scholarly journals Occlusion of Cortical Ascending Venules Causes Blood Flow Decreases, Reversals in Flow Direction, and Vessel Dilation in Upstream Capillaries

2011 ◽  
Vol 31 (11) ◽  
pp. 2243-2254 ◽  
Author(s):  
John Nguyen ◽  
Nozomi Nishimura ◽  
Robert N Fetcho ◽  
Costantino Iadecola ◽  
Chris B Schaffer
Keyword(s):  
Blood Flow ◽  
Nearest Neighbor ◽  
Flow Direction ◽  
Cognitive Disorders ◽  
Laser Pulses ◽  
Vessel Diameter ◽  
Flow Speed ◽  
Femtosecond Laser Pulses ◽  
Brain Diseases ◽  
The Impact

The accumulation of small strokes has been linked to cognitive dysfunction. Although most animal models have focused on the impact of arteriole occlusions, clinical evidence indicates that venule occlusions may also be important. We used two-photon excited fluorescence microscopy to quantify changes in blood flow and vessel diameter in capillaries after occlusion of single ascending or surface cortical venules as a function of the connectivity between the measured capillary and the occluded venule. Clotting was induced by injuring the target vessel wall with femtosecond laser pulses. After an ascending venule (AV) occlusion, upstream capillaries showed decreases in blood flow speed, high rates of reversal in flow direction, and increases in vessel diameter. Surface venule occlusions produced similar effects, unless a collateral venule provided a new drain. Finally, we showed that AVs and penetrating arterioles have different nearest-neighbor spacing but capillaries branching from them have similar topology, which together predicted the severity and spatial extent of blood flow reduction after occlusion of either one. These results provide detailed insights into the widespread hemodynamic changes produced by cortical venule occlusions and may help elucidate the role of venule occlusions in the development of cognitive disorders and other brain diseases.

scholarly journals Advanced Constitutive Modeling of the Thixotropic Elasto-Visco-Plastic Behavior of Blood: Steady-State Blood Flow in Microtubes

Materials ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 367
Author(s):  
Konstantinos Giannokostas ◽  
Yannis Dimakopoulos ◽  
Andreas Anayiotos ◽  
John Tsamopoulos
Keyword(s):  
Blood Flow ◽  
Steady State ◽  
Constitutive Model ◽  
Blood Plasma ◽  
Constitutive Modeling ◽  
Flow Direction ◽  
Momentum Balance ◽  
Plastic Behavior ◽  
Flow Investigation ◽  
The Impact

The present work focuses on the in-silico investigation of the steady-state blood flow in straight microtubes, incorporating advanced constitutive modeling for human blood and blood plasma. The blood constitutive model accounts for the interplay between thixotropy and elasto-visco-plasticity via a scalar variable that describes the level of the local blood structure at any instance. The constitutive model is enhanced by the non-Newtonian modeling of the plasma phase, which features bulk viscoelasticity. Incorporating microcirculation phenomena such as the cell-free layer (CFL) formation or the Fåhraeus and the Fåhraeus-Lindqvist effects is an indispensable part of the blood flow investigation. The coupling between them and the momentum balance is achieved through correlations based on experimental observations. Notably, we propose a new simplified form for the dependence of the apparent viscosity on the hematocrit that predicts the CFL thickness correctly. Our investigation focuses on the impact of the microtube diameter and the pressure-gradient on velocity profiles, normal and shear viscoelastic stresses, and thixotropic properties. We demonstrate the microstructural configuration of blood in steady-state conditions, revealing that blood is highly aggregated in narrow tubes, promoting a flat velocity profile. Additionally, the proper accounting of the CFL thickness shows that for narrow microtubes, the reduction of discharged hematocrit is significant, which in some cases is up to 70%. At high pressure-gradients, the plasmatic proteins in both regions are extended in the flow direction, developing large axial normal stresses, which are more significant in the core region. We also provide normal stress predictions at both the blood/plasma interface (INS) and the tube wall (WNS), which are difficult to measure experimentally. Both decrease with the tube radius; however, they exhibit significant differences in magnitude and type of variation. INS varies linearly from 4.5 to 2 Pa, while WNS exhibits an exponential decrease taking values from 50 mPa to zero.

Dynamics of water dimer in femtosecond laser pulses: a simulation study

2014 ◽  
Vol 28 (22) ◽  
pp. 1450179
Author(s):  
Zhiping Wang ◽  
Fengshou Zhang ◽  
Xuefeng Xu ◽  
Yanbiao Wang ◽  
Chaoyi Qian
Keyword(s):  
Local Density ◽  
General Pattern ◽  
Laser Pulses ◽  
Laser Frequency ◽  
Femtosecond Laser Pulses ◽  
Water Dimer ◽  
Intense Laser ◽  
Intense Laser Pulses ◽  
Typical Sequence ◽  
The Impact

In this paper, we study the electronic and ionic dynamics of the water dimer subject to short and intense laser pulses. The dynamics is described by means of the time-dependent local-density approximation coupled to ionic molecular dynamics (TDLDA-MD) non-adiabatically. The impact of laser frequency on the response of water dimer is discussed by exploring the ionization, the dipole signal and bond lengths of water dimer. Furthermore, it is found that the water donor is more sensitive to the laser field than the water acceptor and the probabilities for the ionic states show the general pattern of the typical sequence of the interlaced production maxima.

scholarly journals Impact of Pre-Patterned Structures on Features of Laser-Induced Periodic Surface Structures

Molecules ◽  
2021 ◽  
Vol 26 (23) ◽  
pp. 7330
Author(s):  
Stella Maragkaki ◽  
Panagiotis C. Lingos ◽  
George D. Tsibidis ◽  
George Deligeorgis ◽  
Emmanuel Stratakis
Keyword(s):  
Laser Pulses ◽  
Laser Wavelength ◽  
Femtosecond Laser Pulses ◽  
Surface Structures ◽  
Periodic Pattern ◽  
Patterned Surfaces ◽  
Periodic Surface ◽  
Multi Scale ◽  
Patterned Structures ◽  
The Impact

The efficiency of light coupling to surface plasmon polariton (SPP) represents a very important issue in plasmonics and laser fabrication of topographies in various solids. To illustrate the role of pre-patterned surfaces and impact of laser polarisation in the excitation of electromagnetic modes and periodic pattern formation, Nickel surfaces are irradiated with femtosecond laser pulses of polarisation perpendicular or parallel to the orientation of the pre-pattern ridges. Experimental results indicate that for polarisation parallel to the ridges, laser induced periodic surface structures (LIPSS) are formed perpendicularly to the pre-pattern with a frequency that is independent of the distance between the ridges and periodicities close to the wavelength of the excited SPP. By contrast, for polarisation perpendicular to the pre-pattern, the periodicities of the LIPSS are closely correlated to the distance between the ridges for pre-pattern distance larger than the laser wavelength. The experimental observations are interpreted through a multi-scale physical model in which the impact of the interference of the electromagnetic modes is revealed.

162 IMPACT OF FLOW SPEED OF ICG FLUORESCENCE IN THE GASTRIC CONDUIT AND THORACIC INLET SPACE ON ANASTOMOTIC LEAKAGE AFTER ESOPHAGECTOMY

2020 ◽  
Vol 33 (Supplement_1) ◽  
Author(s):  
K Koyanagi ◽  
S Ozawa ◽  
Y Ninomiya ◽  
K Yatabe ◽  
T Higuchi ◽  
...  
Keyword(s):  
Blood Flow ◽  
Anastomotic Leakage ◽  
Fluorescence Imaging ◽  
Flow Speed ◽  
Gastric Conduit ◽  
Thoracic Inlet ◽  
Speed Reduction ◽  
Clinicopathological Findings ◽  
Conduit Wall ◽  
The Impact

Abstract   We have previously demonstrated that the flow speed of indocyanine green (ICG) fluorescence in the gastric conduit wall could predict anastomotic leakage after esophagectomy. Surround organs via retrosternal route is considered to affect the blood flow in the gastric conduit and anastomotic leakage. In the study, we investigated the impact of the flow speed of ICG fluorescence in the gastric conduit wall and thoracic inlet space on anastomotic leakage after esophagectomy. Methods A total of 142 patients, who underwent esophagectomy with three-field lymph node dissection, simultaneous reconstruction using a gastric conduit, and cervical anastomosis via retrosternal route, were prospectively investigated. Using ICG fluorescence imaging, blood flow speed of the gastric conduit wall was assessed before and after anastomosis (pre speed and post speed (cm/s)) and correlated with clinicopathological findings. Parameters of thoracic inlet space was assessed using CT scan and correlated with blood flow speed of the gastric conduit wall and anastomotic leakage. Results Median pre speed was 2.54 (0.73–6.10) cm/s and median post speed was dropped by 1.77 (0.32–8.67) cm/s. Speed reduction (pre speed—post speed) and speed reduction rate ((pre speed—post speed)/pre speed) were negatively correlated with thoracic inlet area (TIA) (P = 0.004, P = 0.021). Pre speed and post speed of the patients with anastomotic leakage were significantly slower than those of the patients without anastomotic leakage, respectively (P < 0.001 and P = 0.050). In 115 patients with pre speed more than 1.98 cm/s, TIA was significantly associated with anastomotic leakage after esophagectomy (P < 0.001). Conclusion We clearly demonstrated that retrosternal route reduced the blood flow of the gastric conduit wall using ICG fluorescence imaging. Narrow thoracic inlet space might obstruct the blood flow of the gastric conduit wall and cause anastomotic leakage after esophagectomy.

scholarly journals Influence of tunnel ionization to third-harmonic generation of infrared femtosecond laser pulses in air

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Viktorija Tamulienė ◽  
Greta Juškevičiūtė ◽  
Danas Buožius ◽  
Virgilijus Vaičaitis ◽  
Ihar Babushkin ◽  
...  
Keyword(s):  
Harmonic Generation ◽  
Theoretical Study ◽  
Laser Pulses ◽  
Third Harmonic Generation ◽  
Femtosecond Laser Pulses ◽  
Phase Matching ◽  
Third Harmonic ◽  
The One ◽  
The Impact ◽  
Longitudinal Phase

Abstract Here we present an experimental as well as theoretical study of third-harmonic generation in tightly focused femtosecond filaments in air at the wavelength of $$1.5 \,\upmu \hbox {m}$$ 1.5 μ m . At low intensities, longitudinal phase matching is dominating in the formation of 3rd harmonics, whereas at higher intensities locked X-waves are formed. We provide the arguments that the X-wave formation is governed mainly by the tunnel-like ionization dynamics rather than by the multiphoton one. Despite of this fact, the impact of the ionization-induced nonlinearity is lower than the one from bound–bound transitions at all intensities.

scholarly journals Network-driven anomalous transport is a fundamental component of brain microvascular dysfunction

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Florian Goirand ◽  
Tanguy Le Borgne ◽  
Sylvie Lorthois
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Blood Flow ◽  
Waste Product ◽  
Microvascular Dysfunction ◽  
Anomalous Transport ◽  
Brain Diseases ◽  
High Concentrations ◽  
Critical Regions ◽  
The Impact

AbstractBlood microcirculation supplies neurons with oxygen and nutrients, and contributes to clearing their neurotoxic waste, through a dense capillary network connected to larger tree-like vessels. This complex microvascular architecture results in highly heterogeneous blood flow and travel time distributions, whose origin and consequences on brain pathophysiology are poorly understood. Here, we analyze highly-resolved intracortical blood flow and transport simulations to establish the physical laws governing the macroscopic transport properties in the brain micro-circulation. We show that network-driven anomalous transport leads to the emergence of critical regions, whether hypoxic or with high concentrations of amyloid-β, a waste product centrally involved in Alzheimer’s Disease. We develop a Continuous-Time Random Walk theory capturing these dynamics and predicting that such critical regions appear much earlier than anticipated by current empirical models under mild hypoperfusion. These findings provide a framework for understanding and modelling the impact of microvascular dysfunction in brain diseases, including Alzheimer’s Disease.

The Impact of Multidisciplinary Collaborative Nursing Intervention on Arteriovenous Fistula in Patients Undergoing Hemodialysis

2021 ◽  
pp. 105477382110371
Author(s):  
Danfeng Zha ◽  
Xionghao Yang ◽  
Yan Yang ◽  
Haifen Zhang ◽  
Yan Jin ◽  
...  
Keyword(s):  
Chronic Kidney Disease ◽  
Blood Flow ◽  
Kidney Disease ◽  
Arteriovenous Fistula ◽  
Nursing Intervention ◽  
Vessel Diameter ◽  
Hemodialysis Patients ◽  
Control Group ◽  
The Impact ◽  
Intervention Procedure

This study was conducted to evaluate the effect of multidisciplinary collaborative nursing intervention on AVF in patients with chronic kidney disease (CKD) undergoing hemodialysis. Patients ( n = 84) with CKD who underwent the first autologous AVF were randomly divided into control group and multidisciplinary collaborative nursing intervention (MCNI) group and they received routine nursing procedure and multidisciplinary collaborative nursing intervention procedure, respectively. The natural blood flow and vessel diameter in MCNI group were higher than that in control group at the fourth week after surgery ( p < .05). The vessel diameter in MCNI group at 2 and 4 weeks after operation was significantly larger than that in control group ( p < .05).In conclusions, the implementation of multidisciplinary collaborative nursing intervention procedure can significantly promote the maturation of AVF, effectively increase the blood flow of AVF and promote the growth of vessel diameter.

scholarly journals Precapillary sphincters and pericytes at first-order capillaries as key regulators for brain capillary perfusion

2021 ◽  
Vol 118 (26) ◽  
pp. e2023749118
Author(s):  
Stefan Andreas Zambach ◽  
Changsi Cai ◽  
Hans Christian Cederberg Helms ◽  
Bjørn Olav Hald ◽  
Yiqiu Dong ◽  
...  
Keyword(s):  
Blood Flow ◽  
Smooth Muscle Actin ◽  
Three Dimensional ◽  
Vessel Diameter ◽  
Synaptic Activity ◽  
Guanosine Monophosphate ◽  
Capillary Perfusion ◽  
First Order ◽  
The Impact

Rises in local neural activity trigger local increases of cerebral blood flow, which is essential to match local energy demands. However, the specific location of microvascular flow control is incompletely understood. Here, we used two-photon microscopy to observe brain microvasculature in vivo. Small spatial movement of a three-dimensional (3D) vasculature makes it challenging to precisely measure vessel diameter at a single x–y plane. To overcome this problem, we carried out four-dimensional (x–y–z–t) imaging of brain microvessels during exposure to vasoactive molecules in order to constrain the impact of brain movements on the recordings. We demonstrate that rises in synaptic activity, acetylcholine, nitric oxide, cyclic guanosine monophosphate, ATP-sensitive potassium channels, and endothelin-1 exert far greater effects on brain precapillary sphincters and first-order capillaries than on penetrating arterioles or downstream capillaries, but with similar kinetics. The high level of responsiveness at precapillary sphincters and first-order capillaries was matched by a higher level of α-smooth muscle actin in pericytes as compared to penetrating arterioles and downstream capillaries. Mathematical modeling based on 3D vasculature reconstruction showed that precapillary sphincters predominantly regulate capillary blood flow and pressure as compared to penetrating arterioles and downstream capillaries. Our results confirm a key role for precapillary sphincters and pericytes on first-order capillaries as sensors and effectors of endothelium- or brain-derived vascular signals.

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