Academic literature on the topic 'Microcirculation, laser Doppler flowmetry, biosignal processing'

The article is devoted to the development of laser Doppler flowmetry and analysis of the recorded signal to study the distribution of perfusion over the frequencies of Doppler broadening of laser radiation. The processing algorithm and the necessary technical conditions for the correct registration of the signal are shown. As examples of the proposed method implementation, the data are obtained from a healthy volunteer and a patient with diabetes mellitus type 2 and analyzed. According to the proposed method, processing of recorded data provides a new feature space for data analysis of laser Doppler flowmetry signal.

Microcirculatory disorders play an important role in the pathogenesis of dermatoses, including those caused by the influence of adverse factors of production environment. 158 men from the Astrakhan gas processing plant (AGPS) aged from 28 to 59 years (40.23 ± 0.49 years) and 77 healthy volunteers, resident in the city of Astrakhan in age from 25 to 55 years (38,18 ± 0,99 years) were examined. Depending on the technological stage of processing of reservoir gas workers AGPS had contact with various harmful and dangerous factors, among which were the formation of gas, elementary sulfur, hydrocarbons, saturated and unsaturated aliphatic compound, nitrogen oxides, etc. In more than 90% of cases in the skin of workers AGPS serious violations of blood perfusion in small vessels, and in the surface areas more often than in the deep, while marked asymmetry of cutaneous microcirculation were revealed. Laser Doppler flowmetry can be recommended as a noninvasive method of monitoring the condition of microcirculation and early diagnosis of premorbid changes in the skin of workers of the gas processing plant exposed to adverse factors of production environment.

An overview of three techniques developed by our group for imaging superficial tissue is presented. Firstly, a novel polarized light capillaroscope has been developed for imaging the microcirculation. The capillaroscope has been used to make in vivo measurements of sickle cell disorder sufferers with aim of monitoring the polymerization of sickled red blood cells. Secondly, hyperspectral imaging for measuring oxygen saturation is described. The accuracy of such measurements is affected by the non-linear relationship between scattering and absorption and it is demonstrated that polarization techniques can be used to make the relationship more linear, thus improving accuracy. Finally, the use of smart CMOS optical sensors for laser Doppler blood flowmetry is described. A 32 × 32 pixel imaging array with on-chip processing is described and the potential for full field laser Doppler blood flow imaging is demonstrated through measurement on blood flow of tissue before and after occlusion.

In this article, we introduce a new method of signal processing and data analysis for the digital laser Doppler flowmetry. Our approach is based on the calculation of cumulative sums over the registered Doppler power spectra. The introduced new parameter represents an integral estimation for the redistribution of moving red blood cells over the range of speed. The prototype of the device implementing the technique is developed and tested in preliminary clinical trials. The methodology was verified with the involvement of two age groups of healthy volunteers and in a group of patients with type 2 diabetes mellitus. The main practical result of the study is the development of a set of binary linear classifiers that allow the method to identify typical patterns of the microcirculation for the healthy volunteers and diabetic patients based on the presented diagnostic algorithm.

Aim. To study the nature and extent of the effects of long-term sleep and wake phase disorders (working at night for more than 10 years) on the characteristics of microcirculation in men. Methods. Laser Doppler flowmetry and spectophotometry, optical tissue oximetry, and laser-induced fluorescence spectroscopy were performed in 34 male patients with a mean age of 40.30.9 years and more than 10 years experience of night work to assess the effectiveness of microcirculation. 25 men with a mean age of 40.21.2 without night work experience were used as a control group. Microcirculation was studied on the laser diagnostic complex LAKK-M (LAZMA, Russian Federation). The measurement was carried out on the skin of the palmar surface of the terminal phalanx of the second finger of the hand. The following indicators were analyzed in automatic mode: the mean perfusion value, the index of specific oxygen consumption in the tissue, capillary blood saturation, the relative volume of the red blood cell fraction, arterial blood oxygen saturation, the index of perfusion oxygen saturation in the microcirculation, the efficiency of oxygen exchange and the fluorescent indicator of oxygen consumption. Statistical processing of the results was carried out using the Student's t-test for independent samples. Results. In patients working at night for more than 10 years, a decrease in microcirculation efficiency was revealed. The index of specific oxygen consumption in the tissue was lower than that of healthy volunteers by 34.1% (p=0.000255), and the index of oxygen exchange efficiency by 56.3% (p 0.001). Long-term night work (10 years) can lead to violations of microcirculation parameters and an irreversible decrease in the efficiency of oxygen exchange compared with the control group by an average of 56.3% (18.00.5 for the group with night work experience, 41.20.6 for the group of healthy volunteers, p 0.001), the index of specific oxygen consumption in the tissue by an average of 34.1% (1.530.03 for the group with night work experience, 2.320.2 for the group of healthy volunteers, p=0.000255) and an increase in the index of perfusion oxygen saturation in the microcirculation by 2 times compared with the control group (6.20.05 for the group with night work experience, 3.670.09 for the group of healthy volunteers, p 0.001), which is accompanied by an increase in the saturation of mixed (and venous) blood. Conclusion. The nature of the revealed violations of microcirculatory parameters in the long-term night work suggests their significance in the development of diseases that are currently attributable to the so-called group of diseases of civilization.

Objective: To perform laser Doppler flowmetry (LDF) periodontal microcirculation assessment using custom-made, computer-aided-designed probe holders manufactured by stereolithography (SLA). Methods: 66 young people aged 21-23 years old with clinically healthy periodontium were examined. The first group consisted of subjects where a custom-made probe holder was fabricated using a silicone impression mould technique. The second group consisted of subjects where a custom-made computer-aided-design probe holder made of a photopolymer by SLA was used. The basic microcirculation parameters were analysed to evaluate periodontal microcirculation by the LDF method: the PM – average perfusion value in periodontal tissues; δ – the average square deviation of the amplitude of blood flow fluctuations from the arithmetic mean value, Kv – coefficient of variation (%). Statistical processing of the results was carried out using the software package Statistica 13.0 (StatSoft Inc, USA). Results: Statistical analysis results indicated that the functional characteristics of the periodontal microcirculation using various custom-made fibre optic probe holders used in capillary blood flow monitoring had significant differences p<0.05. The value of the median PM when using a silicone holder in group I was 1.6 times lower than when using a photopolymer holder in group II. The median value of the σ index when using a silicone holder in group I was 2.3 times higher than when using a photopolymer holder in group II. The median value of the Kv when using a silicone holder in group I was 2.5 times higher than when using a photopolymer holder in group II. Conclusion: A photopolymer probe holder, unlike a silicone one, provides a constant fixed distance between the periodontal tissues and the LDF probe, prevents movement or probe displacement, and makes it possible to avoid pressure on the gingival tissue, ensuring high accuracy of laser diagnostics Keywords: Functional diagnostics, LDF, microcirculation, periodontium, CAD, stereolithography.

Cerebral blood flow is monitored in the neurointensive care unit (NICU) to avoid further brain damage caused by secondary insults following subarachnoid hemorrhage and brain trauma. Current techniques are mainly snap-shot based and focus on larger vessels. However, continuous monitoring of the smaller vessels may help detect the onset of secondary insults at an earlier stage. In this study, long-term measurements of brain microcirculation with laser Doppler flowmetry (LDF) were performed and evaluated. The aim was to identify and describe physiological signal variations and separate these from movement artifacts. Fiberoptic probes for subcortical LDF recordings of perfusion and total light intensity (TLI) were implanted in three patients with subarachnoid hemorrhage. Data were successfully collected and visualized in real-time over 4 days, resulting in 34, 12, and 8.5 h per patient. Visual observation, wavelet transforms, moving medians, and peak envelopes were used to identify and describe movement artifacts and physiological changes. Artifacts occurred in &lt;5% of the total recording time and could be identified through signal processing. Identified physiological signal patterns included a slowly increasing perfusion trend over hours, vasomotion mainly at 2 cycles/min both in the perfusion and the TLI, and rapid, synchronized changes in the TLI and the perfusion on 38 occasions. Continuous LDF recordings indicating changes in the microvascular blood flow can increase the understanding of the microcirculation in the injured brain. In the long run, this may become a complement for the detection of secondary insults at an earlier stage than possible with today’s techniques.

The microcirculation is regulated by the complex, and inter-dependent activity of neurogenic, myogenic and endothelial control mechanisms, which dynamically adapt the spatial distribution of the cardiac output in order to meet the local metabolic and thermal demands of the organism. Owing to these physiological mechanisms, and the characteristic waves arising centrally from the cardiac cycle and the rhythmic respiratory activity, the basal microvascular blood flow exhibits separate spontaneous non-stationary components within established frequency ranges. The cutaneous microcirculation provides a unique window on the functional state of the systemic microcirculation and, thanks to its accessibility, permits the non-invasive monitoring of the physiological processes underlying these cardiovascular oscillations. Furthermore, the skin represents a suitable target for testing sympathetic and endothelial vasomotor pathways by means of acute thermal or biochemical stimuli. This has been possible since the introduction of optical techniques such as laser Doppler flowmetry (LDF), able to record data of tissue perfusion at high temporal resolution. The work outlined in the present thesis focuses on the development and application of biosignal processing methods for the analysis of LDF signals of microvascular flow, that might support the early identication of a decline in vascular function and, thus, might have clinical potential in the non-invasive diagnosis and monitoring of subjects with metabolic disease and/or at risk of cardiovascular complications. Hence, the research activities relied on the analysis of LDF perfusion signals, recorded from healthy control subjects, and patients affected by diabetes mellitus. To this end, a wavelet-based time-frequency analytical framework has been adopted for disentangling the physiological components of the microvascular perfusion, since it enables the parallel characterization of the cardiac dynamics and the slower non-stationary fluctuations produced by the local vasomotion. Moreover, a model-based approach has been implemented with the aim to describe the composite hyperaemic response of the cutaneous microcirculation to local thermal stimulation, and to assess the potential impairment of the neurovascular and endothelial mechanisms involved in this thermoregulatory feedback loop. Furthermore, peripheral pulse waveforms are intimately related to the physical properties of the arterial tree within which they propagate; thus, their contour might carry information for the non-invasive diagnosis of vascular alterations. In this regard, a new pulse decomposition algorithm has been developed for deriving an accurate reconstruction of the cardiac pulsatility of LDF signals, via a linear combination of Gaussian bases. This technique paves the way for the robust extraction of physiologically meaningful features: in particular, two biomarkers of large artery stiffness and peripheral wave reflection have been investigated. The present strategy has been successfully applied to the automatic detection of vascular ageing and, moreover, to the automatic assessment of respiratory-vascular couplings and, particularly, the transient neurogenic vasoconstrictive pathway, triggered by a rapid inspiratory manoeuvre.