Back in the 1940s, when oximetry was first being used by wartime pilots in the U.S. military, "aviation ear meters" could indicate the blood/oxygen status of pilots flying at high altitudes. This technology was modified and improved during the '50s and later marketed for use in hospitals in the late 1960s. Unfortunately, these new devices were heavy and cumbersome and had bulky, uncomfortable earpieces. They were also very expensive, selling for somewhere around $10,000.
Today's pulse oximeters, by contrast, are small, easy-to-use devices that can be purchased for less than $20, carried in your pocket and simply slipped over your fingertip any time you want to check the oxygen saturation level of your blood. The technology has continued to improve over the past decades. Today, Pulse-Ox units are primarily utilized in home healthcare environments, in emergency response vehicles and in hospitals and clinics. There is, however, an ever-growing market of users who want the benefits oximeters can offer to tourists visiting areas located in higher altitudes, climbers and athletes competing at high elevations.
What We Learned from Mexico City
Most would agree that the air is "thinner" at higher altitudes and that less oxygen is available for breathing. The fact is, air always consists of the same 20.93% oxygen (O2), regardless of elevation. What does decrease as elevation increases is air pressure. And, as atmospheric pressure lessens so does the amount of oxygen you breathe in with each breath. This, in turn, causes respirations to increase as compensation. There will also be a corresponding drop in the percentage of oxygen saturation in your bloodstream.
Normal blood oxygen readings at sea level are between 95-98%. When you breathe in, the oxygen going into your lungs exerts something called "partial pressure" which corresponds directly to ambient atmospheric pressure. This is important because the partial pressure in your lungs is greater than the pressure in the blood (hemoglobin) surrounding your lungs. At sea level, the partial pressure of O2 is 159mmHg. In Mexico City however, at an altitude of more than 7,200', oxygen's partial pressure is only 125mmHg. It was discovered during the 1968 Olympics in Mexico City that higher elevations meant lower blood oxygen saturation, leading to decreased athletic performance. Breathing supplemental oxygen could bring temporary relief from these low oxygen levels and is now commonly used during competitions at high altitude as well as other activities taking place at higher elevations.
Deadly Airplane Crashes Cause Hypoxia Concerns
In September, 2014, two small airplanes went down and suspicions pointed to pilot unconsciousness due to hypoxia, or inadequate oxygenation of the blood. Symptoms of hypoxia include:
- Headache, lightheadedness
- Hot flashes
- Impaired vision
- Sweating, lip tingling
- Raised heart rate
- Increased respirations
Although symptoms will vary from one individual to another, you might think that avid, experienced pilots, as these two were, would be aware of the problem and do something to remedy it. If, however, confusion is a factor, thoughts may become illogical.
After these incidents occurred, the AOPA (Aircraft Owners and Pilots Association) sent out a message of concern to their members warning of the dangers hypoxia posed to pilots, especially those operating aircraft with non-pressurized cabins. They went on to state that, in their opinion, use of a pulse oximeter "is the best defense against hypoxia," and they recommended the use of these devices to check for blood saturation levels every ten to fifteen minutes while flying.
While FAA regulations require the use of supplemental oxygen for pilots operating at certain altitudes (FAR Part 91, Sec 91.211), none have yet to require use of pulse oximetry for checking blood oxygen levels quickly and dependably.
Normal Home Altitude Saturation Levels
If you're thinking of going on a northern nomadic expedition or, perhaps, climbing Kilimanjaro, you'd be smart to have a pulse oximeter in your pocket. How you respond to being at significant altitudes will depend partly on the elevation where you normally live. Most people living at sea level will have blood oxygen saturation levels of 95%+, which is normal. If, however, those same people were atop Mt Kilimanjaro, which stands at nearly 20,000', a "normal" saturation level is between 70-75%.
In addition, saturation level and saturation tolerance are two different things, and each person will tolerate a reduced oxygen level differently. Although much will have to do with the elevation level at which you normally live, reactions to high altitude also depend on other factors such as:
- Health status
- Tobacco smoking history
- Exercise history, and more
Tourists/vacationers planning to spend time at any high altitudes should definitely take the precaution of having a pulse oximeter in their pockets and ready access to supplemental oxygen. The same goes for climbers, competing athletes and pilots.