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Blood microcirculation is the site of control of tissue perfusion, blood-tissue exchange, and tissue blood volume. Despite the many irregularities, almost ubiquitously, one can recognize in microcirculation vessels a hierarchy of arterioles and venules, organized in tree-like structures, and capillary plexi, organized in net-like structures. Whilst for arterioles and venules it may be envisageable to obtain geometries needed for numerical simulations from imaging techniques, the size and numerosity of capillaries makes this task much more cumbersome. For this reason, it is interesting to study approaches to generate in silico-derived artifacts of capillary networks, even in view of machine-learning based approaches which require a large amount of samples for training. Artificial networks must correctly reflect proper metrics and topology, which in turn, will ensure with proper boundary conditions a physiological blood flux in the net and a sufficient nutrient distribution in the surrounding tissues. In this paper, we introduce the sequence of curves whose limit is the space filling Hilbert curve and we discuss its inherent properties and we obtain the backbone of the artificial capillary network from a suitable element of this sequence. The backbone represents a significant synthesis of basic metric features of the network and, in this context, its properties can be studied analytically. In this framework, the Hilbert curve is a malleable entity which allows to shape the backbone according to the physical indicators. In particular, two significant factors are shown to control the network topology and scaling: the iteration step of the Hilbert curve generation and the characteristic length of the REV, respectively. Based on the points we generate for a certain iteration step, we then obtain via spline interpolation a smoothed version of the curve, which fine–tunes the tortuosity. A volumetric construction is obtained building a tubular neighborhood of the backbone, whose metrics can be computed and tuned as well. Numerical simulations of the blood flow in the obtained geometry show the physical fields occurring in the artificial network. [ABSTRACT FROM AUTHOR]

Laser speckle contrast imaging (LSci) is a non-scanning optical imaging technique with wide field of view for monitoring blood flow velocity. LSci technology has advantages of high temporal-spatial resolution, fast real-time imaging, non-contact, simple structure, and no contrast agent. Here we briefly introduced the basic principles of LSci, structures of reflective-detected LSci and transmissive-detected LSci. in addition, this paper reviewed the latest research progress of LSci in biomedical applications such as skin blood flow, cerebral cortex and retinal blood flow, and makes further prospects for its development, provide theoretical basis and practical guidance for blood flow monitoring. [ABSTRACT FROM AUTHOR]

In this study, we assessed the possibility of using portable laser Doppler flowmeters for determining the state of the blood microcirculatory system in upper and lower limbs of diabetic patients during the treatment course with intravenous α-lipoic acid infusions. A series of experimental studies were conducted in a cohort of ten inpatients with a confirmed diagnosis of type 2 diabetes mellitus. The state of peripheral blood flow of patients was assessed during 5 days on which they received daily doses of intravenous α-lipoic acid infusions. The values of the microcirculation and nutritive blood flow indices, as well as the bypass index, were assessed. To obtain a more extensive analysis, the patients' measurement results were compared with those of the control group composed of ten conditionally healthy volunteers of similar age. To determine changes in the regulatory mechanisms for the microcirculatory bed, we applied the amplitude-spectrum analysis of microvascular blood flow oscillations, using the mathematical tool of wavelet transform. We determined the changes in the index of blood microcirculation and the parameters of microcirculatory blood flow distribution into nutritive and shunt pathways, as well as the differences between these changes in upper and lower limbs. This approach is believed to become prospective as a pharmacotherapy efficacy assessment method based on responses of the system of blood microcirculation. [ABSTRACT FROM AUTHOR]

The article describes a multiparametric approach to the assessment of cutaneous microcirculation in dermatological patients (using the example of psoriasis patients). The multiparametric diagnostic approach consisted of three stages of successive measurements performed according to the methodology of laser speckle contrast imaging (LSCI), laser Doppler flowmetry (LDF), and videocapillaroscopy (VCS). Experimental studies on hemodynamic parameters were conducted in psoriatic patients with a course of conservative treatment. A combined application of optical noninvasive diagnostic methods allowed physicians to record changes taking place in the microcirculatory bed during treatment. It has been found that microcirculatory disorders observed before the start of treatment in the field of psoriatic plaques (an increase in the density of the capillary network, an increase in the indicator of microcirculation, nutritive blood flow and the amplitudes of myogenic and cardiac oscillations) were normalized due to the applied treatment, on which the assessment of its efficacy may be based. The suggested approach may be used for diagnosing microcirculatory disorders emerging in psoriasis in its preclinical stage, as well as for developing and testing new pharmacological means for its treatment. [ABSTRACT FROM AUTHOR]

Objective: Spectral analysis of laser Doppler flowmetry (LDF) signals has been widely used in studies of physiological vascular function regulation. An alternative to LDF is the laser speckle contrast imaging method (LSCI), which is based on the same physical principle. In contrast to LDF, LSCI provides non-scanning full-field imaging of a relatively wide skin area and offers high spatial and temporal resolutions, which allows visualization of microvascular structure. This circumstance, together with a large number of works which had shown the effectiveness of temporal LSCI analysis, gave impetus to experimental studies of the relation between LDF and LSCI used to monitor the temporal dynamics of blood flow. Methods: Continuous wavelet transform was applied to construct a time-frequency representation of a signal. Results: Analysis of 10 minute LDF and LSCI output signals recorded simultaneously revealed rather high correlation between oscillating components. It was demonstrated for the first time that the spectral energy of oscillations in the 0.01–2 Hz frequency range of temporal LSCI recordings carries the same information as the conventional LDF recordings and hence it reflects the same physiological vascular tone regulation mechanisms. Conclusion: The approach proposed can be used to investigate speckle pattern dynamics by LSCI in both normal and pathological conditions. Significance: The results of research on the influence of spatial binning and averaging on the spectral characteristics of perfusion monitored by LSCI are of considerable interest for the development of LSCI systems optimized to evaluate temporal dynamics. [ABSTRACT FROM AUTHOR]

Abstract 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. Highlights • Local thermal test affects averaged and spectral components of cutaneous blood flow. • Spectral pattern of blood flow oscillation caused by local heating differs in controls and DM. • DM is accompanied by impaired vasodilation and lower response of myogenic vascular tone. • The results give deeper insight into the development of vascular abnormalities in diabetes. [ABSTRACT FROM AUTHOR]

The paper shows the possibility of using the laser Doppler flowmetry method for the assessment of system of blood microcirculation in the lower limbs of patients with diabetes mellitus. A series of experimental studies involving 76 patients with diabetes mellitus and 46 healthy volunteers was carried out. The state of peripheral blood flow was assessed during the local heating tests with different temperature regimes. The wavelet analysis of LDF-grams was used to evaluate the adaptive changes of microcirculation during the temperature tests. The data show that the proposed methodology in the form of heating tests and the use of the wavelet transform in the analysis of LDF-grams allows the evaluation of adaptation processes in the microcirculatory bed during thermal tests and the detection of the preclinical stage of trophic disorders. [ABSTRACT FROM AUTHOR]

In daily life, human skin often rubs against external surfaces, causing irritations and friction injuries. Cutaneous irritation is linked to the wear of the Stratum Corneum (SC). The aim of the study is to evaluate the degradation of the SC after repeated friction with two tissues of different softnesses. An in vivo tribometer has been developed to subject the skin's surface to controlled damage. In order to observe and evaluate the skin irritation induced by repeated friction, skin redness, transepidermal water loss (TEWL) and blood microcirculation were evaluated. Finally, the mechanical properties of the skin were quantified with an innovative contactless indentation device to evaluate the degradation of SC. The results revealed that the skin's Young's modulus decreased as the wear of SC increased with both tissues whereas blood flow, TEWL and the redness increased. The softness of the tissues had a direct influence on the degree of irritation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Kinetics of optical tweezers (OT)-induced spontaneous aggregation and disaggregation of red blood cells (RBCs) were studied at the level of cell doublets to assess RBC interaction mechanics. Measurements were performed under in vitro conditions in plasma and fibrinogen and fibrinogen + albumin solutions. The RBC spontaneous aggregation kinetics was found to exhibit different behavior depending on the cell environment. In contrast, the RBC disaggregation kinetics was similar in all solutions qualitatively and quantitatively, demonstrating a significant contribution of the studied proteins to the process. The impact of the study on assessing RBC interaction mechanics and the protein contribution to the reversible RBC aggregation process is discussed. [ABSTRACT FROM AUTHOR]

The influence of low‐intensity laser radiation (LLR) on the rheological characteristics of human blood has been investigated. The results of the investigation of the blood velocity in the human skin capillaries, the erythrocyte aggregation time, and the spectral width of scattering intensity fluctuations depending on the irradiation time are presented. It has been shown that laser irradiation leads to a decrease in the degree of aggregation of erythrocytes and, accordingly, to an increase in the velocity of blood microcirculation, which can be used for laser therapy and diagnostics and treatment of cardiovascular diseases (CVD). To explain the results obtained, a method of the LLR–biotissue interaction is proposed. [ABSTRACT FROM AUTHOR]

Blood rheology is a challenging subject owing to the fact that blood is a mixture of a fluid (plasma) and of cells, among which red blood cells make about 50% of the total volume. It is precisely this circumstance that originates the peculiar behavior of blood flow in small vessels (i.e., roughly speaking, vessel with a diameter less than half a millimeter). In this class we find arterioles, venules, and capillaries. The phenomena taking place in microcirculation are very important in supporting life. Everybody knows the importance of blood filtration in kidneys, but other phenomena, of not less importance, are known only to a small class of physicians. Overviewing such subjects reveals the fascinating complexity of microcirculation. [ABSTRACT FROM AUTHOR]