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My wife and I have been flying with Oxygen using the altitude adjustable

Nelson Flowmeters and reservoir cannulas for about 4 years.  12,000 to

18,000 is a great way to go; sometimes good tailwinds, next to no traffic at

12.5 to 17.5 except jets going up or down, usually less turbulence, very low

fuel consumption, better range and you (usually) feel fresh as a daisy after

4+ hours

at 10,000' and above because your body did not accumulate an oxygen deficit.



BUT, you have got to be careful!  We always monitor the Flowmeters to be

sure

everything is working and assumed we were OK.  However, on a 5 hour flight

at 15.5, followed by a 3 hour flight at 13.5 I had all the symptoms of

Hypoxia.  My judgment and ability to fly the airplane was definitely off, I

had a bad headache (and I don't get headaches).  After talking to a MD

giving a forum on OX use at Oshkosh (the destination), I bought a FlightStat

Pulse Oximeter  at

the Mooney Pilots Assn. booth on his recommendation.  Good Advice!



I found out that I absorb Oxygen at a lower rate than my wife.  If we are at

14.5 I need to have the Flowmeter set at 16 to 16.5 to get my blood at 90%

oxygenated, my wife doesn't.  I did not have a problem for years and many

hours of flying on OX, but I almost found out the hard way.  Your body

operates at density altitude too, or maybe it's ageing (nah, I am only 62,

exercise and quit smoking in the 8th Grade).  The little Oximeter that just

slides over your fingernail will tell you very quickly if you really are OK

or not on every flight.



Steve Colwell   Legacy 2K  Placerville,CA   (530) 621-3408





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Fred Moreno points out another cause of hypoxia which I did not cover in my

last post. Please allow me to explain it a bit more technically than he did.



The problem Fred mentioned is lack of hypoxic drive. To explain, your body

has two chemoreceptor (chemical control) mechanisms for breathing. The

stronger one is the hypercarbic drive. To demonstrate this, simply hold your

breath. Your blood level of carbon dioxide will rise, and hypercarbia (high

CO2) will make your blood a bit acid compared to normal. This will stimulate

you to breathe to eliminate CO2 and bring your blood acidity down.



The second chemoreceptor is for oxygen. And in about 10% of the population,

it doesn't work very well. For non-pilots, this results in Altitude-Mountain

Sickness (AMS). Skiers run into this. When my wife and I went skiing at

Copper Mountain Colorado, (base elevation 9,700 MSL) she got AMS. She

doesn't get the normal drive to increase breathing when her oxygen level

gets low. So when we ski, Nancy takes a drug called Diamox (Acetazolamide)

for 5 days. This drug makes her blood a bit acid, and tricks the CO2

chemoreceptor into making her breathe faster. Now she doesn't get AMS. Of

course, carbonated beverages taste awful...



Many pilots may be subject to AMS when at high cabin pressure altitudes.

They may get hypoxic, sleepy, disoriented, and so on. The cure is oxygen and

lower altitude. This cause of hypoxia CAN be overcome with oxygen, unlike

shunting. It just takes a bit more, since the CO2 level in the lungs is

higher, taking up more of the space for oxygen.



The precaution? An oximeter is again an excellent idea. Diamox is a lousy

idea, since you must start the day before, and if you fly frequently you run

into a host of drug issues that are beyond this posting.

Ted Noel MD



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>> A 90% SaO2 is the normal level of ogygen in your veins, not your

arteries. As such, it should be an absolute lower limit of SaO2 to fly.

Below that you get in trouble FAST. (Again, I won't reproduce the graphs or

equations.)<<



Ted,



Have YOU ever flown to 15K or higher with a pulse oximeter, unpressurized?



I do this often and with a wide variety of pilots.



In my experience,  only  a third of the pilots will maintain more than about

87% using nasal canulas.  NONE are in trouble.



I have seen a significant percentage of people that show  as low as 78 to

83% at 18000', on the pulse oximeter and they stayed that way for hours and

were just fine.



Now... don't jump on me here.  I know that in a hospital setting, somebody

that low is a candidate for a code blue, but it is  *** IN FACT ***  correct

data for people (including myself) who have flown at altitude for years on

nasal canulas.



The first time I saw that on a pulse oximeter,  I was hugely surprised!!!  



I then cranked up the nasal canula flow rate to use the MASK flow rate and

that brought my personal level up from 83 to about 87.



Using the Mountain High pulse units,  I can keep my O2 sat on the pulse

oximeter up in 89 to 92 range routinely.



I absolutely ***DO*** feel much better when I do that at the end of a 3 hour

flight.    



However,  there is something weird going on here between the medical

understanding of  O2 saturations and the real world pilot measurement with

oximeters, since a LOT of pilots fly around at 15 to 18K on canulas, and a

significant  percentage of them have O2sats on the oximeter that are below

85%.



Regards,  George

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Posted for "Eric M. Jones" <emjones [at] charter.net>:



Lack of oxygen is not sensed by the body. What happens when we feel "short

of breath" is that the body responds to excess of CO2 to tell the brain that

there is an oxygen shortage. This worked well on the African savannahs, but

where the oxygen is thin, the CO2 never gets excessive.



In the 1930's when all this was being worked out, it was claimed that

providing the aviator with 3% CO2 (!) would allow him to fly at 17k with the

mental performance of 12k. I leave it to flight surgeons to puzzle this

out---my guess is that it is true.



There were also animal experiments that detailed how long one could survive

at 75k and recover if you were then given oxygen (17 seconds or so as I

recall).



In skydiving one soon discovers that if you want to build a formation, no

advantage is gained above 13k without oxygen; that is, the longer freefall

time is offset by the poor coordination of the participants. I have jumped

from almost 16k (and above 13k for an hour) without oxygen and it is

extremely unpleasant.



Eric

    There have been a lot of good posts on this subject recently - enough information to make anyone think twice about the effects of hypoxia. I think there has been one important factor that has not been mentioned, and that is the time a person has to aclimitize to the higher elevations. Anyone who has spent time in the mountains knows that the body can function very well at high altitude.  I have spent many days at elevations in excess of 15,000 feet, several times over 17,000 feet, including a climb to an 18,300 foot peak. The only effect I felt at the time was very rapid heart and respiration rates during the last several hundred feet of the climb. Also often experienced waking at night gasping for breath (Cheyne-Stokes breathing?). However, there were no lasting effects to report, except possibly the loss of a couple IQ points -- perhaps that's how I got involved in building one of these airplanes!!??!!

   The point of this rambling is that I spent a week or more getting to those high elevations while you who climb into your high performance airplanes can get there in a matter of minutes.

                           Charles





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