This Santamedical device monitors pilots' blood-oxygen saturation levels.
The pulse oximeter allows pilots to monitor the oxygen saturation of hemoglobin in their blood, an invaluable tool when climbing above 10,000 feet.
The use of a pulse oximeter allows pilots to monitor the oxygen saturation of hemoglobin in their blood. How a pulse oximeter works are pretty ingenious. Rather than directly measuring hemoglobin concentration, the small device, which costs about $40 and can be purchased online, takes constant measurements of the absorption of specific wavelengths of light in oxygenated hemoglobin. Blood is red due to the quality of ox hemoglobin it contains, causing it to absorb light of certain wavelengths. The pulse oximeter incorporates two LEDs, one red and one infrared. Infrared light is absorbed by the ox hemoglobin and red light by the reduced hemoglobin. The oxygen saturation of the blood determines the degree of light absorption, and the result is shown on a digital display of oxygen saturation on the pulse oximeters screen.
On the ground, your oxygen saturation level should be around 98 percent. As you climb, your goal is to keep your blood-oxygen level above 90 percent. When using a mask, you should find it easy to keep your blood-oxygen level at 95 percent or higher. If you’re using a cannula and talking a lot or exerting yourself, make sure you take the time to relax and breath through your nose.

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On the ground, your oxygen saturation level should be around 98 percent. As you climb, your goal is to keep your blood-oxygen level above 90 percent.