On reducing abnormal hemodynamics in the femoral end-to-side anastomosis: the influence of mechanical factors

Patient-Specific Hemodynamics of New Coronary Artery Bypass Configurations

PURPOSE

This study aims to quantify the patient-specific hemodynamics of complex conduit routing configurations of coronary artery bypass grafting (CABG) operation which are specifically suitable for off-pump surgeries. Coronary perfusion efficacy and local hemodynamics of multiple left internal mammary artery (LIMA) with sequential and end-to-side anastomosis are investigated. Using a full anatomical model comprised of aortic arch and coronary artery branches the optimum perfusion configuration in multi-vessel coronary artery stenosis is desired.

METHODOLOGY

Two clinically relevant CABG configurations are created using a virtual surgical planning tool where for each configuration set, the stenosis level, anastomosis distance and angle were varied. A non-Newtonian computational fluid dynamics solver in OpenFOAM incorporated with resistance boundary conditions representing the coronary perfusion physiology was developed. The numerical accuracy is verified and results agreed well with a validated commercial cardiovascular flow solver and experiments. For segmental performance analysis, new coronary perfusion indices to quantify deviation from the healthy scenario were introduced.

RESULTS

The first simulation configuration set;-a CABG targeting two stenos sites on the left anterior descending artery (LAD), the LIMA graft was capable of 31 mL/min blood supply for all the parametric cases and uphold the healthy LAD perfusion in agreement with the clinical experience. In the second end-to-side anastomosed graft configuration set;-the radial artery graft anastomosed to LIMA, a maximum of 64 mL/min flow rate in LIMA was observed. However, except LAD, the obtuse marginal (OM) and second marginal artery (m2) suffered poor perfusion. In the first set, average wall shear stress (WSS) were in the range of 4 to 35 dyns/cm² for in LAD. Nevertheless, for second configuration sets the WSS values were higher as the LIMA could not supply enough blood to OM and m2.

CONCLUSION

The virtual surgical configurations have the potential to improve the quality of operation by providing quantitative surgical insight. The degree of stenosis is a critical factor in terms of coronary perfusion and WSS. The sequential anastomosis can be done safely if the anastomosis angle is less than 90 degrees regardless of degree of stenosis. The smaller proposed perfusion index value, O(0.04 - 0) × 10², enable us to quantify the post-op hemodynamic performance by comparing with the ideal healthy physiological flow.

Small diameter helical vascular scaffolds support endothelial cell survival

There is an acute clinical need for small-diameter vascular grafts as a treatment option for cardiovascular disease. Here, we used an intelligent design system to recreate the natural structure and hemodynamics of small arteries. Nano-fibrous tubular scaffolds were fabricated from blends of polyvinyl alcohol and gelatin with inner helices to allow a near physiological spiral flow profile, using the electrospinning technique. Human coronary artery endothelial cells (ECs) were seeded on the inner surface and their viability, distribution, gene expression of mechanosensitive and adhesion molecules compared to that in conventional scaffolds, under static and flow conditions. We show significant improvement in cell distribution in helical vs. conventional scaffolds (94% ± 9% vs. 82% ± 7.2%; P < 0.05) with improved responsiveness to shear stress and better ability to withhold physiological pressures. Our helical vascular scaffold provides an improved niche for EC growth and may be attractive as a potential small diameter vascular graft.

Axillobifemoral Bypasses: Reappraisal of an Extra-Anatomic Bypass by Analysis of Results and Prognostic Factors

BACKGROUND

Axillobifemoral bypass (AFB) is method of second choice. It is reserved for patients at high operative risk or to bypass infected vessels or grafts. In this study, we analyzed prognostic factors for AFB patency and limb salvage rate to facilitate the choice of procedure.

METHODS

Between Jan 2006 and Aug 2013, 45 patients underwent AFB surgery in our department, 24 for critical limb ischemia (CLI) and 23 for infection. Endpoints of study were graft occlusion, graft infection, amputation and patient's death. Prognostic factors were compared by univariate analysis for each indication group. Mean follow-up was 40.2 (±23.2) months.

RESULTS

Complication rate was significantly higher in infection group (88.0 vs. 54.4%, p = 0.003) and in emergency surgery (83.3 vs. 56.9%, p = 0.023). Overall primary patency rate after AFB procedures was 66.7% after 1, 3, and 5 years, while secondary patency rate was 91.1% after 1 year, 82.2% after 3 years and 80.0% after 5 years. The primary and secondary patency rates did not significantly differ between the both groups (p = 0.059 and p = 0.136). Following prognostic factors showed a statistically significant influence on patency rates in CLI group: >1 previous vascular surgical intervention, patch angioplasty at the distal anastomosis site, complications after previous vascular surgery, and perioperative intake of platelet aggregation inhibitor. Only the employed bypass material had a statistical significant influence on the secondary patency rates in the infection group. Overall limb salvage rate was 82.2% after 1 year, 80.0% after 3 years and 77.8% after 5 years. There were statistically significant differences in the limb salvage rates depending on emergency surgery and a 3-vessel-run-off in the lower leg in both indication groups.

CONCLUSION

AFB have acceptable patency and limb salvage rates. AFB is a good alternative in patients with CLI at high operative risk or with infections of aortoiliac segments, even with endovascular approaches. They remain essential tools in vascular surgeon's repertoire.

The Tissue-Engineered Vascular Graft-Past, Present, and Future

Cardiovascular disease is the leading cause of death worldwide, with this trend predicted to continue for the foreseeable future. Common disorders are associated with the stenosis or occlusion of blood vessels. The preferred treatment for the long-term revascularization of occluded vessels is surgery utilizing vascular grafts, such as coronary artery bypass grafting and peripheral artery bypass grafting. Currently, autologous vessels such as the saphenous vein and internal thoracic artery represent the gold standard grafts for small-diameter vessels (<6 mm), outperforming synthetic alternatives. However, these vessels are of limited availability, require invasive harvest, and are often unsuitable for use. To address this, the development of a tissue-engineered vascular graft (TEVG) has been rigorously pursued. This article reviews the current state of the art of TEVGs. The various approaches being explored to generate TEVGs are described, including scaffold-based methods (using synthetic and natural polymers), the use of decellularized natural matrices, and tissue self-assembly processes, with the results of various in vivo studies, including clinical trials, highlighted. A discussion of the key areas for further investigation, including graft cell source, mechanical properties, hemodynamics, integration, and assessment in animal models, is then presented.

Effect of swirling blood flow on vortex formation at post-stenosis

Various clinical observations reported that swirling blood flow is a normal physiological flow pattern in various vasculatures. The swirling flow has beneficial effects on blood circulation through the blood vessels. It enhances oxygen transfer and reduces low-density lipoprotein concentration in the blood vessel by enhancing cross-plane mixing of the blood. However, the fluid-dynamic roles of the swirling flow are not yet fully understood. In this study, inhibition of material deposition at the post-stenosis region by the swirling flow was observed. To reveal the underlying fluid-dynamic characteristics, pathline flow visualization and time-resolved particle image velocimetry measurements were conducted. Results showed that the swirling inlet flow increased the development of vortices at near wall region of the post-stenosis, which can suppress further development of stenosis by enhancing transport and mixing of the blood flow. The fluid-dynamic characteristics obtained in this study would be useful for improving hemodynamic characteristics of vascular grafts and stents in which the stenosis frequently occurred. Moreover, the time-resolved particle image velocimetry measurement technique and vortex identification method employed in this study would be useful for investigating the fluid-dynamic effects of the swirling flow on various vascular environments.

Why Patencies of Femoropopliteal Bypass Grafts with Distal End-to-End Anastomosis are Comparable with End-to-Side Anastomosis

OBJECTIVE

Despite the theoretical favourable hemodynamic advantage of end-to-end anastomosis (ETE), femoropopliteal bypasses with distal ETE and end-to-side anastomosis (ETS) have comparable clinical patencies. We therefore studied the effects of different in vivo anastomotic configurations on hemodynamics in geometrically realistic ETE and ETS in vitro flow models to explain this phenomenon.

METHODS

Four ETE and two ETS models (30° and 60°) were constructed from in vivo computed tomography angiography data. With flow visualization physiological flow conditions were studied.

RESULTS

In ETS, a flow separation and recirculation zone was apparent at anastomotic edges with a shifting stagnation point between them during systole. Secondary flow patterns developed with flow deceleration and reversal. Slight out of axis geometry of all ETE resulted in flow separation and recirculation areas comparable to ETS. Vertical flow patterns were more stable in wider and longer bevelled ETE.

CONCLUSION

Primary flow disturbances in ETE are comparable to ETS and are related to the typical sites where myointimal hyperplasia develops. In ETS, reduction of anastomosis angle will diminish flow disturbances. To reduce flow disturbances in ETE, the creation of a bulbous spatulation with resulting axial displacement of graft in relation to recipient artery should be prevented.

Coronary artery bypass grafting hemodynamics and anastomosis design: a biomedical engineering review

In this paper, coronary arterial bypass grafting hemodynamics and anastomosis designs are reviewed. The paper specifically addresses the biomechanical factors for enhancement of the patency of coronary artery bypass grafts (CABGs). Stenosis of distal anastomosis, caused by thrombosis and intimal hyperplasia (IH), is the major cause of failure of CABGs. Strong correlations have been established between the hemodynamics and vessel wall biomechanical factors and the initiation and development of IH and thrombus formation. Accordingly, several investigations have been conducted and numerous anastomotic geometries and devices have been designed to better regulate the blood flow fields and distribution of hemodynamic parameters and biomechanical factors at the distal anastomosis, in order to enhance the patency of CABGs. Enhancement of longevity and patency rate of CABGs can eliminate the need for re-operation and can significantly lower morbidity, and thereby reduces medical costs for patients suffering from coronary stenosis. This invited review focuses on various endeavors made thus far to design a patency-enhancing optimized anastomotic configuration for the distal junction of CABGs.

Evaluation of a novel vascular graft with a distal bifurcation designed to reduce the development of intimal hyperplasia. Experimental study in a porcine aorta model

OBJECTIVE

Abnormal haemodynamics is commonly agreed to be a major contributor to the development of distal anastomotic intimal hyperplasia. A new vascular graft design proposed by computational studies was used to demonstrate its surgical feasibility and to compare it with the conventional graft in a porcine model.

METHOD

The device was used in 12 eight-month-old pigs, six received the new graft and six had a conventional graft. The proximal graft end was implanted into the aorta, the distal graft end was implanted into the iliac artery. The host artery was ligated in order to simulate occlusion. At 20 weeks after surgery the pigs were killed and the device was excised for histological and morphometric analysis.

RESULTS

In five experimental grafts the reconstruction was occluded due to thrombosis; only one prosthesis was patent showing a minimum of neointimal hyperplasia. In the control group too only three of the six grafts were patent. A histological analysis revealed, as the cause of occlusion, fibrous tissue overgrowth corresponding in structure to neointimal hyperplasia. Differences in the number of obliterations and in occlusion rates between the profiles of the two groups were evaluated using the median test (P<0.05). The results were not statistically significant.

CONCLUSION

Although mathematical modelling had shown significant haemodynamic benefits of a naturally bifurcated graft, our study did not confirm its superiority over conventionally used prostheses.

Effect of anastomosis angle on the localization of disturbed flow in 'side-to-end' fistulae for haemodialysis access

BACKGROUND

Early failure of the vascular access for haemodialysis (HD) after the surgical creation of a radial-cephalic arteriovenous fistula (AVF) occurs mainly due to a juxta-anastomotic stenosis. Even if elevated blood flow induces high wall shear stress, we have recently shown that disturbed flow, characterized by low and reciprocating flow, may develop in zones of the AVF where it can provide a good indication of the sites of future stenoses. The present study was aimed at investigating whether the anastomosis angle influences disturbed flow in radial-cephalic 'side-to-end' AVF.

METHODS

By means of a parametric AVF model we created four equivalent meshes with anastomosis angles of 30°, 45°, 60° and 90°, respectively. We then performed transient, non-Newtonian computational fluid dynamics simulations using, as boundary conditions, previously measured blood volume flow and division ratio in subjects requiring primary access. The relative residence time (RRT), a robust indicator of disturbed flow, was calculated for the overall wall surface and disturbed flow was localized as areas having RRT > 1. Quantitative characterization and statistical tests were employed to assess the difference in RRT medians between the four anastomosis angle cases.

RESULTS

Disturbed flow was located in all AVF models in the same areas where flow recirculation and stagnation occurred, on the inner wall of the swing segment (SS) and on the arterial wall at the anastomosis floor (AF). A smaller angle AVF had smaller disturbed flow areas with lower RRT peak values, either on the venous or the arterial limb. There were significant differences in the RRT medians on the SS and on the AF between sharper (30° and 45°) and wider (60° or 90°) angles.

CONCLUSIONS

We have found that in 'side-to-end' radial-cephalic AVFs for HD, the anastomosis angle does impact on the local disturbed flow patterns. Among the four geometries we considered in this study, the smaller angle (30°) would be the preferred choice that minimizes the development of neointima. Clinicians should consider this at the time of AVF creation because the anastomosis angle is in part amenable to surgical manipulation.

Wall shear stresses remain elevated in mature arteriovenous fistulas: a case study

Maintaining vascular access (VA) patency continues to be the greatest challenge for dialysis patients. VA dysfunction, primarily due to venous neointimal hyperplasia development and stenotic lesion formation, is mainly attributed to complex hemodynamics within the arteriovenous fistula (AVF). The effect of VA creation and the subsequent geometrical remodeling on the hemodynamics and shear forces within a mature patient-specific AVF is investigated. A 3D reconstructed geometry of a healthy vein and a fully mature patient-specific AVF was developed from a series of 2D magnetic resonance image scans. A previously validated thresholding technique for region segmentation and lumen cross section contour creation was conducted in MIMICS 10.01, allowing for the creation of a 3D reconstructed geometry. The healthy vein and AVF computational models were built, subdivided, and meshed in GAMBIT 2.3. The computational fluid dynamic (CFD) code FLUENT 6.3.2 (Fluent Inc., Lebanon, NH) was employed as the finite volume solver to determine the hemodynamics and shear forces within the healthy vein and patient-specific AVF. Geometrical alterations were evaluated and a CFD analysis was conducted. Substantial geometrical remodeling was observed, following VA creation with an increase in cross-sectional area, out of plane curvature (maximum angle of curvature in AVF=30 deg), and angle of blood flow entry. The mean flow velocity entering the vein of the AVF is dramatically increased. These factors result in complex three-dimensional hemodynamics within VA junction (VAJ) and efferent vein of the AVF. Complex flow patterns were observed and the maximum and mean wall shear stress (WSS) magnitudes are significantly elevated. Flow reversal was found within the VAJ and efferent vein. Extensive geometrical remodeling during AVF maturation does not restore physiological hemodynamics to the VAJ and venous conduit of the AVF, and high WSS and WSS gradients, and flow reversal persist. It is theorized that the vessel remodelling and the continued non-physiological hemodynamics within the AVF compound to result in stenotic lesion development.

Computer-Aided Patient-Specific Coronary Artery Graft Design Improvements Using CFD Coupled Shape Optimizer

This study aims to (i) demonstrate the efficacy of a new surgical planning framework for complex cardiovascular reconstructions, (ii) develop a computational fluid dynamics (CFD) coupled multi-dimensional shape optimization method to aid patient-specific coronary artery by-pass graft (CABG) design and, (iii) compare the hemodynamic efficiency of the sequential CABG, i.e., raising a daughter parallel branch from the parent CABG in patient-specific 3D settings. Hemodynamic efficiency of patient-specific complete revascularization scenarios for right coronary artery (RCA), left anterior descending artery (LAD), and left circumflex artery (LCX) bypasses were investigated in comparison to the stenosis condition. Multivariate 2D constraint optimization was applied on the left internal mammary artery (LIMA) graft, which was parameterized based on actual surgical settings extracted from 2D CT slices. The objective function was set to minimize the local variation of wall shear stress (WSS) and other hemodynamic indices (energy dissipation, flow deviation angle, average WSS, and vorticity) that correlate with performance of the graft and risk of re-stenosis at the anastomosis zone. Once the optimized 2D graft shape was obtained, it was translated to 3D using an in-house "sketch-based" interactive anatomical editing tool. The final graft design was evaluated using an experimentally validated second-order non-Newtonian CFD solver incorporating resistance based outlet boundary conditions. 3D patient-specific simulations for the healthy coronary anatomy produced realistic coronary flows. All revascularization techniques restored coronary perfusions to the healthy baseline. Multi-scale evaluation of the optimized LIMA graft enabled significant wall shear stress gradient (WSSG) relief (~34%). In comparison to original LIMA graft, sequential graft also lowered the WSSG by 15% proximal to LAD and diagonal bifurcation. The proposed sketch-based surgical planning paradigm evaluated the selected coronary bypass surgery procedures based on acute hemodynamic readjustments of aorta-CA flow. This methodology may provide a rational to aid surgical decision making in time-critical, patient-specific CA bypass operations before in vivo execution.

Characterization of vascular strain during in-vitro angioplasty with high-resolution ultrasound speckle tracking

Background

Ultrasound elasticity imaging provides biomechanical and elastic properties of vascular tissue, with the potential to distinguish between tissue motion and tissue strain. To validate the ability of ultrasound elasticity imaging to predict structurally defined physical changes in tissue, strain measurement patterns during angioplasty in four bovine carotid artery pathology samples were compared to the measured physical characteristics of the tissue specimens.

Methods

Using computational image-processing techniques, the circumferences of each bovine artery specimen were obtained from ultrasound and pathologic data.

Results

Ultrasound-strain-based and pathology-based arterial circumference measurements were correlated with an R² value of 0.94 (p = 0.03). The experimental elasticity imaging results confirmed the onset of deformation of an angioplasty procedure by indicating a consistent inflection point where vessel fibers were fully unfolded and vessel wall strain initiated.

Conclusion

These results validate the ability of ultrasound elasticity imaging to measure localized mechanical changes in vascular tissue.

Experimental validation of convection-diffusion discretisation scheme employed for computational modelling of biological mass transport

BACKGROUND

The finite volume solver Fluent (Lebanon, NH, USA) is a computational fluid dynamics software employed to analyse biological mass-transport in the vasculature. A principal consideration for computational modelling of blood-side mass-transport is convection-diffusion discretisation scheme selection. Due to numerous discretisation schemes available when developing a mass-transport numerical model, the results obtained should either be validated against benchmark theoretical solutions or experimentally obtained results.

METHODS

An idealised aneurysm model was selected for the experimental and computational mass-transport analysis of species concentration due to its well-defined recirculation region within the aneurysmal sac, allowing species concentration to vary slowly with time. The experimental results were obtained from fluid samples extracted from a glass aneurysm model, using the direct spectrophometric concentration measurement technique. The computational analysis was conducted using the four convection-diffusion discretisation schemes available to the Fluent user, including the First-Order Upwind, the Power Law, the Second-Order Upwind and the Quadratic Upstream Interpolation for Convective Kinetics (QUICK) schemes. The fluid has a diffusivity of 3.125 x 10-10 m2/s in water, resulting in a Peclet number of 2,560,000, indicating strongly convection-dominated flow.

RESULTS

The discretisation scheme applied to the solution of the convection-diffusion equation, for blood-side mass-transport within the vasculature, has a significant influence on the resultant species concentration field. The First-Order Upwind and the Power Law schemes produce similar results. The Second-Order Upwind and QUICK schemes also correlate well but differ considerably from the concentration contour plots of the First-Order Upwind and Power Law schemes. The computational results were then compared to the experimental findings. An average error of 140% and 116% was demonstrated between the experimental results and those obtained from the First-Order Upwind and Power Law schemes, respectively. However, both the Second-Order upwind and QUICK schemes accurately predict species concentration under high Peclet number, convection-dominated flow conditions.

CONCLUSION

Convection-diffusion discretisation scheme selection has a strong influence on resultant species concentration fields, as determined by CFD. Furthermore, either the Second-Order or QUICK discretisation schemes should be implemented when numerically modelling convection-dominated mass-transport conditions. Finally, care should be taken not to utilize computationally inexpensive discretisation schemes at the cost of accuracy in resultant species concentration.

Vascular cell adhesion molecule-1 expression in endothelial cells exposed to physiological coronary wall shear stresses

Atherosclerosis is consistently found in bifurcations and curved segments of the circulatory system, indicating disturbed hemodynamics may participate in disease development. In vivo and in vitro studies have shown that endothelial cells (ECs) alter their gene expression in response to their hemodynamic environment, in a manner that is highly dependent on the exact nature of the applied forces. This research exposes cultured ECs to flow patterns present in the coronary arterial network, in order to determine the role of hemodynamic forces in plaque initiation. Vascular cell adhesion molecule-1 (VCAM-1) was examined as an indicator of plaque growth, as it participates in monocyte adhesion, which is one of the initial steps in the formation of fatty lesions. The hemodynamics of a healthy right and left coronary artery were determined by reconstructing 3D models from cineangiograms and employing computational fluid dynamic models to establish physiological coronary flow patterns. Wall shear stress (WSS) profiles selected from these studies were applied to ECs in a cone and plate bioreactor. The cone and plate system was specifically designed to be capable of reproducing the high frequency harmonics present in physiological waveforms. The shear stresses chosen represent those from regions prone to disease development and healthier arterial segments. The levels of the transcriptional and cell surface anchored VCAM-1 were quantified by flow cytometry and real time RT-PCR over a number of timepoints to obtain a complete picture of the relationship between this adhesion molecule and the applied shear stress. The WSS profiles from regions consistently displaying a higher incidence of plaques in vivo, induced greater levels of VCAM-1, particularly at the earlier timepoints. Conversely, the WSS profile from a straight section of vessel with undisturbed flow indicated no upregulation in VCAM-1 and a significant downregulation after 24 h, when compared with static controls. Low shear stress from the outer wall of a bifurcation induced four times the levels of VCAM-1 messenger ribonucleic acid (mRNA) after four hours when compared with levels of mRNA induced by WSS from a straight arterial section. This shear profile also induced prolonged expression of the surface protein of this molecule. The current study has provided insight into the possible influences of coronary hemodynamics on plaque localization, with VCAM-1 only significantly induced by the WSS from disease prone regions.

Surgical Feasibility Study of a Novel Polytetrafluoroethylene Graft Design for the Treatment of Peripheral Arterial Disease

Disturbed flow patterns, material mismatch, and surgical injury are often cited as being significant contributors to failure at the distal end of femoropopliteal bypass grafts. The objective of this research is to propose a novel bypass graft design concept which seeks to reduce the incidence of disturbed flow in the bypass junction and to establish the surgical feasibility of the proposed device. A preliminary evaluation of the hemodynamic benefit associated with the proposed device was made using computational fluid dynamics. A prototype of the device was then constructed from commercially available materials, and it was prepared for implantation into the aorta of a pig. The computational model of the proposed device showed that significant flow correction was occurring in the in vitro model due to the geometric configuration of the design. The magnitude of the peak wall shear stress in the recirculation region was noted to decrease by 78%. Surgical feasibility of the proposed device was verified by successful implantation into the aorta of the pig. The pig was sacrificed after 7 weeks, the graft and host artery were excised, and histological examination downstream from the distal junction showed that intimal hyperplasia had developed in the host artery. The proposed device is surgically feasible and may offer a significant hemodynamic advantage over current graft designs.

Mass Transport Disturbances in the Distal Graft/Artery Junction of a Peripheral Bypass Graft

Intimal hyperplasia (IH) development is a primary cause of failure of reconstructive bypass surgery. While the exact mechanism by which IH initiates and proliferates has yet to be fully elucidated, it is clear that the abnormal haemodynamics present in the downstream graft/artery junction are intrinsic in its development. Mass transport disturbances owing to abnormal haemodynamics have been associated with atherogenesis and it is for this reason that an investigation into transport of platelet-derived growth factor (PDGF), a known promoter of the intimal hyperplastic response, at the downstream graft/artery junction was carried out. A steady flow analysis in a three-dimensional, idealized, downstream graft/artery junction was carried out using commercial computational fluid dynamics software. It was found that there is a two-and-half fold increase in the transport of PDGF to the artery wall at the bed of the junction when compared with an idealized, healthy artery. The presence of secondary flows in the downstream arterial section also leads to large disturbances in mass transport. It was concluded that PDGF transport in the downstream graft/artery junction tends to be highly disturbed and that there may be a role of this disturbance in the initiation and subsequent development of distal anastomotic intimal hyperplasia.

Injection-moulded models of major and minor arteries: the variability of model wall thickness owing to casting technique

Cardiovascular disease of major and minor arteries is a common cause of death in Western society. The wall mechanics and haemodynamics within the arteries are considered to be important factors in the disease formation process. This paper is concerned with the development of an efficient computer-integrated technique to manufacture idealized and realistic models of diseased major and minor arteries from radiological images and to address the issue of model wall thickness variability. Variations in wall thickness from the original computer models to the final castings are quantified using a CCD camera. The results found that wall thickness variation from the major and minor idealized artery models to design specification were insignificant, up to a maximum of 16 per cent. In realistic models, however, differences were up to 23 per cent in the major arterial models and 58 per cent in the minor arterial models, but the wall thickness variability remained within the limits of previously reported wall thickness results. It is concluded that the described injection moulding procedure yields idealized and realistic castings suitable for use in experimental investigations, with idealized models giving better agreement with design. Wall thickness is variable and should be assessed after the models are manufactured.