Regulation Of Flow Research Articles

Interactions between Beta-Amyloid and Pericytes in Alzheimer's Disease.

Alzheimer's disease (AD) is an age-related progressive neurodegenerative disorder characterized by aberrant amyloid precursor protein (APP) cleavage, pathological aggregations of beta-amyloid (Aβ) that make up Aβ plaques and hyperphosphorylation of Tau that makes up neurofibrillary tangles (NFTs). Although progress has been made in research on AD, the fundamental causes of this disease have not been fully elucidated. Recent studies have shown that vascular dysfunction especially the loss of pericytes plays a significant role in the onset of AD. Pericytes play a variety of important roles in the nervous system including the regulation of the cerebral blood flow (CBF), the formation and maintenance of the blood-brain barrier (BBB), angiogenesis, and the clearance of toxic substances from the brain. Pericytes participate in the transport of Aβ through various receptors, and Aβ acts on pericytes to cause them to constrict, detach, and die. The loss of pericytes elevates the levels of Aβ1-40 and Aβ1-42 by disrupting the integrity of the BBB and reducing the clearance of soluble Aβ from the brain interstitial fluid. The aggravated deposition of Aβ further exacerbates pericyte dysfunction, forming a vicious cycle. The combined influence of these factors eventually results in the loss of neurons and cognitive decline. Further exploration of the interactions between pericytes and Aβ is beneficial for understanding AD and could lead to the identification of new therapeutic targets for the prevention and treatment of AD. In this review, we explore the characterization of pericytes, interactions between pericytes and other cells in the neurovascular unit (NVU), and the physiological functions of pericytes and dysfunctions in AD. This review discusses the interactions between pericytes and Aβ, as well as current and further strategies for preventing or treating AD targeting pericytes.

Adaptation measures to global change in the Serpis River Basin (Spain): An evaluation considering agricultural benefits, environmental flows, and invasive fishes

Damming and flow regulation ensure water availability during dearth periods, but they cause impacts on inhabiting biota and facilitate the establishment of Invasive Alien Species (IAS). Setting environmental flows (e-flows) has proven fundamental to ensure good ecological status of rivers, battle IAS, and sustain ecosystem services. However, ongoing climate change is further straining water resources availability and the fulfilment of e-flows in Spain, which has compelled River Basin Management Plans (RBMPs) to include specific adaptation measures. In this study, we assessed adaptation strategies addressing land use and climate change in the Serpis River (Eastern Spain), based on increasing irrigation efficiency (i.e. moving from gravity to drip irrigation). The evaluation considered two CMIP6 climate change scenarios (Shared Socioeconomic Pathways SSP1-2.6 and SSP5-8.5) for two time horizons (short term 2015–2040 and mid-term 2041–2070), together with three land use change scenarios (changes in irrigated areas and technologies). Future estimations included reservoir flow releases, e-flows fulfilment, agricultural benefits, and changes in the suitable habitat and potential competition for two native (Eastern Iberian chub Squalius valentinus and European eel Anguilla anguilla) and two invasive (common bleak Alburnus alburnus and pumpkinseed Lepomis gibbosus) fish species. Predictions indicated a decrease in the suitable habitat for eel and Eastern Iberian chub, but the established e-flows will be ensured. Although the maximum benefits will rarely be achieved, on average the modernisation expected in the RBMP would sustain agricultural incomes in the optimistic scenario (SSP1-2.6) and for the short term of the pessimistic scenario (SSP5-8.5), showing similar effects than the ongoing redistribution of agricultural plots. Habitat and competition with invasive species will experience little changes due to the strong flow regulation, although the invasive bleak would prevail in the mid-term of the most pessimistic scenario. These results highlight the necessity of proactive adaptation measures beyond those described in the RBMPs (e.g. forest management or crop substitution) to increase water availability and sustain agricultural benefits, in particular for the most pessimistic scenario. They also underscore the difficulties to counteract invasive species through streamflow management under water scarcity scenarios.

Glaucoma Patient with Suspected Flammer Syndrome: Diagnostic Procedures and Therapeutic Implications

If glaucoma damage develops despite normal intraocular pressure or if the damage progresses despite well-controlled intraocular pressure, we usually find other risk factors. One important group are the vascular factors. We should focus not only on the classical risk factors of atherosclerosis, such as arterial hypertension or dyslipidaemia, but also on dysregulation of blood flow, especially on primary vascular dysregulation (PVD). Low blood pressure, either current or in adolescence, low body mass index or frequently cold hands and feet may provide important hints. Very often PVD is coupled with a number of other symptoms and signs, and we then speak of a Flammer Syndrome (FS). If there is any indication of FS, we take a targeted patient history, undertake 24 h blood pressure monitoring, measure retinal venous pressure, and perform a dynamic retinal vessel analysis or nail fold capillary microscopy. This is especially recommended if the patient is relatively young or the damage is progressing rapidly. If the suspicion is confirmed, we then try to reduce the drops in blood pressure, lower the retinal venous pressure, improve the regulation of blood flow and reduce the oxidative stress in the mitochondria.

Human–Machine Collaborative Reinforcement Learning for Power Line Flow Regulation

Human–Machine Collaborative Reinforcement Learning for Power Line Flow Regulation

A Novel Wired/Wireless Hybrid Multiport Energy Router for Dynamic EV Energy Internet With Grid-Tied and Islanded Operations

Energy routers (ERs) are indispensable in deploying energy Internet for electric vehicles (EVs), which flexibly handle the power flow regulation. Combined with the excellent characteristic of wireless power transfer (WPT) technology for non-contact energy transmission, this paper proposes a novel wired/wireless hybrid multi-port energy router (HMER) for future EV energy Internet. First, multiple bidirectional power ports are provided to control the power flow among the grid, various DC power sources, and EVs. Moreover, with grid-tied and islanded operations, the proposed HMER enables dynamic wireless energy exchange for EVs on the move. When moving along the energy exchange lane, the EVs can receive power from the HMER and conduct energy feedback, relieving mileage anxiety while creating economic benefits. Further, a mathematical model of the system is derived, and a control algorithm is introduced to perform decoupled power control for each transceiver. Finally, a SIC experimental prototype is constructed to verify the effectiveness of the proposed HMER system. Experimental results prove the transceivers can get bidirectional wireless energy interconnection on the energy exchange lane in both grid-tied mode and islanded mode, and each transceiver can realize independent power regulation.

Early warning on safety risk of highly aggregated tourist crowds based on VGGT-Count network model.

In the era of mass tourism, more and more people are attracted by internet-famous site. With people's demand for travel surged, tourists are getting together in one scenic spot with doubling numbers, which easily leads to high concentration of tourists with uncontrollable security risks. It needs to be highly valued by the tourism department. Monitoring and issuing warnings for crowd density in scenic areas with Highly Aggregated Tourist Crowds (HATCs) is an urgent challenge that needs to be addressed. In this paper, Highly Aggregated Tourist Crowds is taken as the research objective, and a VGGT-Count network model is proposed to forecast the density of HATCs. The experimental outcomes demonstrated a substantial improvement in counting accuracy for the ShanghaiTech B and UCF-QNRF datasets. Furthermore, the model allows for real-time monitoring of tourist attractions, enabling advanced prediction of high concentrations in scenic areas. This timely information can alert relevant authorities to implement preventive measures such as crowd control and flow regulation, thereby minimizing safety hazards.

Mechanisms of nitric oxide in spinal cord injury.

Spinal cord injury (SCI) is a primary lesion of the spinal cord that results from external forces or diseases, accompanied by a cascade of secondary events. Nitric oxide, an endogenous gas that functions as a signaling molecule in the human body, plays a crucial role in vasodilation of smooth muscles, regulation of blood flow and pressure, and inflammatory response. This article provides a comprehensive overview of the involvement of nitric oxide in SCI and highlights recent advances in basic research on pharmacological agents that inhibit nitric oxide elevation after SCI, offering valuable insights for future therapeutic interventions targeting SCI.

Power Flow Regulation Effect and Parameter Design Method of Phase-Shifting Transformer

In the context of carbon peaking and carbon neutrality goals, the integration of a large number of renewable energy sources may trigger significant tidal changes, leading to transmission congestion, wind and light abandonment, power oscillation, voltage and frequency fluctuations, etc. A phase-shifting transformer is a cost-effective and reliable power flow control equipment, but its key parameters lack systematic design methods. Based on the equivalent model of phase-shifting transformers, detailed design principles and methods have been proposed, and the configuration method of winding turns has been improved to facilitate calculation and control strategy formulation. The regulation effect of the phase-shifting transformer designed through simulation of power flow regulation in a typical 500 kV network is simulated. By adjusting the phase-shifting transformer, the power flow of heavy load lines can be transferred to light load lines, optimizing the power flow distribution and improving the transmission capacity of the cross-section.

Experimental Study of Lubricant Distribution and Lubrication Enhancement Induced by Ball Bearing Cage

Abstract The bearing cage played a pivotal role in affecting the lubricant redistribution and lubrication states. In this study, a cage unit is incorporated into an optical ball-on-disc apparatus for the purpose of a quantitative study of cage-induced lubrication phenomena. It is found that the presence of the lubricant layer on the ball surface, shaped by the cage, affects the inlet lubricant supply of contact between the ball and the glass disc. Thereafter, the oil reservoirs surrounding the contact area and the film thickness were measured. The results showed that the lubricant reservoirs and inlet lubricant supplement were significantly improved with the employment of the cages. In addition, the lubrication state transformed from starved to fully flooded, effectively enhancing the lubrication state. Moreover, the lubricant on the steel ball surface moved from the side bands to the central rolling track, indicating that the lubricant redistribution was the main reason for the lubricating enhancement. Notably, the groove modification on the inner surface of the cage pocket facilitated the directional lubricant migration and the migration effect depended on the groove angles. In conclusion, these results offer an in-depth understanding of the bearing lubrication mechanism, thereby inspiring advancements in cage design and lubricant flow regulation.

ResORR: A globally scalable and satellite data-driven algorithm for river flow regulation due to reservoir operations

We propose a globally scalable algorithm, ResORR (Reservoir Operations driven River Regulation), to predict regulated river flow and tested it over the heavily regulated basin of the Cumberland River in the US. ResORR was found able to model regulated river flow due to upstream reservoir operations of the Cumberland River. Over a mountainous basin dominated by high rainfall, ResORR was effective in capturing extreme flooding modified by upstream hydropower dam operations. On average, ResORR improved regulated river flow simulation by more than 50% across all performance metrics when compared to a hydrologic model without a regulation module. ResORR is a timely software algorithm for understanding human regulation of surface water as satellite-estimated reservoir state is expected to improve globally with the recently launched Surface Water and Ocean Topography (SWOT) mission.

Temporal Alterations in Cerebrovascular Glycocalyx and Cerebral Blood Flow after Exposure to a High-Intensity Blast in Rats.

The glycocalyx is a proteoglycan-glycoprotein structure lining the luminal surface of the vascular endothelium and is susceptible to damage due to blast overpressure (BOP) exposure. The glycocalyx is essential in maintaining the structural and functional integrity of the vasculature and regulation of cerebral blood flow (CBF). Assessment of alterations in the density of the glycocalyx; its components (heparan sulphate proteoglycan (HSPG/syndecan-2), heparan sulphate (HS), and chondroitin sulphate (CS)); CBF; and the effect of hypercapnia on CBF was conducted at 2-3 h, 1, 3, 14, and 28 days after a high-intensity (18.9 PSI/131 kPa peak pressure, 10.95 ms duration, and 70.26 PSI·ms/484.42 kPa·ms impulse) BOP exposure in rats. A significant reduction in the density of the glycocalyx was observed 2-3 h, 1-, and 3 days after the blast exposure. The glycocalyx recovered by 28 days after exposure and was associated with an increase in HS (14 and 28 days) and in HSPG/syndecan-2 and CS (28 days) in the frontal cortex. In separate experiments, we observed significant decreases in CBF and a diminished response to hypercapnia at all time points with some recovery at 3 days. Given the role of the glycocalyx in regulating physiological function of the cerebral vasculature, damage to the glycocalyx after BOP exposure may result in the onset of pathogenesis and progression of cerebrovascular dysfunction leading to neuropathology.

Stand-alone PV-SOFC-battery power system based on ANFIS controller for electric vehicle charging

Purpose This study aims to offer a hybrid stand-alone system for electric vehicle (EV) charging stations (CS), an emerging power scheme due to the availability of renewable and environment-friendly energy sources. This paper presents the analysis of a photovoltaic (PV) with an adaptive neuro-fuzzy inference system (ANFIS) algorithm, solid oxide fuel cell (SOFC) and a battery storage scheme incorporated for EV CS in a stand-alone mode. In previous studies, either the hydrogen fuel of SOFC or the irradiance is controlled using artificial neural network. These parameters are not controlled simultaneously using an ANFIS-based approach. The ANFIS-based stand-alone hybrid system controlling both the fuel flow of SOFC and the irradiance of PV is discussed in this paper. Design/methodology/approach The ANFIS algorithm provides an efficient estimation of maximum power (MP) to the nonlinear voltage–current characteristics of a PV, integrated with a direct current–direct current (DC–DC) converter to boost output voltage up to 400 V. The issue of fuel starvation in SOFC due to load transients is also mitigated using an ANFIS-based fuel flow regulator, which robustly provides fuel, i.e. hydrogen per necessity. Furthermore, to ensure uninterrupted power to the CS, PV is integrated with a SOFC array, and a battery storage bank is used as a backup in the current scenario. A power management system efficiently shares power among the aforesaid sources. Findings A comprehensive simulation test bed for a stand-alone power system (PV cells and SOFC) is developed in MATLAB/Simulink. The adaptability and robustness of the proposed control paradigm are investigated through simulation results in a stand-alone hybrid power system test bed. Originality/value The simulation results confirm the effectiveness of the ANFIS algorithm in a stand-alone hybrid power system scheme.

Cardiac output-mediated regulation of cerebral blood flow during exercise: Clinical perspectives on the indirect impact of muscle metaboreflex.

The muscle metaboreflex stimulates the elevation of arterial blood pressure, aiming to rectify the oxygen deficit by enhancing oxygen delivery to support muscle activity. Moreover, activating the muscle metaboreflex significantly increases cardiac output (CO) by increasingfactors such as heart rate, ventricular contractility, preload, stroke volume and mobilization of central blood volume. Previous studies indicate that ageing and cardiovascular diseases modify the muscle metaboreflex during exercise, limiting the ability to increase CO during physical activity. Alongside reduced exercise capacity, the attenuated rise in CO due to abnormal muscle metaboreflex in these patients impedes the increase in cerebral blood flow during exercise. Considering that CO plays a pivotal role in regulating cerebral blood flow adequately during exercise, this occurrence might contribute to an elevated risk of cerebral diseases, and it could also, at least, reduce the effective role of exercise in preventing cerebral disease and dementia among elderly individuals and patients with cardiovascular conditions. Therefore, it is important to consider this phenomenon when optimizing the effectiveness of exercise rehabilitation in patients with cardiovascular disease to prevent cerebral diseases and dementia.

A multi-objective optimal collaborative gas flow regulation method for non-stationary ventilation network based on improved NSGA-Ⅲ algorithm

After the shockwave of a coal and gas outburst disappears, the influx of a high concentration of gas causes ventilation network disorder. This will further lead to the occurrence of secondary disasters, resulting in serious human and economic losses. This study focuses on solving the cooperative regulation problem of non-stationary ventilation networks (NSVNs) after a disaster. The NSVN solution model is dynamically combined with the ventilation network regulation method to simulate the results of post-disaster cooperative regulation. The Pareto optimal solution for decision variables is obtained with the goals of reducing the affected area, preventing the reversal of branch airflow, and rapidly discharging the high concentration of gas. In this regard, an NSGA-III algorithm based on segmented hybrid coding with conditional distribution sampling is designed to solve the problem of the population crossover operation under the dynamic change of the decision variables. In addition, according to the applicability of the decision variables in the regulation of NSVNs, the sampling distribution function that meets the practical application requirements is selected. Moreover, conditional distribution sampling is carried out for chromosome generation via real number coding, the aim of which is to improve the search efficiency and optimization effect. Via the hierarchical logical relationship between the decision variables, conversion is carried out to generate population individuals of different dimensions to realize the dynamic inputs of the NSVN solution model and calculate the corresponding target values. Finally, the feasibility of the proposed model and solution method is verified by studying and analyzing the case of an airflow disaster in a coal mine in Jiulishan, China. This study provides theoretical support for the cooperative regulation of NSVNs, as well as guidance for the post-disaster emergency rescue work in possible coal and gas herniation accidents.

Circadian and Diurnal Regulation of Cerebral Blood Flow.

Circadian and diurnal variation in cerebral blood flow directly contributes to the diurnal variation in the risk of stroke, either through factors that trigger stroke or due to impaired compensatory mechanisms. Cerebral blood flow results from the integration of systemic hemodynamics, including heart rate, cardiac output, and blood pressure, with cerebrovascular regulatory mechanisms, including cerebrovascular reactivity, autoregulation, and neurovascular coupling. We review the evidence for the circadian and diurnal variation in each of these mechanisms and their integration, from the detailed evidence for mechanisms underlying the nocturnal nadir and morning surge in blood pressure to identifying limited available evidence for circadian and diurnal variation in cerebrovascular compensatory mechanisms. We, thus, identify key systemic hemodynamic factors related to the diurnal variation in the risk of stroke but particularly identify the need for further research focused on cerebrovascular regulatory mechanisms.

Topological Structure and Control Strategy of E-UPFC

This article proposes a unified power flow controller with energy (E-UPFC) installed at the renewable energy grid connection node of the transmission network. Compared with other unified power flow controllers (UPFCs), the proposed E-UPFC can not only regulate the power flow on its connected transmission lines, but also suppress the power fluctuations of grid-connected nodes injected with large-scale renewable energy. At the same time, with the installation position of E-UPFC transferred from the transmission line to the node, the original stiff node can be transformed into a flexible node that can regulate the injected power flexibly. First, the PV grid-connected system with E-UPFC is introduced, and its principle of power flow regulation is detailed. In addition, the topology, mathematical modeling, and control strategies of E-UPFC are discussed. Finally, the E-UPFC is applied to the IEEE 3-generator 9-bus system with large-scale renewable energy integration in Matlab/Simulink in order to verify the correctness and feasibility of E-UPFC and its control strategies.

Modeling, experimental investigation and real-time control of active water cooling system for photovoltaic module

ABSTRACT Photovoltaic (PV) cells are integral in harnessing solar energy, yet their performance is hindered by excessive heat generation, impacting efficiency and sustainability. Addressing the challenge of efficiency loss in photovoltaic (PV) cells due to overheating, this study focuses on optimizing active water cooling control for PV modules. The aim is to develop a dynamic, sustainable model and integrate a PID controller tuned by Sine Cosine Algorithm (SCA), targeting optimal operating temperatures. This study introduces a dynamic model and a closed-loop control system to manage PV cell temperature, investigating the correlation between water flow and temperature regulation. Experimental data is gathered using a pseudo-random binary sequence (PRBS) as an excitation signal, forming the foundation of an Auto Regressive eXogenous (ARX) model. The closed-loop system incorporates a PID controller and tuned using the Sine Cosine Algorithm (SCA) to optimize performance. The resulting model is rigorously validated through experimental investigation, demonstrating its precision in capturing the system’s dynamics. Moreover, the implementation of a controller-based cooling system substantiates the model’s practical efficacy. The research demonstrates significant improvements when implementing a controller-based water-cooling system for photovoltaic (PV) modules. Compared to the baseline scenario without cooling, the system achieves a 34.5% reduction in average PV temperature (from 59.2°C to 38.9°C) and a 9.46% increase in average power output (from 196.7W to 215.3W). Moreover, this system utilizes only 248.8 liters of water, marking a substantial 64% decrease in water consumption compared to traditional free-flow cooling methods, which use 790.9 liters. The research demonstrates that the controller-based cooling approach is a sustainable option, delivering power output comparable to the free-flow method, yet significantly lowering water consumption. This research signifies a turning point for sustainability, offering an efficient and water-conscious approach for enhancing PV system performance, a crucial step toward a greener and more environmentally responsible energy future.

Finding possible diagnostic markers for differentiating benign and malignant thyroid tumors on example investigate of rheological properties1.

The functioning of the thyroid gland is a multi-component process that in some conditions may undergo alterations. The thyroid gland is part of the endocrine system that produces the iodine-containing hormones thyroxine and triiodothyronine. Thyroid hormones, control metabolism and energy, growth processes, maturation of tissues and organs, regulation of blood flow, and, therefore, providing vital functions of the body. The role of thyroid hormones in the regulation of blood flow is determined by the intensity of their production and the quantity in the blood. Presumably, in case of oncological and non-oncological diseases of the thyroid gland, the fluidity of the blood, which depends on the rheological properties, will be different. Our aim was investigating rheological characteristics for studying of changes of rheology in patients with thyrotoxicosis, with benign tumor pathology of the thyroid gland, with thyroid cancer and finding possible diagnostic markers for differentiating benign and malignant thyroid tumors. In this regard, we examined, using modern methods accepted in clinical practice, a standard list of recommended diagnostic tests in the group of patients (thyrotoxicosis: n = 25; benign tumor: n = 47), thyroid cancer: n = 35) and control group (n = 15), and with new original methods, parameters that describe the rheological properties of the blood, such as blood rheological index, volume, thickness, surface area of erythrocytes, erythrocyte aggregation index, deformation index, plasma viscosity, hematocrits. Against the background of relative changes in the studied values, it is necessary to pay attention to the fact that erythrocyte aggregation in patients with a benign form and control, as well as in patients with a malignant form and control, differ significantly from each other, in addition, there is a significant difference between aggregation in the group of patients with benign and control aggregation. malignant forms of the disease. It is significant that aggregability differs in patients with thyrotoxicosis and in controls. This indicates that erythrocyte aggregation is particularly informative. The blood rheological index most clearly demonstrated the difference between benign and malignant forms of the disease. Significantly changed compared to control in various forms of thyroid diseases. Additional diagnostic markers for differentiating benign and malignant thyroid tumors may be consideredeerythrocyte aggregation index and blood rheological index.

Response of ecosystem services and environmental dynamics in large open-pit coal mines: A case study in semi-arid areas

Surface coal mining in semi-arid regions has detrimental impacts on the structure and function of surface ecosystems, thereby impeding the attainment of regional sustainable development goals. Moreover, the impact of climate change on ecological restoration in semi-arid mining areas is an inevitable consideration. To elucidate the response of ecosystem services in mining areas to regional climate change, topography, soil, vegetation and socioeconomic development, this study selected six large-scale surface coal mines located in semi-arid regions of China as research objects. In this study, we aimed to assess the main ecosystem services (carbon sequestration, soil conservation, and flow regulation) provided by these mines. In addition, we analysed the spatial and temporal evolution and interrelationships of these ecosystem services. Furthermore, we explored the underlying mechanisms between ecosystem services and environmental factors. The results showed the following: (1) Geospatially, there was a gradual decrease in carbon sequestration and flow regulation from northeast to southwest in the mining areas. However, the soil conservation exhibited an upward trend. Throughout the research period, the carbon sequestration change rate in the six mining areas displayed an initial downward and subsequent upward trend, the rate of soil conservation exhibited a gradual upward trend, and the flow regulation decline rate followed a downward trend. (2) Change rate of carbon sequestration and soil conservation in the six mining areas showed a significant positive correlation (r = 0.51, p < 0.001), with the strongest correlation observed in the Shengli Mining Area (r = 0.64, p < 0.001). (3) Ecosystem service changes in the mining areas were primarily driven by initial conditions (95.0%), followed by meteorological factors (4.2%). Three ecological restoration models were proposed for the different regions based on driver analyses. The findings of this study offer scientific evidence that can be used to inform ecological management, enhance ecological security, and promote regional sustainable development in mining areas.

Regional pulmonary perfusion, blood volume, and their relationship change in experimental early ARDS

Regional pulmonary perfusion (Q) has been investigated using blood volume (Fb) imaging as an easier-to-measure surrogate. However, it is unclear if changing pulmonary conditions could affect their relationship. We hypothesized that vascular changes in early acute respiratory distress syndrome (ARDS) affect Q and Fb differently. Five sheep were anesthetized and received lung protective mechanical ventilation for 20 h while endotoxin was continuously infused. Using dynamic 18F-FDG and 13NN Positron Emission Tomography (PET), regional Fb and Q were analysed in 30 regions of interest (ROIs) and normalized by tissue content (Fbn and Qn, respectively). After 20 h, the lung injury showed characteristics of early ARDS, including gas exchange and lung mechanics. PET images of Fbn and Qn showed substantial differences between baseline and lung injury. Lung injury caused a significant change in the Fbn-Qn relationship compared to baseline (p < 0.001). The best models at baseline and lung injury were Fbn = 0.32 + 0.690Qn and Fbn = 1.684Qn–0.538Qn2, respectively. Endotoxine-associated early ARDS changed the relationship between Fb and Q, shifting from linear to curvilinear. Effects of endotoxin exposure on the vasoactive blood flow regulation were most likely the key factor for this change limiting the quantitative accuracy of Fb imaging as a surrogate for regional Q.