**5. Conclusions**

In the study, the measurement of perfusion is complemented by a new parameter based on the calculation of cumulative sums from the power spectrum of the photodetector signals. The described diagnostic approach allows for revising the known protocols for characterising blood microcirculation parameters based on LDF measurements. In the context of the proposed signal processing technique, a new feature space can be added to the set of known diagnostic parameters expanding the range of applications for the LDF. The translation of the study results suggests that routine diagnostics procedures do not require significant modifications of the standard configuration of LDF channel. Also, the method does not involve any additional measurement channels (fluorescence, diffuse reflectance spectroscopy, and others) that still demonstrate relatively high accuracy of classification for the diagnostics of impaired blood microcirculation, even being tested in a limited size of the cohort of patients with T2DM.

**Author Contributions:** I.K.: experimental studies, data processing, signal processing, drafting the manuscript. E.Z.: co-supervising, the concept and implementation of the measuring setup, drafting the manuscript, data analysis, funding acquisition. G.M.: the research protocol, experimental studies in hospital. K.P.: finalizing the article; A.D.: supervising, study conceptualisation, discussion, funding acquisition. All authors edited manuscript. All authors have read and agreed to the published version of the manuscript.

**Funding:** The reported study was funded by the Russian Foundation for Basic Research (RFBR), project numbers 19-32-90253. E. Zherebtsov acknowledges the funding from the Academy of Finland (grant number 318281, data analysis) and Russian Science Foundation (grant number 20-75-00123, development of the experimental setup).

**Institutional Review Board Statement:** The study was conducted according to the guidelines of the Declaration of Helsinki, and approved by the Ethics Committee of Orel State University (Minutes No. 15 dated 21 February 2019).

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.

**Conflicts of Interest:** The authors declare no conflict of interest.
