A pulse oximeter is a medical device used to determine blood oxygen saturation indirectly (as the direct method involves taking a sample of arterial blood and analyzing it). The device also measures the heart rate.
A pulse oximeter is a medical device used to determine blood oxygen saturation indirectly (as the direct method involves taking a sample of arterial blood and analyzing it). The device also measures heart rate. The first device was invented in 1940 by Milliken.
How the device works
The device is usually placed around one of the fingers. On one side, the device emits red light and infrared rays, and on the other side there is a light receiver. This receiver measures the amount of absorbed light. It is known that the physical properties of oxygenated hemoglobin differ from those of non-oxygenated hemoglobin, in that oxygenated hemoglobin absorbs infrared rays more than non-oxygenated hemoglobin. While non-oxygenated hemoglobin absorbs red light more and allows infrared rays to pass through.
Thus, the device measures the amount of red light and infrared rays and analyzes the amount of oxygen in the blood. These devices are considered accurate, as the error rate — if the oxygen saturation in the blood is 70-100% — equals ±2.
Notes: The device cannot estimate the amount of oxygenation in the following cases
Impaired blood perfusion at the measurement site
Strong lights, as in operating rooms, may affect the device's performance
The device cannot differentiate between oxygenated hemoglobin and methemoglobin
Nail polish may prevent light from passing through and thus give the device an incorrect reading
