Light dynamics in glass-vanadium dioxide nanocomposite waveguides with thermal nonlinearity

We address the propagation of laser beams in Si02-VO2 nanocomposite waveguides with thermo-optical nonlinearity. We show that the large modifications of the absorption coefficient as well as notable changes of refractive index of VO2 nanoparticles embedded into the SiO2 host media that accompany the semiconductor-to-metal phase transition may lead to optical limiting in the near-infrared wave range.Comment: 13 pages, 3 figures, to appear in Optics Letter

The study of synchronization of rhythms of microvascular blood flow and oxygen saturation during adaptive changes

Multi-functional laser non-invasive diagnostic systems, such as "LAKK-M", allow the study of a number of microcirculatory parameters, including blood microcirculatory index (Im) (by laser Doppler flowmetry, LDF) and oxygen saturation (StO2) of skin tissue (by tissue reflectance oximetry, TRO). Such systems may provide significant information relevant to physiology and clinical medicine. The aim of this research was to use such a system to study the synchronization of microvascular blood flow and oxygen saturation rhythms under normal and adaptive change conditions. Studies were conducted with 8 healthy volunteers - 3 females and 5 males of 21-49 years. Each volunteer was subjected to basic 3 minute tests. The volunteers were observed for between 1-4 months each, totalling 422 basic tests. Measurements were performed on the palmar surface of the right middle finger and the forearm medial surface. Wavelet analysis was used to study rhythmic oscillations in LDF- and TRO-data. Tissue oxygen consumption (from arterial and venal blood oxygen saturation and nutritive flux volume) was calculated for all volunteers during "adaptive changes" as (617±123 AU) and (102±38 AU) with and without arteriovenous anastomoses (AVAs) respectively. This demonstrates increased consumption compared to normal (495±170 AU) and (69±40 AU) with and without AVAs respectively. Data analysis demonstrated the emergence of resonance and synchronization of rhythms of microvascular blood flow and oxygen saturation as an adaptive change in myogenic oscillation (vasomotion) resulting from exercise and potentially from psychoemotional stress. Synchronization of myogenic rhythms during adaptive changes suggest increased oxygen consumption resulting from increased microvascular blood flow velocity

Detection of angiospastic disorders in the microcirculatory bed using laser diagnostics technologies

The evaluation of the microcirculatory bed functional state and the identification of angiospastic disorders with related complications, when the pathological changes are reversible, have an important role in medical practice. The aim of this study was to evaluate the possibility of using optical noninvasive methods and the cold pressor test to solve this problem. A total of 33 patients with rheumatological diseases and 32 healthy volunteers were included in the study. Laser Doppler flowmetry, tissue reflectance oximetry and pulse oximetry were used as optical noninvasive methods. The parameters were recorded before, immediately after and 20(Formula presented.)min after the cold pressor test. Based on the measured parameters, the complex parameters of the microcirculatory bed were calculated. A detailed statistical analysis of the parameter changes for each individual in the two groups displayed diverse microcirculatory bed parameter responses upon cold exposure, with differing recovery of parameters after CPT. New diagnostic criteria were proposed for the identification of angiospastic disorders. According to the proposed criteria, 27 people of the volunteers group were confirmed to not display any disorders. In the patient group, however, 18 people were observed to have a relatively normal functional state of the microcirculatory bed, while 15 people were observed to have a possible tendency to angiospasm. To highlight the differences between a relatively normal state and presence of angiospastic disorders, statistical analysis of experimental data was carried out, which revealed significant differences. Further analysis of data with angiospastic disorders identified a relationship between their diagnoses and the results of laboratory studies. Thus, the evaluation of combined noninvasive optical diagnostic method use, the cold pressor test and proposed diagnostic criteria showed a positive result. This approach can be used to detect the presence of possible angiospastic disorders and related complications, as well as microcirculatory bed disorders against the background of other diseases

Studies of age-related changes in blood perfusion coherence using wearable blood perfusion sensor system

Laser Doppler flowmetry (LDF) was used for detection of age-related changes in the blood microcirculation. The LDF signal was simultaneously recorded from the 3rd fingers' pads of both hands. Amplitudes of the blood flow oscillations and wavelet coherence of the signals were used for the data analysis. A statistical difference in the synchronisation of myogenic oscillations was found between the two studied age groups. Myogenic oscillations of blood perfusion in the younger group had a higher wavelet coherence parameter than in the older group. Observed site-specific and age-related differences in blood perfusion can be used in the future in the design of experimental studies of the blood microcirculation system in patients with different pathologies

Pilot studies of age-related changes in blood perfusion in two different types of skin

Laser Doppler flowmetry (LDF) was utilized to assess age-related changes in the blood microcirculation at the skin sites with different morphology and regulation. The LDF signals obtained from the glabrous skin of the middle finger pad and nonglabrous skin on the dorsal wrist surface were analyzed. Statistically higher baseline perfusion was observed in the zone with glabrous skin in the older group of volunteers compared to younger participants. Observed site-specific and age-related differences in perfusion can be used in the future experimental design for the studies of the blood microcirculation system in patients with different pathologies

The blood perfusion and NADH/FAD content combined analysis in patients with diabetes foot

Skin blood microcirculation and the metabolism activity of tissue were examined on the patients with type 2 diabetes. Laser Doppler flowmetry (LDF) with 1064 nm laser light source and fluorescence spectroscopy (FS) with excitation light of 365 nm and 450 nm have been used to monitor the blood perfusion and the content of coenzymes NADH and FAD. Concluding, the proposed combined LDF and tissue FS approach allows to identify the significant violations in the blood microcirculation and metabolic activity for type 2 diabetes patients

Wearable sensor system for multipoint measurements of blood perfusion: pilot studies in patients with diabetes mellitus

The growing interest in the development of new wearable electronic devices for mobile healthcare provides great opportunities for the development of methods for assessing blood perfusion in this direction. Laser Doppler flowmetry (LDF) is one of the promising methods. A fine analysis of capillary blood ow structure and rhythm in the time and frequency domains, coupled with a new possibility of round-the-clock monitoring can provide valuable diagnostic information about the state of microvascular blood ow. In this study, wearable implementation of laser Doppler flowmetry was utilised for microcirculatory function assessment in patients with diabetes and healthy controls of two distinct age groups. Four wearable laser Doppler flowmetry monitors were used for the analysis of blood microcirculation. Thirty-seven healthy volunteers and 18 patients with type 2 diabetes mellitus participated in the study. The results of the studies have shown that the average perfusion differs between healthy volunteers of distinct age groups and between healthy volunteers of the younger age group and patients with diabetes mellitus. It was noted that the average level of perfusion measured on the wrist in the two groups of healthy volunteers has no statistically significant differences found in similar measurements on the fingertips. The wearable implementation of LDF can become a truly new diagnostic interface to monitor cardiovascular parameters, which could be of interest for diagnostics of conditions associated with microvascular disorders

Comparison of wearable and bedside laser Doppler flowmetry and fluorescence spectroscopy monitors

Advances in the development of ultra-compact semiconductor lasers have opened up new possibilities for the development of wearable devices implementing biophotonic technologies, such as laser Doppler flowmetry (LDF) and fluorescence spectroscopy (FS). This work is aimed to evaluate the correlation between diagnostic parameters simultaneously registered by a newly developed wearable device and a standard bedside fiber-based technique. Experimental studies with healthy volunteers using the occlusion test showed a high correlation between the parameters recorded by the two devices.,,,,,,,,

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

Wireless Dynamic Light Scattering Sensors Detect Microvascular Changes Associated With Ageing and Diabetes

This paper presents clinical results of wireless portable dynamic light scattering sensors that implement laser Doppler flowmetry signal processing. It has been verified that the technology can detect microvascular changes associated with diabetes and ageing in volunteers. Studies were conducted primarily on wrist skin. Wavelet continuous spectrum calculation was used to analyse the obtained time series of blood perfusion recordings with respect to the main physiological frequency ranges of vasomotions. In patients with type 2 diabetes, the area under the continuous wavelet spectrum in the endothelial, neurogenic, myogenic, and cardio frequency ranges showed significant diagnostic value for the identification of microvascular changes. Aside from spectral analysis, autocorrelation parameters were also calculated for microcirculatory blood flow oscillations. The groups of elderly volunteers and patients with type 2 diabetes, in comparison with the control group of younger healthy volunteers, showed a statistically significant decrease of the normalised autocorrelation function in time scales up to 10 s. A set of identified parameters was used to test machine learning algorithms to classify the studied groups of young controls, elderly controls, and diabetic patients. Our conclusion describes and discusses the classification metrics that were found to be most effective