Since 2021, we have been collaborating with the team of Professor Julia Dobrovolná from Masaryk University in Brno on a project to measure stress using an innovative thermodynamic method.
A lot is written and said about stress, but we have almost no direct methods of measuring stress load: we can track something from a blood test, and every smartwatch can show stress load, which it derives from subtle irregularities in heart rate (so-called heart rate variability – HRV). Blood draws are uncomfortable and not suitable for long-term monitoring. HRV is an excellent method, but indirect and inaccurate: stress must affect the autonomic nervous system, which affects the cardiovascular system, and only then do we measure this.
The uniqueness of the new SEL (Stress Entropy Score) method is that both physiological and environmental data are input into the algorithm used for the calculation, and the calculation is based on entropy. This allows direct measurement of the effect of stress on the organism in real time. In layman’s terms – the person being observed is sensed, for example, inhaled and exhaled oxygen, carbon dioxide, skin temperature, and at the same time the temperature and humidity of the environment and the ambient air flow rate are measured.
However, there is no instrument on the market that allows all these variables to be measured simultaneously and ideally processed into an algorithm. So the researchers approached our company to invent and build something like this for them.
The scientific prototype required special electronics and software
For the calculation, we have to measure about forty parameters of the body and the environment using more than twenty sensors. Some of the measurements are standard, but the instruments to measure some parameters don’t exist at all or are only able to work in the lab, you can’t just stick them on an athlete moving around outside. And most importantly, they don’t measure everything together: just downloading data from multiple devices and syncing them in time would be a terrible job.
Sensors for measuring physiological functions
So the first thing we did was come up with the sensor system – what to use, how to place them on the body, how to ensure their smooth operation and reliability of measurement. The most important are the highly accurate skin surface temperature sensors, for which we have subsequently developed a wireless variant to make it more comfortable for the wearer.
A special sensor was made for the respiratory mask because the researchers wanted to focus on details that commonly available instruments do not measure and maintain accuracy comparable to laboratory instruments. In the future, we plan to make this mask completely wireless as well, and to allow measurements without the mask, as the reduction in accuracy does not matter in many cases.
Measurement of environmental data
Ambient sensors are common air flow meters, barometers, hygrometers and thermometers that are placed on the vest so that they are in contact with the environment of the person being measured.
Tailor-made software
The software for the instrument is quite comprehensive. The very basic function we addressed was recording the data onto a memory card, from which scientists can then download and evaluate it. We used the European standard data format EDF+.
Ever since the beginningBut we knew from the beginning that the facility was really many sensors and there is a risk that one of them will not be 100% reliable (it will stick badly, it will be defective…). That’s why we focused on the ability to display raw data in the form of graphs on all inputs using a web interface that you can connect to from a tablet or laptop via wi-fi. Currently, the instrument already calculates the complete analysis and displays the stress score in addition to the raw data.
Even prototypes must be safe
Although it is still a prototype for scientific purposes, it must be safe and meet medical standards. In addition to electrical safety, which is crucial when we connect something to a human being (yes, we also put a few kilovolts into such prototypes as part of our tests to verify the safety of the insulation), biocompatibility is also important.
We addressed biocompatibility both with the temperature sensors themselves, which are glued to the body, and with the breathing mask. For the latter, it was necessary to shape the attachment with the air flow sensor and the sampling tube of the oxygen and CO2 sensor and to ensure the possibility of easy sanitation.
We chose a special softened resin complying with ISO 10993 and FDA-2013-D-0350 as material and used SLS printer for production. This allowed us to create components with very fine details in small series.
In conclusion, we can say that even with a relatively small budget dependent on a research grant, the a working prototype was produced relatively quicklythat serves its intended purpose. It has been in operation for more than 3 years and scientists have used it not only here in the Czech Republic, but also in research at the Czech polar base in Antarctica and on a simulated ESA mission in Iceland. In the future, a mission into space is also being considered.
