Humans require oxygen for everyday life. It is a key component in many body functions so it logically follows that measuring oxygen and oxygen usage in the body can be extremely beneficial. Healthcare and sports are two main fields that come to mind. On the market today, there are hundreds of devices that measure various body metrics and oxygen levels and saturation are no exception. One device that measures the the oxygenation saturation in body tissues is a portable near-infrared spectroscopy (NIRS) apparatus created by Gutwein et al.[1]. Gutwein et al. applied for a patent titled “Method and Apparatus for Assessing Tissue Oxygenation Saturation” on March 22, 2017 and the patent was approved and filed roughly 5 months later on September 28, 2017. Gutwein et al. also had a previous patent “Portable Near-Infrared Spectroscopy Apparatus” filed in October 2016. The basic patent information is outline below[1]:
- Patent title: Method and Apparatus for Assessing Tissue Oxygenation Saturation
- Patent number: US 2017/0273609 A1
- Patent filing date: March 22, 2017
- Patent issue date: September 28, 2017
- Inventors: Luke G. Gutwein, Clinton D. Bahler, Anthony S. Kaleth
- Assignee: Indiana University Research and Technology Corporation
- U.S. Classification: CPC – A61B: 5/14552, 5/6807, 5/02055
- Claims: 20
Invention & Claims
This invention is an apparatus and method developed for assessing tissue oxygenation saturation during physical activity. The portable near-infrared spectroscopy (NIRS) apparatus comprises of a wearable article of clothing, namely a shirt, pair of shorts or a calf sleeve. It also contains a spectroscopy probe, a near-infrared light source and a photodetector coupled to the article of clothing used. The probe is configured to measure oxygenation saturation in skin dermis, adipose tissue (fat) or muscle fascial layer[1].
Figure 1. Image depicting user wearing device. The wireless probe can be incorporated into different wearable articles.
Why Is This Important?
There is a need for such a device in a multiple fields, namely healthcare and sports. This NIRS apparatus has applications in clinical settings, sports industry and in exercise physiology research. Clinicians, doctors and researchers can benefit from a portable NIRS device in monitoring and diagnosing disease states, including:
- septic shock
- real-time tissue perfusion analysis during surgery
- peripheral arterial disease
The NIRS device is highly sensitive to changes in Muscle tissue oxygenation (StO2) and during exercise, the NIRS signal is considered to reflect the balance between oxygen delivery and utilization. This can have multiple applications in sports including looking at how efficient oxygen flow is and to show what muscles are specifically being activated and which aren’t; this can indicate whether or not proper form is being used[1].
Tech Talk: How It Works
NIRS is an optical technique that allows for continuous non-invasive monitoring. This technique is founded on the Beer-Lambert Law. The Beer- Lambert Law is a linear relationship between absorbance and concentration of an absorbing species[2]. 
Where A is the measured absorbance, a(𝜆) is the wavelength-dependent absorptivity coefficient, b is the path length, and c is the analyte concentration.
The NIRS device measures hemoglobin oxygen saturation in microvessels (arterioles, capillaries, venules) by applying this Beer-Lambert Law and the using the differences in light absorption coefficients of oxyhemoglobin and deoxyhemoglobin. The device uses these absorption characteristics to calculate changes in oxygenated & deoxygenated hemoglobin in skin, fat, or muscle tissues[1].
What Sets It Apart?
Early devices that measured oxygenation saturation were mostly limited to research usage. Since then there have been advances in the field leading to the creation of smaller probes and utilizing wireless probes instead. The PortaMon created by Artinis Medical Systems (B.V. Netherlands) is currently the most common portable NIRS device on the market. There are still problems with these devices however. Namely issues with:
- Device size
- Motion signal artifacts
- Adipose (fat) tissue thickness
The size of the probe is based off the required penetration depth. In order to get the 2-6 cm of depth required, the probes tend to be bulkier. Another issue is motion signal artifacts that raise questions concerning the reliability of some devices. These artifacts are created by instabilities (for example, lose of contact) at the skin-probe interface. Finally, the thickness of the adipose tissue can limit the depth of penetration achieved[1].
The main advantage of this device is that it can measure levels in skin, fat or muscle tissue over any sport or activity including running, bicycling, swimming and weightlifting. Some additional features are that this NIRS device and method can measure the user’s heart rate, respiratory rate and body temperature[1].
Citations:
[1] Gutwein et al. (2017). Method and Apparatus for Assessing Tissue Oxygenation Saturation. US 2017/0273609 A1. U.S. Patent and Trademark Office
[2] Beer-Lambert Law. (n.d.). Retrieved March 10, 2020, from http://life.nthu.edu.tw/~labcjw/BioPhyChem/Spectroscopy/beerslaw.htm
