Compliance with ethical standards: the study was approved by the Ethics Committee of Amur State Medical Academy (Protocol № 10 dated November 20, 2019); the study conformed with the guidelines for the medical research involving human subjects. Voluntary informed consent was obtained from all the participants.

Author contribution: Molchanova EE — study design; data acquisition and analysis; manuscript preparation; Polunina VV, Polyaev BA, Plotnikov VP, Lobov AN, Parastaev SA — study concept and manuscript preparation. All authors read and approved the final version of the manuscript.