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Anyone with Aviation Physiology Knowledge?

wawrzynskivp

Well Known Member
Hello All,

How do we use a Pulse Oximeter if we don't live at sea level?

AOPA articles suggest we keep our oxygen saturation above 95% on our pulse oximeters as we climb unpressurized. I live at 6,800' and play much higher. I just got a pulse oximeter with waveform display and PI% ( a good one ). Sitting on my couch I put it on and saw 90-92% oxygen saturation!

I have done the hypoxia chamber many times so I know when I am hypoxic, at that moment I was not. The device must be wrong?

According to available articles and a few folks who work in the general medical industry, what I saw was normal for where I live. Long term exposure to reduced partial pressures of O2 encourage the body to maintain more red blood cells. So normal oxygen transport happens with lower blood saturation.

Okay, great I get that. Probably why it wasn't a struggle to fly around sans oxygen at cabin alts in the 20s when I was wearing a bag.

But how now do I (or anyone else who lives and breaths at altitude) use a pulse oximeter? Anyone come across guidance for this?

Obviously there is trial and error, the 'E' in experimental. But in this case that's probably not the way to go at least not in the cockpit.
 
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O2

No physiology knowledge. Just a data point. I live at 7500'. Sitting at rest, my level is 94. Same at the doctor recently for my physical. Doctor said it was good.
Riding the elliptical, it fluctuates from 88-92 and I'm breathing pretty deep. Comes right up when I stop.
 
No physiology knowledge. Just a data point. I live at 7500'. Sitting at rest, my level is 94. Same at the doctor recently for my physical. Doctor said it was good.
Riding the elliptical, it fluctuates from 88-92 and I'm breathing pretty deep. Comes right up when I stop.

Exactly! So for us, sucking O2 to get to 95% as we taxi for takeoff isn't an economical or meaningful effort. But we do have a number on our pulse oximeters that has meaning for us, how do we find that? A deprivation experience (hypoxia trainer) would do but they just aren't popular enough to be readily available. Looking for the published data.
 
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The way I did it was to fly and carefully monitor my feeling and alertness, comparing that to the reading. I had to do that a number of times to get an idea of what generally to look for. I expect that it'll vary per each person's individual requirements.

Dave
 
Below 85 on room air, reason for concern. If flying at that time dive or get on supplemental O2. EVERYONE physiology is a bit different. My comments are based on being a Respiratory Therapist. YMMV , but I wouldn’t want my O2 sat below 90 if flying.

Yesterday’s response is not a exact indicator of how you might respond today.
 
I'm a fly on the wall. I have an oximeter and play with it. I am at sealevel and sitting in front of the computer I'm at 99/52 percent/pulse. I would like to know an oximeter reading where I should start being concerned.
 
I live at 8000' and I just took a reading and it was 97%. I don't think oxygen saturation is suppose to be altitude compensated, normal levels should be 95% or above no matter what altitude.
 
I live at 8000' and I just took a reading and it was 97%. I don't think oxygen saturation is suppose to be altitude compensated, normal levels should be 95% or above no matter what altitude.

Not sure that's universally correct. Pitfalls of Pulse Oximetry at High Altitude: "Clearly, oxygen saturation should decline with increasing altitude, but what constitutes a ‘‘normal’’ saturation for a given elevation is not entirely clear." Ref: https://hoehenmedizin.eu/wp-content/uploads/2014/07/Pulse-Oximetry-at-High-Altitude.pdf

Once acclimatized to high altitude our physiologies no longer match those acclimatized to sea level pressure. Red blood cell count and blood chemistry actually changes. So yes, a person who recently arrives at 10,000' and has a SPO of 92% is partially hypoxic. But a person acclimatized to those partial pressures is not, even at the same SPO.
 
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Past President of Aerospace Physiology Society

That's the challenge with pulse oximetry and searching for the number at which cognitive deficit from altitude hypoxia creates an unsafe environment.

A couple things to consider. There are 4 types of hypoxia and their effects are cumulative. Stagnant, Hypemic, Hypoxic, histotoxic. A 90 pulse ox doesn't mean the same thing for each of us.

Experimental doesn't mean with us. I used to get frustrated when I put a general aviation pilot in the altitude chamber and they brought their pulse ox with them so that they could correlate what they felt with what they saw on the device.

The military uses 10,000 ft as the threshold for supplemental O2. The FAA uses 12,500. So who is right. Well if you do the math the partial pressure of Oxygen at 10,000 is the right threshold. But the FAA wanted to support parachute operations so allowed higher for 30 min.

While living at altitude definitely provides for physiologic accommodations, such as increased O2 carrying capacity, which helps tremendously when exercising. But for hypoxic hypoxia the math is still the same.

I bring oxygen along every time that I am above 10,000ft, especially at night time. I also monitor pulse ox and if I see anything below 90 Im descending or applying supplemental oxygen. Because I know that low levels of hypoxia are actually more dangerous than acute hypoxia. Because when hypoxic you become a poor judge of your own cognitive deficit.

Thanks for starting the discussion.
 
...and

"...I have done the hypoxia chamber many times so I know when I am hypoxic,..."

...and the perfect reply...

"...low levels of hypoxia are actually more dangerous than acute hypoxia. Because when hypoxic you become a poor judge of your own cognitive deficit..."
 
Thanks Bugsy

Thanks for chiming in, good stuff.

I am in no way fencing with FARs on oxygen usage, rules are rules.

My focus and I am sure you got that was to take a look at the meaning of our Pulse Oximeter numbers. Starting with < 95% as an assumption for supplemental oxygen usage based on SPO may not make sense for everyone. Again, not meddling with FARs just SPO% interpretation.

I taxi around at 5,800' when I leave my hangar. SPO% will be <95% on my oximeter which I have no reason to believe is inaccurate (though just for fun I have a different one on the way for comparison). To beg the question: Is supplemental oxygen called for while I am taxiing?

Acclimatization doesn't affect FARs. But it does seem to affect the interpretation of SPO%

I agree that low level hypoxia is insidious. But I am not at all sure that the AOPA numbers on SPO% that suggest I am living 24/7 in low level hypoxia are dangerous or even meaningful to me. So what is meaningful SPO% for someone acclimatized to high altitude? (the land crawler definition of high altitude >5,000')
 
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Hypoxia

Having spent four years in the Air Force demonstrating hypoxic hypoxia in the chamber, don’t underestimate the insidious nature of low altitude hypoxia. At 43k feet you have roughly 7 seconds to get a pressure mask on, 30k maybe a couple of minutes, but at the lower flight levels you have all the time in the world to drift into a debilitated state of compromised skill or worse.
 
I use pulse oximetry with patients for my day job every day in Denver (at ~5300'). Healthy people run anywhere in the 91-97% range without supplemental oxygen and we view that as normal.

One thing to remember with pulse oximetry is that it uses an internal lookup table (based on series of healthy volunteers) to convert absorbed light ratios to SpO2 %. So even if the measured absorption is perfect, there will be some variability from person to person. In the hospital, we often see differences of several percentage points between the saturation measured with pulse oximetry and that measured by running an arterial blood sample through a gas analyzer.

If it were me (this isn't medical advice), I would find my personal baseline with that particular device at my home elevation. Then, I could use deviations from my baseline as a warning sign. I would not, however, take a normal oximetry reading as a guarantee that all is well.
 
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Thanks for chiming in!

I use pulse oximetry with patients for my day job every day in Denver (at ~5300'). People run anywhere in the 91-97% range and we view that as normal.

One thing to remember with pulse oximetry is that it uses an internal lookup table (based on series of healthy volunteers) to convert absorbed light ratios to SpO2 %. So even if the measured absorption is perfect, there will be some variability from person to person. In the hospital, we often see differences of several percentage points between the saturation measured with pulse oximetry and that measured by running an arterial blood sample through a gas analyzer.

If it were me (this isn't medical advice), I would find my personal baseline with that particular device at my home elevation. Then, I could use deviations from my baseline as a warning sign. I would not, however, take a normal oximetry reading as a guarantee that all is well.


Thanks for that!
 
Duck,

The article Pulse Oximetry at High Altitude pointed out that excess ambient light may produce errors in pulse oximetry readings. I've experienced this myself as RV cockpits are flooded with light. It's difficult to shade the oximeter sufficiently and still be in a position to see the readout.
 
Duck,

The article Pulse Oximetry at High Altitude pointed out that excess ambient light may produce errors in pulse oximetry readings. I've experienced this myself as RV cockpits are flooded with light. It's difficult to shade the oximeter sufficiently and still be in a position to see the readout.

Thanks! That's good to know.
 
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With regard to those who live at high altitude

Duck, Thank you for this discussion.

Your question about living at altitude and measured SPO2

When I was in the service I visited an Indian AB in the Himalayan Mountains. I was stationed in Okinawa so not acclimated to altitude at all. Brought along a bunch of pulse oximeters to look anecdotally at your question. Here is what I found with an N=1 study. When visiting the installation at 16,000 feet. My pulse ox was 88%, another AF physiologist stationed in Albuquerque had pulse ox of 91. The Native born soldier that grew up in Leh India had a pulse ox of 98%. We were taking a medication called Diamox that helps with the CO2/pH imbalance that occurs when we hyperventilate at altitude in response to low O2. Allowed us to breath heavier without getting dizzy.

We know from published studies that the greatest accommodation to altitude occurs from increased ventilation and lung volume for those born at altitude. For those that acclimate to altitude but not born there we see increased Red blood cell density helping with O2 carrying capacity and your muscles ability to scavenge oxygen from the blood. But your still not anything as good as a native born sherpa.

Started my 7A build when stationed at Albuquerque. If I still lived at 6.5K, Id probably take that into consideration personally like you are. But I would also have a tank of O2 in my hanger to refill myself cause I would be facing this question daily. Remember vision is the first effected by low grade hypoxia. So if night flying, I would lower my threshold substantially.
 
When flying with the oximeter at altitude I find I can increase my oxygen saturation by deep, rapid breathing/hyperventilating. Is there a downside to this, does this have the same effect as using supplemental oxygen?
 
When flying with the oximeter at altitude I find I can increase my oxygen saturation by deep, rapid breathing/hyperventilating. Is there a downside to this, does this have the same effect as using supplemental oxygen?

Deep breaths, as opposed to shallow ones, get new air and O2 deep into the lungs. With shallow breaths, a lot of the new air just goes down your throat, then is exhaled back out. Sort of why there are re-breather bags on masks, but carried to an extreme. Not sure I would recommend hyperventilating, that can mess with CO2 levels which bring about their own issues.
 
When flying with the oximeter at altitude I find I can increase my oxygen saturation by deep, rapid breathing/hyperventilating. Is there a downside to this, does this have the same effect as using supplemental oxygen?

The target is not a number on a pulse oximeter, it's appropriate blood oxygenation. You may be able to temporarily increase that by some type of breathing techniques, but you can't do it for long. Rapid breathing to correct oxygen saturation comes at the expense of decreased CO2 and an increase in the blood's pH. You have to keep those three components in appropriate balance in the blood - oxygen, carbon dioxide, and pH. Very complex process. The only thing you can do to keep them all in balance when pO2 begins to drop is increase the percentage of O2 in the air that you're breathing.
 
back pressure while exhaling

When my mom was recovering from lung cancer and had reduced lung capacity, the doc looking after her gave her a technique that seems to work for us as well - increase the "back pressure" when you exhale. I was playing with this technique while flying with the oximeter and no o2 and I was able to increase the number on the oximeter - no idea if that translated into clearer thinking - that's a bit harder to measure.
 
When my mom was recovering from lung cancer and had reduced lung capacity, the doc looking after her gave her a technique that seems to work for us as well - increase the "back pressure" when you exhale. I was playing with this technique while flying with the oximeter and no o2 and I was able to increase the number on the oximeter - no idea if that translated into clearer thinking - that's a bit harder to measure.

This technique is used in endurance sports such as long distance running, instead of just exhaling from open mouth, blow out through pursed lips.

Hyperventilation reduces CO2. Increased CO2 triggers the brain to breath. This can be dangerous if you are holding your breath under water but I don't think it would be a factor hyperventilating while flying. Base camp for Everest is around 17,500' and folks are not on oxygen.
 
Agree with Bugsy

As internal medicine doctor, totally agree with Bugsy. Using pulse ox during xcountry at 12,000 agl I am amazed how quick I get below 90% Satn, and slow down mentally &#55357;&#56842;
 
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What no one has discussed specifically, but some have touched on indirectly, is the relationship between oxygen saturation as measured by the pulse oximeter and the partial pressure of oxygen in blood, which is measured by what is typically called "arterial blood gas". This level - actual pressure of dissolved oxygen in the blood (which decreases with increasing altitude) is expressed as PO2 or pAO2.

What's important is that the relationship between this level (PO2) and oxygen saturation (what we measure with the finger thingy), as demonstrated by studying and understanding the "oxy-hemoglobin dissociation curve" (https://en.wikipedia.org/wiki/Oxygen–hemoglobin_dissociation_curve), is non-linear.

While I do agree that acclimatization is a factor in tolerance of low inspired oxygen levels (as found at higher altitude), that represents only a part of the story. More importantly, this adaptive process takes a long time, and is practical only if you intend to live a long time at high altitude. It has a number of components, including increased hemoglobin / hematocrit (more red blood cells), changes in pulmonary (lung) vascular capacity, and metabolic changes that "shift" the oxy-hemoglobin dissociation curve in a favorable direction - however that might actually represent a hidden risk as there comes a point where this adaptation may tend to mask a much more significant risk. (see next paragraph).

What's most important to understand about this curve is that when oxygen saturation (the measurement from the finger tip device) falls below around 90% (for most people), there quickly comes a point where the oxygen saturation will fall much more rapidly than might be intuitively expected: in other words, a very small change in inspired oxygen (which DOES have a linear relationship with pAO2 and thereby changes in altitude but NOT with oxygen saturation) below 90% oxygen saturation can result in much more significant desaturation and rapid deterioration of cognitive capacity. This is masked by the relatively minor drop in oxygen saturation initially - as PO2 falls from the normal level of 100 or so, to around 65-70% of normal (or even 50% for the "acclimated"), the saturation level will stay pretty high - mostly above 90%. But then as PO2 falls below these levels, oxygen saturation "falls off the cliff" of the curve.

I haven't seen articles recommended maintaining 95% saturation - I have seen some recommending 90%. The main point here is that 90% is (generally) a safe "floor" for oxygen saturation as a target to maintain with supplemental oxygen - anything less and there is substantial risk of very rapid loss of cognitive capacity once this "floor" is broken. Even this rule may not be safe for someone who has underlying medical issues like lung disease, anemia, heart disease etc. I personally - given my age and its risk of yet undiagnosed conditions - might try to use 91 or 92% as a safe "floor". (If AOPA says 95% that's fine but would probably require supplemental oxygen for most people at relatively low altitudes - and many perfectly healthy people have a baseline around 93-95%).

Thinking you can push the envelope just a little more beyond the safe "floor" could get you into big trouble really fast. As others have pointed out, the cognitive decline is insidious and part of the nature of hypoxemia is that you may be incapable of recognizing your own incapacity. I recall once watching a bird colonel sitting dumb and happy in the altitude chamber while an NCO was yelling "sir, put your oxygen mask on or you will die!". As a young flight surgeon, that made a big impression on me...

Regarding question of increasing breaths/depth of breaths: deliberate hyperventilation is a recipe for disaster. You run the risk of incapacitating yourself with either runaway hyperventilation and the resultant physiologic effects that include high pH (alkalosis) and resultant carpopedal spasm (uncontrollable muscle cramps) or eventual respiratory fatigue - inability to maintain the level of hyperventilation needed for desired saturation level.

I'm not by the way recommending anyone target a particular number but just sharing my own experience based on years of practice and training "back in the day" as a flight surgeon. As always, talking with your own healthcare provider is a wise approach.
 
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When flying with the oximeter at altitude I find I can increase my oxygen saturation by deep, rapid breathing/hyperventilating. Is there a downside to this, does this have the same effect as using supplemental oxygen?

Looky here: https://www.uptodate.com/contents/image?imageKey=HEME/81216

When you hyperventilate, you blow off a bunch of CO2, PH increases and you end up on the left-shifted curve. O2 affinity increases which means hemoglobin cannot offload oxygen to the tissues as easily.
The important thing is that your pulse oximeter will show higher O2 levels (you will see a cool 100% if you do this on the ground), but you can't use it.

Slow deep breathing is a much better idea. Keeps in more CO2, PH decreases, curve gets right-shifted, and you can use more oxygen even though you have less to work with, because hemoglobin lets go of them easier.

I'm no physiologist, just like to know how stuff works. A while ago I bought myself a Novametrix Capnography / SpO2 machine that measures and charts CO2 and SpO2 levels, and did some Wim Hof breathing experiments, which is a form of hyperventilation combined with breath holds. Not going to get into the details but just know that lots of freaky things happen during hyperventilation, please don't do it while flying.
 
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This is a great Thread! With all the right components:

--Highly Educational
--Challenges one's previously held beliefs
--Engaging
--Involves Expert Opinion
--Cooperative and supportive
--Potentially life-saving

Fantastic! Rock On..
 
Safety Reminder, not a response to any post

Just for anyone who might have jumped in late:

This discussion is NOT about FARs on oxygen usage, those are our standard practices and are not lessened by pulse oximeter usage. But we may consider using oxygen earlier than FAR requirements if we fully understand what our pulse oximeter feedback means.
 
When my mom was recovering from lung cancer and had reduced lung capacity, the doc looking after her gave her a technique that seems to work for us as well - increase the "back pressure" when you exhale. I was playing with this technique while flying with the oximeter and no o2 and I was able to increase the number on the oximeter - no idea if that translated into clearer thinking - that's a bit harder to measure.

Not a doctor but a flight paramedic who flies lot of intubated/ventilated patients.

This is called "PEEP" or Positive End Expiratory Pressure, and is essentially one of two ways to increase O2 saturation (the other being increased FiO2, or percentage of oxygen in the air your are breathing in). It is generally helpful in people with issues like reduced lung compliance from disease or fluid in the lungs (like in CHF). PEEP helps keep the alveoli (the little sacks where gas exchange occurs) open and adds more surface area to them to increase gas exchange. Sick COVID patients often need massive amounts of PEEP.

In a normal healthy lung, it would be interesting to see how much a little PEEP would improve oxygenation at altitude. You would need a tight-fitting mask to use it, but maybe it could somewhat lower oxygen demand?

Chris
 
Not a doctor but a flight paramedic who flies lot of intubated/ventilated patients.

This is called "PEEP" or Positive End Expiratory Pressure, and is essentially one of two ways to increase O2 saturation (the other being increased FiO2, or percentage of oxygen in the air your are breathing in). It is generally helpful in people with issues like reduced lung compliance from disease or fluid in the lungs (like in CHF). PEEP helps keep the alveoli (the little sacks where gas exchange occurs) open and adds more surface area to them to increase gas exchange. Sick COVID patients often need massive amounts of PEEP.

In a normal healthy lung, it would be interesting to see how much a little PEEP would improve oxygenation at altitude. You would need a tight-fitting mask to use it, but maybe it could somewhat lower oxygen demand?

Chris

High performance military aircraft use pressurized masks for high altitude/unpressurized flight which in effect provide "PEEP". I found the most interesting part of training on this method is that you have to learn how to open glottis to breathe / talk when on pressurized oxygen. As a practical matter I don't think it would work in the GA application - the cost of a safe/usable system and approved regulators/ properly fitted masks would be pretty significant.
 
High performance military aircraft use pressurized masks for high altitude/unpressurized flight which in effect provide "PEEP". I found the most interesting part of training on this method is that you have to learn how to open glottis to breathe / talk when on pressurized oxygen. As a practical matter I don't think it would work in the GA application - the cost of a safe/usable system and approved regulators/ properly fitted masks would be pretty significant.

I actually built a system using standard military regs, hoses, mask, etc, and used it in the RV just to see how it worked - which was fine, but of course, it used O2 at a prodigious rate in 100%/Pressure mode. That’s fine if you’ve got a LOX system in a large airplane providing a supply, but with a portable O2 bottle that is practical for an RV, the duration is pretty disappointing….

Not practical, unless the goal is a short-duration race or high altitude attempt.

Paul
 
Wow, VAF continues to be an amazing resource! I count about 4 MD's and a specialist in flight physiology who have chimed in on this thread - thanks to all!

A question to this group: would our respiration and/or heart rates increase as we go to altitude? Meaning, would this be a normal response to lower PO2 levels?
 
Wow, VAF continues to be an amazing resource! I count about 4 MD's and a specialist in flight physiology who have chimed in on this thread - thanks to all!

A question to this group: would our respiration and/or heart rates increase as we go to altitude? Meaning, would this be a normal response to lower PO2 levels?

Sort answer yes:

"The lung response to acute altitude exposure is mainly hyperventilation which, together with elevated heart rate, aims at achieving an adequate supply of oxygen to the tissues. At rest, ventilation increases by firstly increasing the tidal volume, at least up to 3500 m."

Couple of references:

https://pubmed.ncbi.nlm.nih.gov/204...ed with,may temporarily be slightly increased.

https://www.ncbi.nlm.nih.gov/pmc/ar...The lung response to acute,least up to 3500 m.
 
Positive Pressure at Altitude

Just to keep things interesting. Here's 2 more tid bits.

Above 32,000ft even 100% oxygen will not sustain human life.

You have heard people talking about P02 which is the partial pressure of Oxygen. It is a value that takes into account atmospheric pressure.

Because Atmospheric pressure above 30,000ft is below 100mmHg, even 100% oxygen is not enough to turn your blood from blue to red. So military O2 regulators have an altimeter in them that senses altitude and adds positive pressure to the pure oxygen, driving the pressures high enough to get the O2 into the blood. We are restricted from taking GA pilots in the chamber above 25K so most don't get to experience the 1st stage of positive pressure at 32K and the 2nd stage at 38K which is so much pressure that your cheeks puff out.

Then of course above 50K is Armstrong's line we have the whole blood boiling problem. The beaker of water in the chamber when we train U2 pilots is pretty eye opening. Sitting in there next to a boiling beaker with a pressure suit is memorable.

Oh yes! One more tid bit. One of the pilots in Payne Stewarts learjet that crashed years ago due to hypoxia was an Air Force Physiologist. He knew what he was doing and still ended up loosing his life to hypoxic hypoxia.
 
Paul, I think you need to check your numbers. Atmospheric pressure at 30,000’ is closer to 200 mm Hg than 100. Maybe you meant 40,000’? And strictly speaking partial pressure of oxygen means the pressure due to just the oxygen molecules. It doesn’t have to be related to the atmosphere, although in many practical applications it may be.
 
What is the quantitive effect on smokers?

Sort answer yes:

"The lung response to acute altitude exposure is mainly hyperventilation which, together with elevated heart rate, aims at achieving an adequate supply of oxygen to the tissues. At rest, ventilation increases by firstly increasing the tidal volume, at least up to 3500 m."

Couple of references:

https://pubmed.ncbi.nlm.nih.gov/204...ed with,may temporarily be slightly increased.

https://www.ncbi.nlm.nih.gov/pmc/ar...The lung response to acute,least up to 3500 m.



Hi Doc,

I am not here to disparage smokers but I could not help to think how does smoking enter into this equation? How would smoking affect the levels of O2 and all the other parameters that have been discussed in this informative thread?

Thanks, Bob
 
Oh yes! One more tid bit. One of the pilots in Payne Stewarts learjet that crashed years ago due to hypoxia was an Air Force Physiologist. He knew what he was doing and still ended up loosing his life to hypoxic hypoxia.

I remember that as a profoundly interesting aviation accident.

And just a few months ago, the premier Hi-Altitude Skydiving Instructor in the world - Tom Noonan - succumbed to hypoxia. He knew what he was doing as well. https://www.everestskydive.com/tom-noonan
 
Your right

Bob. You are right. I was Missing a variable. Water vapor at that altitude displaces oxygen requiring pressurized oxygen. The alveolar PO2 is 100mmHG.

Good catch. Keeping it real
 
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I posted this perhaps 8 years ago, but it might be of interest to those following this thread.

I used a somewhat cheapy finger clip oximeter and recorded the reading every minute or two (I don't recall the model, and it is a bunch of snow drifts away from me right now...). My Garmin running watch monitored my heart rate through a chest strap. It also recorded the gps altitude. I made a flight from 900 msl up to 12,500 msl and back down. The data from the oximeter is scattered more broadly than the likely actual PO2's were, but it is interesting nonetheless. Heart rate did not increase. No data on respiration rate, but I recall contemplating recording it at the time but decided the simple act of trying to log it might affect it, so I ignored it.

One can see the PO2 levels as reported went from a baseline of about 98% down to about 90% at altitude. Another fun fact is that there are about three heart rate data points above 80 - I went into steep banks and pulled maybe 2.5 g's a few times on the way back down. I've noticed this correlation numerous times.
 

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Hi Doc,

I am not here to disparage smokers but I could not help to think how does smoking enter into this equation? How would smoking affect the levels of O2 and all the other parameters that have been discussed in this informative thread?

Thanks, Bob

Smoking primarily affects all this by the damage to lungs which is complex but can be thought of most easily as increasing the difference between oxygen level in the alveolus (lung) and the blood: it makes the lungs less efficient in getting oxygen into the blood. So a smoker is likely to need supplemental oxygen at lower altitudes as a simple rule, depending on how much damage has been done to lungs.

Another problem is the presence of carbon monoxide in cigarette smoke: hemoglobin binds preferentially to carbon monoxide over oxygen which makes the transfer of oxygen from lungs to tissues where it's needed less efficient/effective.

This is at the basic level of explanation and does not take into account more severe obstructive disease and bronchospasm which are another topic for another day. Safe to say that when disease is that far advanced/severe the effects are far worse and the risk is higher.
 
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Below 85 on room air, reason for concern. If flying at that time dive or get on supplemental O2. EVERYONE physiology is a bit different. My comments are based on being a Respiratory Therapist. YMMV , but I wouldn’t want my O2 sat below 90 if flying.

Yesterday’s response is not a exact indicator of how you might respond today.

Looks like we have the physiology well covered here.

What's missing is our understanding of pulse ox accuracy. They measure 02 sats indirectly. There is variability between normal individuals not to mention different units.

The oxygen dissociation curve that most people refer to shows a sharp drop around 88-90% saturation. Realize this curve is based on arterial blood gas measurements. ABG measurements are far more accurate than trans-capillary 02 Sats.

Get to know what your pulse ox reads on the ground as a baseline. Go from there.

Don't just rely on a pulse ox absolute value to turn on the tank or descend.


Max Mirot, MD
Pathlogist and Laboratory Medical director
 
High performance military aircraft use pressurized masks for high altitude/unpressurized flight which in effect provide "PEEP". I found the most interesting part of training on this method is that you have to learn how to open glottis to breathe / talk when on pressurized oxygen. As a practical matter I don't think it would work in the GA application - the cost of a safe/usable system and approved regulators/ properly fitted masks would be pretty significant.

That sounds more like CPAP, or maybe BIPAP, than PEEP. I can’t think of a practical way of delivering PEEP in a non-intubated patient.
 
A little information from the Altitude Research Center of CO

I reached out to the Altitude Research Center, and was lucky enough to get a conversation with one of their experts.

Specifically towards the use of a pulse oximeter when living acclimated to high altitude and determining an appropriate baseline and actionable SPO% drops; this article was provided from a Dr Brent Blue for National Business Aviation Association May 2021 'Tips for Flight Crews on Using Supplemental Oxygen at Altitude and Avoiding Hypoxia':

"Working from a baseline saturation level measured at their home airport (usually 95 to 100 percent at sea level), Pilots should use supplemental oxygen when that number falls five points, and they must use oxygen when their saturation level drops 10 points. In both cases, they must adjust the oxygen flow until they saturate back to their home-airport baseline."

Not stated in that clip is our mandatory compliance with FARs on Oxygen usage.

That information came with the troubling warning that 'Monitoring inflight SpO2 can lead to all sorts of problems, even though it might make sense to some folks.' For example Hypemic Hypoxia from CO inhalation will probably be undetectable on a pulse oximeter. Similar problem for Histotoxic Hypoxia. As well as excessive CO2 saturation and hemoglobin dissociation curve shifts mentioned in prior posts.

NOT POO-POOing THE TECHNOLOGY!!! I've now got two and intend to use them. My effort here was to draw out more information so we use them as intelligently as we can. Thank you so very much for all those that have shared!
 
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I reached out to the Altitude Research Center, and was lucky enough to get a conversation with one of their experts.

Specifically towards the use of a pulse oximeter when living acclimated to high altitude and determining an appropriate baseline and actionable SPO% drops; this article was provided from a Dr Brent Blue in an interview with National Business Aviation Association May 2021 'Tips for Flight Crews on Using Supplemental Oxygen at Altitude and Avoiding Hypoxia':

"Working from a baseline saturation level measured at their home airport (usually 95 to 100 percent at sea level), Pilots should use supplemental oxygen when that number falls five points, and they must use oxygen when their saturation level drops 10 points. In both cases, they must adjust the oxygen flow until they saturate back to their home-airport baseline."


Not stated in that clip is our mandatory compliance with FARs on Oxygen usage.

That's a pretty good way of putting it but (for me personally) I would add an asterisk - which would be what I said before: 90-91% as a hard floor for safety. This would avoid getting into a gray zone where cognitive function starts to slip a little, and where some (but not all) individuals would be getting close to the steep part of the oxy-hemoglobin dissociation curve, and helps account for variability in measurements as others have discussed.

Perhaps overly conservative: if I were in my 20s instead of the 2nd half of my 60s I'd be much more comfortable pushing it a little.
 
That sounds more like CPAP, or maybe BIPAP, than PEEP. I can’t think of a practical way of delivering PEEP in a non-intubated patient.

True, we sometimes get lazy with the distinction because we use CPAP as one way to provide PEEP, but they are not the same.

Chris
 
My hypoxia data point

I have discovered that my first (observable) symptom of hypoxia is that... I get pissed off!

I looked it up and this appears to be what the medical folks usually describe as "restlessness or anxiety." But I would call it irritability.

So if you start getting peeved while flying, check that O2!!
 
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