Pulse oximetry in the neck - a proof of concept

Oxygen saturation levels are routinely monitored in clinical settings. Pulse oximetry, in transmittance operation mode, is the most common method of estimating oxygen saturation (SpO₂). This is inexpensive and non-invasive and thus allows for long-term monitoring. However, it suffers from issues such as signal integrity, reliability and patient comfortability. As a result, there is an interest in exploring other locations on the body where oxygen saturation can be measured reliably. In this paper, a wearable device has been designed to study the feasibility of extracting photoplethysmogram (PPG) signals at the neck in reflectance pulse oximetry mode. It explores the signal integrity and strength compared to other locations as well as the presence of motion artefacts in that location. The results demonstrate that the PPG signals acquired at the neck show a very strong correlation (r=0.82) with the SpO₂ values obtained using a commercial device. Further, the SpO₂ values are calculated with an accuracy of 98.6%.

I. Introduction

Oxygen saturation is an essential physiological parameter that indicates the level of oxygen in a person's blood. It is measured using arterial blood gas (ABG) test where a sample of blood is drawn from an artery usually in the wrist or arm of a person. Oxygen saturation (SaO₂) values are indicative of the overall health of an individual. For a healthy person, the SaO₂ value is typically above 90% [1]. Only if the oxygen level is sufficient can the body function properly. Lack of oxygen results in hypoxia which might lead to brain damage or even death. Because of its utility as a primary indicator of wellbeing, it is commonly used in hospital settings to monitor patients with respiratory and cardiac problems as well as those undergoing or recovering from surgical procedures [2].