Investigations in Cardiac Surgery: Physical Aspects of Laser Anastomosis, Thermal Bonding and Arterial Dilation

The work of this thesis examines the application of lasers to cardiac surgery in two areas - laser assisted anastomosis and laser balloon angioplasty. Both techniques utilise laser interactions with tissue, particularly with the blood vessel wall. Modification of the collagen component is a recurring feature of such interactions, frequently determining the general response of the vessel as a whole. Hence an introduction to collagen structure and biochemistry is presented in Chapter 2. Laser Anastomosis Our own exploration of Argon laser anastomosis in vivo is discussed in Chapter 3. This establishes our experience in this area and highlights the shortcomings of the technique (namely inconsistent bonding). In vitro work was undertaken (Chapter 4) to investigate the nature of the bonding process. Tissue bonds were successfully created without the use of a laser, implicating dehydration as an important factor. These bonds were christened 'dry bonds' and a bonding theory based on dehydration was proposed to explain the phenomenon. The results of investigation into the wide variation of the strength of dry bonds (Chapter 5) were in agreement with the dry bonding theory. The work of Chapter 6 undertook a comparison of laser and dry bonds in which the properties of the two bond types were found to be very similar, further implicating dehydration as the mechanism responsible for Argon laser anastomosis. This hypothesis is examined on a theoretical basis in Chapters 7 and 8, the former providing the groundwork of laser tissue interactions and the latter applying a numerical model to describe the bonding process. A theoretical description based on dehydration is shown to account for experimental observations and indicates that dehydration is the mediator of Argon laser anastomosis. The work as a whole is summarised in Chapter 9 to conclude that dehydration is the mechanism of Argon laser bonding. Laser Balloon Anaioplastv Chapter 10 introduces the technique of balloon angioplasty applied to coronary artery disease with consideration of laser recanalisation and laser balloon angioplasty. The latter is an experimental technique designed to 'fix' a stenosed vessel in an expanded state by laser irradiation during balloon inflation. However the temperature dependent processes responsible for this action are not well defined since vessel temperature is difficult to obtain during radiative balloon inflation. In response to this. Chapter 11 describes a technique to simulate the thermal effects of the laser balloon while simultaneously providing accurate vessel temperature. In addition, a technique permitting repeated angiography on an excised section of myocardium is described, enabling analysis of vessel diameter pre- and post angioplasty. Application of the technique to non-diseased coronary arteries in vitro is related in Chapter 12. The results of this work reveal acutely altered vessel diameters and indicate that the technique is both viable and useful. Chapter 13 draws the work to a conclusion and considers its future application