Mechanical Properties of Human Saphenous Vein K. Paranjothi1, U. Saravanan2, R. KrishnaKumar3, K.R. Balakrishnan4 1Research scholar, Department of Engineering Design, IIT Madras. Email: kpjothi@iitm.ac.in 2Assistant Professor, Department of Civil Engineering, IIT Madras. Email: saran@iitm.ac.in 3Professor, Department of Engineering Design, IIT Madras. Email: rkkumar@iitm.ac.in 4Director, Cardiovascular Surgery, Malar Hospitals. Email: cvskrb@gmail.com ABSTRACT Details about custom built experimental set up to perform inflation tests at constant length on blood vessels are presented. Using this displacement controlled set up we can apply and measure pressures up to 100 kPa and axial loads ranging up to 100 N. The surface deformation is determined from tracking twelve markers in 3D space using 2 CCD cameras. Discarded vein tissue from patients undergoing Coronary bypass surgery were collected and stored at 4oC in normal saline and experiments were completed within 24 hours from harvest. Inflation tests at different axial stretch ratios on saphenous vein were conducted. Results show that the deformation of the vein is not axially symmetric. These suggest that the vein is inhomogeneous and/or residually stressed not only in the radial direction, but also in the circumferential and/or axial direction. The loading and unloading path is not different, suggesting that the vein is being subjected to non-dissipative process. Checking for the incompressibility condition, results show that the vein is compressible. These results have implications in the development of constitutive models for the vein. Introduction The great saphenous vein (GSV) is the large (subcutaneous) superficial vein of the leg and thigh and is used widely in coronary artery bypass grafting (CABG). In order to understand how it adopts to changes in its mechanical environment it is important to know the stress and deformation field experienced by this vein due to the altered mechanical environment. For this one requires to develop a constitutive relation for these veins [1, 2]. These constitutive relations would help determine how the graft material has to be handled by the surgeons so that the vein does not get damaged [3]. Because of these needs mechanical tests on GSV has been performed [3-7] but to the knowledge of the authors a constitutive relation for the same has not been reported. This article details experiments conducted on GSV towards arriving at a constitutive relation. Though salient conclusions pertaining to the development of a constitutive relation is arrived at, no such relation is proposed. It is found that the GSV is compressible and is heterogeneous and residually stressed not only along the radial direction but also along the circumferential and/or axial direction. These have implications in the development of constitutive relation for the vein. 2 Material and Methods 2.1 Details of the Experimental Setup The experimental set-up to perform inflation tests at constant length consists of three subsystems. First, a video based system that allows 3D tracking of up to 12 surface markers. By tracking the movement of the surface markers during the experiment the deformation field is found from which the principal invariants of the right Cauchy-Green deformation tensor is obtained. This system consists of two charged couple device (CCD) camera(AVT GUPPY F-146 B) with 1390 by 1040 pixel resolution, each connected to a PCI card (AVT 1394a adapter) and a micro-lens (NAVITAR zoom 6000 lens with 3mm fine focus and internal coaxial illuminator attached to a 1x adapter) whose magnification can be varied from 0.7x to 4x. The lens with a working distance of 92mm, has a field of view of 10mm at 0.7x magnification and 2mm at 4x magnification. The depth of field also varies from 1mm at low magnification to 0.1mm at high magnification. The camera can capture at most 17 frames per second. While one of the camera is vertical, the other is inclined at 45 degrees in the vertical plane (see figure - 1). The camera and the lens are mounted on damped mounting rods using a custom designed mounting system. Second subsystem consists of two computer controlled linear translation stages to apply axial displacement and a syringe pump to inflate the arteries. As seen in figure 1, on top of each of these stages, manually controlled precision stages (25mm travel, 0:01mm resolution) is provided for each of the two directions to allow positioning of the specimen accurately in the field of T. Proulx (ed.), Mechanics of Biological Systems and Materials, Volume 2, Conference Proceedings of the Society for Experimental Mechanics Series 9999, DOI 10.1007/978-1-4614-0219-0_10, © The Society for Experimental Mechanics, Inc. 2011 79
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