XII Международная студенческая научная конференция Студенческий научный форум - 2020

Medical thermography is a diagnostic method that is currently gaining popularity due to its non-invasive nature and it gives also sufficient information.

It was found that under stress in a person, bloodflow in the central region of the forehead increases, and this leads to a local temperature increase, which can be measured using a thermal imager [1]. To determine the level of stress, it is necessary to select a rectangular forehead area that contains the central vessels (Fig. 1)

Figure 1. - selection of the forehead in the thermogram

To maintain the position of the selected area, tracking is performed on head movements. Calculations are carried out using temperatures of 10% of the pixels, which have the highest temperature and correspond to the central vessels of the forehead (Fig. 1).The temperature signal from the forehead is calculated by averaging the temperatures of the warmest points for each frame of the sequence of thermograms.

 To recreate a stressful situation, you can use the Stroop test [3, 1]. This method is based on the fact that the subject is presented with words that indicate the name of the color and have different colored letters. For example, the word "red" is written, and the letters of this word are black. The correct answer in this case is black. Uncertainty in response introduces a conflict between spoken words and visible input.

 During the run of the Stroop test, the time for presenting words gradually decreases, this leads to a stressful situation caused by a decrease in the response time and an increase in the number of incorrect answers.

To determine the stress state, a thermogram of a person in a calm state is preliminarily recorded for 10 minutes, and then the Stroop test is launched, which lasts 10 minutes. In order not to influence the subject, the operator who controls the testing procedure is located behind a screen. Recording is carried out with a frequency of about 30 frames per second; time dependences of temperature, blood flow and blood volume are obtained in a calm state and during the passage of the Stroop test.

Blood flow velocity is inversely proportional to the deviation of skin temperature from the temperature of the core of the human body [2]. Assuming a small component of metabolic heat, the thermodynamic equation for blood flow velocity can be written as:

,

Where Vs is the blood flow at skin level, =37°C (310° K) is the temperature of the human body, Ts is the temperature of skin surface , Kc= 0.168 kcal/(m·hour·К) – skin thermal conductivity, d– distance from the skin surface to the point where the core temperature is measured,
Сand Cs are constant.

The value of is constant. The derivative is calculated by difference approximations, where the temperature increment is calculated by comparing successive frames, and the time increment is equal to the time interval between frames.

Thus, it is possible to count the value , the integration of which gives the blood flow velocity on the surface Vs. Blood volume (Fig. 2.c.) is calculated by summing the values of the time dependence of blood flow velocity (Fig. 2.b.).

The calculated blood volume is used as a heat indicator of stress. The level of stress can be reliably determined by measuring energy consumption by the level of oxygen consumed by a person during breathing.

Figure 2. - Temporal dependences of temperature - a, blood flow velocity - b and blood volume - c. 1 - data obtained in a calm state, 2 - data obtained during the passage of the Stroop test [1]

The dynamics of thermal fields in the face of a person can serve as one of the indicators of changes in his emotional state, which in turn can be used in various fields: when diagnosing the condition of patients in medical organizations, people whose professional activities are associated with the risk of accidents (air traffic controllers, drivers, drivers) or during the training of special forces to assess the body's reactions to various stress loads that arise in certain combat situations.

1.Puri C., Olson L., Pavlidis I., Levine J., Starren J. StressCam: non–contact measurements of users’ emotional states through thermal imaging // Conference for computer–human interaction (CHI), Portland, Oregon, USA. 2005. P.1725 – 1728.

2. Pavlidis I., Levine J. Monitoring of periorbital blood flow rate through thermal image analysis and its applications to polygraph testing //Proc. Of 91 the 23rd Annual EMBS Int. Conf. Istanbul, Turkey. 2001. Vol. 3. P. 2826– 2829 vol.3

41. Stroop J.R. Studies of interference in serial verbal reactions // Journal of Experimental Psychology. 1935. Vol. 18. P. 643 – 662.