Apple's 'iWatch' rumored to use optoelectronics to monitor heart rate, blood oxygen levels

Cupertino, Calif.-based Apple was also considering the addition of blood glucose monitoring, but that feature is believed to have been scrapped due to the "inaccuracy" of using optoelectronics for non-invasive blood glucose testing. Electronics industry analyst Sun Chang Xu made the predictions for China's Electrical Engineering Times.

Broadly speaking, medical sensors using optoelectronics measure changes in light reflected by the body. An array of light-emitting diodes are used to pass light into tissue, and sensors detect the amount and color of the light that bounces back.

Using optoelectronics for monitoring blood oxygen levels is a process known as pulse oximetry. Pulse oximeters —  usually seen as clothesepin-like devices clipped to the end of a person's finger —  use visible red and infrared LEDs to detect how much oxygen is carried in the blood's hemoglobin. Oxygenated hemoglobin absorbs more infrared light, while deoxygenated hemoglobin absorbs more visible red light.

Adding to the report's plausibility, Apple has brought on multiple biomedical experts with expertise in optoelectronic pulse oximetry in recent weeks. New hires Marcelo Malini Lamego and Michael O'Reilly are former executives at pulse oximetry company Masimo Corporation.

For heart rate monitoring, visible light is passed through a person's skin and absorbed by their blood. More light is absorbed when the body pumps more blood, and the changes in reflected light levels are tracked and used to calculate the person's heart rate.

Apple is said to have chosen the light-based technology over electrocardiography, a more accurate method which measures electrical impulses, due to the former's ability to continuously monitor heart rate with no action from the user. Most ECG-based products require multiple contacts, meaning users must either attach multiple diodes to their body or touch the product with both hands to get a reading.

Apple will likely exclude noninvasive blood glucose monitoring due to its "inaccuracy"

Many consumer-grade heart monitors —  like Withings's Pulse —  use optoelectronics. Those that feature single-contact ECG sensors often leverage proprietary and usually patented technology.

Apple has been seen contemplating embedded ECG sensors in the past, though there is little evidence to indicate where the company may be at with the technology. A 2010 patent application hinted at a method for future iPhones to identify users by their ECG signature.

Friday's report is the latest indication that Apple's expected foray into wearable devices will focus on biometrics. Well-connected analyst Ming-Chi Kuo of KGI Securities was the first to make that prediction, a case bolstered by recent hires and the revelation that Apple executives have met with the FDA to discuss "mobile medical applications."