Author contribution: Volkov AA, Budnik NV — study conceptualization and design development, shared responsibility, text preparation; Abdulaev MA — material collection; Volkov AA, Reshetnikov MN, Plotkin DV — statistical data processing; Volkov AA, Zuban ON — obtained data analysis; Volkov AA, Zuban ON, Reshetnikov MN — editing.

Compliance with ethical standards: the study was approved by the ethics committee of the Hospital for War Veterans (Minutes #1 of February 6, 2018). All participants submitted the signed informed consent forms confirming their consent to participate in the study.