In Response to Kevin Ware’s “A Medical Look at Hypoxia” (December)
I want to compliment you on the article you published on hypoxia. It is by far the best article that I have read on the subject, and I am much wiser on the topic as a result of your efforts. You make a great point that just because the aircraft may be doing its job correctly from a pressurization systems perspective, that doesn’t necessarily mean it translates into your body doing its job. I had never heard of hypocapnia nor of the Bohr effect, and for many years I flew a Mirage and Meridian where max PSI differential put the cabin altitude generally between 8,000-9,000 feet depending on altitude.
I also regularly fly a Cirrus SR-22TN and occasionally take it up into the low teens. Whether flying PIC in a pressurized cabin or in a scenario where a cannula is required, the issues you identified are very relevant. Your identification of other physical issues that can amplify the effects of hypoxia was also enlightening. I now have a much better understanding of additional contributing physical factors that can cascade with hypoxia. Going forward, I will be much more vigilant about oxygen levels in my blood while operating as PIC or SIC. Safe flying!
Your article in the December issue of T&T is excellent. I agree that hypoxia in a cabin that is still pressurized normally, is a more likely and frequent occurrence than loss of pressurization.
It occurs to me that whenever a military interception allows a close view of the incapacitated pilot in a slumped-over posture, the lack of frosted windows should indicate that the cabin environment is still normal i.e. no pressurization failure. Perhaps the military crews’ comments could be used to separate the hypoxia accidents into two categories: normal pressurization and loss of pressurization.
Keep up the good work. Since I retired from practicing optometry, I’ve been working as a corporate pilot and as an instructor for advanced ratings. So, I feel we have a bit in common.
Perry G. Wilson, O.D.
Kevin Ware’s excellent article “A Medical Look at Hypoxia” was certainly instructive, and hopefully may save some lives. I have flown a pressurized Aerostar for over 30 years but have never used its supplemental oxygen system. After reading Dr. Ware’s article, I plan to start using supplemental oxygen any time my cabin pressure goes above 10,000 feet, and to make use of my finger pulse oximeter on every flight.
For pilots concerned with inconvenience or cost of using supplemental oxygen, I suggest a system like that produced by the Mountain High Oxygen Company in Redmond, Oregon. Mt. High (www.MHoxygen.com) makes a “Pulse-Demand” system that supplies a ‘puff’ of oxygen to a cannula or mask only during the “inhalation” phase of the user’s breathing cycle. During the “exhalation” phase (which is longer), the oxygen cylinder is not delivering any oxygen. This results in a significant savings of the oxygen supply. Having flown gliders on long cross-country flights for many years, I can attest to the efficiency of this system.
Mt. High systems can be made to operate from a powered aircraft’s supplemental oxygen ports. But it is not inconvenient to use a light-weight oxygen cylinder inside the (warm) cabin of a pressurized aircraft, and recharge it as needed with industrial oxygen which costs only about 10 percent that of “aviators” oxygen. The only difference, as Dr. Ware’s article teaches, is that industrial oxygen is not certified to be absolutely “dry.” But if the cylinder is in a warm cabin, the moisture content is no factor because no ice will form and block the oxygen flow. Oxygen is oxygen.
Another one of your great articles related to the flying I do. Don’t try to scare us old guys! Even though a P-Navajo can hold an 8,000-foot cabin in the mid-20 flight levels, I’m buying an oximeter to check my status. Thanks.