scholarly journals Function of Circle of Willis

2014 ◽  
Vol 34 (4) ◽  
pp. 578-584 ◽  
Author(s):  
Zvonimir Vrselja ◽  
Hrvoje Brkic ◽  
Stefan Mrdenovic ◽  
Radivoje Radic ◽  
Goran Curic
Keyword(s):  
Blood Flow ◽  
Pulse Wave ◽  
Cerebral Arteries ◽  
Arterial Occlusion ◽  
Current Theory ◽  
Circle Of Willis ◽  
Arterial Tree ◽  
Passive Pressure ◽  
Flow Pressure ◽  
The Brain

Nearly 400 years ago, Thomas Willis described the arterial ring at the base of the brain (the circle of Willis, CW) and recognized it as a compensatory system in the case of arterial occlusion. This theory is still accepted. We present several arguments that via negativa should discard the compensatory theory. (1) Current theory is anthropocentric; it ignores other species and their analog structures. (2) Arterial pathologies are diseases of old age, appearing after gene propagation. (3) According to the current theory, evolution has foresight. (4) Its commonness among animals indicates that it is probably a convergent evolutionary structure. (5) It was observed that communicating arteries are too small for effective blood flow, and (6) missing or hypoplastic in the majority of the population. We infer that CW, under physiologic conditions, serves as a passive pressure dissipating system; without considerable blood flow, pressure is transferred from the high to low pressure end, the latter being another arterial component of CW. Pressure gradient exists because pulse wave and blood flow arrive into the skull through different cerebral arteries asynchronously, due to arterial tree asymmetry. Therefore, CW and its communicating arteries protect cerebral artery and blood–brain barrier from hemodynamic stress.

MODELING REDISTRIBUTION CEREBRAL CIRCULATION

2021 ◽  
Vol 1 (4) ◽  
pp. 13-18
Author(s):  
Vladislav Nikolaevich Nikitin ◽  
◽  
Ekaterina Valerevna Kozhemyakina ◽  
Keyword(s):  
Blood Flow ◽  
Internal Carotid ◽  
Cerebral Arteries ◽  
Circle Of Willis ◽  
Entire Body ◽  
Compensatory Mechanisms ◽  
Vertebral Arteries ◽  
The Central Nervous System ◽  
Flow Through ◽  
The Brain

The brain is one of the most important organs responsible for the health and functioning of the entire body. The blood supply to the brain is carried out through 2 internal carotid and 2 vertebral arteries in norm. The brain, like other body systems, has protective (compensatory) mechanisms aimed at maintaining the necessary blood flow, one of which is the circle of Willis. The article proposes a mechanism for how blood flow is redistributed through the arteries feeding the brain, which is based on the assumption that the central nervous system controls in such a way that it minimizes flows through the connective arteries of the circle of Willis, the flows along which are normal (with symmetry of the left and right sides) practically equal to zero. Сase of the structure of the circle of Willis is considered in norm. The indicated redistribution mechanism is still only the first step towards an attempt to predict cases of changes in blood flow through the cerebral arteries, especially in stroke. In further works, it is planned to consider the inverse problem, i.e. determine the flows through the internal carotid and vertebral arteries, provided that the flows through the cerebral arteries extending from the circle of Willis have normal flow values.

An Experimental Study of the Effects Anatomical Variations Have on Collateral Flows Within the Circle of Willis

2011 ◽  
Author(s):  
Paul Fahy ◽  
Patrick Delassus ◽  
Padraig O’Flynn ◽  
Liam Morris
Keyword(s):  
Experimental Study ◽  
Blood Flow ◽  
Cerebral Arteries ◽  
Anatomical Variations ◽  
Flow Patterns ◽  
Circle Of Willis ◽  
Collateral Flow ◽  
Arterial Network ◽  
Flow Feature ◽  
The Brain

The circle of Willis (CoW) is a complex arterial network comprising of major cerebral arteries that converge to form a pentagonal arrangement as shown in Figure 1(A). This arterial network supplies oxygen-enriched blood to the brain. An incomplete CoW can exist in up to 50% of cases [1]. These missing vessels can be accommodated by the collateral flow feature within the CoW configuration. In certain circumstances, anatomical variations within the CoW can result in undesirable flow patterns [2–3]. It is unclear from the literature what effects these variations can have on blood flow collision paths within a complete CoW.

scholarly journals Average dimensions of the vessels at the base of the brain and the embryological basis of its variations

2013 ◽  
Vol 02 (04) ◽  
pp. 180-189
Author(s):  
Iqbal S.
Keyword(s):  
Anterior Part ◽  
Cerebral Arteries ◽  
Cerebral Dominance ◽  
Circle Of Willis ◽  
Detailed Knowledge ◽  
Differential Growth ◽  
Ischemic Attack ◽  
The Individual ◽  
The Right ◽  
The Brain

Abstract Background and aims: The cerebral circulation is constantly maintained by the anastomotic circle of Willis which is often anomalous in more than 50% of the normal adult brains. These anomalies increase the risk of the stroke and transient ischemic attack in older patients. Adequate blood flow through the circle of Willis is often necessary to prevent these ischemic infarctions. The anomalies of cerebral vessels are directly related to the differential growth of various parts of the brain. A detailed knowledge of the individual measurements of the cerebral arteries is useful to neurosurgeon in planning the shunt operations and in the choice of their patients. The present study is aimed to analyze the average dimensions of the vessels at the base of brain and an attempt to explain the common form of variations in terms of embryological development. Materials and methods: Fifty adult cadaveric brains were obtained from routine cadaveric dissections. The base of the brain with the circle of Willis was fixed in 10% formalin and preserved. The circle was analyzed for variations in the size, length and number of the component vessels and any asymmetry in the configuration. The dimensions of the vessels forming the circle were measured using graduated calipers. The observations were recorded and tabulated. Results: Asymmetry was observed in 10% to 36% of the circles in this study. Anomalies were more common in the posterior than in the anterior part of the circle. The posterior anomalies included hypoplastic vessels, absent vessels and embryonic derivation while anterior anomalies were predominantly of accessory vessels. Middle cerebral artery exhibited the least variations. In majority of the circles, left sided vessels were larger in diameter than the right. Conclusions: Variations are more common in the posterior than in the anterior part of the circle and on the right than on the left side of the brain. There was no correlation between the variations of circle of Willis of the right side and the left cerebral dominance. There seems to be no difference between races, concerning the anatomic variations of the brain circulation.

Computational Fluid Dynamics Simulation of the Blood Flow in the Circle of Willis

2002 ◽  
Author(s):  
M. Harazawa ◽  
T. Yamaguchi
Keyword(s):  
Blood Flow ◽  
Blood Supply ◽  
Internal Carotid ◽  
Complex Geometry ◽  
Cerebral Aneurysms ◽  
Cerebrovascular Diseases ◽  
Circle Of Willis ◽  
Dynamics Simulation ◽  
The Brain ◽  
Internal Carotid Arteries

The blood supply for the brain is born by four arteries, that is, two internal carotid arteries and two vertebral arteries. They are mutually connected at the cerebral base, and form a closed arterial circle, called the circle of Willis, so that the safety of the brain blood supply is increased. However their anastomoses show a very wide variety of atypism. If some of anastomses are very thin, or even do not exist, the safety of the blood supply is not secured. This is particularly important when some diseases such as cerebral thrombosis occurs and the blood flow supply stops unilaterally. Redistribution of the blood supply in such cases is thought to be strongly affected by geometrical configuration of the anastomoses. It is also known that cerebral aneurysms, which may induce serious cerebrovascular diseases, preferentially occur at the circle of Willis. Complex blood flow pattern has been suspected of having an influence on this preference. This is again dependent on complex geometry of the circle.

Pulsatile blood flow in the entire coronary arterial tree: theory and experiment

2006 ◽  
Vol 291 (3) ◽  
pp. H1074-H1087 ◽  
Author(s):  
Yunlong Huo ◽  
Ghassan S. Kassab
Keyword(s):  
Blood Flow ◽  
Pulsatile Flow ◽  
Pulse Wave ◽  
Coronary Circulation ◽  
Low Frequency ◽  
Flow Distribution ◽  
Pulsatile Blood Flow ◽  
Arterial Tree ◽  
Cross Section Area ◽  
Theory And Experiment

The pulsatility of coronary circulation can be accurately simulated on the basis of the measured branching pattern, vascular geometry, and material properties of the coronary vasculature. A Womersley-type mathematical model is developed to analyze pulsatile blood flow in diastole in the absence of vessel tone in the entire coronary arterial tree on the basis of previously measured morphometric data. The model incorporates a constitutive equation of pressure and cross-section area relation based on our previous experimental data. The formulation enables the prediction of the impedance, the pressure distribution, and the pulsatile flow distribution throughout the entire coronary arterial tree. The model is validated by experimental measurements in six diastolic arrested, vasodilated porcine hearts. The agreement between theory and experiment is excellent. Furthermore, the present pulse wave results at low frequency agree very well with previously published steady-state model. Finally, the phase angle of flow is seen to decrease along the trunk of the major coronary artery and primary branches toward the capillary vessels. This study represents the first, most extensive validated analysis of Womersley-type pulse wave transmission in the entire coronary arterial tree down to the first segment of capillaries. The present model will serve to quantitatively test various hypotheses in the coronary circulation under pulsatile flow conditions.

scholarly journals HEMODYNAMIC AND BIOELECTRICAL PROPERTIES OF THE BRAIN IN YOUNGER ADULTS WITH NONSTABLE BLOOD PRESSURE

2014 ◽  
Vol 13 (2) ◽  
pp. 12-17
Author(s):  
G. G. Efremushkin ◽  
T. V. Filippova ◽  
A. G. Kharlova ◽  
V. V. Dekhar
Keyword(s):  
Blood Pressure ◽  
Blood Flow ◽  
Flow Velocity ◽  
Blood Flow Velocity ◽  
Cerebral Arteries ◽  
Bioelectrical Activity ◽  
Younger Adults ◽  
Flow Energy ◽  
Blood Filling ◽  
The Brain

Aim.To study macro- and microhemodynamics and bioelectrical properties of the brain in younger adults with nonstable blood pressure (BP).Material and methods.A population of 79 adults at the age of 19–24 (average 19,9±0,9 years) was examined. According to the BP level they were divided into two groups: 1–46 (58,5%) with stable normal BP (SNBP), and 2–33 (41,5%) with high normal BP inside the range for 1stlevel arterial hypertension, whose BP was not stable (UsBP), but changing from normal values to 1st level hypertension. All patients undergone investigation of brachiocephal and intracerebral vessels with blood flow velocity measurement along the vessel direction, the blood sectional volumetric flow and specific kinetic energy. Microcirculation in the brain was measured by rheoencephalography including parameters of the velocity, time and volumetric parameters. Bioelectricity studied by electroencephalography.Results.In patients with UsBP we found the increase of blood flow velocity, blood volume and specific kinetic flow energy in vertebral and general carotid arteries as in basilar and middle cerebral arteries to. In the area of microcirculation in patients with UsBP the blood filling of frontal lobes was decreased comparing to SNBP patients in whom blood filling showed “mosaic” pattern. In UsBP patients we found changes of bioelectrical activity which are related to the functioning of cortical and subcortical portions of the brain.Conclusion.In younger patients with UsBP there is developed discirculatory encephalopathy with damage of cortex and subcortical portions of the brain due to impaired hemodynamic and microcirculation.

Real-time detection of vascular occlusion and reperfusion of the brain during surgery by using infrared imaging

2002 ◽  
Vol 96 (5) ◽  
pp. 918-923 ◽  
Author(s):  
Joseph C. Watson ◽  
Alexander M. Gorbach ◽  
Ryszard M. Pluta ◽  
Ramin Rak ◽  
John D. Heiss ◽  
...  
Keyword(s):  
Blood Flow ◽  
High Resolution ◽  
Real Time ◽  
Infrared Imaging ◽  
Cerebral Arteries ◽  
Infrared Camera ◽  
Collateral Flow ◽  
Content Type ◽  
The Brain ◽  
Fine Print

Object. Application of sensitive infrared imaging is ideally suited to observe blood vessels and blood flow in exposed organs, including the brain. Temporary vascular occlusion is an important part of neurosurgery, but the capacity to monitor the effects of these occlusions in real time is limited. In surgical procedures that require vascular manipulation, such as those involving aneurysms, arteriovenous malformations (AVMs), or tumors, the ability to visualize blood flow in vessels and their distribution beds would be beneficial. The authors recount their experience in the use of a sensitive (0.02°C), high-resolution (up to 50 µm/pixel) infrared camera with a rapid shutter speed (up to 2 msec/frame) for localizing cortical function intraoperatively. They observed high-resolution images of cerebral arteries and veins. The authors hypothesized that infrared imaging of cerebral arteries, performed using a sensitive, high-resolution camera during surgery, would permit changes in arterial flow to be be seen immediately, thus providing real-time assessment of brain perfusion in the involved vascular territory. Methods. Cynomolgus monkeys underwent extensive craniectomies, exposing the frontal, parietal, and temporal lobes. Temporary occlusions of the internal carotid artery and middle cerebral artery branches (30 events) were performed serially and were visualized with the aid of an infrared camera. Arteries and veins of the monkey brain were clearly visualized due to cooling of the exposed brain, which contrasted with blood within the vessels that remained at core temperature. Blood flow changes in vessels were seen immediately (< 1 second) in real time during occlusion and reopening of the vessels, regardless of the duration of the occlusion. Areas of decreased cortical blood flow rapidly cooled (−0.3 to 1.3°C) and reheated in response to reperfusion. Rewarming occurred faster in arteries than in the cortex (for a 20-minute occlusion, the change in temperature per second was 2 × 10−2°C in the artery and 7 × 10−3°C in the brain). Collateral flow could be evaluated by intraoperative observations and data processing. Conclusions. Use of high-resolution, digital infrared imaging permits real-time visualization of arterial flow. It has the potential to provide the surgeon with a means to assess collateral flow during temporary vessel occlusion and to visualize directly the flow in parent arteries or persistent filling of an aneurysm after clipping. During surgery for AVMs, the technique may provide a new way to assess arterial inflow, venous outflow, results of embolization, collateral flow, steal, and normal perfusion pressure breakthrough.

scholarly journals Aging alters the dampening of pulsatile blood flow in cerebral arteries

2016 ◽  
Vol 36 (9) ◽  
pp. 1519-1527 ◽  
Author(s):  
Laleh Zarrinkoob ◽  
Khalid Ambarki ◽  
Anders Wåhlin ◽  
Richard Birgander ◽  
Bo Carlberg ◽  
...  
Keyword(s):  
Blood Flow ◽  
Pulse Wave Velocity ◽  
Wave Velocity ◽  
Pulsatile Flow ◽  
Pulsatility Index ◽  
Aortic Stiffness ◽  
Pulse Wave ◽  
Cerebral Arteries ◽  
Age Groups ◽  
Healthy Elderly

Excessive pulsatile flow caused by aortic stiffness is thought to be a contributing factor for several cerebrovascular diseases. The main purpose of this study was to describe the dampening of the pulsatile flow from the proximal to the distal cerebral arteries, the effect of aging and sex, and its correlation to aortic stiffness. Forty-five healthy elderly (mean age 71 years) and 49 healthy young (mean age 25 years) were included. Phase-contrast magnetic resonance imaging was used for measuring blood flow pulsatility index and dampening factor (proximal artery pulsatility index/distal artery pulsatility index) in 21 cerebral and extra-cerebral arteries. Aortic stiffness was measured as aortic pulse wave velocity. Cerebral arterial pulsatility index increased due to aging and this was more pronounced in distal segments of cerebral arteries. There was no difference in pulsatility index between women and men. Dampening of pulsatility index was observed in all cerebral arteries in both age groups but was significantly higher in young subjects than in elderly. Pulse wave velocity was not correlated with cerebral arterial pulsatility index. The increased pulsatile flow in elderly together with reduced dampening supports the pulse wave encephalopathy theory, since it implies that a higher pulsatile flow is reaching distal arterial segments in older subjects.

History of migraine with aura and cortical spreading depression from 1941 and onwards

Cephalalgia ◽  
2009 ◽  
Vol 30 (7) ◽  
pp. 780-792 ◽  
Author(s):  
PC Tfelt-Hansen
Keyword(s):  
Blood Flow ◽  
Migraine With Aura ◽  
Cortical Spreading Depression ◽  
Spreading Depression ◽  
Cerebral Arteries ◽  
Familial Hemiplegic Migraine ◽  
Migraine Aura ◽  
History Of ◽  
Dramatic Shift ◽  
The Brain

Several personal descriptions of migraine with aura from 1870 onwards reported a slow, gradual progression of symptoms. Lashley in 1941 meticulously chartered his own auras and concluded that the symptomatology reflected a cortical process progressing with a speed of 3 mm/min across the primary visual cortex. Leão described cortical spreading depression (CSD) in rabbits in 1944 and noticed its similarity to the migraine aura. Despite these scattered pieces of evidence, the prevailing theory was that the migraine aura was caused by a vasospasm and cortical ischaemia. The advent of a technique for measurements of regional cerebral blood flow (rCBF) in 1974 made it possible to detect spreading oligaemia during migraine aura. Between 1981 and 1990 a series of studies of rCBF during migraine attacks showed reduced brain blood flow posteriorly spreading slowly and contiguously anteriorly and crossing borders of supply of major cerebral arteries. These observations refuted the ischaemic hypothesis. The human studies showed initial hyperaemia followed by prolonged hypoperfusion. The relation between aura and CSD was known to cause short-lasting, and therefore not obvious vasodilation and it was considerably strengthened by the demonstration of a long-lasting oligaemia in rats in the wake of CSD. In the primates CSD is not easily elicited, but it has in recent years been clearly demonstrated in patients with brain trauma and stroke. Finally, mutations for familial hemiplegic migraine have been expressed in mice and lower the threshold for CSD. The seminal papers on rCBF and CSD published in the 1980s caused a dramatic shift in our concepts of migraine aura. They moved attention from ischaemia to CSD and thereby to the brain itself, and paved the way for subsequent discoveries of brainstem mechanisms.

scholarly journals Impaired myogenic response and autoregulation of cerebral blood flow is rescued in CYP4A1 transgenic Dahl salt-sensitive rat

2015 ◽  
Vol 308 (5) ◽  
pp. R379-R390 ◽  
Author(s):  
Fan Fan ◽  
Aron M. Geurts ◽  
Sydney R. Murphy ◽  
Mallikarjuna R. Pabbidi ◽  
Howard J. Jacob ◽  
...  
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Cerebral Arteries ◽  
Cerebral Injury ◽  
Transgenic Rat ◽  
Myogenic Response ◽  
Cerebral Vasculature ◽  
Synthesis Inhibitor ◽  
Middle Cerebral Arteries ◽  
The Brain

We have reported that a reduction in renal production of 20-HETE contributes to development of hypertension in Dahl salt-sensitive (SS) rats. The present study examined whether 20-HETE production is also reduced in the cerebral vasculature of SS rats and whether this impairs the myogenic response and autoregulation of cerebral blood flow (CBF). The production of 20-HETE, the myogenic response of middle cerebral arteries (MCA), and autoregulation of CBF were compared in SS, SS-5BN rats and a newly generated CYP4A1 transgenic rat. 20-HETE production was 6-fold higher in cerebral arteries of CYP4A1 and SS-5BN than in SS rats. The diameter of the MCA decreased to 70 ± 3% to 65 ± 6% in CYP4A1 and SS-5BN rats when pressure was increased from 40 to 140 mmHg. In contrast, the myogenic response of MCA isolated from SS rats did not constrict. Administration of a 20-HETE synthesis inhibitor, HET0016, abolished the myogenic response of MCA in CYP4A1 and SS-5BN rats but had no effect in SS rats. Autoregulation of CBF was impaired in SS rats compared with CYP4A1 and SS-5BN rats. Blood-brain barrier leakage was 5-fold higher in the brain of SS rats than in SS-5BN and SS.CYP4A1 rats. These findings indicate that a genetic deficiency in the formation of 20-HETE contributes to an impaired myogenic response in MCA and autoregulation of CBF in SS rats and this may contribute to vascular remodeling and cerebral injury following the onset of hypertension.

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