Blood Flow In Cerebral Vessels Research Articles

Static and dynamic analysis of cerebral blood flow in fifty-six large arterial vessel networks

Objective. The cerebral vasculature is formed of an intricate network of blood vessels over many different length scales. Changes in their structure and connection are implicated in multiple cerebrovascular and neurological disorders. In this study, we present a novel approach to the quantitative analysis of the cerebral macrovasculature using computational and mathematical tools in a large dataset. Approach. We analysed a publicly available vessel dataset from a cohort of 56 (32/24F/M) healthy subjects. This dataset includes digital reconstructions of human brain macrovasculatures. We then propose a new mathematical model to compute blood flow dynamics and pressure distributions within these 56-representative cerebral macrovasculatures and quantify the results across this cohort. Main results. Statistical analysis showed that the steady state level of cerebrovascular resistance (CVR) gradually increases with age in both men and women. These age-related changes in CVR are in good agreement with previously reported values. All subjects were found to have only small phase angles (<6°) between blood pressure and blood flow at the cardiac frequency. Significance. These results showed that the dynamic component of blood flow adds very little phase shift at the cardiac frequency, which implies that the cerebral macrocirculation can be regarded as close to steady state in its behaviour, at least in healthy populations, irrespective of age or sex. This implies that the phase shift observed in measurements of blood flow in cerebral vessels is caused by behaviour further down the vascular bed. This behaviour is important for future statistical models of the dynamic maintenance of oxygen and nutrient supply to the brain.

РЕГУЛЯЦИЯ МОЗГОВОГО КРОВООБРАЩЕНИЯ ПРИ КОГНИТИВНОЙ ДЕЯТЕЛЬНОСТИ ЧЕЛОВЕКА. ЭКСПЕРИМЕНТ «МАРС-500»

Investigation of cerebral arterial circulation during cognitive testing was performed before and after prolonged isolation of 6 healthy subjects imitating a mission to space. The ultrasonic technique was used to measure linear blood velocity (LBV) in the medial cerebral artery (MCA) in the course of verbal and tactile testing. Analysis of MCA LBV both before and after isolation showed that at rest and during testing blood flow changes were equally wave-like; however, the amplitude made a significant increase at testing. It was found that LBV fluctuations occurred within the low-frequency band (LFB) and were consistent with the regular changes in tone of resistive vessels, primarily due to own myogenic activity. The wave-like LBV dynamics was observed over all testing time in all the subjects irrespective of central hemodynamics and respiration parameters. Analysis of LBV dynamics revealed a reliable seasonal (periodic) component supporting to the wave-like LBV fluctuations during testing. At large, prolonged isolation did not influence cerebral circulation much but for the reaction to the verbal testing after isolation completion when we registered a reliable rise of the LFB amplitude in left CMA due to activation of the left hemisphere resulting from specifics of communication in a small isolated group. We assume that the wave-like blood flow in cerebral vessels is an adaptive mechanism of autoregulation capable to meet the metabolic demand of the brain during cognitive testing and protect from local hyperthermia.

Co-administration of liposomal fasudil and tissue plasminogen activator ameliorated ischemic brain damage in occlusion model rats prepared by photochemically induced thrombosis

Delivery of neuroprotectants with liposomes has been shown to be effective for the treatment of ischemic stroke. We have recently revealed that intravenous administration of liposomal fasudil (Fasudil-Lip), a Rho-kinase inhibitor, prior to thrombolysis with tissue plasminogen activator (t-PA) can extend the narrow therapeutic time window (TTW) of t-PA. In the present study, we examined the influence of t-PA treatment on liposomal accumulation into the ischemic region and cerebroprotective effect of combined treatment with Fasudil-Lip and t-PA performed at the same timing after the onset of ischemia in middle cerebral artery occlusion (MCAO) prepared by photochemically induced thrombosis. The t-PA administration into MCAO rats 3 h after occlusion brought about significantly higher accumulation of intravenously injected PEGylated liposomes in wide area of ischemic region. Confocal images showed that extravasation of the liposomes from cerebral vessels into brain parenchyma was markedly facilitated by the t-PA treatment which increased blood flow in cerebral vessels. Importantly, co-administration of Fasudil-Lip and t-PA after 3 h occlusion, beyond the TTW of t-PA in MCAO rats, significantly suppressed brain cell damage compared with t-PA treatment alone. These findings suggest that co-administration of Fasudil-Lip and t-PA should lead to prolong t-PA's TTW and become a useful therapeutic option for ischemic stroke.

The analysis of solutions behaviour of Van der Pol Duffing equation describing local brain hemodynamics

This article proposes the generalized model of Van der Pol — Duffing equation for describing the relaxation oscillations in local brain hemodynamics. This equation connects the velocity and pressure of blood flow in cerebral vessels. The equation is individual for each patient, since the coefficients are unique. Each set of coefficients is built based on clinical data obtained during neurosurgical operation in Siberian Federal Biomedical Research Center named after Academician E. N. Meshalkin. The equation has solutions of different structure defined by the coefficients and right side. We investigate the equations for different patients considering peculiarities of their vessel systems. The properties of approximate analytical solutions are studied. Amplitude-frequency and phase-frequency characteristics are built for the small-dimensional solution approximations.

Haemodynamics of giant cerebral aneurysm: A comparison between the rigid-wall, one-way and two-way FSI models

In this paper a computer simulation of a blood flow in cerebral vessels with a giant saccular aneurysm at the bifurcation of the basilar artery is performed. The modelling is based on patient-specific clinical data (both flow domain geometry and boundary conditions for the inlets and outlets). The hydrodynamic and mechanical parameters are calculated in the frameworks of three models: rigid-wall assumption, one-way FSI approach, and full (two-way) hydroelastic model. A comparison of the numerical solutions shows that mutual fluid- solid interaction can result in qualitative changes in the structure of the fluid flow. Other characteristics of the flow (pressure, stress, strain and displacement) qualitatively agree with each other in different approaches. However, the quantitative comparison shows that accounting for the flow-vessel interaction, in general, decreases the absolute values of these parameters. Solving of the hydroelasticity problem gives a more detailed solution at a cost of highly increased computational time.

Viscous dissipation energy as a risk factor in multiple cerebral aneurysms

AbstractThe hydrodynamic properties of the blood flow in cerebral vessels with multiple aneurysms are studied in the paper. We compare the sets of parameters derived from the dissipation energy appearing due to the blood viscosity and computed for different aneurysms of one patient. Numerical simulations show that in most cases the dissipation energy and its derived parameters are lower in the case of ruptured aneurysm. Moreover, the average dissipation energy per unit volume is lower in all cases studied here.

Clip readjustment in aneurysm surgery after flow evaluation using the ultrasonic perivascular probe: case report

Occlusion or stenosis of a parent vessel or its distal branches is a major cause of poor patient outcome after cerebral aneurysm surgery. Despite great attempts to preserve patency at the time of clip application, intraoperative visual observation may not reveal arterial compromise or occlusion. Quantitative measurement of blood flow in cerebral vessels during aneurysm surgery can help prevent ischaemia and improve patient outcome. We report a case of a large complex middle cerebral artery (MCA) aneurysm in which perivascular microflow probes were used to measure blood flow quantitatively in MCA and its branches before and after aneurysm clipping. Following aneurysm clipping, blood flow in the MCA branches were significantly reduced to less than its initial baseline value with occlusion of the inferior M2 segment. Prompt detection of compromised blood flow gave the surgeon the opportunity to adjust the clip. This adjustment was performed several times until restore MCA flow to its preclipping values. Intraoperative quantitative vessel-flow measurements were safe and may have prevented cerebral ischaemia and neurological deficit to this patient.

Intracranial oscillations of cerebrospinal fluid and blood flows: analysis with magnetic resonance imaging.

To detect oscillations of the cerebrospinal fluid (CSF) flow related to the heartbeat and frequencies lower than 0.6 Hz and to compare these oscillations of CSF and blood flow in cerebral vessels by using echo planar imaging in real time mode. The existence of such waves has been well known but has not yet been shown by MRI. In a slice perpendicular to the aqueduct, CSF flow as well as CBF, could be determined in sagittal sinus, basilar artery, and capillary vessels. After Fourier analysis, four frequency bands were assigned. In the very high-frequency (heart rate) range, the integrals under the CSF curves were more closely related to arterial CBF than to changes in the sinus. Also, in the high-frequency (respiration rate), low-frequency (0.05-0.15 Hz), and very-low-frequency (0.008-0.05 Hz) ranges, the integrals under the CSF curves corresponded with arterial and capillary CBF. Slow and fast oscillations in CSF flow are detectable in healthy persons with a proportional allotment to arterial and capillary CBF.

Power M-mode Doppler (PMD) for observing cerebral blood flow and tracking emboli

Difficulties in location of transcranial ultrasound (US) windows and blood flow in cerebral vessels, and unambiguous detection of microemboli, have limited expansion of transcranial Doppler US. We developed a new transcranial Doppler modality, power M-mode Doppler (PMD), for addressing these issues. A 2-MHz digital Doppler (Spencer Technologies TCD100M) having 33 sample gates placed with 2-mm spacing was configured to display Doppler signal power, colored red and blue for directionality, in an M-mode format. The spectrogram from a user-selected depth was displayed simultaneously. This system was then explored on healthy subjects and patients presenting with varying cerebrovascular pathology. PMD facilitated window location and alignment of the US beam to view blood flow from multiple vessels simultaneously, without sound or spectral clues. Microemboli appeared as characteristic sloping high-power tracks in the PMD image. Power M-mode Doppler is a new paradigm facilitating vessel location, diagnosis, monitoring and microembolus detection. (E-mail: mm@spencertechnologies.com)

Alteration in the pulsatility index values of the internal carotid and middle cerebral arteries after suspension of postmenopausal hormone replacement therapy: A randomized crossover study

OBJECTIVE: The aim of the study was to investigate the effect of the suspension of hormone replacement therapy on blood flow in the internal carotid and the middle cerebral arteries. STUDY DESIGN: Doppler ultrasonography was used to measure the pulsatility index of the internal carotid and middle cerebral arteries of 23 women. The patients were all receiving continuous transdermal estradiol replacement therapy (50 μg/day) with a cyclic supplementation of medroxyprogesterone acetate every second month (10 mg/day for 12 days). The duration of the study was 12 months. The patients were randomly assigned to one of two groups. The first group (11 subjects) continued therapy for the first 6 months and then suspended it for the following 6 months; the second group (12 subjects) interrupted hormone replacement therapy for the first 6 months and then resumed it for the following 6 months. The internal carotid and middle cerebral artery pulsatility index was measured at the start of the 12-month period and then every 3 months. Serum estradiol levels were measured to check compliance. RESULTS: A statistically significant difference was found between the internal carotid and middle cerebral artery pulsatility index values of the two groups at each of the measurements after the first one. Over the first 6 months the pulsatility index values rapidly increased in the patients kept off hormone replacement therapy and remained stable in those receiving hormone replacement therapy. After the crossover at 6 months, the pulsatility index rapidly dropped to values similar to those at baseline in the patients who resumed hormone replacement therapy and increased in those who suspended therapy. CONCLUSIONS: Resistance to blood flow in cerebral vessels of postmenopausal women rapidly changes after hormone replacement therapy suspension. In postmenopausal women estrogen administration should be continued to maintain the favorable variations of vascular reactivity induced by hormone replacement therapy. (Am J Obstet Gynecol 1996;175:606-11.)

Electron-immunocytochemistry of peptides in endothelial cells of rabbit cerebral vessels following perfusion with a perfluorocarbon emulsion

This study describes the localization of endothelin-1-, vasopressin- and substance P-like immunoreactivity in a subpopulation of endothelial cells of the basilar and posterior communicating arteries of the (i) normal rabbit brains and (ii) rabbit brains perfused with a perfluorocarbon emulsion (PFC). Following perfusion with the PFC at increased flow the endothelial cell ultrastructure appeared normal, although there was a decrease of immunoreactivity to these peptides. This suggests that these peptides may be involved in endothelial control of blood flow in cerebral vessels.

THE CEREBRAL CIRCULATION

Our purpose in this investigation was to study the effect of alterations in cerebrospinal fluid pressure on the intracranial velocity of blood flow. In previous communications 1 were reported the results of direct observations through a tightly sealed glass window on the velocity of blood flow in cerebral vessels. By the method used, it was impossible to detect any but gross variations in the speed of blood flow. The following investigation was undertaken to study these changes more accurately. METHOD Preparation of the Animal. —Cats of approximately uniform size were used. The weights of the animals averaged 2.9 Kg., the largest differing from the smallest by 1.31 Kg. The heavier animals were pregnant, and so some of the weight may be discounted. Anesthesia was produced by intraperitoneal injection of from 8 to 9 cc. per kilogram of 1 per cent amytal (iso-amyl-ethyl barbituric acid). The animals were studied in the