Pulse oximetry has been used in medicine for some time, but since the coronavirus pandemic, the public has been starting to use them more frequently to measure their own oxygen saturation. A pulse oximeter effectively tells us how much oxygen is in our blood at any one time.
To understand how pulse oximetry works, we need to first understand how oxygen is carried around your bloodstream. Oxygen is absorbed through specialised membranes in the lungs and diffuses into your blood, however, oxygen does not simply float around in our bloodstream. In order for it to be effectively transported to the tissues, it binds itself to haemoglobin.
When haemoglobin has oxygen bound to it, it is called oxyhaemoglobin (O2Hb) and when there is no oxygen bound, it’s called deoxyhaemoglobin (HHb). Pulse oximetry is based on the principle that O2Hb and HHb absorb red and near-infrared (IR) light to different extents.
