Electronic assistant to detect stress

In principle stress is a healthy reaction. In the short term, the stress reaction helps the body to adapt to the stressor. However, if the organism has no time to recover and the stress reaction proceeds over longer time, this can have adverse effects like cardiovascular diseases or mental illness. Within the EU, stress is regarded as the second biggest cause of work-related health problems.

In order to measure stress levels in everyday life, Bert Arnrich, Cornelia Setz, Gerhard Tröster and their teams of researchers at ETH Zurich's Electronics Laboratory have devised an electronic stress assistant. This has been described in recent publications.

The researchers used different indicators to determine stress levels, including the skin conductance on the fingers, the heart and breathing rates, and the amount of the stress hormone cortisol in saliva. Furthermore, they measured leg, foot and arm movements and covered a chair with pressure sensors to record how often a person changes his or her posture while seated.

Stressing people

To test the accuracy of their measurement system, the ETH-Zurich researchers conducted a large-scale study in collaboration with psychologists Roberto La Marca and Ulrike Ehlert from the Psychological Institute of the University of Zurich. Over 30 subjects were invited to take part in their stress study which was disguised as a simple mental arithmetic test. In reality, however, they had to solve specific mathematical problems on a computer under time and social pressure.

If the subject was good at solving mathematical tasks, the program automatically selected more difficult tasks. As a result none of the subjects was able to solve more than half of the tasks, even if they were adept in mathematics. Moreover, subjects were constantly shown that their performances were below average compared to a "standard group." Finally, the investigator placed the participants under additional pressure by giving them harsh feedback on their performances. "The condition simulated here comes very close to actual work situations" explains Roberto La Marca. The subjects were then given a second opportunity to tackle the tasks without any time pressure or pressure from the investigators.

Assistant measures stress accurately

The results of the study revealed that the stress assistant worked well: in 83 percent of the cases the system was able to recognize stress levels correctly based on skin conductance. This is due to the fact that the body secretes more sweat when under stress, especially on the palms and soles of the feet. As a result the conductance of the skin is increased. "The value obtained is very high," says Arnrich.

The pressure sensors on the chair also provided useful information for stress recognition and allowed to recognize stress reliably in 73 percent of the cases. Although some subjects froze, most of the subjects moved back and forth more often on the chair when under stress.

"One method alone is not enough to determine stress reliably," stresses Arnrich. Researchers are only able to make assertions about a person's stress level after combining methods and excluding other factors that cause sweating such as physical exertion.

Fire fighters and manic depressives

Professor Gerhard Tröster's senior assistant is now developing electronic stress recognition further within two new EU-funded projects. He would like to study stress levels and physical condition of fire fighters who work under time pressure and high mental strain. This makes them prone to stress. The researchers would also like to find out whether their methods can be used on patients who suffer from manic depressive disorders. They want to investigate whether manic and depressive conditions can be measured and how severe they are. "This would support the work of psychotherapists who could then measure how well the therapy is working," hopes Arnrich.

Some research still needs to be done to permanently monitor stress at work and recognize it at an early stage. "Some of the sensors are still too uncomfortable," Arnrich points out. Moreover, the scientists have to devise suitable methods for accurately discerning the daily stress level from the acquired data.

Sensors in your socks?

For the time being, however, the technology could help monitor stress in individual cases and provide the users with feedback on their stress levels. Arnrich's team is already planning ahead, and are developing more comfortable sensors. Options include measuring skin conductance on feet since the inner side of the feet react similarly to the palm of your hand, i.e. with increased perspiration. Appropriate sensors could be integrated into normal socks. Therefore it could soon be possible for people and doctors to access information on daily stress levels around the clock and prevent stress-related illnesses.