Dynamics of Respiratory Rate and Heart Rate Variability when Performing a Cognitive Task of Two Levels of Complexity

The study examined heart rate variability (HRV) and respiration rate during a cognitive task (reading) at two difficulty levels. Time, frequency, and nonlinear analysis of HRV was used. It has been shown that both some indicators of HRV (HR, SDNN, RMSSD, SD2, SD2/SD1) and respiratory rate change with increasing mental load, however, they do not separately demonstrate significant differences at all three stages of the study. Therefore, for the first time for cognitive studies, an integral indicator was used that connects the parameters of the heart and respiration, the physiological cost of activity (PhysCost), which was previously used in work with athletes when they performed physical exercises to failure. Changes in the PhysCost showed that differences between a simple and complex task are observed at all stages of the study. Thus, it has been established that the difference in the functional state of a person in the process of performing a continuous task of two levels of complexity is most reliably revealed when using an integrative indicator connecting the activity of the respiratory system and the circulatory system.