AOPA Pilot Magazine - December 2021 - 26

FLIGHT MD
CPAP in aircraft?
A simple solution below 12,500 feet
BY DR. BRENT BLUE
IT IS ALWAYS FUN when one receives a phone call with a question
and a light bulb goes off. I had one of those moments when an
experienced pilot called me to discuss why he had no problem flying
between 8,000 and 10,000 feet msl but would feel hung over
when flying between 10,000 to 12,000 feet. Thinking it might be a
breathing issue, he was wondering if a CPAP device, normally used
for sleep apnea at night, might help.
When Mike Busch and I introduced portable digital pulse
oximetry to general aviation in the 1990s, I noticed that pilots
engaged in period breathing, or Cheyne-Stokes breathing. This
is an altitude effect that had only been reported in the scientific
literature in mountain climbers at night. I called Dr. Peter
Hackett, who ran the clinic on Mount Everest for years, and he
confirmed that no one at that time had looked at climbers during
the day since their exercise dictated their breathing patterns.
Cheyne-Stokes breathing is a phenomenon where one breathes
deeply, then progressively shallower, then pauses breathing for a
period. This corresponds to a relatively normal blood oxygen level
that falls with the corresponding breathing rate. It is not an oxygen
problem but a ventilation issue and is thought to be related to
pressure sensors in the pulmonary arteries.
As we climb in an unpressurized aircraft, the percentage of
oxygen does not change but the density of the air does. That
means for every volume of air one takes in during ascent, one
gets fewer oxygen molecules. That results in lower oxygen levels,
particularly if one is not breathing deeply. At sea level, normal
oxygen saturation is 95 to 100 percent At 6,000 feet msl, normal
is 90 to 95 percent. My recommendation is that pilots should
use oxygen when their saturation drops five points below their
home oxygen level, and they must use oxygen when it drops 10
points below (using home saturation as a baseline accounts for
pilots who live at altitude) to avoid adverse effects.
When supplemental oxygen
is used, even at altitudes
that are lower than the FAA
mandates above 12,500 and
14,000 msl (see sidebar at
right), the percentage of molecules
per breath increases,
which allows more oxygen
DR. BRENT BLUE is
a senior AME based in
Jackson Hole, Wyoming. He
flies a Noorduyn Norseman
out of Driggs-Reed
Memorial Airport (DIJ) in
Idaho, just west of Jackson.
26
AOPA PILOT / December 2021
to be perfused through the lung tissue. This counteracts some
of the effect of the periodic breathing seen at altitude. However,
there may be alternatives.
We know that forced deep breathing will increase ventilation
at altitude, but it is very hard to maintain-and deep breathing will
decrease carbon dioxide in one's system which may have its own
deleterious effects. Similar methods include singing and breathing
with pursed lips which creates a positive back pressure-both
are also difficult to maintain during an entire flight, not counting
the mental health effects it might have on passengers.
The idea posed by the pilot who called me is intriguing. CPAP,
which is continuous positive airway pressure, or APAP, which is
automatic positive airway pressure, essentially creates a method
to " remind " the brain to breathe deeply. CPAP/APAP is delivered
via a nasal " pillow " or a full-face mask. The full-face mask
would work better in an aircraft environment but would require
a microphone inserted through it with a seal at the point of entry.
Why CPAP/APAP instead of oxygen? Size, cost, and simplicity
are the basic reasons. CPAP/APAP machines are less expensive
than most oxygen setups and do not have to be refilled like an oxygen
tank. Conversion to 12 or 24 volts would be simple. Although
the units are officially prescription-based, that issue that can easily
be remedied with a phone call or an email to a local physician.
Obviously more research needs to be done but using CPAP/
APAP below 12,500 feet is a promising technology for pilots and
passengers. brentblue@wyoming.com
The FAA regulations requiring oxygen for pilots when
between 12,500 and 13,999 feet msl for more than 30
minutes and anytime at 14,000 feet and above, were
promulgated in the 1950s when measuring oxygen levels in
flight was complicated and oxygen equipment was expensive
and heavy. The numbers were extrapolated and did not
consider variation between individuals. The general aviation
population lobbied for the 12,500 portion of the rule since
it allowed for aircraft crossing mountains in the continental
United States without needed oxygen equipment. In actuality,
many pilots should use oxygen (or maybe CPAP/APAP) at
much lower altitudes.
AOPA Pilot Magazine - December 2021

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