Restoring Performance

CUE INFOMERCIAL: I’m here today to tell you about a miraculous substance that will significantly increase your cognitive function, clear your head and improve your night vision. It is absolutely legal with proven safety and reliability, and you will see immediate improvement in your physical, mental and visual performance. You are probably asking, what is this miracle substance? The answer is supplemental oxygen, and you can buy it at an FBO near you.

Shortly after I splurged on my first aircraft, my dad excitedly offered to buy me an aviation accessory. Was there anything I could use to improve my safety, but likely wouldn’t buy for myself? I looked at my shopping list and suggested supplemental oxygen equipment. At the time, it seemed like a luxury I could delay, but it turned out to be one of the most valuable aviation accessories I own. It demonstrated its value right away. With it, I had the ability to leisurely cruise-climb up and over mountain passes. On cross-country flights, I climbed to where I could pick up 30-to-60-knot tailwinds. In winter, when intermittent cloud tops are often around 11-14,000 feet, I could avoid them by getting on top. As a simple GA pilot, supplemental oxygen was a game changer. 

More than a decade later, I find myself increasingly reaching for oxygen at lower and lower altitudes, particularly at night. This miracle inhalant has dual properties: it not only increases cognitive ability, but also improves night vision.

“I don’t have any specific data, but anecdotally, it seems like an increasing number of pilots are flying with supplemental oxygen systems,” said Dr. Brent Blue. Blue is an FAA Senior Aviation Medical Examiner and a frequent lecturer in the areas of aviation medicine, hypoxia and carbon monoxide poisoning. In 1994, he and partner Mike Busch founded Aeromedix.com to help bring oxygen aids, like pulse oximeters, and other equipment into regular use in general aviation. 

SAFE VS. LEGAL

According to Blue, FAA rules on supplemental oxygen were mostly designed to promote rather than inhibit aviation. They provide just enough latitude for us to navigate up and over high passes in the Western U.S. without pressurization or the burden of oxygen systems that were prohibitively expensive at the time. So if you thought the FAA’s altitude-based oxygen rules are designed primarily around medical and physiological data, you would be wrong. 

Blue has a simple 5-10 rule of thumb for knowing your own particular oxygen needs, as individual to you as your weight or height: “Start at your home base by using a pulse oximeter to measure your baseline blood oxygen saturation level. At flying altitude, when your blood oxygen level has dropped by five percentage points off your baseline, you should be on oxygen. If or when your oxygen saturation drops below 10 percent off your baseline, you need to be on oxygen.” This rule of thumb factors in your individual baseline physiology and the altitude of your home.

Doc Blue’s 5-10 rule is useful because pilot physiology and acclimatization are baked in. Pilots living at higher altitudes where there is less oxygen typically have lower blood oxygen levels in their blood, but they are acclimated to deal with it by having more red blood cells. Think of the energy delivered to your body as a 100-car coal train, each car 100-percent full at sea level. At altitude, that same train of energy may only be 90-percent full. The only way to supply the missing energy is to add more cars. In this metaphor, red blood cells are the extra cars. Someone who lives in Denver or Sante Fe, both at higher altitudes, may still have a full load with a baseline 92-percent blood-oxygen saturation because they have more blood cells carrying the freight. It depends on your home base.

“From medical studies of mountaineers, we know that our bodies adapt to living at altitude,” said Blue. “It takes the human body roughly 90 days at a given altitude to acclimatize through the production of extra red blood cells to carry the lower pressure oxygen. You can’t go by an absolute number, say, 92-percent blood oxygen for example, as the threshold for needing supplemental oxygen because a person living at altitude may have 92 percent as their baseline and not need supplemental oxygen. Meanwhile, a person coming from sea level, whose oxygen levels are typically around 100 percent, may desperately need oxygen when they have dropped to 92 percent.” 

Regardless of what altitude you are flying, Blue’s 5-10 rule will keep you safe and the FAA’s regulatory altitude (where oxygen is required) will keep you legal. For any given person, the two may or may not always correspond.

OXYGEN AND LONGEVITY

In addition to acclimatization and red blood cell count, there are three other factors affecting blood oxygen levels. “The four greatest factors affecting longevity are: 1) heredity, 2) smoking and exposure to tobacco products, 3) body weight and 4) exercise,” said Blue. “You don’t get to pick your parents so you have no control over the first one. But the remaining three factors, which are known to extend life, also affect oxygen uptake at altitude.” 

The first controllable factor is smoking and tobacco. Blue says if you smoke, vape or consume other smoky inhalants, you are damaging your respiratory system and making it less able to do its job. “The damage from smoking or vaping not only reduces your body’s ability to deliver oxygen to the blood, it increases your susceptibility to respiratory infections such as bronchitis, the flu or COVID-19,” said Blue. “Don’t smoke.”

Next is obesity. “There is no delicate way to put it,” said Blue, “but if you are obese, you are going to have significantly more oxygen issues than someone who is at their ideal weight.” This isn’t fat-shaming; it is just the relationship between physiognomy and the act of breathing, particularly when sitting. “The compression of the pulmonary cavity, when it is physically displaced by body fat, makes it harder and harder to draw a deep enough breath,” said Blue. “The more fat in the pulmonary cavity, the less room for lung expansion.”

The third controllable factor, weight, is actually addressed by the FAA from a regulatory perspective. This is because some obese pilots will suffer from sleep apnea, which interrupts sleep cycles and results in inadequate rest. Blue believes that because obesity interferes with the ability to draw deep-enough breaths while seated, it is also an aeromedical factor that is clearly detrimental to a pilot’s ability to intake sufficient oxygen.

Exercise is the fourth factor that Blue cites as affecting oxygen uptake. He recommends at least 30 minutes of exercise every day, with a sustained heart rate in the medical target zone of 70-85 percent of your maximum heart rate. Maximum heart rate is equivalent to subtracting your age in years from 220. I calculated it for my 56-year-old self: 220-56=164, so I need to exercise at least 30 minutes every day with a heart rate consistently between 115-139 (70-85 percent). And seven days a week. 

“Really?” I asked, cringing. Blue says, “If you seriously strive for seven days a week, you should be able to actually manage 4-5 days a week. If you aim for 4-5 days, chances are you will only hit a couple days. Compliance goes down. It isn’t easy, but if you want to live long and fly at altitude, I recommend 30 minutes of real sustained heart rate exercise, and yes, seven days a week. The key is working it into your schedule and finding activities that you can, at a minimum, tolerate, but better yet, enjoy.” 

FINALLY, NIGHT VISION

If you’re still not convinced of supplemental oxygen’s value to pilots, consider night operations. Night vision is dominated by rod cells, which are on the periphery of the retina. The less light-sensitive cones, which provide color vision, are concentrated in the center of the visual field. A result is that we tend to have slight tunnel blindness at night, because the least-sensitive receptors are in the main focal field, while our peripheral vision is more sensitive. 

Just as the brain is an energy/oxygen hog, the same is true for the rods and cones. A 2006 paper, published in the journal “Vision Research,” looked at the effects of hypoxia (low oxygen), hypocapnia (low carbon dioxide) and hyperoxia (high oxygen) on night vision, compared to normal oxygen levels. The conclusion was that “…aircrew should consider using supplementary oxygen if they are reliant upon viewing scotopic external scenes (less than full moonlight) when flying at night.” It went on to conclude, “At night, supplementary oxygen may benefit aircrew visual sensitivity, even at ground level.”

If you spend much time in unpressurized aircraft at or above 10,000 feet, or at night above 5000 feet, supplemental oxygen—and a pulse oximeter—should be considered mandatory equipment.