Pulse oximetry (blood oxygen saturation level in %SpO2) and pulse rate (in beats per minute) have been performed with clamp on the finger measurements for many years. With their built-in display, they are intended for either a health care professional or even the user reading of the measurements. In some instances, these devices even provide a waveform for greater detail and more thorough analysis. These readings along with blood pressure and temperature measurements provide basic readings for well and sick patient monitoring. They are so well established that they are even part of the sensing capability built into smart watches.
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The readings are performed with photo optic sensors using red and infrared (IR) LEDs to determine deoxygenated and oxygenated hemoglobin. The process involves sending IR light into capillaries in the finger and then measuring how much light is reflected off the gases. One sensor supplier offers four standard IR LED wavelength choices of 880 nm, 905 nm, 910 nm and 940nm. Alternate locations to make this measurement include toes or earlobes.
Making the same measurements as an integral part of a smart watch is one way to take the sensing technique to a new level. However, it is still just a single point in time measurement. For overnight measuring and recording for sleep apnea and other monitoring situations additional technology is required. In addition to adding continuous monitoring/recording capability, one differentiating approach is how the data is communicated to the user or healthcare professional.
Three examples of a wrist worn form factor for the electronics and a modified soft and flexible finger worn sensor demonstrate the different existing approaches. One approach intended for cardio-ambulatory monitoring, remote wireless monitoring and overnight studies uses USB to communicate the data. It has a display so periodic readings can be observed by the wearer.
The second approach displays more information and the data is transmitted by a cable connected download. The third approach does not have a display for its continuous blood oxygen and heart rate tracking. Instead, recorded data is transferred by a Bluetooth download to a smart phone.