Altered Flow Research Articles

Transverse sinus pathologies, vestibular migraine and intracranial hypertension without papilledema

BackgroundIn the absence of papilledema, the presentation of migraine and idiopathic intracranial hypertension (IIH) is very similar. In this respect, an IIH could be presented as a vestibular migraine. Our main objective in this case report is to demonstrate the similarities between IIH and vestibular migraine. CasesThis is a report of 14 patients who have IIH without papilledema presented as vestibular migraine to the clinic and followed from 2020 to 2022. ResultsThe common presentation of patients was ear-facial pain, dizziness, and frequent pulsatile tinnitus. One-fourth of the patients reported episodes of true episodic vertigo. The average age was 37.8, the average BMI was 37.4, and the average lumbar puncture-opening pressure was 25.6 cm H2O. Transverse sinus venous flow alterations caused neuroimaging findings of sigmoid sinus dehiscence, empty sella, or tonsillar ectopia. Most patients improved with carbonic anhydrase inhibitors, and one patient was treated with a dural sinus stent. ConclusionA transverse sinus stenosis, even in the non-dominant site, may elevate the CSF pressure in obese individuals. This stenosis causes dural sinus-related pulsatile tinnitus with characteristics different from those of an arterial origin. Dizziness is a common complaint in patients with IIH, just like VM. In our opinion, episodic vertigo in these patients is the direct effect of CSF flow alterations into the inner ear's vestibule. Patients with mild elevations will be presented to the clinic, similar to migraines with or without the presence of pulsatile tinnitus. Treatment requires lowering intracranial pressure and managing migraine symptoms.

Transcranial Doppler Ultrasonography detection on cerebrovascular flow for evaluating neonatal hypoxic-ischemic encephalopathy modeling.

This study aimed to investigate the feasibility of Transcranial Doppler Ultrasonography (TCD) in evaluating neonatal hypoxic-ischemic encephalopathy (NHIE) modeling through monitoring the alteration of cerebrovascular flow in neonatal hypoxic-ischemic (HI) rats. Postnatal 7-day-old Sprague Dawley (SD) rats were divided into the control group, HI group, and hypoxia (H) group. TCD was applied to assess the changes of cerebral blood vessels, cerebrovascular flow velocity, and heart rate (HR) in sagittal and coronal sections at 1, 2, 3, and 7 days after the operation. For accuracy, cerebral infarct of rats was examined by 2,3,5-Triphenyl tetrazolium chloride (TTC) staining and Nissl staining to simultaneously verify the establishment of NHIE modeling. Coronal and sagittal TCD scans revealed obvious alteration of cerebrovascular flow in main cerebral vessels. Obvious cerebrovascular back-flow was observed in anterior cerebral artery (ACA), basilar artery (BA), middle cerebral artery (MCA) of HI rats, along with accelerated cerebrovascular flows in the left internal carotid artery (ICA-L) and BA, decreased flows in right internal carotid artery (ICA-R) relative to those in the H and control groups. The alterations of cerebral blood flows in neonatal HI rats indicated successful ligation of right common carotid artery. Besides, TTC staining further validated the cerebral infarct was indeed caused due to ligation-induced insufficient blood supply. Damage to nervous tissues was also revealed by Nissl staining. Cerebral blood flow assessment by TCD in neonatal HI rats contributed to cerebrovascular abnormalities observed in a real-time and non-invasive way. The present study elicits the potentials to utilize TCD as an effective means for monitoring the progression of injury as well as NHIE modeling. The abnormal appearance of cerebral blood flow is also beneficial to the early warning and effective detection in clinical practice.

Evolution and concept of environmental flows (e-flows): meta-analysis

Abstract River ecosystems have become fragile due to river flow alterations in the wake of expending structural controls triggered by the ever-increasing demands of freshwater. The efforts to alleviate the effects of river flow alterations have paved the way for the emergence and expansion of the concept of e-flows. The role of e-flows in ecosystem protection and water resources management is not yet fully understood and practiced. This review summarizes the historical evolution of the concept of e-flows and recaps its assessment methods; analyzes the impacts of river flow alterations; indicates the challenges e-flows have been facing and identifies the gaps in the focus of e-flows research. A total of 303 articles published since 2010 were collected and systematically assessed. Most of the publications are focused on describing the effects and management of river flow alterations. According to the findings of this meta-analysis, less attention is given to basin-scale, social and policy aspects of e-flows. Furthermore, little consideration is given to the part played by groundwater in e-flows along with the roles of e-flows in maintaining the health of floodplains and e-flows of intermittent rivers and ephemeral streams.

An assessment of microvascular hemodynamics in human macula

An adequate blood supply to meet the energy demands is essential for any tissue, particularly for high energy demand tissues such as the retina. A critical question is: How is the dynamic match between neuronal demands and blood supply achieved? We present a quantitative assessment of temporal and spatial variations in perfusion in the macular capillary network in 10 healthy human subjects using a non-invasive and label-free imaging technique. The assessment is based on the calculation of the coefficient of variation (CoV) of the perfusion signal from arterioles, venules and capillaries from a sequence of optical coherence tomography angiography images centred on the fovea. Significant heterogeneity of the spatial and temporal variation was found within arterioles, venules and capillary networks. The CoV values of the capillaries and smallest vessels were significantly higher than that in the larger vessels. Our results demonstrate the presence of significant heterogeneity of spatial and temporal variation within each element of the macular microvasculature, particularly in the capillaries and finer vessels. Our findings suggest that the dynamic match between neuronal demands and blood supply is achieved by frequent alteration of local blood flow evidenced by capillary perfusion variations both spatially and temporally in the macular region.

Pancreaticoduodenectomy with celiac artery resection (PD-CAR) for unresctable locally advanced pancreatic ductal adenocarcinoma

Locally advanced pancreatic ductal adenocarcinoma (LA-PDAC) involving the celiac artery (CeA), the common hepatic artery and the gastroduodenal artery (GDA) is considered unresectable. We developed the novel procedure of pancreaticoduodenectomy with celiac artery resection (PD-CAR) for such LA-PDACs. From 2015 to 2018, we performed curative pancreatectomy with major arterial resection for 13 LA-PDACs as a clinical study (UMIN000029501). Of those, four patients with pancreatic neck cancer involving the CeA and GDA were candidates for PD-CAR. Prior to surgery, blood flow alterations were performed to unify the blood flow to the liver, stomach, and pancreas, resulting in feeding from the cancer-free artery. During PD-CAR, arterial reconstruction of the unified artery was performed as needed. Based on the records of PD-CAR cases, we retrospectively analyzed the validity of the operation. R0 resection was achieved in all patients. Arterial reconstruction was performed in three patients. In another patient, the hepatic arterial flow was maintained by preserving of the left gastric artery. The mean operative time was 669min, and the mean blood loss was 1003ml. Although Clavien-Dindo classification III-IV postoperative morbidities occurred in three patients, no reoperations nor mortalities occurred. Although two patients died of cancer recurrence, one patient survived for 26months without recurrence (died of cerebral infarction), and another is alive at 76months without recurrence. PD-CAR, which enabled R0 resection and preservation of the residual stomach, pancreas, and spleen, provided acceptable postoperative outcomes.

Quantification of the impact of pore pressure on relative permeability curves utilizing coreflood unit with gamma ray scanning capability

Physics of multiphase flow in porous media at Darcy scale heavily relies on the concept of relative permeability. Moreover, relative permeability is an important input parameter for numerical reservoir simulation for multiphase flow in porous media. Often fixed set of relative permeability curves is applied for the entire complex large-scale reservoir models whilst the pressure typically declines during a field’s production. In this study, we are experimentally focusing on investigating the effect of high pressures on relative permeability curves.We use a state-of-the-art custom-made relative permeability steady-state flow system with integrated gamma-ray scanning. We limit the fluids to a model oil, brine, and rock to avoid any secondary effects of fluid-rock interactions, such as wettability alteration, asphaltenes, and gas-dissolution, miscibility, and interaction of phase behavior and flow. We run the relative permeability scans at a fixed temperature (isotherm) and at several pore pressure values (isobars), such as 2000, 4000, 6000, and 8000 psi with fixed and variable net confining pressures. To be able to perform the analysis more diligently, we observe the in-situ phase saturations via two methods: mass balance and gamma-ray scanning. The resulting relative permeability curves are then compared to each other to examine the impact of pressure. We did not observe significant pressure effect on relative permeability measurements in simple model system used in this work, where minimal fluid-fluid and fluid-rock interactions occur. However, the outcome of this work should not be extended to more complex systems where strong fluid-fluid and rock-fluid interactions take place, such as gas flooding with strong solubility effects, and chemical flooding.Systematic analysis of the pressure effect on relative permeability is extremely scarce in the literature, even though the pressure varies significantly in the reservoir during the lifetime of the field. Therefore, it is essential to understand pressure effect on relative permeability under well controlled laboratory conditions. The outcomes of this paper may help engineers to improve their model predictions during field development and therefore decision-making processes.

Centering Margins in Organ Assembly

Centering Margins in Organ Assembly

The role of the autonomic nervous system in cerebral blood flow regulation in stroke: A review.

Stroke is a pathophysiological condition which results in alterations in cerebral blood flow (CBF). The mechanism by which the brain maintains adequate CBF in presence of fluctuating cerebral perfusion pressure (CPP) is known as cerebral autoregulation (CA). Disturbances in CA may be influenced by a number of physiological pathways including the autonomic nervous system (ANS). The cerebrovascular system is innervated by adrenergic and cholinergic nerve fibers. The role of the ANS in regulating CBF is widely disputed owing to several factors including the complexity of the ANS and cerebrovascular interactions, limitations to measurements, variation in methods to assess the ANS in relation to CBF as well as experimental approaches that can or cannot provide insight into the sympathetic control of CBF. CA is known to be impaired in stroke however the number of studies investigating the mechanisms by which this occurs are limited. This literature review will focus on highlighting the assessment of the ANS and CBF via indices derived from the analyses of heart rate variability (HRV), and baroreflex sensitivity (BRS), and providing a summary of both clinical and animal model studies investigating the role of the ANS in influencing CA in stroke. Understanding the mechanisms by which the ANS influences CBF in stroke patients may provide the foundation for novel therapeutic approaches to improve functional outcomes in stroke patients.

National‐Scale Detection of Reservoir Impacts Through Hydrological Signatures

AbstractReservoirs play a vital role in the supply and management of water resources and their operation can significantly alter downstream flow. Despite this, reservoirs are frequently excluded or poorly represented in large‐scale hydrological models, which can be partly attributed to a lack of open‐access data describing reservoir operations, inflow and storage. To help inform the development of reservoir operation schemes, we collate a suite of hydrological signatures designed to detect the impacts of reservoirs on the flow regime at large‐scales from downstream flow records only. By removing the need for pre‐and‐post‐reservoir flow timeseries (a requirement of many pre‐existing techniques), these signatures facilitate the assessment of flow alteration across a much wider range of catchments. To demonstrate their application, we calculate the signatures across Great Britain in 111 benchmark (i.e., near‐natural) catchments and 186 reservoir catchments (where at least one upstream reservoir is present). We find that abstractions from water resource reservoirs induce deficits in the water balance, and that pre‐defined flow releases (e.g., the compensation flow) reduce variability in the downstream flow duration curve and in intra‐annual low flows. By comparing signatures in benchmark and reservoir catchments, we define thresholds above which the influence of reservoirs can be distinguished from natural variability and identify 40 catchments significantly impacted by the presence of reservoirs. The signatures also provide insights into local reservoir operations, which can inform the development of tailored reservoir operation schemes, and identify locations where current modeling practices (which lack reservoir representation) will be insufficient.

Coronary Perfusion After Valve-in-Valve Transcatheter Aortic Valve Implantation in Small Aortic Root: In Vitro Experimental Assessment.

Coronary flow obstruction following transcatheter aortic valve-in-valve implantation (VIV-TAVI) is associated with a high mortality risk. The aim of this work was to quantify the coronary perfusion after VIV-TAVI in a high-risk aortic root anatomy. 3D printed models of small aortic root were used to simulate the implantation of a TAVI prosthesis (Portico 23) into surgical prostheses (Trifecta 19 and 21). The aortic root models were tested in a pulsatile in vitro bench setup with a coronary perfusion simulator. The tests were performed at baseline and post-VIV-TAVI procedure in aligned and misaligned commissural configurations under simulated hemodynamic rest and exercise conditions. The experimental design provided highly controllable and repeatable flow and pressure conditions. The left and right coronary mean flow did not differ significantly at pre- and post-VIV-TAVI procedure in any tested configurations. The commissural misalignment did not induce any significant alterations to the coronary flow. High-risk aortic root anatomy did not trigger coronary ostia obstruction or coronary flow alteration after transcatheter aortic valve implantation in a surgical bioprosthesis as shown from in-vitro flow loop tests.

Early effects of inactivated (CoronaVac) SARS-CoV-2 vaccine on retrobulbar vascular blood flow and retinal vascular density

AimsWe aimed to investigate the early effects of inactivated SARS-CoV-2 vaccine on retrobulbar vascular blood flow and retinal vascular density in healthy subjects. MethodsThirty-four eyes of 34 healthy volunteers who received the CoronaVac (Sinovac Life Sciences, China) were included in this prospective study. Resistive index (RI), pulsatility index (PI) and peak systolic velocity (PSV) of the ophthalmic artery (OA), central retinal artery (CRA), and the temporal and nasal posterior ciliary arteries (PCA) were evaluated with color Doppler ultrasonography (CDUS) before vaccination, at the 2nd and 4th weeks after vaccination. Superficial capillary plexus (SCP) and deep capillary plexus (DCP) vessel density (VD), foveal avascular zone (FAZ), and choriocapillaris blood flow (CCF) measurements were made using optical coherence tomography angiography (OCTA). ResultsWhen compared to the pre-vaccination values, there was no significant change in OA-PSV, temporal-nasal PCA-PSV, CRA-EDV, temporal-nasal PCA-EDV at 2nd and 4th weeks after vaccination. However statistically significant reductions were found in the OA-RI, OA-PI, CRA-RI, CRA-PI, temporal-nasal PCA-RI, temporal-nasal PCA-PI values, CRA-PSV at post-vaccination 2nd week (p<0.05 for all). While there was sustained reduction in OA-RI, OA-PI, CRA-PSV, and nasal PCA-RI values at 4th week after vaccination, the change in CRA-RI, CRA-PI, temporal PCA-RI, temporal-nasal PCA-PI values were not significant compared to pre-vaccination values. There was no statistically significant difference in the SCP-VD, DCP-VD, FAZ and CCF measurements. ConclusionsOur findings demonstrating that CoronaVac vaccine did not affect retinal vascular density in the early period, but it caused alterations in the retrobulbar blood flow.

Anatomical variations and flow alterations of the uncal vein and its clinical implications in petroclival meningiomas.

The Uncal vein (UV), downstream of the deep middle cerebral vein (DMCV), has a similar drainage pattern to the superficial middle cerebral vein (SMCV) and may be involved in venous complications during the anterior transpetrosal approach (ATPA). However, in petroclival meningioma (PCM), where the ATPA is frequently used, there are no reports evaluating drainage patterns of the UV and the risk of venous complications associated with the UV during the ATPA. Forty-three patients with petroclival meningioma (PCM) and 20 with unruptured intracranial aneurysm (control group) were included. Preoperative digital subtraction angiography was used to evaluate UV and DMCV drainage patterns on the side of the tumor and bilaterally in patients with PCM and the control group, respectively. In the control group, the DMCV drained to the UV, UV and BVR, and BVR in 24 (60.0%), eight (20.0%), and eight (20.0%) hemispheres, respectively. Conversely, the DMCV in the patients with PCM drained to the UV, UV and BVR, and BVR in 12 (27.9%), 19 (44.2%), and 12 (27.9%) patients, respectively. The DMCV was more likely to be drained to the BVR in the PCM group (p < 0.01). In three patients with PCM (7.0%), the DMCV drained only to the UV, and furthermore, the UV drained to the pterygoid plexus via the foramen ovale, posing a risk for venous complications during the ATPA. In the patients with PCM, the BVR functioned as a collateral venous pathway of the UV. Preoperative evaluation of the UV drainage patterns is recommended to reduce venous complications during the ATPA.

Reactive Hyperemia and Cardiovascular Autonomic Neuropathy in Type 2 Diabetic Patients: A Systematic Review of Randomized and Nonrandomized Clinical Trials.

Objective: This work aimed to determine the relationship between the autonomic nervous system and reactive hyperemia (RH) in type 2 diabetes patients with and without cardiovascular autonomic neuropathy (CAN). Methodology: A systematic review of randomized and nonrandomized clinical studies characterizing reactive hyperemia and autonomic activity in type 2 diabetes patients with and without CAN was performed. Results: Five articles showed differences in RH between healthy subjects and diabetic patients with and/or without neuropathy, while one study did not show such differences between healthy subjects and diabetic patients, but patients with diabetic ulcers had lower RH index values compared to healthy controls. Another study found no significant difference in blood flow after a muscle strain that induced reactive hyperemia between normal subjects and non-smoking diabetic patients. Four studies measured reactive hyperemia using peripheral arterial tonometry (PAT); only two found a significantly lower endothelial-function-derived measure of PAT in diabetic patients than in those without CAN. Four studies measured reactive hyperemia using flow-mediated dilation (FMD), but no significant differences were reported between diabetic patients with and without CAN. Two studies measured RH using laser Doppler techniques; one of them found significant differences in the blood flow of calf skin after stretching between diabetic non-smokers and smokers. The diabetic smokers had neurogenic activity at baseline that was significantly lower than that of the normal subjects. The greatest evidence revealed that the differences in RH between diabetic patients with and without CAN may depend on both the method used to measure hyperemia and that applied for the ANS examination as well as the type of autonomic deficit present in the patients. Conclusions: In diabetic patients, there is a deterioration in the vasodilator response to the reactive hyperemia maneuver compared to healthy subjects, which depends in part on endothelial and autonomic dysfunction. Blood flow alterations in diabetic patients during RH are mainly mediated by sympathetic dysfunction. The greatest evidence suggests a relationship between ANS and RH; however, there are no significant differences in RH between diabetic patients with and without CAN, as measured using FMD. When the flow of the microvascular territory is measured, the differences between diabetics with and without CAN become evident. Therefore, RH measured using PAT may reflect diabetic neuropathic changes with greater sensitivity compared to FMD.

Changes in water flow alter community dynamics in oyster reefs

AbstractFluid (air or water) movements are key determinants of living systems from cellular to community levels of organization. Water flow can influence individual fitness and local population dynamics, but less is known about the collective response of natural communities to alteration in water flow because parameter responses to flow may be additive, juxtaposed, or interactive. To examine how changes in water flow affected initial larval settlement patterns of epifaunal and infaunal animals, colonization of larger individuals, and prey survival, we manipulated water flow (−50% or +47%) in situ using large wooden channels over small experimental oyster reefs. To test whether initial settlement patterns were additive or influenced by early post‐settlement processes (i.e., predation or competition reduced the densities), we compared patterns in short‐duration trials (two weeks) to those in longer duration deployments (six weeks). We found that minor changes in water flow (5–10 cm s−1) resulted in large changes in settlement of many species, predation levels, and the modification of initial settlement patterns. Settlement (two‐week intervals) and subsequent recruitment (six‐week intervals) increased for several species as flow rate increased. For most species, this relationship peaked at mid‐level flows (mud crabs, barnacles, and bivalves), whereas others (oysters) continued to increase with higher flow rates. Settlement patterns were best preserved in recruitment under high flow conditions where post‐settlement mortality was lower. Collectively, our results demonstrate how biological and physical processes are coupled in oyster reef systems, with relatively minor changes in water flow affecting pre‐ and post‐settlement processes.

Eagle Syndrome with Internal Carotid Artery Compression causing Recurred Syncope: A Case Report.

We herein report a 54-year-old man with eagle syndrome who presented with repeated episodes of syncope, especially after moving his head to a downward position. Computed tomography with contrast revealed a bilateral elongated styloid process. The left internal carotid artery was obviously compressed by the left elongated styloid processes. A transcranial Doppler examination detected a significantly decreased blood flow velocity in the left middle cerebral artery when the patient slightly lowered his head position. After surgery, the positional cerebral blood flow alteration disappeared. No further similar syncope episodes have been reported to date.

Insonation angle impact on micro-Doppler evaluation in cerebrovascular surgery: technical note

Introduction: The insonation angle consideration is important in the Doppler-sonographic evaluation of blood flow velocities and volume, however, the concept is rarely applied to the intraoperatively used micro-Doppler.This technical note aims to emphasize the possibility and necessity of insonation angle correction and preservation for the blood flow assessment in cerebrovascular surgery.Methods: Bi-directional surgical Doppler with a 20MHz flexible bayonet 1.2mm diameter probe was used for the intraoperative blood flow assessment, with the variable insonation angle on the straight parts of the arteries, and the results were recorded to demonstrate the importance.Results: The measurements performed confirmed that the blood flow features, including the direction, velocity, and especially the volume, are highly susceptible to the insonation angle variations. Although there were significant alterations, positioning the probe at an angle of ~60 degrees resulted in the variable but less altering measurements.Conclusion: Positioning the probe at ~60 degrees is desirable; however, it appears that it is even more important to maintain the same insonation angle and probe position when assessing the vessels repeatedly for blood flow alterations that might occur in the course of cerebrovascular surgery.

Association of intrauterine growth restriction and low birth weight with acute kidney injury in preterm neonates.

Preterm birth alters nephrogenesis and reduces the total nephron number. Intrauterine growth restriction (IUGR) seems to worsen nephron loss, but only a few studies have investigated its role in neonatal kidney impairment. We investigated whether IUGR, defined as reduced estimated fetal growth and/or placental flow alterations and low birth weight z-score, increases the risk of developing acute kidney injury (AKI) in very preterm infants. We performed a retrospective study including infants born with a birth weight (BW) ≤ 1500g and/or gestational age (GA) ≤ 32weeks admitted to our center between January 2016 and December 2021. Neonatal AKI was defined according to the neonatal KDIGO classification based on the decline of urine output and/or creatinine elevation. We used multivariable linear regressions to verify the association between AKI and GA, BW z-score, IUGR definition, and hemodynamically significant patent ductus arteriosus (PDA). We included 282 infants in the analysis, with a median (IQR) GA = 29.4 (27.4, 31.3) weeks, BW = 1150 (870, 1360) g, and BW z-score = - 0.57 (- 1.64, 0.25). AKI was diagnosed in 36 (13%) patients, and 58 (21%) had PDA. AKI was significantly associated with BW z-score (beta (std. error) = - 0.08 (0.03), p = 0.008) and severe IUGR (beta (std. error) = 0.21 (0.08), p = 0.009), after adjusting for GA and PDA. Our data suggest that low BW z-score and IUGR could represent adjunctive risk factors for kidney impairment in preterm babies. A higher resolution version of the Graphical abstract is available as Supplementary information.

Hydrothermal alteration of surficial rocks at Los Humeros geothermal field, Mexico: a magnetic susceptibility approach

Utility of the geothermal surface manifestations (GSMs; thermal springs, geysers, fumaroles, and zones of hydrothermal alteration) in the studies related to the geothermal exploration is widely recognized. The identification of hydrothermally altered rocks and zones of alteration is very important because their presence indicates the type and size of the geothermal reservoir and existing thermal conditions. The use of traditional methods (i.e., geochemistry, mineralogy, and petrography) requires expensive equipment, time-consuming, and laborious sample preparation methods. Some of the rock magnetic parameters, like magnetic susceptibility (χlf) and percentage of frequency-dependent magnetic susceptibility (χfd%), are potential to become effective additional tools in identification of the hydrothermal rocks during the initial stages of geothermal exploration. Three chemical methods, Chemical Index of Alteration (CIA), loss-on-ignition (LOI), and the binary plot (CaO + Na2O + K2O) vs. (Fe2O3 + MnO + MgO), along with two rock magnetic methods, χlf and the binary plot (χlf vs. χfd%), are applied to nine intensively altered andesite reference rocks. All the five methods have correctly identified that 99 out of the total 350 studied rocks are altered. More altered rocks are distributed surrounding the several faults in the study area. Various faults (e.g., Los Humeros fault and the Loma Blanca fault) favor fluid flow and present strong hydrothermal alteration at the surface. However, there are no altered rocks on the surface region between the E-W trending Las Papas and Las Viboras faults. The presence of only the deeper fluid pathway toward the east in the surroundings of these two faults result into the almost absence of hydrothermal alteration along their strike at the surface. Consequently, there are not many altered rocks observed surroundings these two faults at the surface. These features suggest that the surface hydrothermal alteration at Los Humeros Geothermal Field (LHGF) is controlled by faults. χlf and χfd% are reliable, simple to measure, fast, cost-effective, and have the potential to become reliable additional tools for future exploration studies.

Both network architecture and micro cracks effects on lacuno-canalicular liquid flow efficiency within the context of multiphysics approach for bone remodeling

When physical forces are applied to bone, its mechanical adaptive behaviors change according to the microarchitecture configuration. This leads to changes in biological and physical thresholds in the remodeling cell population, involving sensor cells (osteocytes) interacting with each other and changes in osteocyte shape due to variation in lacunar shape. The resulting alterations in fluid flow leads to changes in the membrane electrical potential and shear stress. Eventual creation of microcracks, may lead in turn to modify cell activity. In contrast, the redundancy in the lacuno canalicular network (LCN) interconnectivity maintains partial flow. Our goal was to investigate the role of fluid flow in LCN by proposing a model of electro-mechanical energy spread through inhomogeneous microarchitectures. We focused on mechano-sensitivity to changes in load-induced flow impacted by neighboring micro cracks and quantifying its critical role in changing, velocity, shear stress and orientation of liquid mass transportation from one cell to another. To enhance the concept of intricacy LCN micro-structure to fluid flow, we provide a new combined effects factor considered as osteocytes sensor efficiency. We customized an influence function for each osteocyte, coupling: in one hand, the spatial distribution within remodeling influence areas, conducting a significant fluid spread, leading hydro-dynamic behavior and impacted further by presence of micro cracks and; in other hand, the fluid electro kinetic behavior.As an attempt to fill the limitations stated by many of the recent studies, we reveal in numerical simulation, some results which cannot be measured in vitro/in vivo studies. Numerical calculations were performed in order to evaluate, among many others, how liquid flow conditions changes between lacunas, how the orientation and the magnitude of the governing flow in LCN can regulate osteocytes efficiency. In addition to be regulated by osteocytes, a direct effects of fluid flow are also acting on osteoblast activity. In summary, this new approach considers mechano-sensitivity in relation to liquid flow dynamic and suggests additional pathway for Osseo integration via osteoblast regulation. However, this novel modeling approach may help improve the mapping and design bone scaffolds and/or selection of scaffold implantation regions.

Failure of an ASTM A213 T12 steel tube of a circulating fluidized bed boiler

During a maintenance shutdown, a localized bulging was observed in a section of the outermost tube of the superheater, an ASTM A213 grade T12 (UNS K11562), Cr-0.5Mo ferritic steel. The objective of this work was to investigate the failure of the steel tube, part of a L-shape superheater of a CFB boiler. The investigation was performed through microstructural characterization, chemical analysis, thermodynamic calculations, hardness measurements, tensile and creep tests, measurements of the oxide scale thickness on selected regions of the failed tube for determination of the remaining life assessment. It was concluded that the failure was due to a conjunction of long time overheating and creep. A welding defect (root dropout) caused an alteration of the steam flow and, therefore, impaired the proper heat transfer between the tube and the steam. In addition, the uneven flow of the flue gas induced a heterogeneous heat distribution along the tube length, particularly in the area facing the flue gas, evidenced by the erosion marks. The high local temperature resulted in intense oxidation, decarburization and degradation of the microstructure. As a consequence, the steel strength was reduced, with consequent bulging and failure. These points were reinforced by the results of the RUL assessment, where the value was negative at the referred region, meaning the end of its operational life.