Hypergravity and Multiple Reflections in Wave Propagation in the Aorta

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
J. M. B. Kroot ◽  
C. G. Giannopapa
Keyword(s):  
Blood Flow ◽  
Wave Propagation ◽  
Cerebral Blood Flow ◽  
Total Pressure ◽  
Loss Of Consciousness ◽  
Pressure Waves ◽  
Multiple Reflections ◽  
One Dimensional ◽  
Gravity Changes ◽  
Pressure Part

Hypergravity and gravity changes encountered in, e.g., airplanes, rollercoasters, and spaceflight can result in headaches or loss of consciousness due to decreased cerebral blood flow. This paper describes the effect of hypergravity and gravity changes on the pressure in the aorta and the distension of its wall. The model presented consists of a pressure part caused by gravity and a part representing pressure waves propagating through the vessel. The total pressure is described by a one-dimensional formulation in the frequency domain. To accommodate for geometrical and material variations, the vessel is modeled as a series of sections in which multiple reflections can occur. Results are presented for constant and varying gravity in straight and tapered flexible vessels.

Hyper-Gravity and Multiple Reflections in Wave Propagation in the Aorta

2010 ◽  
Author(s):  
J. M. B. Kroot ◽  
C. G. Giannopapa
Keyword(s):  
Blood Flow ◽  
Wave Propagation ◽  
Cerebral Blood Flow ◽  
Total Pressure ◽  
Loss Of Consciousness ◽  
Pressure Waves ◽  
Multiple Reflections ◽  
One Dimensional ◽  
Gravity Changes ◽  
Pressure Part

Hypergravity and gravity changes encountered in e.g. airplanes, rollercoasters and spaceflight can result in headaches or loss of consciousness due to decreased cerebral blood flow. This paper describes the effect of hypergravity and gravity changes on the pressure in the aorta and the distension of its wall. The model presented consists of a pressure part caused by gravity and a part representing pressure waves propagating through the vessel. The total pressure is described by a one-dimensional formulation in the frequency domain. To accommodate for geometrical and material variations, the vessel is modeled as a series of sections in which multiple reflections can occur. Results are presented for constant and varying gravity in straight and tapered flexible vessels.

Syncope in older patients

1999 ◽  
Vol 9 (2) ◽  
pp. 117-126 ◽  
Author(s):  
Andrew J Davies ◽  
Rose Ann Kenny
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Broad Spectrum ◽  
Older Patients ◽  
Loss Of Consciousness ◽  
Appropriate Use ◽  
Postural Tone

The term syncope has been used to describe collapse of any nature but this is not the appropriate use of the word. Syncope originates from the Greek and means ‘cessation’ or ‘interruption’. The specific application of the word syncope is a temporary loss of cerebral blood flow, resulting in loss of consciousness and postural tone, thus leading to collapse. Although other conditions resulting in collapse may be difficult to disentangle from a syncopal event, it is the broad spectrum of diagnoses resulting in syncope to which this article is dedicated.

scholarly journals Cerebral hemodynamics: a mathematical model including autoregulation, baroreflex and extracranial peripheral circulation

2021 ◽  
Author(s):  
Francisco Ambrosio Garcia ◽  
Deusdedit Lineu Spavieri Junior ◽  
Andreas Linninger
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Mean Arterial Pressure ◽  
Arterial Pressure ◽  
Cerebral Autoregulation ◽  
Peripheral Circulation ◽  
Flow Regulation ◽  
Pressure Waves ◽  
Vascular Bed ◽  
Blood Flow Regulation

Increasing evidence supports that cerebral autoregulation and mean arterial pressure regulation via baroreflex contribute to cerebral blood flow regulation. It is unclear whether the extracranial vascular bed of the head and neck helps reestablishing cerebral blood flow during changes in mean arterial pressure. Current computational models of cerebral blood flow regulation do not address the relationships between the intracranial and extracranial blood flow dynamics. We present a model of cerebral autoregulation, extracranial peripheral circulation and baroreflex control of heart rate and of peripheral vasculature that was included to the model of intracranial dynamics proposed by Linninger et al. (2009), which incorporates the fully coupled blood, cerebrospinal fluid and brain parenchyma systems. Autoregulation was modelled as being pressure-mediated at the arteries and arterioles and flow-mediated at the microcirculation. During simulations of a bout of acute hypotension, cerebral blood flow returns rapidly to baseline levels with a very small overshoot, whereas the blood flow to the peripheral circulation of the head and neck suffers a prolonged suppression in accordance with experimental evidence. The inclusion of baroreflex regulation at the extracranial vascular bed had a negligible effect on cerebral blood flow regulation during dynamic changes in mean arterial pressure. Moreover, the results suggest that the extracranial blood flow carries only modest information about cerebral blood flow in dynamic situations in which cerebral autoregulation is preserved and mean arterial pressure suffers alterations. This information is likely higher when the autoregulation is impaired. Steady-state cerebral blood flow in the model is kept within normal ranges despite variations in mean arterial pressure from 50 to 175 mmHg. By inputting aortic pressure waves from individuals with increasing arterial rigidity, increasing arterial systolic and pulse pressures, the model predicts the generation of intracranial pressure waves with accordingly increasing peaks and amplitudes.

Comparative Study of Viscoelastic Arterial Wall Models in Nonlinear One-Dimensional Finite Element Simulations of Blood Flow

2011 ◽  
Vol 133 (8) ◽  
Author(s):  
Rashmi Raghu ◽  
Irene E. Vignon-Clementel ◽  
C. Alberto Figueroa ◽  
Charles A. Taylor
Keyword(s):  
Finite Element ◽  
Blood Flow ◽  
Wave Propagation ◽  
Comparative Study ◽  
Abdominal Aorta ◽  
Elastic Model ◽  
One Dimensional ◽  
Viscoelastic Models ◽  
Wide Range ◽  
Wall Models

It is well known that blood vessels exhibit viscoelastic properties, which are modeled in the literature with different mathematical forms and experimental bases. The wide range of existing viscoelastic wall models may produce significantly different blood flow, pressure, and vessel deformation solutions in cardiovascular simulations. In this paper, we present a novel comparative study of two different viscoelastic wall models in nonlinear one-dimensional (1D) simulations of blood flow. The viscoelastic models are from papers by Holenstein et al. in 1980 (model V1) and Valdez-Jasso et al. in 2009 (model V2). The static elastic or zero-frequency responses of both models are chosen to be identical. The nonlinear 1D blood flow equations incorporating wall viscoelasticity are solved using a space-time finite element method and the implementation is verified with the Method of Manufactured Solutions. Simulation results using models V1, V2 and the common static elastic model are compared in three application examples: (i) wave propagation study in an idealized vessel with reflection-free outflow boundary condition; (ii) carotid artery model with nonperiodic boundary conditions; and (iii) subject-specific abdominal aorta model under rest and simulated lower limb exercise conditions. In the wave propagation study the damping and wave speed were largest for model V2 and lowest for the elastic model. In the carotid and abdominal aorta studies the most significant differences between wall models were observed in the hysteresis (pressure-area) loops, which were larger for V2 than V1, indicating that V2 is a more dissipative model. The cross-sectional area oscillations over the cardiac cycle were smaller for the viscoelastic models compared to the elastic model. In the abdominal aorta study, differences between constitutive models were more pronounced under exercise conditions than at rest. Inlet pressure pulse for model V1 was larger than the pulse for V2 and the elastic model in the exercise case. In this paper, we have successfully implemented and verified two viscoelastic wall models in a nonlinear 1D finite element blood flow solver and analyzed differences between these models in various idealized and physiological simulations, including exercise. The computational model of blood flow presented here can be utilized in further studies of the cardiovascular system incorporating viscoelastic wall properties.

Fit Vs Faint: Assessing Work Causation in “Idiopathic Fall” Cases

2014 ◽  
Vol 19 (5) ◽  
pp. 3-12
Author(s):  
Lorne Direnfeld ◽  
David B. Torrey ◽  
Jim Black ◽  
LuAnn Haley ◽  
Christopher R. Brigham
Keyword(s):  
Blood Flow ◽  
Electrical Activity ◽  
Loss Of Consciousness ◽  
Brain Electrical Activity ◽  
Medical Terminology ◽  
Scientific Analysis ◽  
Medical Causation ◽  
The Individual ◽  
The Brain ◽  
Current Science

Abstract When an individual falls due to a nonwork-related episode of dizziness, hits their head and sustains injury, do workers’ compensation laws consider such injuries to be compensable? Bearing in mind that each state makes its own laws, the answer depends on what caused the loss of consciousness, and the second asks specifically what happened in the fall that caused the injury? The first question speaks to medical causation, which applies scientific analysis to determine the cause of the problem. The second question addresses legal causation: Under what factual circumstances are injuries of this type potentially covered under the law? Much nuance attends this analysis. The authors discuss idiopathic falls, which in this context means “unique to the individual” as opposed to “of unknown cause,” which is the familiar medical terminology. The article presents three detailed case studies that describe falls that had their genesis in episodes of loss of consciousness, followed by analyses by lawyer or judge authors who address the issue of compensability, including three scenarios from Arizona, California, and Pennsylvania. A medical (scientific) analysis must be thorough and must determine the facts regarding the fall and what occurred: Was the fall due to a fit (eg, a seizure with loss of consciousness attributable to anormal brain electrical activity) or a faint (eg, loss of consciousness attributable to a decrease in blood flow to the brain? The evaluator should be able to fully explain the basis for the conclusions, including references to current science.

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