scholarly journals The Effects of Transit Time Heterogeneity on Brain Oxygenation during Rest and Functional Activation

2015 ◽  
Vol 35 (3) ◽  
pp. 432-442 ◽  
Author(s):  
Peter M Rasmussen ◽  
Sune N Jespersen ◽  
Leif Østergaard
Keyword(s):  
Blood Flow ◽  
Transit Time ◽  
Capillary Flow ◽  
Regional Blood Flow ◽  
Flow Patterns ◽  
Blood Oxygenation ◽  
Compartment Models ◽  
Oxygen Conductance ◽  
Arteriolar Tone ◽  
Diffusion Properties

The interpretation of regional blood flow and blood oxygenation changes during functional activation has evolved from the concept of ‘neurovascular coupling’, and hence the regulation of arteriolar tone to meet metabolic demands. The efficacy of oxygen extraction was recently shown to depend on the heterogeneity of capillary flow patterns downstream. Existing compartment models of the relation between tissue metabolism, blood flow, and blood oxygenation, however, typically assume homogenous microvascular flow patterns. To take capillary flow heterogeneity into account, we modeled the effect of capillary transit time heterogeneity (CTH) on the ‘oxygen conductance’ used in compartment models. We show that the incorporation of realistic reductions in CTH during functional hyperemia improves model fits to dynamic blood flow and oxygenation changes acquired during functional activation in a literature animal study. Our results support earlier observations that oxygen diffusion properties seemingly change during various physiologic stimuli, and posit that this phenomenon is related to parallel changes in capillary flow patterns. Furthermore, our results suggest that CTH must be taken into account when inferring brain metabolism from changes in blood flow- or blood oxygenation-based signals .

Regional Blood Flow Patterns along the Length of the Rodent Cochlea

1987 ◽  
Vol 103 (5) ◽  
pp. 176-181 ◽  
Author(s):  
Norma Slepecky ◽  
Clarence Angelborg ◽  
Hans-Christian Larsen
Keyword(s):  
Blood Flow ◽  
Regional Blood Flow ◽  
Flow Patterns ◽  
Blood Flow Patterns

scholarly journals Hippocampus has lower oxygenation and weaker control of brain blood flow than cortex, due to microvascular differences

2019 ◽  
Author(s):  
K. Shaw ◽  
L. Bell ◽  
K. Boyd ◽  
D.M. Grijseels ◽  
D. Clarke ◽  
...  
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Blood Flow ◽  
Cell Function ◽  
Regional Blood Flow ◽  
Blood Oxygenation ◽  
Endothelial Cell Function ◽  
Function Modelling ◽  
Visual Cortical

AbstractThe hippocampus is essential for spatial and episodic memory but is damaged early in Alzheimer’s disease and is very sensitive to hypoxia. Understanding how it regulates its oxygen supply is therefore key for designing interventions to preserve its function. However, studies of neurovascular function in the hippocampus in vivo have been limited by its relative inaccessibility. Here we compared hippocampal and visual cortical neurovascular function in awake mice, using two photon imaging of individual neurons and vessels and measures of regional blood flow and haemoglobin oxygenation. We show that blood flow, blood oxygenation and neurovascular coupling were decreased in the hippocampus compared to neocortex, because of differences in both the vascular network and pericyte and endothelial cell function. Modelling oxygen diffusion indicates that these features of the hippocampal vasculature could explain its sensitivity to damage during neurological conditions, including Alzheimer’s disease, where the brain’s energy supply is decreased.

Regional Blood Flow Patterns along the Length of the Rodent Cochlea

1987 ◽  
Vol 103 (3-4) ◽  
pp. 176-181 ◽  
Author(s):  
Norma Slepecky ◽  
Clarence Angelborg ◽  
Hans-Christian Larsen
Keyword(s):  
Blood Flow ◽  
Regional Blood Flow ◽  
Flow Patterns ◽  
Blood Flow Patterns

Evaluation of a transit-time system for the chronic measurement of blood flow in conscious sheep

1995 ◽  
Vol 78 (2) ◽  
pp. 524-530 ◽  
Author(s):  
J. A. Bednarik ◽  
C. N. May
Keyword(s):  
Blood Flow ◽  
Cardiac Output ◽  
Transit Time ◽  
Regional Blood Flow ◽  
Flow Probe ◽  
Time Flow ◽  
Bilateral Carotid ◽  
Conscious Sheep

The accuracy of transit-time ultrasonic flow probes for measurement of regional blood flow and cardiac output was evaluated after long-term implantation in sheep. Transit-time flow probes (3, 4, 6, and 20 mm) accurately measured flow in vitro. Recalibration in vivo demonstrated that this accuracy was maintained after 1–9 mo of implantation on the left circumflex coronary (3-mm probe), cranial mesenteric (6-mm probe), left renal (4-mm probe), and left external iliac (6-mm probe) arteries of sheep. The flow probes also showed good zero stability. However, a transit-time flow probe (20 mm) chronically implanted on the pulmonary trunk significantly underestimated cardiac output compared with thermodilution or timed collection of blood. Although this flow probe underestimated flow, the response was linear. Bilateral carotid occlusion caused mesenteric, renal, and iliac vasoconstrictions, confirming that innervation of these vascular beds was undamaged. For experimental purposes, regional blood flow was measured with transit-time flow probes and cardiac output was measured with electromagnetic flow probes calibrated against thermodilution. In summary, transit-time flow probes reliably and accurately measure regional blood flow over many months in adult sheep, but, to measure cardiac output in sheep, the probes must be calibrated in vivo against another reference technique.

scholarly journals Neurovascular coupling and oxygenation are decreased in hippocampus compared to neocortex because of microvascular differences

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
K. Shaw ◽  
L. Bell ◽  
K. Boyd ◽  
D. M. Grijseels ◽  
D. Clarke ◽  
...  
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Blood Flow ◽  
Cell Function ◽  
Regional Blood Flow ◽  
Neurovascular Coupling ◽  
Blood Oxygenation ◽  
Endothelial Cell Function ◽  
Function Modelling

AbstractThe hippocampus is essential for spatial and episodic memory but is damaged early in Alzheimer’s disease and is very sensitive to hypoxia. Understanding how it regulates its oxygen supply is therefore key for designing interventions to preserve its function. However, studies of neurovascular function in the hippocampus in vivo have been limited by its relative inaccessibility. Here we compared hippocampal and visual cortical neurovascular function in awake mice, using two photon imaging of individual neurons and vessels and measures of regional blood flow and haemoglobin oxygenation. We show that blood flow, blood oxygenation and neurovascular coupling were decreased in the hippocampus compared to neocortex, because of differences in both the vascular network and pericyte and endothelial cell function. Modelling oxygen diffusion indicates that these features of the hippocampal vasculature may restrict oxygen availability and could explain its sensitivity to damage during neurological conditions, including Alzheimer’s disease, where the brain’s energy supply is decreased.

Assessment of the incorporation of revascularized fibula grafts used for mandibular reconstruction with F-18-PET

2001 ◽  
Vol 40 (02) ◽  
pp. 51-58 ◽  
Author(s):  
H. Schliephake ◽  
van den Hoff ◽  
W. H. Knapp ◽  
G. Berding
Keyword(s):  
Blood Flow ◽  
Regional Blood Flow ◽  
Venous Blood ◽  
Mandibular Reconstruction ◽  
Reference Region ◽  
Osteoblastic Activity ◽  
Non Union ◽  
Range Of Values ◽  
Measured Input

Summary Aim: Determination of the range of regional blood flow and fluoride influx during normal incorporation of revascularized fibula grafts used for mandibular reconstruction. Evaluation, if healing complications are preceded by typical deviations of these parameters from the normal range. Assessment of the potential influence of using “scaled population-derived” instead of “individually measured” input functions in quantitative analysis. Methods: Dynamic F-l 8-PET images and arterialized venous blood samples were obtained in 11 patients early and late after surgery. Based on kinetic modeling regional blood flow (K1) and fluoride influx (Kmlf) were determined. Results: In uncomplicated cases, early postoperative graft K1 - but not Kmlf -exceeded that of vertebrae as reference region. Kmn values obtained in graft necrosis (n = 2) were below the ranges of values observed in uncomplicated healing (0.01 13-0.0745 ml/min/ml) as well as that of the reference region (0.0154-0.0748). Knf values in mobile non-union were in the lower range - and those in rigid non-union in the upper range of values obtained in stable union (0.021 1-0.0694). If scaled population-derived instead of measured input functions were used for quantification, mean deviations of 23 ± 17% in K1 and 12 ± 16% in Kmlf were observed. Conclusions: Normal healing of predominantly cortical bone transplants is characterized by relatively low osteoblastic activity together with increased perfusion. It may be anticipated that transplant necrosis can be identified by showing markedly reduced F− influx. In case that measured input functions are not available, quantification with scaled population-derived input functions is appropriate if expected differences in quantitative parameters exceed 70%.

Basic Ideas and Principles for Quantifying Regional Blood Flow with Nuclear Medical Techniques

1996 ◽  
Vol 35 (05) ◽  
pp. 181-185 ◽  
Author(s):  
H. Herzog
Keyword(s):  
Blood Flow ◽  
Nuclear Medicine ◽  
Regional Blood Flow ◽  
Visual Presentation ◽  
Regional Cerebral Blood ◽  
Basic Principles ◽  
Parametric Images ◽  
Major Application ◽  
Basic Ideas ◽  
The Brain

SummaryThe measurement of blood flow in various organs and its visual presentation in parametric images is a major application in nuclear medicine. The purpose of this paper is to summarize the most important nuclear medicine procedures used to quantify regional blood flow. Starting with the first concepts introduced by Fick and later by Kety-Schmidt the basic principles of measuring global and regional cerebral blood are discussed and their relationships are explained. Different applications and modifications realized first in PET- and later in SPECT-studies of the brain and other organs are described. The permeability and the extraction of the different radiopharmaceuticals are considered. Finally some important instrumental implications are compared.

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