Author contribution: Setko NP — study design and concept, manuscript editing; Zhdanova OM — manuscript writing, collection and processing of the material, statistical processing; Setko AG — manuscript writing, editing; all authors — approval of the final version of the article, responsibility for integrity of all of its parts.

Compliance with ethical standards: the study was conducted in compliance with the principles of the Declaration of Helsinki (Fortaleza, 2013). Each participant of the study submitted a signed voluntary informed consent form.