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Stupid question - M20K Oxygen


JRam

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28 minutes ago, jaylw314 said:

If he is a smoker (chronic CO exposure), chronic hypoxia from a lung condition, or peripheral circulatory problems, he will feel fine (relatively) at those sort of numbers.

He is none of those. He is a hard working TV sound man (A1). He travels all over the country doing sports. His typical work day is 12 to 15 hours. He is 60 years old. Healthy as a horse.

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3 hours ago, N201MKTurbo said:

A couple of things...

I have researched how pulse oximeters work and they are not prone to errors. I bet that your new oximeter reads the same as your old one.

That being said, I have a friend who went to Oshkosh with me in '13. We were on a high altitude leg and I got out the oximeter and I was at 94%. I put it on him and it read 72%!!!

I asked him if he felt OK and he said he felt fine. I told him he should be in a hospital. He said doctors always freak out when they put one of those things on him. He said they always read in the 70s. I have no explanation for it, and he said the doctors can't explain it either. I think he is an alien...

MKTurbo... 

Actually, pulse oximeters can be pretty iffy. I rely on them daily at work (ER) and they can be fussy and/or really unreliable. Like any small electronic device, individual pulse oximeters can be quirky, incorrectly calibrated, or just "lemons". In the medical setting we use oximeter transducers that connect directly to our wall monitors, which are much more reliable than the compact portable battery-powered devices. Even then, it's not uncommon to have to switch from one hand or digit to another because of quirks in getting good readings. Taped-on transducers work better than the ones that are held on by spring pressure, also. We routinely check our portable pulse oximeters against the wall units, and often have to replace the portable units because of inaccurate readings. 

A pulse oximeter measures the percentage of hemoglobin molecules in the blood that are saturated by oxygen, which induces a color change; as such, it detects hypoxemia, or low blood oxygen concentration. This isn't the same thing as hypoxia,  which denotes low oxygen concentration in the tissues, most immediately in the brain. One can have transient hypoxemia without being clinically (or aeronautically!) hypoxic. Transient hypoxemia is anticipated above certain density altitudes (arbitrarily 12,500, but this is by no means a "safe" altitude), but this will usually not cause clinically significant hypoxia unless the hypoxemia persists for longer than a few minutes. This is why the FAA gives you 30 minutes of leeway between 12,500' and 14,000' MSL. However, there is no clearly "safe" level of hypoxemia and some brain functions are demonstrably impaired at altitudes as low as 6000' MSL, at which point retinal function becomes impaired and night vision degrades measurably. 

It was in consideration of these factors that I decided to get some good baseline measurements of my SpO2 (oxygen saturation readings) before flying my new-to-me M20K above 14,000' MSL. As jlunseth suggested, the portable pulse-ox I bought may not be giving accurate readings, but it definitely shows trends that suggest caution when using my on-board supplemental oxygen equipment. I had noted in my pre-O's days in my Cessna 172 that I felt a little breathless at 11,000' and above... and my pulse oximeter showed my SpO2 was definitely trending downward above 8000-9000', and O's were required at 12,000'. Interestingly, I get higher readings in my middle finger than my index finger, and in my left hand rather than my right. Higher readings are more likely to be accurate. Also, when I checked my wife's SpO2, she got readings in the 70's... but she wears thick red nail polish. Other factors can confound the pulse-ox, as well: cold hands, thickened fingernails due to onychomycosis, and so forth. 

As for your hypoxemic flightmate in 2013:  jaylw34 commented, people with chronic disease can be perfectly comfortable with quite low SpO2's... but in the 70's, it's highly unlikely he would be able to tolerate this and not have blue lips and hands. Most likely he has an anatomic or other functional impediment to good SpO2 readings. 

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4 hours ago, N201MKTurbo said:

He is none of those. He is a hard working TV sound man (A1). He travels all over the country doing sports. His typical work day is 12 to 15 hours. He is 60 years old. Healthy as a horse.

probably rules out the first two, but I suppose he still could have some local circulatory abnormalities.  He'd be a good test case to try the pulse ox out on his various fingers and toes for comparison!

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On 10/2/2018 at 5:57 AM, JRam said:

It was at around 1800 when I picked it up and now shows 1500, so it definitely had oxygen at one time. But maybe now it doesn't. 

I hate having my plane so far away (1hr+ during late day traffic) that I can't make a quick trip to look. 

if it was 95 degrees sitting in the sun when you picked it up and 40 now, you might not have a leak/big leak.  

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Thank you all for your help. So I got out to the aircraft today and looked at the bottle. As the switch turned, nothing happened with the cable at the bottle. The cable looks fully intact in the back, so I'm assuming the cable was disconnected at the switch inside the cabin. 

I went ahead and used my finger to open the flow at the bottle and heard a little pop. Got in to the cabin and at 4000 tested the flow and had full oxygen flow. 

I left it on and will watch to see if it ends up leaking out or not over time. 

Again, really appreciate the help!

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I have the Mountain High O2D2 Oxygen conserver:

http://www.mhoxygen.com/index.php/portable-pulse-demand

It is well worth the price.  It will accommodate 2 people.  It works well as a conserver.  A 7 hour flight drops my O2 cylinder pressure from 1800 --> 1500 psi.  

When you breath ism you can hear as feel the puff of O2 so you know the system is working.  It is quite comforting, kind of like a clock ticking.  When you don't hear and feel it with each breath, you will know it and the box will alert you.   Highly recommended.

John Breda

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