Putting your finger on detecting sleep apnea

Belgian start-up, Ectosense, has developed a finger sensor to determine if sleep apnea is the cause of fatigue. The NightOwl home sleep test sensor uses Nordic Semiconductor’s nRF52832 and nRF52810 SoCs, depending on the model.

There are two versions of the NightOwl –  a three-day rechargeable or a 10-night disposable model. Both take the form of a small, wearable finger sensor. The device records photoplethysmography (PPG) readings using a 50Hz optical reflective sensor. This shines light onto the finger and from the intensity of reflections determines the oxygen saturation level of the blood (SpO2). Sudden changes in this blood oxygen level have been found to be the most accurate indicator of the presence of sleep apnea where an individual’s breathing stops temporarily while asleep. This forces the patient to wake up continuously, preventing them from getting a good night’s sleep.

The optical sensor is supported by an accelerometer that can be used to pause monitoring to conserve battery power if the wearer wakes up and starts moving about during a typical analysis period (eight to 10 hours). Collected data is continuously streamed to a user’s smartphone via Bluetooth Low Energy using the SoC. It is processed in the cloud using a sensor data algorithm developed by Ectosense, which looks for sleep apnea events. Collected results are displayed on an on-line dashboard which doctors can log-in to.

“We’ve long been trying to convince doctors that the NightOwl is as effective at detecting sleep apnea as some of the more traditional and clunky equipment used in medical sleep labs,” explains Wout Geeurickx, an electronic system design engineer at Ectosense. “The closure of sleep labs due to Covid-19 has seen many doctors forced to trial our NightOwl device until they can have their patients undergo a traditional all-wired sleep testing procedure again when the labs reopen. Our disposable variant also addresses an urgent need for devices free of contamination risk,” he added.

Geeurickx says the Nordic Bluetooth Low Energy SoCs helped the NightOwl to be one of the smallest home sleep apnea monitors available. This is important so that wearing it is comfortable and unobtrusive so as not to interfere with the patient’s sleep and affect the test accuracy. The device is the size of a fingertip, and is self-contained – it does not require an external, wrist worn device common, which competitive devices do.

Ectosense also points out that the NightOwl is designed to accurately measure drops in blood oxygen levels, and these are proving to be a key indicator of a serious health deterioration in those who have contracted Covid-19. The company says it is investigating how the NightOwl to be adapted or repurposed into a low-cost, medical wireless pulse oximeter to help protect hospital and medical staff.

The NightOwl is FDA- and CE-approved for medical home sleep testing. The NightOwl can also store data internally for specific offline use cases where the user does not have access to a smartphone.


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