[Ultrastructure of neointima of native and artificial elements of the blood circulatory system]. / Ul'trastruktura neointimy nativnykh i iskusstvennykh elementov sistemy krovoobrashcheniya.

OBJECTIVE: To compare the neointima structure in conduits for coronary bypass grafting, bioprosthetic heart valves, tissue-engineered vascular grafts, and metal stents. MATERIAL AND METHODS: The objects of the study were the fragments of the human internal thoracic artery, experimental biodegradable vascular prostheses, leaflets of xenopericardial bioprostheses of heart valves, and fragments of stented vessels. Tissue samples were fixed in formalin and post-fixed in osmium tetroxide. After dehydration and epoxy resin embedding, the samples were ground and polished. Samples were counterstained with uranyl acetate and lead citrate and visualized by means of backscattered scanning electron microscopy. RESULTS: Neointimal pattern in all samples was similar. Neointima was comprised of endothelial cells, smooth muscle cells, fibroblasts, and the extracellular matrix. Endothelial cells showed significant diversity both between different elements of the circulatory system and within the same tissue, having either elongated or polygonal shape. Adhesion of leukocytes testified to the endothelial cell activation. In the absence of inflammation in the superficial layer of the neointima, the arrangement of smooth muscle cells and extracellular matrix fibers was parallel to the endothelium. Clusters of foam cells were frequently detected around the neointimal layers with solid inclusions (metal stents or calcium deposits). Thickening of the neointima was accompanied by the presence of capillaries and capillary-like structures. CONCLUSION: Neointima formation is a typical response to the damage inflicted to the elements of the circulatory system. Neointima underwent a constant remodeling characterized by an altered cellular composition, macrophage invasion, neovascularization, and calcification.

[Surgical treatment of protoplasmic astrocytoma of sylvian aqueduct involving posterior part of the third ventricle]. / Khirurgicheskoe lechenie protoplazmaticheskoi astrotsitomy sil'vieva vodoprovoda s rasprostraneniem na zadnii otdel tret'ego zheludochka.

It is presented case report of extremely rare pathology - protoplasmic astrocytoma of sylvian aqueduct involving posterior section of the third ventricle. The main principles of treatment were considered. Dynamics of neurological status was demonstrated. An effectiveness of treatment strategy was assessed.

[Surgical treatment of a patient with saccular arterial aneurysm of the cavernous-ophthalmic segment]. / Khirurgicheskoe lechenie bol'nogo s meshotchatoi arterial'noi anevrizmoi kavernozno-oftal'micheskogo segmenta.

Presented in the article are the results of surgical management of a patient with an extremely rare pathology - a saccular arterial aneurysm of the cavernous-ophthalmic segment of the left internal carotid artery. We performed multistage open surgical intervention in the following scope: osteoplastic pterional craniotomy on the left, creation of a wide-lumen anastomosis between the left external carotid artery and M2 segment of the left middle cerebral artery with the use of the radial artery, ligation of the cervical portion of the left internal carotid artery and clipping of its supraclinoid portion. The chosen surgical policy made it possible to create sufficient volumetric blood flow through the shunt, comparable to the blood flow through the internal carotid artery, which helped avoid ischaemic stroke after exclusion of the aneurysm from circulation. A conclusion was drawn on efficacy of this method of treatment.

[Computer-assisted simulation of haemodynamic parameters of carotid artery bifurcation after carotid endarterectomy]. / Komp'iuternoe modelirovanie gemodinamicheskikh pokazatelei v bifurkatsii sonnykh arterii posle karotidnoi éndarteréktomii.

Computer-aided simulation appropriately using the method of computational fluid dynamics (CFD) makes it possible to determine the elevated-risk zones of most probable formation of restenosis. The main idea of the method described in our article consists in a possibility of creating by the model of the geometrical shape of the vessel and characteristics of the flow at inlets and outlets the parameters of flow in each point of a vessel. The curves of velocity are used to create the curves of pressure at inlets and outlets, which are used in a CFD model. The resulting from CFD simulation of blood flow are nonstationary three-dimensional fields of pressure and velocity in the area under study. Visual examination of the dynamics of these fields makes it possible to judge about possible problem zones inside the area of flow and on the internal wall of the vessel. This article also presents a clinical case report illustrating the use of this technique.

[In-hospital outcomes of transcutaneous coronary intervention and carotid endarterectomy in hybrid and staged regimens]. / Gospital'nye rezul'taty chreskozhnogo koronarnogo vmeshatel'stva i karotidnoi éndarteréktomii v gibridnom i poétapnom rezhimakh.

The aim of this study was comparative assessment of in-hospital outcomes after hybrid and staged surgical management of patients presenting with haemodynamically significant lesions of the coronary (CA) and brachiocephalic arteries (BCA) treated by means of either endovascular or surgical techniques. Over the period from 2010 to 2017, we operated on a total of 197 patients with stenotic lesions of the carotid and coronary arteries. The strategy of revascularization included transcutaneous coronary intervention (TCI) and carotid endarterectomy (CEA). Of these, 73 (37%) patients underwent staged revascularization of the brain and myocardium in various sequence (TCI-CEA or CEA-TCI), with a mean interval between the operations amounting to 9.89±7.36 months. Unfavourable outcomes were regarded as the development of such significant cardiovascular events as myocardial infarction (MI), acute impairment of cerebral circulation, death, repeat unplanned revascularization. For hybrid strategy (TCI+CEA) the index period of assessing the outcomes was the single in-hospital period, whereas for the staged strategy it was the time period beginning from the in-hospital period of the primary operation and ending by the in-hospital period of the second stage. The groups were comparable by the absolute majority of the parameters. More than half of the patients were elderly males. One third had a history of MI. The findings of coronary angiography most often revealed lesions of 1-2 CAs. The average parameters of carotid artery stenosis, according to the BCA angiography varied from 74.9 to 82.6%, with bilateral occlusive stenotic lesions being revealed in every third patient. In connection with more frequent involvement of 1-2 CAs the patients underwent implantation of 1-2 stents. In our sample we used a total of 247 stents. Of these, 119 were uncoated and 128 were drug-eluting stents. No between-group significant differences in the development of unfavourable cardiovascular events during the in-hospital postoperative period were revealed. However, despite this, a pronounced negative tendency of the complication rate was noted in the group of staged revascularization. Non-optimal time intervals between the stages of the operations in a third of cases exceeded one year on the patient's own initiative. Nearly a quarter of patients did not come for the second stage of revascularization. An important finding of our study was no increase in the risk of stent thrombosis in hybrid operations compared with the staged approach, despite administration of a loading dose of clopidogrel after CEA, but not before TCI. Another significant result was the fact of greater availability of revascularization of the myocardium and the brain within the framework of the hybrid strategy as compared with the staged one, which may play an important role in prevention of ischaemic unfavourable events in the remote period of follow up.

Photoluminescence Enhancement through Symmetry Breaking Induced by Defects in Nanocrystals.

We present a theoretical model for the effect of symmetry breaking introduced by the doping of semiconductor nanocrystals with Coulomb impurities. The presence of a Coulomb center breaks the nanocrystal symmetry and affects its optical properties through the mixing of the hole spin and parity sublevels, breaking the selection rules responsible for the exciton dark state in undoped nanocrystals. After reviewing the effects on the exciton fine structure and optical selection rules using symmetry theory, we present a perturbative model to quantify the effects. We find that the symmetry breaking proceeds by two mechanisms: First, mixing by even parity terms in the Coulomb multipole expansion results in an exciton fine structure consisting of three optically active doublets which are polarized along x, y, and z axes with a ground optically passive dark exciton state, and second, odd parity terms which break inversion symmetry significantly activate optical transitions which are optically forbidden in the unperturbed nanocrystal due to both spin and parity selection rules. In the case of small sized "quasi-spherical" nanocrystals, the introduction of a single positively charged Coulomb center is shown here to result in significant enhancement of the radiative decay rate at room temperatures by up to a factor of 10.

[Carotid endarterectomy: three-year results of follow up within the framework of a single-centre register]. / Karotidnaia éndarteréktomiia: trekhletnie rezul'taty nabliudeniia v ramkakh odnotsentrovogo registra.

The purpose of the study was to determine the incidence rate and structure of cardiovascular complications in patients presenting with lesions of the carotid arteries and multifocal atherosclerosis, having endured carotid endarterectomy (CEA), during a three-year period within the framework of a single-centre register. The study included a total of 1,035 patients subjected to CEA over the period from 2011 to 2016. The duration of the long-term follow up averagely amounted to 42.4±18.6 months. The outcome measures assessed were as follows: death, myocardial infarction (MI), acute cerebral circulation impairment (transitory ischaemic attack) [ACCI (TIA)], clinically significant haemorrhage according to the BARC scale, unplanned repeat revascularization. In the remote period of follow up, the mortality rate did not exceed 2.3%. Of the unfavourable outcomes, most frequently observed turned out to be ACCI (TIA), with less often observed being MI. Two times a year, all patients underwent duplex scanning of the carotid arteries, whose findings revealed haemodynamically significant restenosis in 3.28% of cases. The average period of formation of restenosis amounted to 14.0±3.1 months after the operation. Three patients underwent repeat CEA and a further 16 patients endured stenting of the internal carotid artery (with 2 patients having developed intraoperative TIA). In the remote period, no cases of secondary restenosis were revealed this group of patients. It was determined that restenosis more often developed in patients having sustained classical.

[Simultaneous operation in a patient with stenosis of the extracranial portion and an intracranial aneurysm of the internal carotid artery]. / Simul'tannaia operatsiia u bol'nogo so stenozom ékstrakranial'nogo otdela i intrakranial'noi anevrizmoi vnutrennei sonnoi arterii.

Presented herein is a clinical case report concerning surgical treatment of a patient with a rare combination of two pathologies, i. e., a haemodynamically significant stenosis of the extracranial portion and a sacciform aneurysm of the communicative portion of the right internal carotid artery on the background of multifocal atherosclerosis. The patient underwent a simultaneous operation consisting in clipping of the sacciform arterial aneurysm of the communicative portion of the right internal carotid artery and carotid endarterectomy on the right. The chosen surgical policy ensured effective prevention of the development of ischaemic stroke and rupture of the arterial aneurysm, whose risks would have been high in staged treatment and sequentially performing two operations.

Issues concerning spectral analysis of water samples for monitoring and treatment of public water resources.

Experimental measurements conducted in the laboratory, involving hyperspectral analysis of water samples taken from public water resources, have motivated a re-evaluation of issues concerning the potential application of this type of analysis for water monitoring, treatment and evaluation prior to filtration. One issue concerns hyperspectral monitoring of contaminants with respect to types and relative concentrations. This implies a need to better understand the statistical profiles of water contaminants in terms of spatial-temporal distributions of electromagnetic absorption spectra ranging from the ultraviolet to infrared, which are associated with specific water resources. This issue also implies the need to establish correlations between hyperspectral signatures and types of contaminants to be found within specific water resources. Another issue concerns the use of absorption spectra to determine changes in chemical and physical characteristics of contaminants after application of water treatments, in order to determine levels of toxicity with respect to the environment. This paper presents a prototype spectral analysis showing various aspects relevant to water monitoring and discusses the use of basic theory for the interpretation of spectral features associated with water contaminants, as well as discussing inverse analysis of hyperspectral measurements.

[Stenting of the first segment of the spinal artery in the acutest period of ischemic stroke in the vertebrobasilar territory]. / Stentirovanie pervogo segmenta pozvonochnoi arterii v ostreishem periode ishemicheskogo insul'ta v vertebral'no-bazilyarnoi sisteme.

OBJECTIVE: To analyze hospital and long-term results of stenting of the V1 segment of the vertebral artery (VA) in the first hours after acute cerebral hemopoiesis/transient ischemic attack (stroke/TIA) in the vertebrobasilar territory (VT). MATERIAL AND METHODS: The current retrospective study from 2012 to 2019 included 169 patients with hemodynamically significant stenosis of the V1 segment of the VA, who underwent emergency stenting in the first hours after the onset of stroke. The mean time between the development of stroke and correction was 368.5±129.8 minutes. The average time between admission to the medical institution and submission to the X-ray operating room was 89.2±10.7 minutes. VA stenting was performed through the transfemoral approach. In 118 cases (69.8%) a drug eluting stent was implanted, in 51 (30.2%) a bare metal stent was implanted. 90% of VA segment V1 stenosis was diagnosed in 48 patients before the onset of stroke. Of these, 33 received conservative therapy for vertebrobasilar insufficiency (VBI) for 2.5±1.0 months in anticipation of regression of the disease. The remaining 15 did not have VBI symptoms and did not need active drug treatment. Ultimately, within this sample, the time interval between the visualization of stenosis and the onset of stroke was 3.0±1.0 months. In 17 patients, stroke/TIA in VT became recurrent. The period between two neurological events was 1.5±0.5 months. Nine patients did not wait for the planned intervention due to the development of an adverse neurological event before the appointed date of hospitalization. The other 8 did not appear for the interventional correction on time due to subjective reasons and were again admitted to the medical facility on an urgent basis. RESULTS: During the hospital follow-up period, no adverse cardiovascular events were recorded. When assessing the dynamics in the neurological status, there was a significant regression of the deficit by the time of discharge from the hospital. In the long-term follow-up period (38.2±20.4 months), a fatal outcome was recorded in 2.4% of cases (n=4). Non-fatal myocardial infaction was diagnosed in 5 patients (2.9%). Restenosis of the stent in the VA was visualized in 56 patients (33.1%). In 17 cases, it became symptomatic (10.0%). All patients underwent repeated stenting with a successful result of the procedure. CONCLUSION: Emergency stenting of hemodynamically significant stenosis of the V1 segment of the VA in the acute period of stroke in VT is a safe and effective method of revascularization characterized by the absence of adverse cardiovascular events at the hospital stage of observation.

[A multicenter study on the influence of different kinds of carotidal endarterectomy on the course of resistant arterial hypertension]. / Mnogotsentrovoe issledovanie vliyaniya razlichnykh vidov karotidnoi endarterektomii na techenie rezistentnoi arterial'noi gipertenzii.

OBJECTIVE: To analyze the dynamics of systolic blood pressure (SBP) and the results of various types of carotid endarterectomy (CEE) in patients with resistant arterial hypertension (RAH). MATERIALS AND METHODS: The study included 1577 patients with hemodynamically significant stenosis of the internal carotid artery (ICA) and RAH for more than 3 years. Patients were enrolled from January 2014 to December 2020. Depending on the implemented revascularization strategy, 5 groups were formed: group 1 (n=289 (18.3%)) with classical CEE with plasty of the reconstruction zone with a patch, group 2 (n=472 (29.9%)) with eversional CEE with cut-off of carotid glomus (CG); group 3 (n=109 (6.9%)) with the formation of a new bifurcation; group 4: (n=117 (7.4%)) with autoarterial reconstruction; group 5: (n=590 (37.4%)) with glomus-saving CEE. RESULTS: In the postoperative period, no significant differences were obtained in the frequency of deaths (0.34% for group 1; 0.63% for group 2; 0% for groups 3, 4 and 5), myocardial infarction (0.34%, 0.84%, 1.83, 0.85%, 0.33%, respectively); ischemic stroke (0.34%, 1.27%, 0.91%, 0.85%, 0.17%, respectively), hemorrhagic transformation (0%, 0.84%, 0.91%, 0.85%, 0%, respectively). However, according to the frequency of the combined endpoint (death + myocardial infarction + ischemic stroke + hemorrhagic transformation), the lowest rates were observed in the group of classical carotid endarterectomy with plasty of the reconstruction zone with a patch and glomus-sparing CEE (1.03%, 3.6%, 3.67%, 2.56%, 0.5%, respectively). This is due to the absence of cases of labile AH and hypertensive crises among patients of groups 1 and 5, which was ensured by the preservation of carotid glomus (CG). As a result, the number of patients with 2 and 3 degrees of hypertension in these groups decreased statistically significantly. The vast majority of patients after these operations achieved a stable target SBP. In groups 2, 3, and 4, there was a statistically significant increase in the number of patients with 2 and 3 degrees of AH, which is associated with excision of the CG. CONCLUSION: Classical CEE and glomus-sparing CEE techniques make it possible to achieve a stable target SBP level in patients with RAH as a result of CG preservation. Removal or traumatization of the latter during eversional CEE, the formation of a new bifurcation, autoarterial reconstruction is accompanied by the development of labile hypertension, an increase in the degree of hypertension and a high risk of hemorrhagic transformation in the brain. Thus, the most effective and safe types of CEE in the presence of RAH are classical CEE with plasty of the reconstruction zone with a patch and glomus-sparing CEE.

Thermal activation of non-radiative Auger recombination in charged colloidal nanocrystals.

Applications of semiconductor nanocrystals such as biomarkers and light-emitting optoelectronic devices require that their fluorescence quantum yield be close to 100%. However, such quantum yields have not been obtained yet, in part, because non-radiative Auger recombination in charged nanocrystals could not be suppressed completely. Here, we synthesize colloidal core/thick-shell CdSe/CdS nanocrystals with 100% quantum yield and completely quenched Auger processes at low temperatures, although the nanocrystals are negatively photocharged. Single particle and ensemble spectroscopy in the temperature range 30-300 K shows that the non-radiative Auger recombination is thermally activated around 200 K. Experimental results are well described by a model suggesting a temperature-dependent delocalization of one of the trion electrons from the CdSe core and enhanced Auger recombination at the abrupt CdS outer surface. These results point to a route for the design of core/shell structures with 100% quantum yield at room temperature.

Directing nuclear spin flips in InAs quantum dots using detuned optical pulse trains.

We find that detuning an optical pulse train from electronic transitions in quantum dots controls the direction of nuclear spin flips. The optical pulse train generates electron spins that precess about an applied magnetic field, with a spin component parallel to the field only for detuned pulses. This component leads to asymmetry in the nuclear spin flips, providing a way to stabilize and control the nuclear spin polarization. This effect is observed using two-color, time-resolved Faraday rotation and ellipticity.

Nuclei-induced frequency focusing of electron spin coherence.

The hyperfine interaction of an electron with the nuclei is considered as the primary obstacle to coherent control of the electron spin in semiconductor quantum dots. We show, however, that the nuclei in singly charged quantum dots act constructively by focusing the electron spin precession about a magnetic field into well-defined modes synchronized with a laser pulse protocol. In a dot with a synchronized electron, the light-stimulated fluctuations of the hyperfine nuclear field acting on the electron are suppressed. The information about electron spin precession is imprinted in the nuclei and thereby can be stored for tens of minutes in darkness. The frequency focusing drives an electron spin ensemble into dephasing-free subspaces with the potential to realize single frequency precession of the entire ensemble.

Multiexciton generation by a single photon in nanocrystals.

We have theoretically shown that efficient generation of multi-electron-hole pairs by a single photon observed recently in semiconductor nanocrystals1-4 is caused by breaking the single electron approximation for carriers with kinetic energy above the effective energy gap. Due to strong Coulomb interaction, these states form a coherent superposition with charged excitons of the same energy. This concept allows us to define the conditions for dominant two-exciton generations by a single photon: the thermalization rate of a single exciton, initiated by light, should be lower than both the two-exciton state thermalization rate and the rate of Coulomb coupling between single and two exciton states. Possible experimental manifestations of our model are discussed.

Mode locking of electron spin coherences in singly charged quantum dots.

The fast dephasing of electron spins in an ensemble of quantum dots is detrimental for applications in quantum information processing. We show here that dephasing can be overcome by using a periodic train of light pulses to synchronize the phases of the precessing spins, and we demonstrate this effect in an ensemble of singly charged (In,Ga)As/GaAs quantum dots. This mode locking leads to constructive interference of contributions to Faraday rotation and presents potential applications based on robust quantum coherence within an ensemble of dots.

Optical control of spin coherence in singly charged (In,Ga)As/GaAs quantum dots.

Electron spin coherence has been generated optically in n-type modulation doped (In,Ga)As/GaAs quantum dots (QDs) which contain on average a single electron per dot. The coherence arises from resonant excitation of the QDs by circularly polarized laser pulses, creating a coherent superposition of an electron and a trion. Time dependent Faraday rotation is used to probe the spin precession of the optically oriented electrons about a transverse magnetic field. The coherence generation can be controlled by pulse intensity, being most efficient for (2n+1)pi pulses.

Optical pumping of the electronic and nuclear spin of single charge-tunable quantum dots.

We present a comprehensive examination of optical pumping of spins in individual GaAs quantum dots as we change the net charge from positive to neutral to negative with a charge-tunable heterostructure. Negative photoluminescence polarization memory is enhanced by optical pumping of ground state electron spins, which we prove with the first measurements of the Hanle effect on an individual quantum dot. We use the Overhauser effect in a high longitudinal magnetic field to demonstrate efficient optical pumping of nuclear spins for all three charge states of the quantum dot.