Group of flight instructors at the reactor school.

Group of students at the reactor school.

The HR HRV interval of the heartbeat (variations in the time interval between beats) was used as a measure of autonomous modulation, and the Firstbeat Bodyguard monitor (Firstbeat Technologies, Jyväskylä, Finland) was used to record HRV data during the session with emergency situations in the flight simulator. Data was downloaded from the devices to a computer using Firstbeat Uploader software (Firstbeat Technologies), and all R-R interval series were imported into the Kubios software package (University of Eastern Finland, Kuopio, Finland). To calculate the autonomous equilibrium, the commonly used HRV method based on the Poincaré graph was used (Brennan et al., 2001; Mourot et al., 2004).

It indicates the degree of activation of the Parasympathetic Nervous System on the cardiovascular system. It is obtained from the square root of the mean value of the sum of the squared differences of all successive RR intervals. This parameter reports the short-term variations of the RR intervals. It is directly associated with short-term variability.

It is an index described by Naranjo-Orellana et al. to facilitate physiological interpretation of Poincaré plot. It is expressed as the inverse of the SD2 diameter multiplied by 1000 and is considered directly proportional to the sympathetic activity in the sinus node.

It is also described by Naranjo-Orellana et al., S/PS is expressed as the quotient of SS and SD1, and it is considered to reflect autonomic balance - that is, the relationship between sympathetic and parasympathetic activity

It indicates the sensitivity of short-term variability in HRV non-linear spectrum. It is considered an indicator of parasympathetic activity.