SMU Unveils New Research for Monitoring Breathing Modes via In-Ear Microphones

This innovative research can open doors for new uses of in-ear wearables for personalised health monitoring to improve athletic performance

By the SMU Corporate Communications team

06 Nov 2024

If you love running with your earbuds, you can up your game with a new piece of sensing technology developed by researchers at Singapore Management University (SMU) who have developed an innovative technology using in-ear microphones to monitor breathing modes.

The breathing mode monitoring system is called BreathPro, and is developed by a research team led by Assistant Professor Ma Dong of SMU's School of Computing and Information Systems, with collaborators from the University of Cambridge.

Breathing modes are related to performance

Running is practised by some four in 10 people in Singapore at least once a week, especially men aged in their 20s and 30s, like hundreds of millions worldwide. Runners breathe using their mouth or nose, or a mix of both. The best breathing mode during running depends on the intensity of the run, the temperature and humidity of the environment.

By monitoring four breathing modes used during running (namely breathing in and out through the nose, and breathing in and out through the mouth) which correlate with the volume of oxygen exchange by the runner, runners can run more efficiently and improve their endurance. For example, they can be guided with different breathing techniques, at different stages of a run to help them perform better as athletes.

This breakthrough offers a non-invasive, cost-effective and most importantly, a motion-resilient solution for monitoring vital signs during exercise in real-life scenarios. BreathPro is a novel piece of research as commercial wearable devices currently cannot detect whether a runner is breathing through the mouth or the nose. Should the runner show symptoms like overbreathing, or shortness of breath, the BreathPro system can identify these in real time and runners can be to relieve them or even be trained learn to avoid them.

"The same principle can be also extended to heart rate monitoring during running. Consequently, there is potential for collaboration with health and exercise experts to develop a personalised and adaptive coaching system for runners, whatever their age or fitness levels, based on the measured heart rate and breathing mode. The technology opens doors to more reliable heart and breathing monitoring in daily life conditions," said Asst Prof Ma Dong. He has been studying this area since 2020 when he was doing his post-doctoral studies at the University of Cambridge and his research is among the first to explore this application.

How BreathPro works

The biggest advantage of BreathPro is that it is noise- and motion-resilient and can maintain reliable estimation when he or she is moving in noisy conditions. This is unlike current wearables on the market, which rely on a conventional technology called PPG (photoplethysmorgraphy). PPG generally also cannot measure breathing modes, and the data PPG collects is easily distorted by the wearer's movements.

The innovation relies on a phenomenon called the occlusion effect, which is the increased sensitivity or volume of sounds produced by the body when someone's ears are covered. Normally, the different organs in the human body create different sounds that move through bone conduction and escape from the opening of the ear canal. When wearing wireless earbuds, the opening of the ear canal is blocked, forming a closed space between the earbuds and the eardrum. With the canal blocked, the sound waves will be trapped within this cavity which can amplify the low-frequency sound that the device can detect.

The SMU team recruited 25 participants, who used in-ear and out-ear microphones to capture a strong breathing signal with clear inhale and exhale transitions. Researchers also attached another microphone under each participant's nose in direct contact with the breathing airflow, with the collected audio serving as ground truth for validation. The team meticulously designed a comprehensive suite of signal processing and machine learning techniques, by leveraging out-ear signals to attenuate environmental noise, thereby improving the quality of in-ear breathing sounds for accurate breathing mode estimation.

The results demonstrated that BreathPro achieves an accuracy of 98.52% in classifying four breathing modes, namely nasal inhalation, nasal exhalation, oral inhalation, and oral exhalation. Then they tested the trained model on new participants in new environments, and the results demonstrated that the developed approaches can be generalised to various real-world motion scenarios.

This fills a gap in the fitness monitoring landscape as there is no commercial wearable device that can detect breathing mode during physical training.

Using BreathPro for running

In addition to breathing mode monitoring, the in-ear microphone sensor can also capture the landing poses, namely forefoot strike, heel strike, and overstride. This is critical for the safety of runners. Specifically, every foot strike generates a vibration during landing, which is transmitted to the ear canal through bone conduction and amplified by the occlusion effect. Depending on the landing posture, the vibration signals received inside the ear exhibit various patterns, which can be differentiated with machine learning.

The SMU team tested the foot striking monitoring system with the same 25 subjects, and achieved 87.8% accuracy in detecting three different landing poses. This project demonstrates portable, accurate, and lightweight running gait monitoring, facilitating safer and more efficient running practices.

SMU exploring prospects for commercialisation

A provisional patent for BreathPro has been secured, and SMU's Institute of Innovation and Entrepreneurship (IIE) is exploring opportunities for commercialisation.

Said Dr Sze Tiam Lin, the Senior Licensing Advisor of SMU's Institute of Innovation and Entrepreneurship: "Using ear microphones to monitor breathing mode is truly novel. IIE looks forward to working with companies to commercialise this non-invasive, real-time solutions to track respiratory health. It provides seamless integration into wearable devices offers potential applications in healthcare, sports and wellness."

In recent years, in-ear wearables have offered a new platform for ubiquitous computing by enhancing ear-worn devices with sensing technology. Also, the market for wearable technology industry is growing rapidly, as users appreciate its convenience and interactivity.

This has prompted researchers to explore what such small in-ear wearables can detect, as the ears offer a space to collect data that is less vulnerable to distortions caused by the motion of the wrists. As the ears are located close to the brain, the heart, and facial muscles, a wealth of data can be harvested with potential benefits. BreathPro is one step forward in improving the efficiency of runners across different terrains and weather conditions.

Enclosure: BreathPro research