The Experts below are selected from a list of 251784 Experts worldwide ranked by ideXlab platform
Randall B Griepp - One of the best experts on this subject based on the ideXlab platform.
-
the collateral Network Concept remodeling of the arterial collateral Network after experimental segmental artery sacrifice
The Journal of Thoracic and Cardiovascular Surgery, 2011Co-Authors: Christoph S Mueller, Fabian A Kari, Robert M Brenner, Randall B GrieppAbstract:Objective A comprehensive strategy to prevent paraplegia after open surgical or endovascular repair of thoracoabdominal aortic aneurysms requires a thorough understanding of the response of the collateral Network to extensive segmental artery sacrifice. Methods Ten Yorkshire pigs underwent perfusion with a low-viscosity acrylic resin. With the use of cardiopulmonary bypass, 2 animals each were perfused in the native state and immediately, 6 hours, 24 hours, and 5 days after sacrifice of all segmental arteries (T4–L5). After digestion of surrounding tissue, the vascular cast of the collateral Network underwent analysis of arterial and arteriolar diameters and the density and spatial orientation of the vasculature using light and scanning electron microscopy. Results Within 24 hours, the diameter of the anterior spinal artery had increased significantly, and within 5 days the anterior spinal artery and the epidural arterial Network had enlarged in diameter by 80% to 100% ( P P P = .0002), and a significant realignment of arterioles parallel to the spinal cord had occurred ( P = .0005). Conclusions Within 5 days after segmental artery occlusion, profound anatomic alterations in the intraspinal and paraspinous arteries and arterioles occurred, providing the anatomic substrate for preservation of spinal cord blood flow via collateral pathways.
-
the collateral Network Concept a reassessment of the anatomy of spinal cord perfusion
The Journal of Thoracic and Cardiovascular Surgery, 2011Co-Authors: Fabian A Kari, Christoph S Mueller, Daniel Silovitz, Robert M Brenner, Randall B GrieppAbstract:Objective Prevention of paraplegia after repair of thoracoabdominal aortic aneurysm requires understanding the anatomy and physiology of the spinal cord blood supply. Recent laboratory studies and clinical observations suggest that a robust collateral Network must exist to explain preservation of spinal cord perfusion when segmental vessels are interrupted. An anatomic study was undertaken. Methods Twelve juvenile Yorkshire pigs underwent aortic cannulation and infusion of a low-viscosity acrylic resin at physiologic pressures. After curing of the resin and digestion of all organic tissue, the anatomy of the blood supply to the spinal cord was studied grossly and with light and electron microscopy. Results All vascular structures at least 8 μm in diameter were preserved. Thoracic and lumbar segmental arteries give rise not only to the anterior spinal artery but to an extensive paraspinous Network feeding the erector spinae, iliopsoas, and associated muscles. The anterior spinal artery, mean diameter 134 ± 20 μm, is connected at multiple points to repetitive circular epidural arteries with mean diameters of 150 ± 26 μm. The capacity of the paraspinous muscular Network is 25-fold the capacity of the circular epidural arterial Network and anterior spinal artery combined. Extensive arterial collateralization is apparent between the intraspinal and paraspinous Networks, and within each Network. Only 75% of all segmental arteries provide direct anterior spinal artery–supplying branches. Conclusions The anterior spinal artery is only one component of an extensive paraspinous and intraspinal collateral vascular Network. This Network provides an anatomic explanation of the physiological resiliency of spinal cord perfusion when segmental arteries are sacrificed during thoracoabdominal aortic aneurysm repair.
-
spinal cord perfusion and protection during descending thoracic and thoracoabdominal aortic surgery the collateral Network Concept
The Annals of Thoracic Surgery, 2007Co-Authors: Randall B Griepp, Eva B GrieppAbstract:In the last two decades, as an increasing number of patients with descending thoracic and thoracoabdominal aneurysms are being diagnosed and treated, a more sophisticated understanding of spinal cord perfusion has become important in the attempt to minimize the frequency of spinal cord injury. The synthesis of information from laboratory studies and clinical experience has led to the collateral Network Concept, a framework for understanding spinal cord perfusion and thereby improving spinal cord protection during treatment of aneurysmal disease of the aorta distal to the left subclavian artery. Application of principles based on the collateral Network Concept has resulted in falling rates of spinal cord injury, which now approach 1% in descending thoracic aneurysm resection and less than 10% in extensive thoracoabdominal resections. These accomplishments suggest that, with further investigation, routine sacrifice of segmental aortic branches can be carried out in a way that will allow surgical and endovascular therapy of extensive distal aortic aneurysms without neurologic injury.
Otto Raspe - One of the best experts on this subject based on the ideXlab platform.
-
On the Economic Foundation of the Urban Network Paradigm: Spatial Integration, Functional Integration and Economic Complementarities within the Dutch Randstad:
Urban Studies, 2010Co-Authors: Frank Van Oort, Martijn Burger, Otto RaspeAbstract:Conceptually, the degrees of spatial and functional integration and urban complementarities in economic Network relations are hypothesised to be important. In this paper, data on interfirm relations in the Dutch Randstad are used to test conditions for integration and the existence of economic complementarities. A clear hierarchy is observed in the different types of spatial interdependencies in the Randstad, in which the central place model prevails. Furthermore, no evidence is found for the functional integration of municipalities in the Randstad. It is concluded that, at this moment, the Randstad does not function as a spatially and functionally integrated region and that spatial economic policy can better focus on smaller regions within the Randstad. This also calls into question the applicability of the urban Network Concept in general, as the Dutch Randstad is usually seen as a prime example of an economically successful polycentric urban system.
-
on the economic foundation of the urban Network paradigm spatial integration functional integration and economic complementarities within the dutch randstad
2009Co-Authors: Frank Van Oort, Martijn Burger, Otto RaspeAbstract:The current debate on polycentric urban development suggests that inter-firm relations are important for the creation and sustainment of urban Networks. Conceptually, the degrees of spatial and functional integration and urban complementarities in economic Network relations are hypothesised to be important. However, the theoretical economic rationale has not been convincingly tested. In this paper, we use data on inter-firm relations in the Dutch Randstad to test conditions for integration and the existence of economic complementarities within this region. Contrary to the ‘polycentricity hypothesis’, we observe a clear hierarchy in the different types of spatial interdependencies in the Randstad, in which the central place model prevails. Furthermore, we do not find evidence for the functional integration of municipalities in the Randstad. We conclude that at this moment the Randstad does not function as a spatially and functionally integrated region, and that spatial economic policy can better focus on smaller regions within the Randstad when urban economic complementarities and integration are desired. This also calls into question the applicability of the urban Network Concept in general, as the Dutch Randstad is usually seen as a prime example of an economically successful polycentric urban system.
N Wilson - One of the best experts on this subject based on the ideXlab platform.
-
atm based transport architecture for multiservices wireless personal communication Networks
IEEE Journal on Selected Areas in Communications, 1994Co-Authors: Dipankar Raychaudhuri, N WilsonAbstract:This paper presents an ATM-based transport architecture for next-generation multiservices personal communication Networks (PCN). Such "multimedia capable" integrated services wireless Networks are motivated by an anticipated demand for wireless extensions to future broadband Networks. An ATM compatible wireless Network Concept capable of supporting a mix of broadband ISDN services including constant bit-rate (CBR), variable bit-rate (VBR), and packet data transport is explored from an architectural viewpoint. The proposed system uses a hierarchical ATM switching Network for interconnection of PCN microcells, each of which is serviced by high-speed, shared-access radio links based on ATM-compatible cell, relay principles. Design issues related to the physical (modulation), media access control (MAC), and data-link layers of the ATM-based radio link are discussed, and preliminary technical approaches are identified in each case. An example multiservice dynamic reservation (MDR) TDMA media access protocol is then considered in further detail, and simulation results are presented for an example voice/data scenario with a proportion of time-critical (i.e., multimedia) packet data. Time-of-expiry (TOE) based queue service disciplines are also investigated as a mechanism for improving the quality-of-service (QoS) in this scenario. >
Frank Van Oort - One of the best experts on this subject based on the ideXlab platform.
-
On the Economic Foundation of the Urban Network Paradigm: Spatial Integration, Functional Integration and Economic Complementarities within the Dutch Randstad:
Urban Studies, 2010Co-Authors: Frank Van Oort, Martijn Burger, Otto RaspeAbstract:Conceptually, the degrees of spatial and functional integration and urban complementarities in economic Network relations are hypothesised to be important. In this paper, data on interfirm relations in the Dutch Randstad are used to test conditions for integration and the existence of economic complementarities. A clear hierarchy is observed in the different types of spatial interdependencies in the Randstad, in which the central place model prevails. Furthermore, no evidence is found for the functional integration of municipalities in the Randstad. It is concluded that, at this moment, the Randstad does not function as a spatially and functionally integrated region and that spatial economic policy can better focus on smaller regions within the Randstad. This also calls into question the applicability of the urban Network Concept in general, as the Dutch Randstad is usually seen as a prime example of an economically successful polycentric urban system.
-
on the economic foundation of the urban Network paradigm spatial integration functional integration and economic complementarities within the dutch randstad
2009Co-Authors: Frank Van Oort, Martijn Burger, Otto RaspeAbstract:The current debate on polycentric urban development suggests that inter-firm relations are important for the creation and sustainment of urban Networks. Conceptually, the degrees of spatial and functional integration and urban complementarities in economic Network relations are hypothesised to be important. However, the theoretical economic rationale has not been convincingly tested. In this paper, we use data on inter-firm relations in the Dutch Randstad to test conditions for integration and the existence of economic complementarities within this region. Contrary to the ‘polycentricity hypothesis’, we observe a clear hierarchy in the different types of spatial interdependencies in the Randstad, in which the central place model prevails. Furthermore, we do not find evidence for the functional integration of municipalities in the Randstad. We conclude that at this moment the Randstad does not function as a spatially and functionally integrated region, and that spatial economic policy can better focus on smaller regions within the Randstad when urban economic complementarities and integration are desired. This also calls into question the applicability of the urban Network Concept in general, as the Dutch Randstad is usually seen as a prime example of an economically successful polycentric urban system.
Fabian A Kari - One of the best experts on this subject based on the ideXlab platform.
-
the collateral Network Concept a reassessment of the anatomy of spinal cord perfusion
The Journal of Thoracic and Cardiovascular Surgery, 2011Co-Authors: Fabian A Kari, Christoph S Mueller, Daniel Silovitz, Robert M Brenner, Randall B GrieppAbstract:Objective Prevention of paraplegia after repair of thoracoabdominal aortic aneurysm requires understanding the anatomy and physiology of the spinal cord blood supply. Recent laboratory studies and clinical observations suggest that a robust collateral Network must exist to explain preservation of spinal cord perfusion when segmental vessels are interrupted. An anatomic study was undertaken. Methods Twelve juvenile Yorkshire pigs underwent aortic cannulation and infusion of a low-viscosity acrylic resin at physiologic pressures. After curing of the resin and digestion of all organic tissue, the anatomy of the blood supply to the spinal cord was studied grossly and with light and electron microscopy. Results All vascular structures at least 8 μm in diameter were preserved. Thoracic and lumbar segmental arteries give rise not only to the anterior spinal artery but to an extensive paraspinous Network feeding the erector spinae, iliopsoas, and associated muscles. The anterior spinal artery, mean diameter 134 ± 20 μm, is connected at multiple points to repetitive circular epidural arteries with mean diameters of 150 ± 26 μm. The capacity of the paraspinous muscular Network is 25-fold the capacity of the circular epidural arterial Network and anterior spinal artery combined. Extensive arterial collateralization is apparent between the intraspinal and paraspinous Networks, and within each Network. Only 75% of all segmental arteries provide direct anterior spinal artery–supplying branches. Conclusions The anterior spinal artery is only one component of an extensive paraspinous and intraspinal collateral vascular Network. This Network provides an anatomic explanation of the physiological resiliency of spinal cord perfusion when segmental arteries are sacrificed during thoracoabdominal aortic aneurysm repair.
-
the collateral Network Concept remodeling of the arterial collateral Network after experimental segmental artery sacrifice
The Journal of Thoracic and Cardiovascular Surgery, 2011Co-Authors: Christoph S Mueller, Fabian A Kari, Robert M Brenner, Randall B GrieppAbstract:Objective A comprehensive strategy to prevent paraplegia after open surgical or endovascular repair of thoracoabdominal aortic aneurysms requires a thorough understanding of the response of the collateral Network to extensive segmental artery sacrifice. Methods Ten Yorkshire pigs underwent perfusion with a low-viscosity acrylic resin. With the use of cardiopulmonary bypass, 2 animals each were perfused in the native state and immediately, 6 hours, 24 hours, and 5 days after sacrifice of all segmental arteries (T4–L5). After digestion of surrounding tissue, the vascular cast of the collateral Network underwent analysis of arterial and arteriolar diameters and the density and spatial orientation of the vasculature using light and scanning electron microscopy. Results Within 24 hours, the diameter of the anterior spinal artery had increased significantly, and within 5 days the anterior spinal artery and the epidural arterial Network had enlarged in diameter by 80% to 100% ( P P P = .0002), and a significant realignment of arterioles parallel to the spinal cord had occurred ( P = .0005). Conclusions Within 5 days after segmental artery occlusion, profound anatomic alterations in the intraspinal and paraspinous arteries and arterioles occurred, providing the anatomic substrate for preservation of spinal cord blood flow via collateral pathways.