EARSATS-19: In-ear Measurement of Blood Oxygen Saturation in COVID-19 Follow up

Non-invasive ambulatory estimation of blood oxygen saturation (SpO2) has emerged as an important clinical requirement to detect hypoxia (low blood oxygen) in the delayed post-infective phase of COVID- 19, where dangerous hypoxia may occur in the absence of subjective breathlessness. This now commonly termed 'silent' hypoxia presents an immediate clinical driver.

The COVID-19 pandemic places substantial pressure on clinical resources with ambulatory patients who were often discharged home to be cared for on virtual wards with daily telephone consults. Now the initial surge has settled, we are beginning to understand the challenge of following up patients who have had COVID-19 at volumes that mean doing this in a timely fashion is not possible (BTS Guidance 6 weeks).

There is mounting concern that the huge number of COVID-19 survivors will be at increased risk of chronic lung diseases such as pulmonary fibrosis, where early capture of patterns of low SpO2 could unearth desperately needed insights for preventing disease progression. The inconveniences, impracticalities and inaccuracies of conventional measurement of SpO2 (the percentage unit of blood oxygen) using a conventional finger probe for discrete readings are well established. A user-friendly, remote continuous SpO2 monitoring tool would therefore allow the rapid identification of any deterioration post discharge and also track longer-term recovery, allowing the accurate triage of patients to limited follow up resources.

Hearables and In-Ear Photoplethysmography

Reflective photoplethysmography (PPG), which uses a changes in the ratio between red and infrared light to estimate SpO2, can be measured from any site with skin that has vasculature, but for SpO2 measurement has conventionally been from fingers or sometimes the earlobe. The recent interest in the development of Hearables9 has promoted the ear canal as a preferred site for the measurement of vital signs in digital health technology. Indeed, the ear canal, which acts as a shield from external electrical noise (resembling a nature-built Faraday cage), represents a unique opportunity for physiological measurements, due to its general fixed position relative to the heart (ear-electrocardiogram) and proximity to the brain (ear-electroencephalogram). Relative to limbs, the head moves less in daily life and this is one property that has helped establish the feasibility of wearables to detect Ear-ECG and Ear-EEG.