Evgeny Zherebtsov

Combined use of laser Doppler flowmetry and skin thermometry for functional diagnostics of intradermal finger vessels

We introduce a noninvasive diagnostic approach for functional monitoring of blood microflows in capillaries and thermoregulatory vessels within the skin. The measuring system is based on the combined use of laser Doppler flowmetry and skin contact thermometry. The obtained results suggest that monitoring of blood microcirculation during the occlusion, performed in conjunction with the skin temperature measurements in the thermally stabilized medium, has a great potential for quantitative assessment of angiospatic dysfunctions of the peripheral blood vessels. The indices of blood flow reserve and temperature response were measured and used as the primarily parameters of the functional diagnostics of the peripheral vessels of skin. Utilizing these parameters, a simple phenomenological model has been suggested to identify patients with angiospastic violations in the vascular system.

Multimodal optical measurement for study of lower limb tissue viability in patients with diabetes mellitus.

According to the International Diabetes Federation, the challenge of early stage diagnosis and treatment effectiveness monitoring in diabetes is currently one of the highest priorities in modern healthcare. The potential of combined measurements of skin fluorescence and blood perfusion by the laser Doppler flowmetry method in diagnostics of low limb diabetes complications was evaluated. Using Monte Carlo probabilistic modeling, the diagnostic volume and depth of the diagnosis were evaluated. The experimental study involved 76 patients with type 2 diabetes mellitus. These patients were divided into two groups depending on the degree of complications. The control group consisted of 48 healthy volunteers. The local thermal stimulation was selected as a stimulus on the blood microcirculation system. The experimental studies have shown that diabetic patients have elevated values of normalized fluorescence amplitudes, as well as a lower perfusion response to local heating. In the group of people with diabetes with trophic ulcers, these parameters also significantly differ from the control and diabetes only groups. Thus, the intensity of skin fluorescence and level of tissue blood perfusion can act as markers for various degrees of complications from the beginning of diabetes to the formation of trophic ulcers.

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.

Impact of blood volume changes within the human skin on the diffuse reflectance measurements in visible and NIR spectral ranges

We consider changes in the volume of blood and oxygen saturation caused by a pulse wave and their influence on the diffuse reflectance spectra in the visible/NIR spectral range. CUDA-based Monte-Carlo model was used for routine simulation of detector depth sensitivity (sampling volume) and skin spectra, and their variations associated with physiological changes in the human skin. The results presented in the form of animated graphs of sampling volume changes for scaling of the parameters of the main human skin layers related to the results of experimental measurements are of particular interest for pulse oximetry, photoplethysmography, Doppler flowmetry, reflectance spectroscopy.

Laser Doppler flowmetry in blood and lymph monitoring, technical aspects and analysis

The aim of this work was to study the possibilities of the laser Doppler flowmetry method for the joint study of microhaemo- and lymph circulation of human skin. Conducting a series of experimental studies allowed to trace the relationship of recorded signals of microcirculation of blood flow and lymph flow, as well as to study their oscillation nature by using wavelet analysis.

Spectral analysis of the blood flow in the foot microvascular bed during thermal testing in patients with diabetes mellitus

Timely diagnostics of microcirculatory system abnormalities, which are the most severe diabetic complications, is one of the major problems facing modern health care. Functional abnormalities manifest themselves earlier than the structural ones, and therefore their assessment is the issue of primary importance. In this study Laser Doppler flowmetry, a noninvasive technique for the cutaneous blood flow monitoring, was utilized together with local temperature tests and wavelet analysis. The study of the blood flow in the microvascular bed of toes was carried out in the control group of 40 healthy subjects and in two groups of 17 type 1 and 23 type 2 diabetic patients. The local temperature tests demonstrated that the diabetic patients have impaired vasodilation in response to local heating. The tendency for impaired low frequency pulsations of the blood flow associated with endothelial and neurogenic activities in both diabetes groups was observed. Local thermal tests induced variations in perfusion and its spectral characteristics, which were different in the groups under study. In our opinion, the obtained preliminary results can be a basis for further research and provide a deeper understanding of pathological processes that drive microvascular abnormalities caused by diabetes mellitus.

Hyperspectral imaging aided by artificial neural networks for functional skin characterization (Conference Presentation)

We introduce a portable hand-held hyperspectral imaging system for the functional diagnostics of skin and vascular system. Hyperspectral image analysis aided by artificial neural networks (ANN) allows to reconstruct major physiological parameters of human skin nearly in real-time. The developed device provides spatial distribution of blood volume fraction, oxygenation and melanin content within skin. Special attention has been paid on the system validation and calibration using specially developed skin mimicking phantoms with confirmed optical properties. The device was built on the basis of unique hyperspectral snapshot camera utilizing a micro Fabry-Perot filter providing real spectral response in each pixel (no interpolation is used in image formation). A broadband illumination unit combined with the camera is based on the fiber-optic illuminator providing uniform distribution of light intensity and utilizes halogen lamp. The specially developed ANN algorithm was used to perform the inverse problem solution for quantitative assessment of major parameters of skin based on the measured hyperspectral images. A set of diffuse reflectance spectra of human skin imitated by the Monte Carlo method developed in-house has been used extensively for the training of ANN. The volume fraction of blood, oxygen saturation, melanin content and thickness of the epidermal layer were used variable parameters in the utilized seven-layer Monte Carlo-based skin model. The total training set contained 45,198 spectra in the range of 505–800 nm simulated with a step of 5 nm. The developed imaging system has been successfully used to perform the occlusion test measurements with healthy volunteers.

Fibre-optic probe for fluorescence diagnostics with blood influence compensation

To minimise the influence of blood content on the fluorescence measurements in vivo, a fibre optical probe combining fluorescence and diffuse reflectance measurements was developed. For the inverse solution of the blood content recovery, a set of neural networks trained by the Monte Carlo generated learning set was used. An approach of fluorescence measurements triggered by simultaneous real-time measurements of blood content in living tissue during moderate changes in contact pressure of the optic probe is proposed. The method allows one to decrease the necessary pressure on the probe as well as increase the repeatability of the measurements. The developed approach was verified in a series of experiments on volunteers with fluorescence excitation at 365 nm and 450 nm. The proposed technology is of particular interest in the development of new fluorescence-based optical biopsy systems.

Use of fluorescent optical fibre probe for recording parameters of brain metabolism in rat model

This studiy was carried out on groups of clinically healthy male Wistar rats. Animals received distilled drinking water ad libitum for 1 month, water containing succinic acid, water containing zinc sulphate and succinate zinc. Using the method of fluorescence spectroscopy, the parameters of brain metabolism in vivo in a model of laboratory rats was investigated. Based on data obtained by fluorescence spectroscopy, we have registered a change in the degree of cellular respiration in different structures of the cerebral cortex with the toxic effect of zinc compounds and succinic acid on the oxygen exchange process.

Verification of NADH content measurements by portable optical diagnostic system in living brain tissue

The overall aim of this study was verification of the possibility to register the change of NADH fluorescence in live tissue by a portable diagnostical laser system with fibre optical probe output and excitation by compact semiconductor UV light source. The measurements were conducted in fresh brain tissue slices of Wistar rat pups. The fluorescence measurements were conducted simultaneously at intervals of 5 s by the microscopic system with excitation at 360 nm and registering of the emitted fluorescence light at 455 nm and by the tested diagnostical system equipped with the fibre optical probe with excitation at 365 nm and registration of the fluorescence spectrum by the inbuilt spectroscopic subsystem. To modulate the mitochondrial function in the living cells, in the chamber sequentially were added 1 μM FCCP and 1 mM NaCN. The comparisons between the curves registered by the methods allowed us to find well agreement between the microscopic measurements and measurements by the fibre optical probe. The obtained results prove that the tested diagnostic system is capable of sensing the changes in brain metabolic activity associated with the NADH content alterations within the physiological range.