agar and Arteriosclerosis

Ultrasonic contrast agents are currently being developed to target and bind to specific areas of interest such as atheromous plaque. A microbubble has been developed in-house which can be targeted to attach to specific cell-lines. To assess the feasibility of using the microbubble in vivo, the shear stresses which the bound microbubbles can withstand need to be known. A flow chamber was developed for use with intravascular ultrasound (IVUS) and laser Doppler anemometry (LDA). Biotin was incorporated into the microbubble shells and streptavidin was used to attach them to agar. IVUS at 40 MHz was then used to image the attached microbubbles under steady flow at a range of flow rates from 75 to 480 mL min(-1) through a flow area of 9 mm(2). LDA was employed to find high resolution velocity profiles of the flow in the chamber at a selection of these flow rates and the shear stresses on the bubbles were calculated. The bubbles were found to remain attached to the agar for shear stresses of up to 3.4 Pa. This compares with mean physiological arterial shear stresses of less than 1.5 Pa for pulsatile flow.

Topics: Agar; Arteriosclerosis; Biotin; Contrast Media; Humans; Laser-Doppler Flowmetry; Microbubbles; Pulsatile Flow; Rheology; Streptavidin; Stress, Mechanical; Ultrasonography, Interventional

A Nd-YAG laser (1064 nm) coupled to a silica fiber (0.6 mm core diameter) was used to create defects in a model of arterial vascular obstruction. We employed transparent agar doped with black ink as atheromatous material and studied the size and shape of defects created by various lasing parameter settings. By adding calcium sulphate to the agar its scattering properties were enhanced. The created defects correspond to a temperature boundary. The optical properties of the agar greatly influenced the size and shape of the created defects. In the agar with enhanced scattering properties, the created defects showed an unfavourable penetration width-depth ratio. Maximum width of penetration always exceeded the fiber diameter. This may contribute to an increased risk of vessel wall perforation in small vessels and, if the fiber is positioned close to the vessel wall, even when a coaxial position is maintained. With increasing cumulative energy, both maximum depth and width of penetration leveled off in both agars. The results suggest that agar can be used to obtain empirically the lasing parameters that will minimize the risk of vessel wall perforation by an axially positioned fiber. The agar model needs further study to determine its limitations, but agar seems to be a useful substitute for atheroma in the study of laser catheter angioplasty.

Topics: Agar; Angioplasty, Balloon; Arteriosclerosis; Humans; Laser Therapy; Models, Biological

Discs of agar gel mixed with ink were used to study ablation effects with an argon laser as a light source. Varying amounts of ink were added resulting in a variation of the attenuation coefficient between 0.45 and 6.3 mm-1. For laser beam irradiation horizontally incident on a vertical sample, the average velocity of ablation was found to be approximately constant for thicknesses up to 1.7 mm. When the laser beam was directed vertically on a sample held horizontally, the vaporized debris present in the beam attenuated the incident laser energy to such a degree that the average ablation velocity decreased by a factor of approximately five. Horizontal beam experiments for various attenuation coefficients showed that an attenuation coefficient of about 1.7 mm-1 is optimal for fast penetration of discs thicker than 4 mm. Thus, based upon the optical properties of a given tissue, there may exist an optimum laser wavelength to maximise ablation velocity.

Topics: Agar; Arteriosclerosis; Humans; Laser Therapy; Models, Biological; Thrombosis

Topics: Agar; Arteriosclerosis; C-Reactive Protein; Humans; Immune Sera; Immunodiffusion

Topics: Agar; Animals; Antigens; Aorta; Aortic Diseases; Arteriosclerosis; Chemical Precipitation; Humans; Immunoelectrophoresis; Rabbits

Topics: Agar; Animals; Aorta; Arteries; Arteriosclerosis; Autoradiography; Chemical Precipitation; Cholesterol; Diet, Atherogenic; Electrophoresis; Epinephrine; Glycosaminoglycans; Immunoelectrophoresis; In Vitro Techniques; Lipid Metabolism; Lipids; Lipoproteins; Methods; Phospholipids; Rabbits; Triglycerides; Tritium