CPAP in aircraft

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 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.

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