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Ibrahimy A, Huang CWC, Bezuidenhout AF, Allen PA, Bhadelia RA, Loth F. Association Between Resistance to Cerebrospinal Fluid Flow Near the Foramen Magnum and Cough-Associated Headache in Adult Chiari Malformation Type I. J Biomech Eng 2021; 143:051003. [PMID: 33454731 PMCID: PMC8086178 DOI: 10.1115/1.4049788] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2020] [Revised: 12/18/2020] [Indexed: 01/03/2023]
Abstract
Cough-associated headaches (CAHs) are thought to be distinctive for Chiari malformation type I (CMI) patients and have been shown to be related to the motion of cerebrospinal fluid (CSF) near the foramen magnum (FM). We used computational fluid dynamics (CFD) to compute patient-specific resistance to CSF motion in the spinal canal for CMI patients to determine its accuracy in predicting CAH. Fifty-one symptomatic CMI patients with cerebellar tonsillar position (CTP) ≥ 5 mm were included in this study. The patients were divided into two groups based on their symptoms (CAH and non-CAH) by review of the neurosurgical records. CFD was utilized to simulate CSF motion, and the integrated longitudinal impedance (ILI) was calculated for all patients. A receiver operating characteristic (ROC) curve was evaluated for its accuracy in predicting CAH. The ILI for CMI patients with CAH (776 dyn/cm5, 288-1444 dyn/cm5; median, interquartile range) was significantly larger compared to non-CAH (285 dyn/cm5, 187-450 dyn/cm5; p = 0.001). The ILI was more accurate in predicting CAH in CMI patients than the CTP when the comparison was made using the area under the ROC curve (AUC) (0.77 and 0.70, for ILI and CTP, respectively). ILI ≥ 750 dyn/cm5 had a sensitivity of 50% and a specificity of 95% in predicting CAH. ILI is a parameter that is used to assess CSF blockage in the spinal canal and can predict patients with and without CAH with greater accuracy than CTP.
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Affiliation(s)
- Alaaddin Ibrahimy
- Department of Mechanical Engineering, The University of Akron, 302 E Buchtel Avenue, Akron, OH 44325
| | - Chi-Wen Christina Huang
- Department of Radiology, Wan Fang Hospital, Taipei Medical University, No. 250, Wuxing Street, Xinyi District, Taipei City 110, Taiwan
| | - Abraham F. Bezuidenhout
- Beth Israel Deaconess Medical Center, Department of Radiology, Harvard Medical School, 330 Brookline Avenue, Boston, MA 02215
| | - Philip A. Allen
- Department of Psychology, The University of Akron, 302 E Buchtel Avenue, Akron, OH 44325
| | - Rafeeque A. Bhadelia
- Beth Israel Deaconess Medical Center, Department of Radiology, Harvard Medical School, 330 Brookline Avenue, Boston, MA 02215
| | - Francis Loth
- Department of Mechanical Engineering, The University of Akron, 302 E Buchtel Avenue, Akron, OH 44325
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Reliability of preoperative venous mapping ultrasonography in predicting for autogenous arteriovenous fistula maturation. J Vasc Surg 2020; 73:1787-1793. [PMID: 33091513 DOI: 10.1016/j.jvs.2020.09.035] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2020] [Accepted: 09/23/2020] [Indexed: 11/30/2022]
Abstract
BACKGROUND Autogenous arteriovenous fistula creation is the preferred route for vascular access for hemodialysis. Although preoperative venous mapping ultrasonography has been advocated as an operative planning adjunct and recently incorporated into the Society for Vascular Surgery clinical guidelines, controversy remains regarding its usefulness for predicting access success. The purpose of the present retrospective clinical study was to test the hypothesis that vein size measured on routine preoperative venous mapping is a poor predictor of primary fistula maturation. METHODS Consecutive upper extremity autogenous arteriovenous fistulas created by three dedicated vascular surgeons were retrospectively reviewed. The demographic characteristics, preoperative venous mapping, functional maturation, and patency were analyzed. The clinically relevant variables were tested for predictive significance using a logistic regression model. RESULTS A total of 199 upper extremity autogenous arteriovenous fistulas had been created during a 5-year period. Patients were aged 70 ± 16 years (range, 20-96 years), and 62% were men. Most had already been undergoing dialysis before fistula creation (83%), usually via a tunneled central venous catheter (62%). Radial-cephalic, brachial-cephalic, and brachial-basilic arteriovenous fistulas had been created in 82 patients (41%), 76 patients (38%), and 10 patients (5%), respectively. Fistula maturation, defined as a palpable thrill and/or successful cannulation of the fistula with the ability to deliver a flow rate of 400 mL/min, was achieved in 67% of the patients. A higher body mass index was associated with nonmaturation on both univariate and multivariate analyses (success, 28.6 ± 7.7 kg/m2; vs failed, 31.6 ± 9.4 kg/m2; P = .029; odds ratio [OR], 1.06; 95% confidence interval [CI], 1.02-1.10; P < .01). On univariate analysis, the maximum target vein diameter assessed by preoperative venous mapping was slightly larger in the group achieving successful maturation (2.9 ± 1.1 mm vs 2.6 ± 0.9 mm; P = .014). However, neither the maximum target vein diameter nor a target vein size >3 mm was significantly predictive of maturation on multivariate analysis (maximum vein diameter: OR, 0.65; 95% CI, 0.35-1.22; P = .176; vein size >3 mm: OR, 0.91; 95% CI, 0.32-2.60; P = .857). After a median follow-up of 15 months (interquartile range, 26 months), the primary functional patency, primary-assisted patency, and secondary patency rates were 39.1% ± 0.6%, 94.5% ± 0.6%, and 97.9% ± 0.5%. No association of vein diameter with long-term patency was found. CONCLUSIONS Despite the national fistula-first initiatives, most patients still undergo access via catheter at the initiation of hemodialysis. The use of routine preoperative venous mapping does not predict successful primary maturation. Also, no clinically useful predictor of fistula maturation was identified in the present study.
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Chandiwal A, Balasubramanian V, Baldwin ZK, Conte MS, Schwartz LB. Gene Therapy for the Extension of Vein Graft Patency: A Review. Vasc Endovascular Surg 2016; 39:1-14. [PMID: 15696243 DOI: 10.1177/153857440503900101] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
The mainstay of treatment for long-segment small-vessel chronic occlusive disease not amenable to endovascular intervention remains surgical bypass grafting using autologous vein. The procedure is largely successful and the immediate operative results almost always favorable. However, the lifespan of a given vein graft is highly variable, and less than 50% will remain primarily patent after 5 years. The slow process of graft malfunction is a result of the vein's chronic maladaptive response to the systemic arterial environment, its primary component being the uncontrolled proliferation of vascular smooth muscle cells (SMCs). It has recently been suggested that this response might be attenuated through pre-implantation genetic modification of the vein, so-called gene therapy for the extension of vein graft patency. Gene therapy seems particularly well suited for the prevention or postponement of vein graft failure since: (1) the stimulation of SMC proliferation appears to largely be an early and transient process, matching the kinetics of current gene transfer technology; (2) most veins are relatively normal and free of disease at the time of bypass allowing for effective gene transfer using a variety of systems; and (3) the target tissue is directly accessible during operation because manipulation and irrigation of the vein is part of the normal workflow of the surgical procedure. This review briefly summarizes the current knowledge of the incidence and basic mechanisms of vein graft failure, the vector systems and molecular targets that have been proposed as possible pre-treatments, the results of experimental genetic modification of vein grafts, and the few available clinical studies of gene therapy for vascular proliferative disorders.
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Affiliation(s)
- Amito Chandiwal
- Section of Vascular Surgery, Department of Surgery, University of Chicago, IL 60637, USA
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Heidari Pahlavian S, Yiallourou T, Tubbs RS, Bunck AC, Loth F, Goodin M, Raisee M, Martin BA. The impact of spinal cord nerve roots and denticulate ligaments on cerebrospinal fluid dynamics in the cervical spine. PLoS One 2014; 9:e91888. [PMID: 24710111 PMCID: PMC3977950 DOI: 10.1371/journal.pone.0091888] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2013] [Accepted: 02/17/2014] [Indexed: 12/29/2022] Open
Abstract
Cerebrospinal fluid (CSF) dynamics in the spinal subarachnoid space (SSS) have been thought to play an important pathophysiological role in syringomyelia, Chiari I malformation (CM), and a role in intrathecal drug delivery. Yet, the impact that fine anatomical structures, including nerve roots and denticulate ligaments (NRDL), have on SSS CSF dynamics is not clear. In the present study we assessed the impact of NRDL on CSF dynamics in the cervical SSS. The 3D geometry of the cervical SSS was reconstructed based on manual segmentation of MRI images of a healthy volunteer and a patient with CM. Idealized NRDL were designed and added to each of the geometries based on in vivo measurments in the literature and confirmation by a neuroanatomist. CFD simulations were performed for the healthy and patient case with and without NRDL included. Our results showed that the NRDL had an important impact on CSF dynamics in terms of velocity field and flow patterns. However, pressure distribution was not altered greatly although the NRDL cases required a larger pressure gradient to maintain the same flow. Also, the NRDL did not alter CSF dynamics to a great degree in the SSS from the foramen magnum to the C1 level for the healthy subject and CM patient with mild tonsillar herniation (∼6 mm). Overall, the NRDL increased fluid mixing phenomena and resulted in a more complex flow field. Comparison of the streamlines of CSF flow revealed that the presence of NRDL lead to the formation of vortical structures and remarkably increased the local mixing of the CSF throughout the SSS.
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Affiliation(s)
- Soroush Heidari Pahlavian
- Center of Excellence in Design and Optimization of Energy Systems (CEDOES), School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran
| | - Theresia Yiallourou
- Laboratory of Hemodynamics and Cardiovascular Technology, EPFL, Lausanne, Switzerland
| | - R. Shane Tubbs
- Children's of Alabama, Birmingham, Alabama, United States of America
| | - Alexander C. Bunck
- Department of Radiology, University Hospital of Cologne, Cologne, Germany
| | - Francis Loth
- Conquer Chiari Research Center, Dept. of Mech. Engineering, University of Akron, Akron, Ohio, United States of America
| | - Mark Goodin
- SimuTech Group, Hudson, Ohio, United States of America
| | - Mehrdad Raisee
- Center of Excellence in Design and Optimization of Energy Systems (CEDOES), School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran
- Hydraulic Machinery Research Institute, School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran
| | - Bryn A. Martin
- Conquer Chiari Research Center, Dept. of Mech. Engineering, University of Akron, Akron, Ohio, United States of America
- * E-mail:
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Martin BA, Kalata W, Shaffer N, Fischer P, Luciano M, Loth F. Hydrodynamic and longitudinal impedance analysis of cerebrospinal fluid dynamics at the craniovertebral junction in type I Chiari malformation. PLoS One 2013; 8:e75335. [PMID: 24130704 PMCID: PMC3794956 DOI: 10.1371/journal.pone.0075335] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2013] [Accepted: 08/11/2013] [Indexed: 02/02/2023] Open
Abstract
Elevated or reduced velocity of cerebrospinal fluid (CSF) at the craniovertebral junction (CVJ) has been associated with type I Chiari malformation (CMI). Thus, quantification of hydrodynamic parameters that describe the CSF dynamics could help assess disease severity and surgical outcome. In this study, we describe the methodology to quantify CSF hydrodynamic parameters near the CVJ and upper cervical spine utilizing subject-specific computational fluid dynamics (CFD) simulations based on in vivo MRI measurements of flow and geometry. Hydrodynamic parameters were computed for a healthy subject and two CMI patients both pre- and post-decompression surgery to determine the differences between cases. For the first time, we present the methods to quantify longitudinal impedance (LI) to CSF motion, a subject-specific hydrodynamic parameter that may have value to help quantify the CSF flow blockage severity in CMI. In addition, the following hydrodynamic parameters were quantified for each case: maximum velocity in systole and diastole, Reynolds and Womersley number, and peak pressure drop during the CSF cardiac flow cycle. The following geometric parameters were quantified: cross-sectional area and hydraulic diameter of the spinal subarachnoid space (SAS). The mean values of the geometric parameters increased post-surgically for the CMI models, but remained smaller than the healthy volunteer. All hydrodynamic parameters, except pressure drop, decreased post-surgically for the CMI patients, but remained greater than in the healthy case. Peak pressure drop alterations were mixed. To our knowledge this study represents the first subject-specific CFD simulation of CMI decompression surgery and quantification of LI in the CSF space. Further study in a larger patient and control group is needed to determine if the presented geometric and/or hydrodynamic parameters are helpful for surgical planning.
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Affiliation(s)
- Bryn A. Martin
- Conquer Chiari Research Center, University of Akron, Ohio, United States of America
- Department of Mechanical Engineering, University of Akron, Ohio, United States of America
- * E-mail:
| | - Wojciech Kalata
- Spraying Systems Inc., Wheaton, Illinois, United States of America
| | - Nicholas Shaffer
- Conquer Chiari Research Center, University of Akron, Ohio, United States of America
- Department of Mechanical Engineering, University of Akron, Ohio, United States of America
| | - Paul Fischer
- Mathematics and Computer Science Division, Argonne National Laboratory, Illinois, United States of America
| | - Mark Luciano
- Department of Neurosurgery, Cleveland Clinic Foundation, Ohio, United States of America
| | - Francis Loth
- Conquer Chiari Research Center, University of Akron, Ohio, United States of America
- Department of Mechanical Engineering, University of Akron, Ohio, United States of America
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Berard X, Déglise S, Alonso F, Saucy F, Meda P, Bordenave L, Corpataux JM, Haefliger JA. Role of hemodynamic forces in the ex vivo arterialization of human saphenous veins. J Vasc Surg 2013; 57:1371-82. [PMID: 23351647 DOI: 10.1016/j.jvs.2012.09.041] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2012] [Revised: 08/31/2012] [Accepted: 09/10/2012] [Indexed: 10/27/2022]
Abstract
BACKGROUND Human saphenous vein grafts are one of the salvage bypass conduits when endovascular procedures are not feasible or fail. Understanding the remodeling process that venous grafts undergo during exposure to arterial conditions is crucial to improve their patency, which is often compromised by intimal hyperplasia. The precise role of hemodynamic forces such as shear stress and arterial pressure in this remodeling is not fully characterized. The aim of this study was to determine the involvement of arterial shear stress and pressure on vein wall remodeling and to unravel the underlying molecular mechanisms. METHODS An ex vivo vein support system was modified for chronic (up to 1 week), pulsatile perfusion of human saphenous veins under controlled conditions that permitted the separate control of arterial shear stress and different arterial pressure (7 mm Hg or 70 mm Hg). RESULTS Veins perfused for 7 days under high pressure (70 mm Hg) underwent significant development of a neointima compared with veins exposed to low pressure (7 mm Hg). These structural changes were associated with altered expression of several molecular markers. Exposure to an arterial shear stress under low pressure increased the expression of matrix metalloproteinase (MMP)-2 and MMP-9 and tissue inhibitor of metalloproteinase (TIMP)-1 at the transcript, protein, and activity levels. This increase was enhanced by high pressure, which also increased TIMP-2 protein expression despite decreased levels of the cognate transcript. In contrast, the expression of plasminogen activator inhibitor-1 increased with shear stress but was not modified by pressure. Levels of the venous marker Eph-B4 were decreased under arterial shear stress, and levels of the arterial marker Ephrin-B2 were downregulated under high-pressure conditions. CONCLUSIONS This model is a valuable tool to identify the role of hemodynamic forces and to decipher the molecular mechanisms leading to failure of human saphenous vein grafts. Under ex vivo conditions, arterial perfusion is sufficient to activate the remodeling of human veins, a change that is associated with the loss of specific vein markers. Elevation of pressure generates intimal hyperplasia, even though veins do not acquire arterial markers. CLINICAL RELEVANCE The pathological remodeling of the venous wall, which leads to stenosis and ultimately graft failure, is the main limiting factor of human saphenous vein graft bypass. This remodeling is due to the hemodynamic adaptation of the vein to the arterial environment and cannot be prevented by conventional therapy. To develop a more targeted therapy, a better understanding of the molecular mechanisms involved in intimal hyperplasia is essential, which requires the development of ex vivo models of chronic perfusion of human veins.
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Affiliation(s)
- Xavier Berard
- Department of Vascular Surgery, Pellegrin Hospital, University of Bordeaux, Bordeaux, France
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Sahtout W, Salah RB. Influence of the distensibility of large arteries on the longitudinal impedance: application for the development of non-invasive techniques to the diagnosis of arterial diseases. NONLINEAR BIOMEDICAL PHYSICS 2012; 6:2. [PMID: 22507310 PMCID: PMC3442960 DOI: 10.1186/1753-4631-6-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/27/2011] [Accepted: 03/15/2012] [Indexed: 05/31/2023]
Abstract
BACKGROUND This study shows that the arterial longitudinal impedance constitutes a hemodynamic parameter of interest for performance characterization of large arteries in normal condition as well as in pathological situations. For this purpose, we solved the Navier-Stokes equations for an incompressible flow using the finite element analysis method and the Arbitrary Lagrangian Eulerian (ALE) formulation. The mathematical model assumes a two-dimensional flow and takes into account the nonlinear terms in the equations of fluid motion that express the convective acceleration, as well as the nonlinear deformation of the arterial wall. Several numerical simulations of the blood flow in large vessels have been performed to study the propagation along an arterial vessel of a pressure gradient pulse and a rate flow pulse. These simulations include various deformations of the wall artery leading to parietal displacements ranging from 0 (rigid wall) to 15% (very elastic wall) in order to consider physiological and pathological cases. RESULTS The results show significant changes of the rate flow and the pressure gradient wave as a function of aosc, the relative variation in the radius of the artery over a cardiac cycle. These changes are notable beyond a critical value of aosc equal to 0.05. This critical value is also found in the evolution of the longitudinal impedance. So, above a variation of radius of 5%, the convective acceleration, created by the fluid-wall interactions, have an influence on the flow detectable on the longitudinal impedance. CONCLUSIONS The interpretation of the evolution of the longitudinal impedance shows that it could be a mean to test the performance of large arteries and can contribute to the diagnosis of parietal lesions of large arteries. For a blood vessel with a wall displacement higher than 5% similar to those of large arteries like the aorta, the longitudinal impedance is substantially greater than that obtained in the absence of wall displacement. This study also explains the effects of convective acceleration, on the shape of the decline of the pressure gradient wave and shows that they should not be neglected when the variation in radius is greater than 5%.
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Affiliation(s)
- Wassila Sahtout
- Biomedical Engineering Department, Higher Institute of Biotechnology of Sfax, Route de la Soukra BP261, 3032, Sfax, Tunisie
- Unit of research of Biophysics, Faculty of Medicine of Sousse, Sousse, Tunisie
| | - Ridha Ben Salah
- Unit of research of Biophysics, Faculty of Medicine of Sousse, Sousse, Tunisie
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Spiguel LRP, Chandiwal A, Vosicky JE, Weichselbaum RR, Skelly CL. Concomitant proliferation and caspase-3 mediated apoptosis in response to low shear stress and balloon injury. J Surg Res 2010; 161:146-55. [PMID: 19482308 PMCID: PMC2906117 DOI: 10.1016/j.jss.2008.11.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2008] [Revised: 10/28/2008] [Accepted: 11/03/2008] [Indexed: 12/28/2022]
Abstract
BACKGROUND Arterial remodeling occurs as a response to hemodynamic change and direct vessel wall injury through the process of neointimal hyperplasia (NH). A concomitant response of vascular smooth muscle cell (VSMC) proliferation and apoptosis exists. The purpose of this study is to assess the cellular response of vessels following exposure to low shear stress (tau) and balloon injury in order to further elucidate the mechanisms underlying vascular injury. Our hypothesis is that the combination of low tau and balloon injury results in NH approximating that seen in clinical arterial restenosis, and that quantitative analysis of VSMC proliferation and apoptosis correlates with the associated increase in arterial remodeling. METHODS AND RESULTS New Zealand White rabbits underwent surgery on the carotid artery creating low tau (n =11), balloon injury (n = 11), combined low tau and balloon injury (n =11), and sham (n = 13) groups. Experiments were terminated at 1, 3, and 28 d. Day 1 and 3 arteries were analyzed with immunohistochemistry for apoptotic markers, terminal transferase dUTP nick end labeling (TUNEL), and activated caspase-3, and a cellular proliferation marker, accumulated proliferating cell nuclear antigen (PCNA), as well as immunoblot analysis for activated caspase-3 and PCNA at day 3. There was significantly greater apoptosis in the combined group as compared with the other groups assessed by quantitative TUNEL and activated caspase-3 levels at both days 1 and 3. Similarly, an increase in cellular proliferation assessed by PCNA expression, was significantly greater in the combined group as compared with the other groups. At 28 d there was no difference in NH observed in the low tau (26 +/- 3 microm) and balloon injury (51 +/- 17 microm) groups. However, significantly more NH was observed in the combined group (151 +/- 35 microm) as compared with the other groups. CONCLUSIONS An increase in VSMC apoptosis via a caspase-3 dependent pathway is up-regulated by 24 h in the face of combined low shear stress and balloon-induced vessel wall injury. Paradoxically, this increase in VSMC apoptosis is associated with a significant increase in neointimal thickening at 28 d. The concomitant increase of both apoptosis and proliferation are indicative of a robust arterial remodeling response.
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Affiliation(s)
- Lisa R P Spiguel
- Section of Vascular Surgery, Department of Surgery, University of Chicago, Chicago, Illinois 60637, USA.
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Owens CD. Adaptive changes in autogenous vein grafts for arterial reconstruction: clinical implications. J Vasc Surg 2009; 51:736-46. [PMID: 19837532 DOI: 10.1016/j.jvs.2009.07.102] [Citation(s) in RCA: 111] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2009] [Revised: 07/20/2009] [Accepted: 07/24/2009] [Indexed: 01/22/2023]
Abstract
For patients with the most severe manifestations of lower extremity arterial occlusive disease, bypass surgery using autogenous vein has been the most durable reconstruction. However, the incidence of bypass graft stenosis and graft failure remains substantial and wholesale improvements in patency are lacking. One potential explanation is that stenosis arises not only from over exuberant intimal hyperplasia, but also due to insufficient adaptation or remodeling of the vein to the arterial environment. Although in vivo human studies are difficult to conduct, recent advances in imaging technology have made possible a more comprehensive structural examination of vein bypass maturation. This review summarizes recent translational efforts to understand the structural and functional properties of human vein grafts and places it within the context of the rich existing literature of vein graft failure.
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Affiliation(s)
- Christopher D Owens
- Division of Vascular and Endovascular Surgery, University of California San Francisco, San Francisco, CA 94143, USA.
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Jiang Z, Yu P, Tao M, Fernandez C, Ifantides C, Moloye O, Schultz GS, Ozaki CK, Berceli SA. TGF-beta- and CTGF-mediated fibroblast recruitment influences early outward vein graft remodeling. Am J Physiol Heart Circ Physiol 2007; 293:H482-8. [PMID: 17369455 DOI: 10.1152/ajpheart.01372.2006] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Luminal shearing forces have been shown to impact both geometric remodeling and the development of intimal hyperplasia. Less well studied is the influence of intramural wall stresses on vessel growth and adaptation. Using a vein graft-fistula configuration to isolate the impact of circumferential wall stress, we identify the reorganization of adventitial myofibroblasts as the dominant histological event that limits early outward remodeling of vein grafts in response to elevated wall stress. We hypothesize that increased production of transforming growth factor-beta (TGF-beta) and connective tissue growth factor (CTGF) induces recruitment of myofibroblasts, promotes adventitial reorganization, and limits early outward remodeling in response to increased intramural wall stress. Vein grafts with a distal arteriovenous fistula in the neck of rabbits were constructed, resulting in a fourfold differential in circumferential wall stress. Using this model, we demonstrate 1) elevated wall stress augments the production of TGF-beta and CTGF, 2) increased TGF-beta expression and CTGF expression are correlated with the enhanced differentiation from fibroblasts to myofibroblasts, as evidenced by the significant increase in the alpha-actin-positive cells in adventitia, and 3) the levels of TGF-beta, CTGF, and alpha-actin are inversely correlated with the magnitude of outward remodeling of the graft wall. Increased wall stress after vein graft implantation appears to induce a TGF-beta- and CTGF-mediated recruitment of adventitial fibroblasts and a conversion to a myofibroblast phenotype. Although important in the maintenance of wall stability in the face of an increased mechanical load, this adventitial adaptation limits early outward remodeling of the vein conduit and may prove deleterious in maintaining long-term vein graft patency.
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Affiliation(s)
- Zhihua Jiang
- University of Florida College of Medicine, Gainesville, FL 32610-0286, USA
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Lee SW, Curi MA, Baldwin ZK, Balasubramanian V, Loth F, Schwartz LB. Theoretical hydraulic consequences of vein graft taper. J Vasc Surg 2003; 38:785-92. [PMID: 14560231 DOI: 10.1016/s0741-5214(03)00609-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
OBJECTIVE Internal diameter is a strong predictor of patency of infrainguinal vein grafts. However, most vein grafts are tapered, with variable diameter along their length. It is unknown which diameter is most important in determining graft resistive properties, that is, its mean diameter, minimum diameter, or some geometric combination thereof. The purpose of this analysis was to examine the hydraulic consequences of vein graft tapering, with longitudinal impedance (Z(L)), a conduit-specific measure of pulsatile resistance along straight rigid tubes. METHODS Proximal and distal graft pressure, pressure gradient (DeltaP), and blood flow (Q) were measured intraoperatively in a 100 cm bypass graft and digitally recorded for 10 seconds at 200 Hz. With the Womersley solution for fully developed fluid flow in a rigid tube, a series of DeltaP waveforms were generated for graft diameters ranging from 1.2 to 8.2 mm. With an axisymmetric form of the Navier-Stokes equations, a second series of DeltaP waveforms were computed for grafts with long smooth symmetric tapers ranging from 0% to 90%, with geometric mean diameter of 3.2, 4.2, and 5.2 mm (%Taper = 100 x [proximal diameter - distal diameter]/proximal diameter). For each set of DeltaP and Q, Z(L) was calculated as DeltaP/Q, plotted over a range of 8 Hz, and integrated over 4 Hz to yield integral Z(L). RESULTS The architecture of the calculated DeltaP and Z(L) waveforms closely approximated their measured counterparts, validating the method. As expected, Z(L) was highly diameter-dependent in a nonlinear fashion. With a clinically relevant boundary of less than 50 x 10(3) dyne/cm(5) as "acceptable," the minimum acceptable diameter of nontapered 100 cm bypass conduits was 4.3 mm. Analysis of graft taper revealed that small amounts of taper in large conduits were well-tolerated. For example, introduction of 32% taper in a 5.2 mm graft (6.2 mm --> 4.2 mm) caused only an 8% increase in integral Z(L) (from 32 to 35 x 10(3) dyne/cm(5)). More pronounced taper in smaller conduits rendered them unacceptable. For example, 53% taper of a 4.2 mm graft (5.7 mm --> 2.7 mm) created a conduit with integral Z(L) of 70 x 10(3) dyne/cm(5), well above the acceptable limit. The relationship between Z(L) and percent taper was nonlinear and strongly dependent on mean diameter. CONCLUSIONS The relationship between Z(L) and diameter in vein grafts is nonlinear; thus Z(L) increases rapidly in conduits smaller than 4 mm. Tapered vein grafts behave hydraulically like nontapered grafts, provided their geometric mean is greater than 4 mm and their degree of taper is less than 40%. Tapered veins are satisfactory conduits for long-segment bypass grafts, provided their mean diameter is acceptable.
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Affiliation(s)
- Sang-Wook Lee
- Department of Mechanical and Industrial Engineering, University of Illinois at Chicago, Chicago, IL, USA
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