scholarly journals Biofluid modeling of the coupled eye-brain system and insights into simulated microgravity conditions

2019 ◽  
Author(s):  
Fabrizia Salerni ◽  
Rodolfo Repetto ◽  
Alon Harris ◽  
Peter Pinsky ◽  
Christophe Prud’homme ◽  
...  
Keyword(s):  
Blood Flow ◽  
Simulated Microgravity ◽  
Circulation Model ◽  
Venous Drainage ◽  
Ocular Blood Flow ◽  
Whole Body ◽  
Microgravity Conditions ◽  
Venous Function ◽  
Vascular Beds ◽  
The Brain

AbstractThis work aims at investigating the interactions between the flow of fluids in the eyes and the brain and their potential implications in the development of visual impairment in astronauts, a condition also known as spaceflight associated neuro-ocular syndrome (SANS). To this end, we propose a reduced (0-dimensional) mathematical model of fluid flow in the eyes and brain, which is embedded into a simplified whole-body circulation model. In particular, the model accounts for: (i) the flows of blood and aqueous humor in the eyes; (ii) the flows of blood, cerebrospinal fluid and interstitial fluid in the brain; and (iii) their interactions. The model is used to simulate variations in intraocular pressure, intracranial pressure and blood flow due to microgravity conditions, which are thought to be critical factors in SANS. Specifically, the model predicts that both intracranial and intraocular pressures increase in microgravity, even though their respective trends may be different. In such conditions, ocular blood flow is predicted to decrease in the choroid and ciliary body circulations, whereas retinal circulation is found to be less susceptible to microgravity-induced alterations, owing to a purely mechanical component in perfusion control associated with the venous segments. These findings indicate that the particular anatomical architecture of venous drainage in the retina may be one of the reasons why most of the SANS alterations are not observed in the retina but, rather, in other vascular beds, particularly the choroid. Thus, clinical assessment of ocular venous function may be considered as a determinant SANS factor, for which astronauts could be screened on earth and in-flight.

Cerebral blood flow and metabolism during exercise: implications for fatigue

2008 ◽  
Vol 104 (1) ◽  
pp. 306-314 ◽  
Author(s):  
Neils H. Secher ◽  
Thomas Seifert ◽  
Johannes J. Van Lieshout
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Perceived Exertion ◽  
Cerebral Oxygenation ◽  
Metabolic Response ◽  
Work Of Breathing ◽  
Whole Body ◽  
Strenuous Exercise ◽  
Glycogen Depletion ◽  
The Brain

During exercise: the Kety-Schmidt-determined cerebral blood flow (CBF) does not change because the jugular vein is collapsed in the upright position. In contrast, when CBF is evaluated by 133Xe clearance, by flow in the internal carotid artery, or by flow velocity in basal cerebral arteries, a ∼25% increase is detected with a parallel increase in metabolism. During activation, an increase in cerebral O2 supply is required because there is no capillary recruitment within the brain and increased metabolism becomes dependent on an enhanced gradient for oxygen diffusion. During maximal whole body exercise, however, cerebral oxygenation decreases because of eventual arterial desaturation and marked hyperventilation-related hypocapnia of consequence for CBF. Reduced cerebral oxygenation affects recruitment of motor units, and supplemental O2 enhances cerebral oxygenation and work capacity without effects on muscle oxygenation. Also, the work of breathing and the increasing temperature of the brain during exercise are of importance for the development of so-called central fatigue. During prolonged exercise, the perceived exertion is related to accumulation of ammonia in the brain, and data support the theory that glycogen depletion in astrocytes limits the ability of the brain to accelerate its metabolism during activation. The release of interleukin-6 from the brain when exercise is prolonged may represent a signaling pathway in matching the metabolic response of the brain. Preliminary data suggest a coupling between the circulatory and metabolic perturbations in the brain during strenuous exercise and the ability of the brain to access slow-twitch muscle fiber populations.

Generalized decrease in brain glucose metabolism during fasting in humans studied by PET

1989 ◽  
Vol 256 (6) ◽  
pp. E805-E810 ◽  
Author(s):  
C. Redies ◽  
L. J. Hoffer ◽  
C. Beil ◽  
E. B. Marliss ◽  
A. C. Evans ◽  
...  
Keyword(s):  
Blood Flow ◽  
Blood Volume ◽  
Ketone Bodies ◽  
Oxygen Metabolism ◽  
Whole Body ◽  
Transfer Coefficients ◽  
Oxygen Utilization ◽  
Whole Brain ◽  
Brain Glucose ◽  
The Brain

In prolonged fasting, the brain derives a large portion of its oxidative energy from the ketone bodies, beta-hydroxybutyrate and acetoacetate, thereby reducing whole body glucose consumption. Energy substrate utilization differs regionally in the brain of fasting rat, but comparable information has hitherto been unavailable in humans. We used positron emission tomography (PET) to study regional brain glucose and oxygen metabolism, blood flow, and blood volume in four obese subjects before and after a 3-wk total fast. Whole brain glucose utilization fell to 54% of control (postabsorptive) values (P less than 0.002). The whole brain rate constant for glucose tracer phosphorylation fell to 51% of control values (P less than 0.002). Both parameters decreased uniformly throughout the brain. The 2-fluoro-2-deoxy-D-glucose lumped constant decreased from a control value of 0.57 to 0.43 (P less than 0.01). Regional blood-brain barrier transfer coefficients for glucose tracer, regional oxygen utilization, blood flow, and blood volume were unchanged.

Quantification and Distribution of Cerebral Emboli during Cardiopulmonary Bypass in the Swine 

1999 ◽  
Vol 90 (1) ◽  
pp. 183-190 ◽  
Author(s):  
Walter Plochl ◽  
David J. Cook
Keyword(s):  
Blood Flow ◽  
Cardiopulmonary Bypass ◽  
Ocular Blood Flow ◽  
Fluorescent Microspheres ◽  
Tissue Samples ◽  
Blood Flows ◽  
Cerebral Embolization ◽  
Before And After ◽  
Aortic Cannula ◽  
The Brain

Background Patients undergoing cardiac surgery have a substantial incidence of neurologic complications related to cerebral embolization during cardiopulmonary bypass. The purpose of this study was to determine if adjustments in the arterial carbon dioxide (PaCO2) level can reduce cerebral and ocular embolization. Methods Twenty pigs underwent cardiopulmonary bypass at 38 degrees C. At either hypercarbia (PaCO2 = 50-55 mmHg, group H, n = 10) or hypocarbia (PaCO2 = 25-30 mmHg, group L, n = 10), an embolic load of 1.2 x 10(50 67-microm orange fluorescent microspheres was injected into the aortic cannula. Before and after embolization, cerebral and ocular blood flows were determined at normocapnia using 15-microm fluorescent microspheres. After cardiopulmonary bypass was completed, the eyes were enucleated and brain tissue samples were collected. Microspheres were isolated and the fluorescence was measured. Results In groups H and L, the mean PaCO2 values at embolization were 52+/-3 mmHg and 27+/-2 mmHg, respectively (P < 0.0001). Total and regional embolization were significantly less in hypocapnia than in hypercapnic animals: 142% more emboli were detected in the brain in group H than in group L (P < 0.0001). Cerebral blood flow after embolization was unchanged in both groups. Similarly, fewer ocular emboli occurred in hypocapnic animals than in hypercapnic animals (P = 0.044), but in contrast to the brain, ocular blood flow decreased significantly in both groups after embolization. Conclusions Cerebral embolization is determined by the PaCO2 at the time of embolization. In cardiopulmonary bypass practice, reductions in PaCO2 during periods of embolic risk may reduce the risk for brain injury.

scholarly journals Mathematical modeling of ocular and cerebral hemo-fluid dynamics: application to VIIP

2018 ◽  
Vol 2 (2) ◽  
pp. 64-68
Author(s):  
Fabrizia Salerni ◽  
Rodolfo Repetto ◽  
Alon Harris ◽  
Peter Pinsky ◽  
Christophe Prud’homme ◽  
...  
Keyword(s):  
Mathematical Modeling ◽  
Ciliary Body ◽  
Circulation Model ◽  
The Other ◽  
Upper Body ◽  
Whole Body ◽  
Fluid Circulation ◽  
Fluid Redistribution ◽  
Flow Circulation ◽  
The Brain

This work aims at investigating the interactions between the flow of fluids in the brain and eyes, and their potential implications in the development of visual impairment and intracranial pressure (VIIP) syndrome in astronauts. We propose a reduced (0-D) mathematical model of fluid circulation in the eyes and brain, which is embedded into a simplified whole-body circulation model. This model allows us to predict fluid redistribution in the upper body vasculature as well as variation of the intracranial (ICP) and intraocular (IOP) pressures. The model results suggest that, by taking into account some eff ects of microgravity, it is possible to observe, on one hand, an increase in IOP, and on the other, a decrease in blood flow circulation in the choroid and ciliary body. These findings provide clues for the role that vascular components may play in VIIP pathogenesis, for which astronauts could be screened on Earth and in-flight.

scholarly journals Coupling between arterial and venous cerebral blood flow during postural change

2016 ◽  
Vol 311 (6) ◽  
pp. R1255-R1261 ◽  
Author(s):  
Shigehiko Ogoh ◽  
Takuro Washio ◽  
Hiroyuki Sasaki ◽  
Lonnie G. Petersen ◽  
Niels H. Secher ◽  
...  
Keyword(s):  
Blood Flow ◽  
Healthy Subjects ◽  
Internal Carotid ◽  
Jugular Vein ◽  
Venous Drainage ◽  
Postural Change ◽  
Venous Outflow ◽  
Venous Flow ◽  
End Tidal ◽  
The Brain

In supine humans the main drainage from the brain is through the internal jugular vein (IJV), but the vertebral veins (VV) become important during orthostatic stress because the IJV is partially collapsed. To identify the effect of this shift in venous drainage from the brain on the cerebral circulation, this study addressed both arterial and venous flow responses in the “anterior” and “posterior” parts of the brain when nine healthy subjects (5 men) were seated and flow was manipulated by hyperventilation and inhalation of 6% carbon dioxide (CO2). From a supine to a seated position, both internal carotid artery (ICA) and IJV blood flow decreased ( P = 0.004 and P = 0.002), while vertebral artery (VA) flow did not change ( P = 0.348) and VV flow increased ( P = 0.024). In both supine and seated positions the ICA response to manipulation of end-tidal CO2 tension was reflected in IJV ( r = 0.645 and r = 0.790, P < 0.001) and VV blood flow ( r = 0.771 and r = 0.828, P < 0.001). When seated, the decrease in ICA blood flow did not affect venous outflow, but the decrease in IJV blood flow was associated with the increase in VV blood flow ( r = 0.479, P = 0.044). In addition, the increase in VV blood flow when seated was reflected in VA blood flow ( r = 0.649, P = 0.004), and the two flows were coupled during manipulation of the end-tidal CO2 tension (supine, r = 0.551, P = 0.004; seated, r = 0.612, P < 0001). These results support that VV compensates for the reduction in IJV blood flow when seated and that VV may influence VA blood flow.

Changes in distribution of cardiac output by surface-induced deep hypothermia in dogs

1976 ◽  
Vol 40 (6) ◽  
pp. 876-882 ◽  
Author(s):  
Y. Kawashima ◽  
K. Okada ◽  
I. Kosugi ◽  
H. In-Nami ◽  
Y. Yamaguchi
Keyword(s):  
Blood Flow ◽  
Cardiac Output ◽  
Deep Hypothermia ◽  
Total Output ◽  
Organ Blood Flow ◽  
Relative Distribution ◽  
Low Cardiac Output ◽  
Vascular Beds ◽  
The Brain ◽  
Distribution Of Cardiac Output

The effects of surface-induced deep hypothermia on organ blood flow and on the distribution of cardiac output were investigated in the anesthetized dog. Organ flows were determined by the radioactive microsphere technique. Phenoxybenzamine (POB) was administered prior to hypothermia to minimize vasoconstriction and hence facilitate cooling. Measurements were made before POB, on stabilization after POB, and during hypothermia. Cardiac output was reduced by POB as was blood flow to the pancreas, small intestine, and skeletal muscle. Hypothermia, following POB, produced a further fall in Q and during this maneuver blood flow fell in all organs and vascular beds studied. The relative distribution of Q during hypothermia was essentially the same as in the control except the brain, kidneys, and pancreas received a smaller fraction of the total output. The relatively normal distribution of a reduced cardiac output during hypothermia was in marked contrast to distribution of comparable low cardiac output induced by hemorrhage. In the latter condition, the fraction of the cardiac output perfusing the brain, kidneys, adrenals, and hepatic artery was increased.

scholarly journals Respiratory and circulatory control during sleep.

1982 ◽  
Vol 100 (1) ◽  
pp. 223-244
Author(s):  
J H Coote
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Partial Pressure ◽  
Arterial Blood ◽  
Circulatory Control ◽  
Differential Pattern ◽  
Vascular Beds ◽  
The Brain

A survey of the literature on a large number of vertebrate animals shows that sleep is associated with profound cardiovascular and respiratory adjustments which are very similar in each species. A hypothesis is advanced that these adjustments are 'goal directed' by neural structures in the brainstem, to ensure an adequate O2 and CO2 transport to and from the brain whilst at the same time reducing energy cost. During synchronised sleep there is a vagal bradycardia leading to reduced cardiac output and a fall in blood pressure; despite this cerebral blood flow increases. During desynchronized sleep there is a tonic fall in blood pressure and heart rate resulting from a unique repatterning of sympathetic discharge, that to heart, kidney, splanchnic and pelvic vascular beds decreasing whilst that to skeletal muscle increasing; cerebral blood flow shows a further increase. This differential pattern is probably initiated by neurones located in the caudal raphe nucleus obscurus. Phasic increases in blood pressure and heart rate also occur during desynchronized sleep mainly as a consequence of increases in sympathetic activity. Ventilation decreases during synchronized sleep accompanied by an increase in partial pressure of arterial CO2, which vasodilates cerebral blood vessels, indicating that the influence of CO2 on the level of ventilation has changed. During desynchronized sleep ventilation increases and becomes very irregular but the partial pressure of O2 and CO2 in arterial blood is little changed from wakefulness. Control of respiration is shifted to a central generator which apparently is different to the automatic/metabolic one which is normally dominant during wakefulness. Reflex control of the circulation and respiration is mainly governed by peripheral chemoreceptors, the threshold of most other afferent inputs being significantly raised during sleep.

scholarly journals A trial of the use of perfusion computed tomography of the brain in combination with transcranial Doppler ultrasonography of blood vessels in patients with acute cerebrovascular accident

2020 ◽  
Vol 101 (1) ◽  
pp. 124-131
Author(s):  
K G Valeeva ◽  
S K Perminova ◽  
A Ya Nazipova ◽  
S V Kurochkin ◽  
A A Yakupova
Keyword(s):  
Computed Tomography ◽  
Blood Flow ◽  
Transcranial Doppler ◽  
Cerebrovascular Accident ◽  
Doppler Ultrasonography ◽  
Transcranial Doppler Ultrasonography ◽  
Perfusion Computed Tomography ◽  
Acute Cerebrovascular Accident ◽  
Vascular Beds ◽  
The Brain

Aim. Assessment of cerebral blood flow in various vascular beds in patients with an acute cerebrovascular accident in the acute period by perfusion computed tomography in combination with transcranial Doppler ultrasonography of cerebral vessels. Methods. Data was analyzed from perfusion computed tomography of the brain and transcranial Doppler ultrasonography in 35 patients with an acute cerebrovascular accident, based at the vascular centre of the City Clinical Hospital No. 7 of Kazan. The study included 18 (51.4%) women and 17 (48.6%) men who had arrived in the first hours after a vascular accident. When analyzing the stroke subtype, atherothrombotic subtype was determined in 27 (77.1%) patients, cardioembolic subtype in 5 (14.3%) patients, and 3 (8.6%) patients had had a transient ischemic attack. Results. Perfusion computed tomography is a method that allowed evaluation of the structure of the brain, and blood supply to the anterior cerebral (in 2.9% of the studied patients), middle cerebral (in 62.9% of the studied patients), posterior cerebral (in 11.4% of the studied patients) and vertebral (in 14.2% of the studied patients) arteries of patients with a stroke. The method revealed a zone of critical perfusion (ischemic penumbra) by quantitatively processing perfusion indicators in the anterior cerebral blood flow system (decrease in rate and increase in average volume of cerebral blood flow and average transit time) and in the posterior cerebral circulation system (decrease in blood flow and prolongation of transit time) in the bed of the right vertebral artery). The method also aided the construction of perfusion maps. Transcranial Doppler ultrasonography of cerebral vessels revealed breaches in the cerebral circulation: a decrease in the linear velocity of blood flow in the right middle cerebral arterial bed and in the posterior circulatory system of blood flow in the brain, and an increase in the pulsatility index in all the studied vascular beds. Conclusion. Perfusion computed tomography of the brain in combination with transcranial Doppler ultrasonography is applicable to patients with stroke in various vascular beds, followed by determination of indications for thrombolytic therapy and thrombectomy.

Control of translation in the cold: implications for therapeutic hypothermia

2015 ◽  
Vol 43 (3) ◽  
pp. 333-337 ◽  
Author(s):  
John R.P. Knight ◽  
Anne E. Willis
Keyword(s):  
Blood Flow ◽  
Therapeutic Hypothermia ◽  
Heart Surgery ◽  
Whole Body ◽  
Potential Importance ◽  
Therapeutic Gain ◽  
Body Cooling ◽  
Whole Body Cooling ◽  
The Brain ◽  
Reduced Temperature

Controlled whole-body cooling has been used since the 1950s to protect the brain from injury where cerebral blood flow is reduced. Therapeutic hypothermia has been used successfully during heart surgery, following cardiac arrest and with varied success in other instances of reduced blood flow to the brain. However, why reduced temperature is beneficial is largely unknown. Here we review the use of therapeutic hypothermia with a view to understanding the underlying biology contributing to the phenomenon. Interestingly, the benefits of cooling have recently been extended to treatment of chronic neurodegenerative diseases in two mouse models. Concurrently studies have demonstrated the importance of the regulation of protein synthesis, translation, to the cooling response, which is also emerging as a targetable process in neurodegeneration. Through these studies the potential importance of the rewarming process following cooling is also beginning to emerge. Altogether, these lines of research present new opportunities to manipulate cooling pathways for therapeutic gain.

Cerebrospinal Physiology

2019 ◽  
pp. 74-78
Author(s):  
Joseph Zachariah
Keyword(s):  
Blood Flow ◽  
Critical Care ◽  
Intensive Care ◽  
Cerebral Blood Flow ◽  
Cerebral Circulation ◽  
Cerebral Perfusion ◽  
Venous Drainage ◽  
Factors Affecting ◽  
Irreversible Injury ◽  
The Brain

With its high metabolic rate and lack of substrate stores, the brain is dependent on a constant supply of oxygen and glucose. If blood flow stops, alterations in brain function occur within seconds and irreversible injury can occur within a few minutes. Many patients admitted to neurosciences intensive care units have acute strokes, are eligible for endovascular procedures, and may need other measures to preserve adequate cerebral blood flow. An understanding of the blood supply, venous drainage, and factors affecting cerebral perfusion is thus pivotal to the practice of neurologic critical care. This chapter reviews the anatomical and physiologic principles governing cerebral circulation and blood flow.

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