Funding: ordered by the state under the research topic "Impact of the new coronavirus infection SARS-CoV-2 on the functional parameters of respiratory system during the convalescence period" (code: "Post-COVID functional diagnostics").

Acknowlegements: we would like to thank Zaitov M. R., engineer of ZAO Meditsinskioye Sistemy, for technical support.

Author contribution: Savushkina OI — study design development, clinical material collection, analysis and interpretation of the results, article authoring; Malashenko MM — clinical material collection, interpretation of the results; Chernyak AV — study design development, clinical material collection, analysis and interpretation of the results, article editing; Kryukov EV — article concept development, editing; Sinitsyn EA — interpretation of the results, article editing; Zykov KA — article editing, approval of the final version of the manuscript.

Compliance with ethical standards: the study was approved by the Ethics Committee of the Pulmonology Scientific Research Institute of the FMBA of Russia (minutes № 01-21 of May 14, 2021). All study participants signed informed consent.