Just talking hypoxia makes me dizzy

[Aye Effaar]

Can anyone help me understand why the FAA classifies Carbon Monoxide poisoning as a form of hypemic hypoxia, while most of the scientific community classifies it as histotoxic hypoxia? And yet the FAA correctly classifies cyanide gas poisoning (from burning plastics) as histotoxic? Seems contradictory, no?

For that matter, can anyone find a science based (non-FAA) reference for the term hypemic hypoxia? The closest science based reference is to anemic hypoxia.

 

[DFH65]

Me Pilot. Me fly airplane. Me no understand fancy science talk.

 

[texasclouds]

Well those scientists are stuck on the ground. Everything changes ones airborne.

 

[Aye Effaar]

I'll take things that don't matter when you're passed out for $600, Alex.

Sure -- all forms of hypoxia are dangerous, but CFI in training needs an explanation that makes sense to student pilots. Trying to-do better than "read this and memorize it".

 

[Aye Effaar]

Never talked about types of hypoxia on my CFI ride, and I don't go into vast medical detail with my students because frankly it's unimportant, and falls into the category of no one gives a crap except for people who want to look like they know everything. Do what I do with my students: "The FAA doesn't always get their **** right, here's one example. Memorize it for your check ride, or your written, and use your head. I'm not Jesus, what I say isn't gospel. If you think I'm wrong, let's talk it over, and discuss it, because I might be."

Understood -- thanks

 

[Velocity173]

Well not scientific by any means but the Army’s aeromedical training for aviators uses Hypemic Hypoxia to describe CO poisoning. They also list anemia under that category of hypoxia.

 

[dmspilot]

Hypemic hypoxia is an inability to transport oxygen, histotoxic is an inability to use it once it's there.

"Histotoxic hypoxia (also called histoxic hypoxia) is the inability of cells to take up or use oxygen from the bloodstream, despite physiologically normal delivery of oxygen to such cells and tissues."

https://en.wikipedia.org/wiki/Histotoxic_hypoxia

It would seem your "scientific" sources are incorrect, since CO poisoning does not result in "normal delivery of oxygen" to cells.

 

[Aye Effaar]

Hypemic hypoxia is an inability to transport oxygen, histotoxic is an inability to use it once it's there.

"Histotoxic hypoxia (also called histoxic hypoxia) is the inability of cells to take up or use oxygen from the bloodstream, despite physiologically normal delivery of oxygen to such cells and tissues."

https://en.wikipedia.org/wiki/Histotoxic_hypoxia

It would seem your "scientific" sources are incorrect, since CO poisoning does not result in "normal delivery of oxygen" to cells.

https://pubmed.ncbi.nlm.nih.gov/269028/

 

[Rgbeard]

I guess if your student is also from the NIH, they might have an issue.

Moreso they'll just probably look at the FAA stuff and chuckle. Are you also a doctor, or work for NIH? Just curious. Your level of knowledge on this seems to be well-above what's required.

 

[Aye Effaar]

I guess if your student is also from the NIH, they might have an issue.

Moreso they'll just probably look at the FAA stuff and chuckle. Are you also a doctor, or work for NIH? Just curious. Your level of knowledge on this seems to be well-above what's required.

No -- not particularly knowledge (nor intelligent). Working on my CFI and one thing I detest is a teacher who says to me "just memorize this stuff". I always found it easier when there was an explanation I could understand. I've been parroting the four types of hypoxia since my Student Pilot days, and thought maybe I could do better for future students.

But as EdFred puts it -- the aeromedical stuff is probably just best to memorize for various exams/checkrides and move on (he's probably right).

 

[dmspilot]

https://pubmed.ncbi.nlm.nih.gov/269028/

You definitely don't understand what you are reading if you think that is saying CO poisoning is a form of histotoxic hypoxia.

 

[Tantalum]

needs an explanation that makes sense to student pilots

..but that is not this:

hypemic hypoxia, while most of the scientific community classifies it as histotoxic hypoxia

Trying to-do better than "read this and memorize it"

agree there, an easy way to conceptualize the mechanism of hypoxia is using the plane's own engine as simile. Since the air gets thinner the engine loses about 3% to 5% of its power for every 1K feet in elevation (other factors obviously impacting, but that's a good-ish rule).. by the time you get to 10K there's less air, less oxygen, and your engine is making only about 65% or so of its available power. Keep in mind it's not linear either, the higher you go the faster that air depletes. So the same reason your engine gets weaker is why your body does too. It really doesn't matter what you call it, you're not going to function well because your body is getting less oxygen

 

[Bill Watson]

Just interpreting the words, the difference may be that CO is not toxic and damaging tissue, it just impairs the ability of blood to work the way it should. Cyanide is toxic and destroys tissue.

Talking out of my ass, I’m thinking the CO hypoxia can be stopped and possibly reversed without bodily harm. Cyanide is damaging stuff because it is toxic.

From an aviation perspective, both can kill so there’s that.


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[Albany Tom]

Wait, what, the FAA got it right?

Some of the more dangerous parts of CO are that it's lethal in tiny quantities, and that it's absorbed almost instantly but only released very slowly - it takes hours. (I was bored waiting for a meeting with a local building inspector one day, before smart phones, and read all the pamphlets in his office.)

https://www.abe.iastate.edu/extension-and-outreach/carbon-monoxide-poisoning-health-effects-aen-166/