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Journal of Cerebral Blood Flow and... Feb 2016Pericytes, spatially isolated contractile cells on capillaries, have been reported to control cerebral blood flow physiologically, and to limit blood flow after... (Review)
Review
Pericytes, spatially isolated contractile cells on capillaries, have been reported to control cerebral blood flow physiologically, and to limit blood flow after ischaemia by constricting capillaries and then dying. Paradoxically, a recent paper dismisses the idea of pericytes controlling cerebral blood flow, despite confirming earlier data showing a role for pericytes. We show that these discrepancies are apparent rather than real, and depend on the new paper defining pericytes differently from previous reports. An objective definition of different sub-classes of pericyte along the capillary bed is needed to develop novel therapeutic approaches for stroke and disorders caused by pericyte malfunction.
Topics: Animals; Capillaries; Cerebrovascular Circulation; Humans; Pericytes; Terminology as Topic
PubMed: 26661200
DOI: 10.1177/0271678X15610340 -
Comprehensive Physiology Jan 2012The pulmonary vasculature comprises three anatomic compartments connected in series: the arterial tree, an extensive capillary bed, and the venular tree. Although, in... (Review)
Review
The pulmonary vasculature comprises three anatomic compartments connected in series: the arterial tree, an extensive capillary bed, and the venular tree. Although, in general, this vasculature is thin-walled, structure is nonetheless complex. Contributions to structure (and thus potentially to function) from cells other than endothelial and smooth muscle cells as well as those from the extracellular matrix should be considered. This review is multifaceted, bringing together information regarding (i) classification of pulmonary vessels, (ii) branching geometry in the pulmonary vascular tree, (iii) a quantitative view of structure based on morphometry of the vascular wall, (iv) the relationship of nerves, a variety of interstitial cells, matrix proteins, and striated myocytes to smooth muscle and endothelium in the vascular wall, (v) heterogeneity within cell populations and between vascular compartments, (vi) homo- and heterotypic cell-cell junctional complexes, and (vii) the relation of the pulmonary vasculature to that of airways. These issues for pulmonary vascular structure are compared, when data is available, across species from human to mouse and shrew. Data from studies utilizing vascular casting, light and electron microscopy, as well as models developed from those data, are discussed. Finally, the need for rigorous quantitative approaches to study of vascular structure in lung is highlighted.
Topics: Animals; Capillaries; Endothelium, Vascular; Humans; Intercellular Junctions; Lung; Microscopy, Electron; Models, Anatomic; Muscle, Smooth, Vascular; Pulmonary Artery; Pulmonary Veins; Radiography; Species Specificity
PubMed: 23606929
DOI: 10.1002/cphy.c100081 -
Annual Review of Vision Science Sep 2021Advances in retinal imaging are enabling researchers and clinicians to make precise noninvasive measurements of the retinal vasculature in vivo. This includes... (Review)
Review
Advances in retinal imaging are enabling researchers and clinicians to make precise noninvasive measurements of the retinal vasculature in vivo. This includes measurements of capillary blood flow, the regulation of blood flow, and the delivery of oxygen, as well as mapping of perfused blood vessels. These advances promise to revolutionize our understanding of vascular regulation, as well as the management of retinal vascular diseases. This review provides an overview of imaging and optical measurements of the function and structure of the ocular vasculature. We include general characteristics of vascular systems with an emphasis on the eye and its unique status. The functions of vascular systems are discussed, along with physical principles governing flow and its regulation. Vascular measurement techniques based on reflectance and absorption are briefly introduced, emphasizing ways of generating contrast. One of the prime ways to enhance contrast within vessels is to use techniques sensitive to the motion of cells, allowing precise measurements of perfusion and blood velocity. Finally, we provide a brief introduction to retinal vascular diseases.
Topics: Capillaries; Humans; Retina; Retinal Diseases; Retinal Vessels; Tomography, Optical Coherence
PubMed: 34171198
DOI: 10.1146/annurev-vision-093019-113719 -
Acta Neuropathologica Oct 2018Many central nervous system diseases currently lack effective treatment and are often associated with defects in microvascular function, including a failure to match... (Review)
Review
Many central nervous system diseases currently lack effective treatment and are often associated with defects in microvascular function, including a failure to match the energy supplied by the blood to the energy used on neuronal computation, or a breakdown of the blood-brain barrier. Pericytes, an under-studied cell type located on capillaries, are of crucial importance in regulating diverse microvascular functions, such as angiogenesis, the blood-brain barrier, capillary blood flow and the movement of immune cells into the brain. They also form part of the "glial" scar isolating damaged parts of the CNS, and may have stem cell-like properties. Recent studies have suggested that pericytes play a crucial role in neurological diseases, and are thus a therapeutic target in disorders as diverse as stroke, traumatic brain injury, migraine, epilepsy, spinal cord injury, diabetes, Huntington's disease, Alzheimer's disease, diabetes, multiple sclerosis, glioma, radiation necrosis and amyotrophic lateral sclerosis. Here we report recent advances in our understanding of pericyte biology and discuss how pericytes could be targeted to develop novel therapeutic approaches to neurological disorders, by increasing blood flow, preserving blood-brain barrier function, regulating immune cell entry to the CNS, and modulating formation of blood vessels in, and the glial scar around, damaged regions.
Topics: Animals; Blood-Brain Barrier; Capillaries; Humans; Nervous System Diseases; Pericytes
PubMed: 30097696
DOI: 10.1007/s00401-018-1893-0 -
Comparative Biochemistry and... Mar 2021The capillary bed constitutes the obligatory pathway for almost all oxygen (O) and substrate molecules as they pass from blood to individual cells. As the largest organ,... (Review)
Review
The capillary bed constitutes the obligatory pathway for almost all oxygen (O) and substrate molecules as they pass from blood to individual cells. As the largest organ, by mass, skeletal muscle contains a prodigious surface area of capillaries that have a critical role in metabolic homeostasis and must support energetic requirements that increase as much as 100-fold from rest to maximal exercise. In 1919 Krogh's 3 papers, published in the Journal of Physiology, brilliantly conflated measurements of muscle capillary function at rest and during contractions with Agner K. Erlang's mathematical model of O diffusion. These papers single-handedly changed the perception of capillaries from passive vessels serving at the mercy of their upstream arterioles into actively contracting vessels that were recruited during exercise to elevate blood-myocyte O flux. Although seminal features of Krogh's model have not withstood the test of time and subsequent technological developments, Krogh is credited with helping found the field of muscle microcirculation and appreciating the role of the capillary bed and muscle O diffusing capacity in facilitating blood-myocyte O flux. Today, thanks in large part to Krogh, it is recognized that comprehending the role of the microcirculation, as it supports perfusive and diffusive O conductances, is fundamental to understanding skeletal muscle plasticity with exercise training and resolving the mechanistic bases by which major pathologies including heart failure and diabetes cripple exercise tolerance and cerebrovascular dysfunction predicates impaired executive function.
Topics: Animals; Capillaries; Diffusion; Humans; Muscle Cells; Muscles; Oxygen
PubMed: 33242636
DOI: 10.1016/j.cbpa.2020.110852 -
Journal of Biophotonics Dec 2020Optical coherence tomography angiography (OCTA) is capable of non-invasively imaging the vascular networks within circulatory tissue beds in vivo. Following improvements...
Optical coherence tomography angiography (OCTA) is capable of non-invasively imaging the vascular networks within circulatory tissue beds in vivo. Following improvements in OCTA image quality, it is now possible to extract vascular parameters from imaging data to potentially facilitate the diagnosis and treatment of human disease. In this paper, we present a method for automated mapping of vessel diameter down to the individual capillary level, through gradient-guided minimum radial distance (MRD). During validation using well-characterized microfluidic flow phantoms, this method demonstrated superior consistency and a nearly threefold decrease in error when compared to currently accepted techniques. In addition, the MRD technique exhibited a high tolerance to rotation of the vasculature pattern. We also incorporated a modified A* path searching algorithm to trace vessel branches and calculate the diameter of each branch from the OCTA images. After validation in vitro, we applied these algorithms to the in vivo setting through analysis of mouse cortical vasculature. Our algorithm returned results that followed Murray's law, until reaching the capillary level, agreeing well with known physiological data. From our tracing process, vessel tortuosity and branching angle could also be measured. Our techniques provide a platform for the automated evaluation of the vasculature and may aid in diagnosis of vascular diseases, especially those resulting in regional early-stage morphological changes.
Topics: Algorithms; Angiography; Capillaries; Retinal Vessels; Tomography, Optical Coherence
PubMed: 32857462
DOI: 10.1002/jbio.202000248 -
Cells Dec 2019Atherosclerosis and associated ischemic organ dysfunction represent the number one cause of mortality worldwide. While the key drivers of atherosclerosis, arterial... (Review)
Review
Atherosclerosis and associated ischemic organ dysfunction represent the number one cause of mortality worldwide. While the key drivers of atherosclerosis, arterial hypertension, hypercholesterolemia and diabetes mellitus, are well known disease entities and their contribution to the formation of atherosclerotic plaques are intensively studied and well understood, less effort is put on the effect of these disease states on microvascular structure an integrity. In this review we summarize the pathological changes occurring in the vascular system in response to prolonged exposure to these major risk factors, with a particular focus on the differences between these pathological alterations of the vessel wall in larger arteries as compared to the microcirculation. Furthermore, we intend to highlight potential therapeutic strategies to improve microvascular function during atherosclerotic vessel disease.
Topics: Arteries; Atherosclerosis; Capillaries; Diabetes Mellitus; Endothelial Cells; Humans; Hypercholesterolemia; Hypertension; Microvessels; Plaque, Atherosclerotic
PubMed: 31878229
DOI: 10.3390/cells9010050 -
Clinical & Experimental Optometry Jan 2020The eye has long been recognised as the window to pathological processes occurring in the brain and other organs. By imaging the vasculature of the retina we have... (Review)
Review
The eye has long been recognised as the window to pathological processes occurring in the brain and other organs. By imaging the vasculature of the retina we have improved the scientific understanding and clinical best practice for a diverse range of conditions, ranging from diabetes, to stroke, to dementia. Mounting evidence suggests that damage to the smallest and most delicate vessels in the body, the capillaries, is the first sign in many vasculopathies. These are the most critical vessels involved in the exchange of metabolites with tissue. Accurate assessment of retinal capillary structure and function would therefore be of great benefit across a broad range of disciplines in medical science; however, their small size does not make this an easy task. This has led to the development of high-resolution adaptive optics imaging methods to non-invasively explore retinal microvascular networks in living human eyes. This review describes the present state of the art in the field, the scientific breakthroughs that have been made possible in the understanding of vessel structure and function in health and disease, and future directions for this emerging technology.
Topics: Capillaries; Humans; Microvessels; Optical Imaging; Regional Blood Flow; Retinal Vessels
PubMed: 31797452
DOI: 10.1111/cxo.12988 -
Journal of the Royal Society, Interface Aug 2022Capillary blood vessels in the body partake in the exchange of gas and nutrients with tissues. They are interconnected via multiple vascular junctions forming the...
Capillary blood vessels in the body partake in the exchange of gas and nutrients with tissues. They are interconnected via multiple vascular junctions forming the microvascular network. Distributions of blood flow and red cells (RBCs) in such networks are spatially uneven and vary in time. Since they dictate the pathophysiology of tissues, their knowledge is important. Theoretical models used to obtain flow and RBC distribution in large networks have limitations as they treat each vessel as a one-dimensional segment and do not explicitly consider cell-cell and cell-vessel interactions. High-fidelity computational models that accurately model each individual RBC are computationally too expensive to predict haemodynamics in large vascular networks and over a long time. Here we investigate the applicability of machine learning (ML) techniques to predict blood flow and RBC distributions in physiologically realistic vascular networks. We acquire data from high-fidelity simulations of deformable RBC suspension flowing in the networks. With the flow and haematocrit specified at an inlet of vasculature, the ML models predict the time-averaged flow rate and RBC distributions in the entire network, time-dependent flow rate and haematocrit in each vessel and vascular bifurcation in isolation over a long time, and finally, simultaneous spatially and temporally evolving quantities through the vessel hierarchy in the networks.
Topics: Blood Flow Velocity; Capillaries; Erythrocytes; Hematocrit; Hemodynamics; Machine Learning
PubMed: 35946164
DOI: 10.1098/rsif.2022.0306 -
Investigative Ophthalmology & Visual... Jul 2016Optical coherence tomography angiography (OCTA) is a noninvasive approach that can visualize blood vessels down to the capillary level. With the advent of high-speed OCT... (Review)
Review
Optical coherence tomography angiography (OCTA) is a noninvasive approach that can visualize blood vessels down to the capillary level. With the advent of high-speed OCT and efficient algorithms, practical OCTA of ocular circulation is now available to ophthalmologists. Clinical investigations that used OCTA have increased exponentially in the past few years. This review will cover the history of OCTA and survey its most important clinical applications. The salient problems in the interpretation and analysis of OCTA are described, and recent advances are highlighted.
Topics: Capillaries; Choroidal Neovascularization; Fluorescein Angiography; Fundus Oculi; Humans; Retinal Vessels; Tomography, Optical Coherence
PubMed: 27409483
DOI: 10.1167/iovs.15-19043