Evaluation of microcirculatory disturbances in patients with rheumatic diseases by the method of diffuse reflectance spectroscopy

Immunoinflammatory reactions affecting the state of the microvasculature play the key role in the genesis of rheumatic diseases. Therefore, it is important to develop new methods for the early detection of microcirculatory disorders. The purpose of this study was to assess the possibilities of diffuse reflectance spectroscopy used to identify microcirculatory disturbances in patients with rheumatic diseases by measuring skin blood supply and oxygenation rate and their relationship with the varying degrees of inflammatory activity. A total of 36 patients with rheumatic diseases and 31 healthy volunteers took part in the study. We analyzed the skin diffuse reflectance spectra recorded on the palmar side of the distal phalange of the right middle finger using a FLAME spectrometer. The erythema index and saturation rate were calculated to quantify the content of hemoglobin and oxygen saturation of tissues in both groups. The differences in the parameters under study between the groups were found to be statistically significant. The average value of erythema index was twofold higher in patients with rheumatic diseases with the second degree of inflammatory activity and about 2.5-fold higher in patients with the third degree of inflammatory activity, compared to the control group. This fact indicates impaired blood circulation with increased blood flow caused by inflammatory processes. Thus, diffuse reflectance spectroscopy can be used as an additional non-invasive diagnostic test for assessing the severity of microcirculatory disturbances and the activity of inflammation in rheumatic diseases.