A spectrometer that compares the returns of infrared and red light on a patient’s fingernail is finding more and more use by people who need or want to know their blood oxygen levels. Finger pulse oximeters are now so cheap that people purchase them at pharmacies. The oximeters clip onto the end of a finger, and scan the patient’s fingernail, painting it with both a red visible light and an infrared beam (which is invisible to the human eye).
The amount of red light reflected back from the patient’s skin is compared to the amount of infrared light reflected. The infrared rebound is 100%, but as the patient’s oxygen-carrying hemoglobin levels vary, the return of red light varies. The finger pulse oximeter is able to provide constant and instantaneous blood oxygen level reports, typically using a digital display. Since the amount of red increases with each pulse, the oximeter also works as a pulse detector. A good oxygen level is between 90 and 100. An alarm can be set off for people on supplemental oxygen when their level drops too low, so that they can get to an air mask before losing consciousness.
The oximeter was invented in the 1960s, and it has traditionally been used in medicine to monitor patients, and used by pilots operating in unpressurized aircrafts, and also with miners operating in environments where non-oxygen gases are present. The finger pulse oximeters started gaining home use in the 1980s, when prices started to come down, and now they are only around fifty bucks.
They have gained a lot of acceptance with everyone from people who rely on supplemental oxygen tanks to high performance athletes who want to know how well their cardiovascular system is working during training. When athletes move to a high-altitude location (like Denver for a game or a race),they use the oximeters to determine how well they’re acclimatizing.