| Summary: | Laser assisted vascular anastomosis has been reported to have potential advantages over sutured anastomosis, such as reduced operating time, reduced foreign body reactions and lower potential for vessel constriction. The anastomosis of graft material during coronary bypass surgery is one possible use of laser anastomosis. Although laser anastomosis has achieved some success, a major limitation of the approach has been the lack of knowledge regarding the optimal laser exposure necessary to produce a consistent weld. The first section of this thesis describes an investigation into the interaction of light within vascular tissue. Utilising the conventional kubelka-Munk treatment of reflectance and transmission measurements, values of the absorption and scattering coefficients were obtained. Additionally, spatially resolved reflection measurements, (typically used for determining the optical properties of highly scattering homogenious samples such as silica and aluminium oxide), were performed on sections of porcine aorta to determine absorption, scattering and anisotropy coefficients. The suitability of a series of chromophores to ·enhance the absorption of laser radiation at the site of anastomosis have been assessed from the aspect of spectral profile, temperature generating ability, and determination of the fluorescence quantum yield. The second section introduces the use of the Argon ion laser for tissue bonding. A range of in vitro experiments are detailed involving the repair of longitudinal arteriotomies and end-to-end anastomoses in porcine splenic arteries. These vessels have a similar wall thickness and diameter to human coronary arteries, furthermore, they have fewer side branches. An Argon laser was used with and without a range of chromophores and various protein additives. The use of a suitably absorbing chromophore and a reinforcing protein coagulant significantly increased the strength of blood vessel repair. Histological examination of the anastomotic sites, and the results of bursting pressure tests on end-toend anastomoses are detailed. The final section involved the development of chromophores whose absorption characteristics could be altered by irradiation . Steady state irradiation of various compositions of dye/reducing agent has allowed detennination of the quantum yields of photobleaching. Used in conjunction with a results of bursting pressure experiments, where the optimum irradiating conditions for successful bonding were detennined, a system has been created whereby over-irradiation of blood vessels during anastomosis can be eradicated. The assessment of this system is presented. Histological examination and bursting pressure tests performed on end-to-end anastomoses of porcine splenic arteries are detailed. Nanosecond laser flash photolysis studies have been used to investigate the process of dye photobleaching. These studies have shown that the process of photofading is somewhat complicated, however, a mechanism involving the triplet excited state of the Eosin Y dimer has been proposed.
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