High altitude flight (relatively speaking)

[Hank]

7 hours ago, tgardnerh said:

Which direction is your experience--do you find that for a given pressure higher DA means worse oxygen saturation? On first principles (and per my wife, who did a year of anesthesia before switching to IM), the air at the alveolar membrane is 98.6 degrees and 100% RH, so ambient temperature *shouldn't* matter.

Ambient conditions matter because that determines what you inhale. Air at sea level on a standard day outs much higher O2 partial pressure to you lungs than is available at 10,000 msl when temps are ISA +20°C.

[Jeff Uphoff]

On 7/16/2023 at 10:05 PM, M20F said:

The RayJay adds a few pounds but it makes up for it. 

I took my '65 M20C up to FL205 once, and it didn't have a Rajay--nothing more than normal aspiration.

I still had 300-400 FPM climb left in her--it was a cool day, and I was light--but I didn't have an oximeter along and so chose not to push my luck by going any higher. (ATC had given me a block up to FL220, as I recall.)

--Up.

[M20F]

34 minutes ago, Jeff Uphoff said:

I took my '65 M20C up to FL205 once, and it didn't have a Rajay--nothing more than normal aspiration.

I still had 300-400 FPM climb left in her--it was a cool day, and I was light--but I didn't have an oximeter along and so chose not to push my luck by going any higher. (ATC had given me a block up to FL220, as I recall.)

--Up.

One of Bill Kershner’s protégés took a 150 to 18000 and spun it all the way down.  If a 150 can make it, anything can make it. 
 
I want to say there was a T210 that got to FL380 or thereabouts.  I looked around for that one and can’t find it. 
 

 

[tgardnerh]

3 hours ago, Hank said:

Ambient conditions matter because that determines what you inhale. Air at sea level on a standard day outs much higher O2 partial pressure to you lungs than is available at 10,000 msl when temps are ISA +20°C.

Ambient conditions change what goes into your nose, but by the time it reaches the gas exchange membrane in your lungs, the gas is going to be 98 degrees, 100% RH, 21% oxygen, and whatever the ambient pressure is. The only part that depends on the ambient conditions is pressure, so pressure altitude should be what controls the partial pressure of oxygen where it counts (unless you boost the %O2 of course).

[ilovecornfields]

10 hours ago, tgardnerh said:

Which direction is your experience--do you find that for a given pressure higher DA means worse oxygen saturation? On first principles (and per my wife, who did a year of anesthesia before switching to IM), the air at the alveolar membrane is 98.6 degrees and 100% RH, so ambient temperature *shouldn't* matter.

But also a stunning number of things in medicine that come down to "ehh, it seems like this causes that, nobody knows why," so I know better than to trust first principles here.

I’ve found that my oxygen saturation seems to correlate more with density than pressure altitude. I agree with your wife about the temperature and humidity but not on the IM switch - I hated taking the internal medicine boards. I might reach out to someone who actually studied aerospace medicine and try to get a rap answer.

I did do some more reading and found this which suggests that the oxygen uptake depends on partial pressure of oxygen. I guess the part I’m still not sure about is the effect of density altitude. Let’s say you take a deep breath and hold it - at higher density altitude you’ll have less oxygen molecules in your lungs than you would at a lower density altitude. As the oxygen gets replaced by CO2 I would imagine it would take less time to see your oxygen level drop because there’s less oxygen there to begin with. At lower density altitudes there are more oxygen molecules so it seems you would take longer to desat. Since there are other physiologic changes with altitude and temperature as well I’m not sure how these all balance out.

I do know what my numbers seem to correlate more with density than pressure altitude but maybe I’m imagining the effect. I’ve never rigorously studied it.

“Oxygen combines with hemoglobin, although much less avidly than does carbon monoxide. The partial pressure of oxygen in blood flowing through the pulmonary capillaries equals the partial pressure of oxygen within the alveolus by the time the red blood cell travels along about one third of the capillary length.

Diffusion of oxygen across the alveolar capillary membrane is normally perfusion limited.”

https://www.medmastery.com/guides/blood-gas-analysis-clinical-guide/diffusion-versus-perfusion-limited-gas-exchange
 

[Rick Junkin]

21 hours ago, aviatoreb said:

I have the exact model - its fantastic - especially because it is doing continuous O2Sat monitoring and vibrates when you are too low - like low 90s is it?

The level at which the alarm vibrates is adjustable through the iPhone app.

I have mine set at 88%. After a career of visiting the altitude chamber every 5 years for an aerospace physiology refresher course I learned my critical O2 sat level is 85%. Yours will be different. Up to that point I still have good cognitive capacity, but lower than that things start to go down hill. And I consistently recognize my hypoxia symptom onset at 85%. That has saved me a couple of times when I had a pinched O2 line and didn't realize it until symptom onset. That was before I got the Wellue O2 ring. Had I been wearing it I would have been alerted earlier to look for a problem sooner.

All of the technical and academic discussion is interesting, but knowing how to recognize and immediately mitigate hypoxia is the goal. Everyone is affected differently and at different conditions, and these can vary from day to day. O2 saturation monitors are a great tool but as has been discussed already they can have limitations, especially if you aren't using a wearable monitor.

I highly recommend prioritizing attendance at a Pilot Reduced Oxygen Training Enclosure (PROTE) or baro chamber training session as part of every pilot's continuing training plan. Experiencing and learning to recognize your own early hypoxia symptoms can be life saving. This training is free, you just need to sign up and travel to Oklahoma City, or find an event where the PROTE will be available. The Civil Aerospace Medical Institute (CAMI) travels around the country with the PROTE to make it as widely available as possible. We were fortunate to have it at the Mooney Summit a few years ago.

Here's the link to information on attending the training in Oklahoma City. https://www.faa.gov/pilots/training/airman_education/aerospace_physiology

Click on the "How To Enroll at the CAMI Training Facility" link on this page to get signed up. https://www.faa.gov/pilots/training/airman_education/aerospace_physiology/cami_enrollment

For those who want the Reader's Digest version, here's the number to call.

To obtain available class dates and/or enroll for class seats please call (405) 954-4837, Monday through Friday from 7:30 AM to 4:00 PM (CT).

I haven't figured out where to find a schedule of where the PROTE will be and when, but I'm still looking.

Cheers,
Rick

[Pinecone]

On 7/19/2023 at 10:55 AM, ilovecornfields said:

I think your experience is pretty typical and representative of the FAA’s dated guidance on the subject. Most CFIs at the pilot mill schools don’t seem to do a lot of XC trips (since they can’t afford it) so they do a poor job teaching about real-world hypoxia and oxygen use in primary training. 

There is no density altitude issue as the air in your lungs is maintained at the same temp and humidity through most conditions.  So only pressure matteres.

[M20F]

If this was a Bonanza forum we would have a doctor to tell us how O2 works.  Time to go to Beechtalk.  

[Ragsf15e]

1 hour ago, M20F said:

If this was a Bonanza forum we would have a doctor to tell us how O2 works.  Time to go to Beechtalk.  

Or a lawyer to help us figure out a way to file some lawsuits against someone for our low pulse ox readings!

[Ragsf15e]

Trying out a new (and expensive) inogen G5 right now. At 8500’, I was 90 without it, ~96 with it on setting 4.

The battery is good for a couple hours, but charging it isn’t necessarily easy as the dc adapter draws 10amps at 12v!  My cig lighter is only 3amps.  Tested the circuit breaker though, it works!

[ilovecornfields]

44 minutes ago, Pinecone said:

There is no density altitude issue as the air in your lungs is maintained at the same temp and humidity through most conditions.  So only pressure matteres.

I understand that concept and quoted that as well, but it doesn’t match my empirical observations and seems a little simplistic. Maybe my observations are wrong, or maybe there’s more to it. If “only pressure matters” then that means there are no other significant physiologic effects with change in temperature and we know that’s not true. Changes in respiratory rate, tidal volume, heart rate, metabolic oxygen demand and even the sensation of dyspnea are all affected my temperature so I’m not sure I’m ready to say “nothing else matters.”

I couldn’t find a study on this so I’m going to do one- for the next year, one hour into my flight I’m going to take the oxygen off and see where my SpO2 stabilizes. I’ll use the same pulse ox and finger and record the HR, SpO2, indicated altitude, pressure altitude, inside air temperature and outside air temp. Then I’ll plot things out and see what fits best. I’m going to hypothesize that “cabin density altitude” will provide the best fit, but we’ll see. Anyone else want to do the same?

[GMBrown]

If you want O2 training on the west coast, Edwards AFB installed a new high altitude chamber in 2017 (Bldg 1250) and it is available for civilians.  Contact the training center at 661-277-3958/3978 for details/scheduling.

[Rick Junkin]

8 hours ago, ilovecornfields said:

I couldn’t find a study on this so I’m going to do one- for the next year, one hour into my flight I’m going to take the oxygen off and see where my SpO2 stabilizes.

Umm... you'll be flying with a safety pilot who remains on O2 while you do this, correct?

[tgardnerh]

I understand that concept and quoted that as well, but it doesn’t match my empirical observations and seems a little simplistic. Maybe my observations are wrong, or maybe there’s more to it. If “only pressure matters” then that means there are no other significant physiologic effects with change in temperature and we know that’s not true. Changes in respiratory rate, tidal volume, heart rate, metabolic oxygen demand and even the sensation of dyspnea are all affected my temperature so I’m not sure I’m ready to say “nothing else matters.”
I couldn’t find a study on this so I’m going to do one- for the next year, one hour into my flight I’m going to take the oxygen off and see where my SpO2 stabilizes. I’ll use the same pulse ox and finger and record the HR, SpO2, indicated altitude, pressure altitude, inside air temperature and outside air temp. Then I’ll plot things out and see what fits best. I’m going to hypothesize that “cabin density altitude” will provide the best fit, but we’ll see. Anyone else want to do the same?

Here's a conjecture that reconciles the theory and experience:
When it's hot out, we spend a non-trivial amount of energy rejecting heat, managing sub-clinical dehydration, and otherwise using up our physiological reserve. This both increases our O2 demand (so we get hypoxic faster), and impairs our cognition, so it becomes an ADM sooner.

Re: internal medicine, she's freakishly good at keeping many many balls in the air at once, and at noticing when something is just not quite right. Its like her personality is perfect for IM (and a great case study of why its good I never got into med school).


Sent from my iPhone using Tapatalk

[Hank]

44 minutes ago, tgardnerh said:

Its like her personality is perfect for IM (and a great case study of why its good I never got into med school).

Freshman Chemistry was all I needed to avoid any and all medical-related occupations. So I ended up in plastics, then medical device manufacturing. But as an engineer, no doctor-type stuff required. Don't even need doctor-level statistics.

[ilovecornfields]

4 hours ago, Rick Junkin said:

Umm... you'll be flying with a safety pilot who remains on O2 while you do this, correct?

Safety pilot, shmafety pilot.

I actually rarely fly above 12k’. Of course if I see my sat dropping I’ll just put on the oxygen and abort the experiment. I’m not going to sacrifice myself in the name of science.

[Pinecone]

20 hours ago, M20F said:

If this was a Bonanza forum we would have a doctor to tell us how O2 works.  Time to go to Beechtalk.  

What do you want to know about how O2 works?

Gas exchange in the lungs is driven by the partial pressure of O2 in the lungs.  So at sea level (14.7 PSI, 21% O2) you have a partial pressure of just over 3 PSI.  The minimum allowable O2 concentration for workers under OSHA is 16.5%, or a sea level partial pressure of about 2.42 PSI.  But the OSHA limit is based on work at concievable altitudes.  So in Denver (12.23 PSI), that same 16.5% is a partial pressure of 2.02.

The air pressure at 10,000 feet is 10.1 PSI, so normal air (21% O2) gives you a partial pressure of 2.12, or better than Denver at the OSHA minimum O2 %.  

At 20,000 feet, the pressure is 6.75 PSI or a partial pressure of O2 of 1.42 PSI.  Which is not good.  So what we do is increase the % O2 in what we are breathing to increase the partial pressure.  So at 20,000 feet, if you raise the O2 % to 30%, you get a partial pressure of 2 PSI, or about the OSHA minimum in Denver.

[aviatoreb]

7 hours ago, ilovecornfields said:

Safety pilot, shmafety pilot.

I actually rarely fly above 12k’. Of course if I see my sat dropping I’ll just put on the oxygen and abort the experiment. I’m not going to sacrifice myself in the name of science.

You could bring some mosquitoes and get bitten by the Malaria infection or perhaps give yourself bacterial ulcers or something good.  This isn't exciting enough.

[Hank]

21 hours ago, ilovecornfields said:

I couldn’t find a study on this so I’m going to do one- for the next year, one hour into my flight I’m going to take the oxygen off and see where my SpO2 stabilizes. I’ll use the same pulse ox and finger and record the HR, SpO2, indicated altitude, pressure altitude, inside air temperature and outside air temp. Then I’ll plot things out and see what fits best. I’m going to hypothesize that “cabin density altitude” will provide the best fit, but we’ll see. Anyone else want to do the same?

1 hour ago, aviatoreb said:

You could bring some mosquitoes and get bitten by the Malaria infection or perhaps give yourself bacterial ulcers or something good.  This isn't exciting enough.

This is hardly Dr. Jekyll level of self-experimentation!

[aviatoreb]

2 hours ago, Hank said:

This is hardly Dr. Jekyll level of self-experimentation!

no - true - but Dr Jekyll didn't win a Nobel prize...

[Hank]

2 hours ago, aviatoreb said:

no - true - but Dr Jekyll didn't win a Nobel prize...

I bet if Hyde had asked for one, they'd have given it to him. If the Prizes had been established by then . . . .

[ilovecornfields]

The closest I’ll ever get to winning a Nobel prize was parking my motorcycle in the “Nobel Laureate” parking space in college.I figured if they gave me a ticket I could always just ask for a refund once I won my Nobel prize. I miss being young and knowing everything.
 

Not to brag, but I don’t think @aviatoreb’s department had any “nobel laureate” parking spaces. They did have the Unabomber, though.

[aviatoreb]

3 hours ago, ilovecornfields said:

The closest I’ll ever get to winning a Nobel prize was parking my motorcycle in the “Nobel Laureate” parking space in college.I figured if they gave me a ticket I could always just ask for a refund once I won my Nobel prize. I miss being young and knowing everything.
 

Not to brag, but I don’t think @aviatoreb’s department had any “nobel laureate” parking spaces. They did have the Unabomber, though.

Berkeley - yes - I was there too.  I know exactly where that Nobel parking lot is.  They have the coolest parking sticker for their Nobel cars .    I heard they gave parking passes on a special basis to fields medalists (math) (even though there is no Nobel in math reputed because of some affair).  But the unibombef didn’t win the Nobel or fields.

[ilovecornfields]

1 hour ago, aviatoreb said:

But the unibombef didn’t win the Nobel or fields.

No, but he was an assistant professor in the math department.

[aviatoreb]

10 hours ago, ilovecornfields said:

No, but he was an assistant professor in the math department.

Boy I misspelled that.

I thought he was just an instructor.