Sergey S. Sindeev

THE EXPERIMENTAL STUDY OF STRESS-RELATED PATHOLOGICAL CHANGES IN CEREBRAL VENOUS BLOOD FLOW IN NEWBORN RATS ASSESSED BY DOCT

In experiments on newborn rats with stress-related intracranial hemorrhage (ICH) using Doppler optical coherence tomography (DOCT) we have shown that latent stage of ICH (4 h after stress) is characterized by decrease of venous blood outflow and the loss of sensitivity of sagittal vein to vasoconstrictor effect of adrenaline. The incidence of ICH (24 h after stress) was accompanied by progression of early pathological changes in cerebral venous blood flow (CVBF) and development of venous insufficiency. Taking into consideration of this fact, we suggest that the suppression of CVBF related to the severity to the deleterious effect of stress on the brain hemodynamics in newborn rats. These facts allow us to conclude that the venous insufficiency with the loss of vasoconstrictor response to adrenaline is an informative and sensitive component of pattern of CVBF that can be important diagnostic criteria of risk of ICH development in newborns.

WAVELET-BASED ANALYSIS OF CEREBROVASCULAR DYNAMICS IN NEWBORN RATS WITH INTRACRANIAL HEMORRHAGES

Intracranial hemorrhage (IH) is a major problem of neonatal intensive care. The incidence of IH is typically asymptomatic and cannot be effectively detected by standard diagnostic methods. The mechanisms underlying IH are unknown but there is evidence that stress-induced disorders in adrenergic regulation of cerebral venous blood flow (CVBF) are among the main reasons. Quantitative and qualitative assessment of CVBF could significantly advance understanding of the nature of IH in newborns. In this work, we analyze variations of CVBF in newborn rats with an experimental model of stress-induced IH and adrenaline injection. Our analysis is based on the Doppler optical coherence tomography (DOCT) and a proposed adaptive wavelet-based approach that provides sensitive markers of abnormal reactions of the sagittal vein to external factors. The obtained results demonstrate that the incidence of IH in newborn rats is accompanied by a suppression of CVBF with the development of venous insufficiency and areactivity to adrenaline. We introduce a numerical measure θ, quantifying reactions of CVBF and show that the values θ < 1.23 estimated in the low-frequency (LF) spectral range corresponding to the sympathicus indicate abnormal reactions associated with the development of IH. We conclude that the revealed areactivity of the cerebral veins to adrenaline represents a possible mechanism responsible for pathological changes in CVBF.

Changes in the cerebral blood flow in newborn rats assessed by LSCI and DOCT before and after the hemorrhagic stroke

The incidence of perinatal hemorrhagic stroke (HS) is very similar to that in the elderly and produces a significant morbidity and long-term neurologic and cognitive deficits. There is strong evidence that cerebral blood flow (CBF) abnormalities make considerable contribution to HS development. However, the mechanisms responsible for pathological changes in CBF in infants with HS are not established. Therefore, quantitative assessment of CBF may significantly advance the understanding of the nature of neonatal stroke. The aim of this investigation was to determine the particularities of alterations in macro- microcirculation in the brain of newborn rats in the different stages of stress-related development of HS using three-dimensional Doppler optical coherence tomography (DOCT) and laser speckle contrast imaging (LSCI).Our results show that cerebral veins are more sensitive to harmful effect of stress compared with microcirculatory vessels. Stress-induced progressive dilation of cerebral veins with the fall of blood flow velocity precedes HS while pathological changes in microcirculatory vessels are accompanied by development of HS. The further detailed study of cerebral venous and microcirculatory circulation would be a significant advance in development of prognostic criteria for a HS risk during the first days after birthday.

Use of Submicron Vaterite Particles Serves as an Effective Delivery Vehicle to the Respiratory Portion of the Lung

Nano- and microencapsulation has proven to be a useful technique for the construction of drug delivery vehicles for use in vascular medicine. However, the possibility of using these techniques within the lung as an inhalation delivery mechanism has not been previously considered. A critical element of particle delivery to the lung is the degree of penetrance that can be achieved with respect to the airway tree. In this study we examined the effectiveness of near infrared (NIR) dye (Cy7) labeled calcium carbonate (vaterite) particles of 3.15, 1.35, and 0.65 μm diameter in reaching the respiratory portion of the lung. First of all, it was shown that, interaction vaterite particles and the components of the pulmonary surfactant occurs a very strong retardation of the recrystallization and dissolution of the particles, which can subsequently be used to create systems with a prolonging release of bioactive substances after the particles penetrate the distal sections of the lungs. Submicro- and microparticles, coated with Cy7 labeled albumin as a model compound, were delivered to mouse lungs via tracheostomy with subsequent imaging performed 24, 48, and 72 h after delivery by in vivo fluorescence. 20 min post administration particles of all three sizes were visible in the lung, with the deepest penetrance observed with 0.65 μm particles. In vivo biodistribution was confirmed by fluorescence tomography imaging of excised organs post 72 h. Laser scanning confocal microscopy shows 0.65 μm particles reaching the alveolar space. The delivery of fluorophore to the blood was assessed using Cy7 labeled 0.65 μm particles. Cy7 labeled 0.65 μm particles efficiently delivered fluorescent material to the blood with a peak 3 h after particle administration. The pharmacokinetics of NIR fluorescence dye will be shown. These studies establish that by using 0.65 μm particles loaded with Cy7 we can efficiently access the respiratory portion of the lung, which represents a potentially efficient delivery mechanism for both the lung and the vasculature.

The assessment of pathological changes in cerebral blood flow in hypertensive rats with stress-induced intracranial hemorrhage using Doppler OCT: Particularities of arterial and venous alterations/Die Beurteilung von pathologischen Veränderungen der Hirndurchblutung bei hypertensiven Ratten mit Stress-induzierten intrakraniellen Blutungen mittels Doppler-OCT: Besonderheiten von arteriellen und venösen Veränderungen

Abstract Background and objectives: Hemorrhagic insult is a major source of morbidity and mortality in both adults and newborn babies in the developed countries. The mechanisms underlying the non-traumatic rupture of cerebral vessels are not fully clear, but there is strong evidence that stress, which is associated with an increase in arterial blood pressure, plays a crucial role in the development of acute intracranial hemorrhage (ICH), and alterations in cerebral blood flow (CBF) may contribute to the pathogenesis of ICH. The problem is that there are no effective diagnostic methods that allow for a prognosis of risk to be made for the development of ICH. Therefore, quantitative assessment of CBF may significantly advance the understanding of the nature of ICH. The aim of this study was to determine the particularities of alterations in arterial and venous cerebral circulation in hypertensive rats at different stages of stress-related development of ICH using three-dimensional Doppler optical coherence tomography (DOCT). Material and methods: Experiments were performed in mongrel adult rats. To induce ICH, hypertensive rats underwent stress (effect of severe sound, 120 dB during 2 h). To induce the renal hypertension (two kidneys, one clip) the rats were clipped at the left renal artery with a silver clip. Seven weeks after clipping, the hypertensive rats were used in the experiment. The monitoring of CBF was performed in anesthetized rats with fixed heads using a commercially available swept source OCT system (OCS1300SS; Thorlabs) in the masked period of ICH (4 h after stress) and during ICH (24 h after stress). Results: It could be shown that in stressed rats, compared with non-stressed animals, the latent stage of stress-induced ICH (4 h after stress-off) is characterized by an increase in diameter of the superior sagittal vein with decrease in speed of the blood flow in the venous network, whereas no changes in the CBF in the arterial tree were found in this period. These facts suggest that the masked period of ICH is accompanied by decreasing venous outflow and the development of venous insufficiency. The incidence of ICH, 24 h after stress, is associated with progression of pathological alterations in cerebral venous circulation. All hypertensive rats with ICH demonstrated a greater increase in the diameter of the superior sagittal vein than stressed rats at the latent stage of ICH (in 2.5-fold, p<0.05) and healthy animals (in 3.7-fold, p<0.05). The velocity of blood flow in the dilated sagittal vein of rats with ICH decreased more than stressed rats without ICH and healthy animals. The progression of venous insufficiency was accompanied by relaxation of cerebral arteries with a fall in the speed of blood flow in the arterial tree, reflecting the development of intracranial hypotension. Conclusion: In summary, using DOCT we have shown that the latent stage of stress-induced ICH is characterized by a decrease in venous outflow. The incidence of ICH is associated with the progression of pathological alterations in cerebral venous circulation that is accompanied by a decrease in blood flow in the arterial tree. The evaluation of cerebral venous insufficiency is an important diagnostic approach for the prognosis of the risk of developing cerebral hypotension and ICH. Zusammenfassung Hintergrund und Zielsetzung: Schlaganfälle sind in den entwickelten Ländern eine der Hauptursachen für Morbidität und Mortalität bei Erwachsenen und Neugeborenen. Die Mechanismen, die zur nicht-traumatischen Ruptur von Hirngefäßen führen, sind nicht vollständig klar. Doch gibt es starke Hinweise darauf, dass Spannungen, die mit einer Erhöhung des arteriellen Blutdrucks einhergehen, eine entscheidende Rolle bei der Entwicklung akuter intrakranieller Hirnblutungen spielen und Änderungen des zerebralen Blutflusses zur Pathogenese beitragen können. Das Problem ist, dass es bislang keine effektive diagnostische Methode gibt, mit der sich das Risiko für die Entwicklung intrakranieller Hirnblutungen vorhersagen lässt. Daher kann eine quantitative Beurteilung des zerebralen Blutflusses erheblich zum besseren Verständnis beitragen. Das Ziel dieser Studie war es daher, die Besonderheiten der Veränderungen in der arteriellen und venösen zerebralen Durchblutung in hypertensiven Ratten in verschiedenen Stadien der Stress-Entwicklung mittels dreidimensionaler Doppler-OCT (3D-DOCT) zu untersuchen. Material und Methoden: Die Experimente wurden an erwachsenen Mischlingsratten durchgeführt. Um interkranielle Hirnblutungen zu induzieren, wurden die hypertensiven Ratten Stress ausgesetzt (Beschallung mit 120 dB über eine Zeit von 2 h). Um eine renale Hypertonie zu erzeugen, wurde bei den Ratten die linke Nierenarterie mit einem Silberclip abgeklemmt. Nach 7 Wochen wurden die hypertensiven Ratten im Experiment verwendet. Die Messung des zerebralen Blutflusses erfolgte 4 h und 24 h nach Stress-Belastung mittels eines kommerziellen OCT-Systems (OCS1300SS; Thorlabs), wobei die narkotisierten Ratten am Kopf fixiert wurden. Ergebnisse: Im Vergleich zu nicht gestressten Tieren war bei den gestressten Ratten die latente Stufe der Stress-induzierten intrakraniellen Hirnblutung (4 h nach Stressende) durch eine Zunahme des Durchmessers der Hirnvene bei gleichzeitiger Verlangsamung des Blutflusses im venösen Gefäßsystem gekennzeichnet. Im arteriellen Gefäßbaum wurde hingegen keine Veränderung des zerebralen Blutflusses festgestellt. Dies legt nahe, dass die latente Phase einer intrakraniellen Hirnblutung mit einer Verringerung des venösen Abflusses und der Entwicklung einer Veneninsuffizienz einhergeht. 24 h nach Belastung kommt es zu einem Fortschreiten der pathologischen Veränderungen im zerebralen venösen Blutkreislauf. Alle hypertensiven Ratten mit akuter intrakranieller Hirnblutung zeigten eine größere Zunahme des Durchmessers der Hirnvene als die gestressten Ratten im latenten Stadium (um das 2,5fache, p<0,05) bzw. als die gesunden Tiere (um das 3,7fache; p<0,05). Die Geschwindigkeit des Blutflusses in der dilatierten sagittalen Vene von Ratten mit akuter intrakranieller Hirnblutung verringerte sich mehr als bei Ratten ohne Hirnblutung und bei gesunden Tieren. Das Fortschreiten der Veneninsuffizienz ging mit einer Entspannung der zerebralen Arterien bei gleichzeitigem Rückgang der Geschwindigkeit des Blutflusses in den arteriellen Gefäßen einher, was die Entwicklung der intrakraniellen Hypotonie widerspiegelte. Fazit: Es lässt sich schlussfolgern, dass unter Verwendung der DOCT gezeigt werden konnte, dass die latente Phase der Stress-induzierten interkraniellen Hirnblutung durch eine Abnahme des venösen Abflusses gekennzeichnet ist. Die Inzidenz einer interkraniellen Hirnblutung ist mit dem Fortschreiten von pathologischen Veränderungen in der zerebralen venösen Zirkulation assoziiert und wird durch eine Verringerung des Blutflusses im arteriellen Gefäßbaum begleitet. Die Auswertung der zerebralen venösen Insuffizienz ist ein wichtiges diagnostisches Vorgehen für die Prognose des Risikos der Entwicklung von zerebraler Hypotonie und intrakranieller Hirnblutung.

Study of cerebral bloodflow autoregulation in rats assessed by LSCI

Using the method of laser speckle imaging, which has been extended to the simultaneous study of macro- and microcirculation of cerebral vessels in healthy rats, shows that the mechanisms of maintaining the “autonomy” of cerebral circulation depends on the initial conditions. Pharmacological dose-dependent stimulation of peripheral arterial pressure caused different reactions in maless and females macro- and microcirculation.

The sex differences in nature of vascular endothelial stress: nitrergic mechanisms

Here we studied the role of nitric oxide in cardiovascular regulation in male and female hypertensive rats under normal and stress conditions. We found that the severity of hypertension in females was lower than in males. Hypertensive females demonstrated more favorable pattern of cardiovascular responses to stress. Nitric oxide blockade by NG-nitro-L-arginine methyl ester (L-NAME) increased the mean arterial pressure and decreased the heart rate more effectively in females than in males. During stress, L-NAME modified the stress-induced cardiovascular responses more significantly in female compared with male groups. Our data show that hypertensive females demonstrated the more effective nitric oxide control of cardiovascular activity under normal and especially stress conditions than male groups. This sex differences may be important mechanism underlying greater in females vs. males stress-resistance of cardiovascular system and hypertension formation.

Multifractal analysis of macro- and microcerebral circulation in rats

Application of noninvasive optical coherent-domain methods and advanced data processing tools such as the wavelet-based multifractal formalism allows revealing effective markers of early stages of functional distortions in the dynamics of cerebral vessels. Based on experiments performed in rats we discuss a possibility to diagnose a hidden stage of the development of intracranial hemorrhage (ICH). We also consider responses of the cerebrovascular dynamics to a pharmacologically induced increase in the peripheral blood pressure. We report distinctions occurring at the levels of macro- and microcerebral circulation.

Recognition of short-term changes in physiological signals with the wavelet-based multifractal formalism

In this paper we address the problem of revealing and recognition transitions between distinct physiological states using quite short fragments of experimental recordings. With the wavelet-based multifractal analysis we characterize changes of complexity and correlation properties in the stress-induced dynamics of arterial blood pressure in rats. We propose an approach for association revealed changes with distinct physiological regulatory mechanisms and for quantifying the influence of each mechanism.

A New Model of Сerebral hemorrhages in newborns rats

Here we describes a new model of stress-induced cerebral hemorrhage in newborn rats. Using histological and laser speckle imaging, we characterized changes in the brain tissues and circulation associated with the pre- and post-hemorrhage periods.