Looking for A-14 (or similar) pressure breathing diluter demand regulator

On 11/3/2018 7:51 AM, Tango Eight wrote:
On Friday, November 2, 2018 at 6:55:07 PM UTC-4, Duster wrote:

The issue with the U2 pilots was that they were wearing uninflated suits
in a cabin pressure way too low.

Okay... you're an insider then? Can you please amplify?

This isn't a great topic to speculate about.

Here are the facts as I know them:

The suit is backup for cabin pressure failure, only.

Nominal cabin pressure is 29K.

Pilot is on 100% ox (from two hours before takeoff).

This isn't a hypoxia problem.

The inference that can be drawn is that neurological DCS is more insidious
than most realize. That was the point of linking the article.

T8

Some time in the past two months I happened to watch (on YouTube) a
(non-USAF, I seem to recall) nominally hour-long program on precisely this
issue. It named names, and included interview snippets of some of the key
principals - U2 pilots - involved. I *think* it was filmed ca. 2012-ish...as
in after confirmation of the info in TB's linked article, but wouldn't bet my
retirement on that being an accurate remembrance...but I seem to remember it
stating to the effect: "certain medically-detectable
brain-differences/potential-anomalies have been noted in former U2 pilots."

I would bet *some* of my retirement on the accuracy of remembering that ca.
2003 the USAF changed the cabin pressure of U2s from 29k to the 10k range.
Regrettably I don't remember the name of the program, and leave it to the
interested reader to ferret a link out for personal use...

Bob W.

P.S. By way of hoping to head-off RAS Thread Nazis (and I've occasionally been
one of 'em), I'll note I used - in pre EDS days - an A14-based system to soar
to ~31k feet...one time, without a backup system, and more than quite enough
for my then-somewhat-youthful risk tolerance.

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BobW: More recent than that, around 2012 or so.

T8: But you can be hypoxic even breathing pure oxygen. Yes, I was part (albeit in a small role) of the research team that lead to a series of articles on identifying white matter lesions in U2 pilots using MRI. These and other published studies convinced the Air Force to change the U2 cabin pressure from ~30K' to ~15K' (similar to Perlan II) fairly recently in a program called "C.A.R.E.". Although these brain lesions can arise via different mechanisms, they are reminiscent of damage resulting from emboli or clots. While the lower cockpit pressure had been used for many decades, one theory is that after 911, these pilots flew more frequently, for longer sorties and were tasked heavily both physically and mentally than previously. And, no, hypoxia is a problem in those conditions. Breathing 100% O2 at sea level is vastly different physiologically than at extreme altitudes since the absolute alveolar PO2 value needs to be at least ~14kPa. Even at less extreme heights breathing 100% oxygen is about as efficient as breathing air at around 12,000ft. Robert Harris for his 1986 49,009ft altitude record flew in an unpressurized Grob 102. He was forced to come down when his O2 system started to fail, apparently suffering from medical issues for some time thereafter.

Original article:
https://www.ncbi.nlm.nih.gov/pmc/art...ihms488856.pdf

On Saturday, November 3, 2018 at 9:27:22 PM UTC-4, wrote:
BobW: More recent than that, around 2012 or so.

T8: But you can be hypoxic even breathing pure oxygen. Yes, I was part (albeit in a small role) of the research team that lead to a series of articles on identifying white matter lesions in U2 pilots using MRI. These and other published studies convinced the Air Force to change the U2 cabin pressure from ~30K' to ~15K' (similar to Perlan II) fairly recently in a program called "C.A.R.E.". Although these brain lesions can arise via different mechanisms, they are reminiscent of damage resulting from emboli or clots. While the lower cockpit pressure had been used for many decades, one theory is that after 911, these pilots flew more frequently, for longer sorties and were tasked heavily both physically and mentally than previously. And, no, hypoxia is a problem in those conditions. Breathing 100% O2 at sea level is vastly different physiologically than at extreme altitudes since the absolute alveolar PO2 value needs to be at least ~14kPa. Even at less extreme heights breathing 100% oxygen is about as efficient as breathing air at around 12,000ft. Robert Harris for his 1986 49,009ft altitude record flew in an unpressurized Grob 102. He was forced to come down when his O2 system started to fail, apparently suffering from medical issues for some time thereafter.

Original article:
https://www.ncbi.nlm.nih.gov/pmc/art...ihms488856.pdf

Thanks for that!

Following some links, I ran across this statement:
"The DCS risk per [high U2] flight was 0.076% from 1994-2005 but increased to 0.23% from 2006-2010."

That is to say, not terribly common, but not very darned rare.

T8

On 11/3/2018 7:27 PM, wrote:

BobW: More recent than that, around 2012 or so.


Thanks for the time-correction...(and not taking me up on my possible bet;
good thing I might've bet only *part* of my retirement!).


T8: But you can be hypoxic even breathing pure oxygen. Yes, I was part (albeit in a small role) of the research team that lead to a series of articles on identifying white matter lesions in U2 pilots using MRI. These and other published studies convinced the Air Force to change the U2 cabin pressure from ~30K' to ~15K' (similar to Perlan II) fairly recently in a program called "C.A.R.E.". Although these brain lesions can arise via different mechanisms, they are reminiscent of damage resulting from emboli or clots. While the lower cockpit pressure had been used for many decades, one theory is that after 911, these pilots flew more frequently, for longer sorties and were tasked heavily both physically and mentally than previously. And, no, hypoxia is a problem in those conditions. Breathing 100% O2 at sea level is vastly different physiologically than at extreme altitudes since the absolute alveolar PO2 value needs to be at least ~14kPa. Even at less extreme heights breathing 100% oxygen is about as efficient as breathing air at around 12,000ft. Robert Harris for his 1986 49,009ft altitude record flew in an unpressurized Grob 102. He was forced to come down when his O2 system started to fail, apparently suffering from medical issues for some time thereafter.

Original article:
https://www.ncbi.nlm.nih.gov/pmc/art...ihms488856.pdf

And thanks for the link (not yet absorbed). More knowledge definitely more
better...

Bob W.


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