mostly to Adrian’s good advice at the PFD clinic. He has a lot of knowledge of Yoga and taught me some relaxation techniques to use during the hold.
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