https://iopscience.iop.org/article/10.1088/0031-9155/35/9/001/pdf

Physics of thermal processes in laser-tissue interaction

The purpose of this study was to evaluate the effect of temperature on shrinkage and the histologic properties of glenohumeral joint capsular tissue. Six fresh-frozen cadaveric shoulders were used for this study. Seven joint capsule specimens were taken from different regions from each glenohumeral joint and assigned to one of seven treatment groups (37 degrees, 55 degrees, 60 degrees, 65 degrees, 70 degrees, 75 degrees, 80 degrees C) using a randomized block design. Specimens were placed in a tissue bath heated to one of the designated temperatures for 10 minutes. Specimens treated with temperatures at or above 65 degrees C experienced significant shrinkage compared with those treated with a 37 degrees C bath. The posttreatment lengths in the 70 degrees, 75 degrees, and 80 degrees C groups were significantly less than the pretreatment lengths. Histologic analysis revealed significant thermal alteration characterized by hyalinization of collagen in the 65 degrees, 70 degrees, 75 degrees, and 80 degrees C groups. This study demonstrated that temperatures at or above 65 degrees C caused significant shrinkage of glenohumeral joint capsular tissue. These results are consistent with histologic findings, which revealed significant thermal changes of collagen in the 65 degrees, 70 degrees, 75 degrees, and 80 degrees C groups. To verify the validity of laser application for shrinkage of joint capsule, studies designed to compare these findings with the effects of laser energy must be performed.

The Effect of Thermal Heating on the Length and Histologic Properties of the Glenohumeral Joint Capsule

Laser techniques for joining tissue, in combination with other surgical technologies, will be a hallmark of surgery in the next century. At present, there are many clinical applications of tissue welding and soldering which are beginning to achieve wide spread acceptance. These exciting clinical developments are the result of many advances which have been made in the past few years in our understanding of the mechanism of laser tissue welding. Also contributing to this progress are many important technical refinements such as tissue solders and feedback control of the laser device. In this article, we describe in depth the history and development of laser tissue welding including key theoretical concepts as well as crucial experiments which have added to our insight into this phenomenon. We also review the evolving concepts of its clinical application and indicate clinical applications which are likely to become more important in the future.

Laser tissue welding : a comprehensive review of current and future clinical applications

Kinetic models of thermal damage in tissues can be used to describe pathologic end points obtained with laser irradiation. Many treatment end-point goals involve relatively low temperature coagulation or desiccation of tissue, and these end points can be conveniently described by rate process models. Thermal damage is exponentially dependent on temperature and linearly dependent on time of exposure. Damage processes can be modeled as first-order rate processes for which two experimentally derived coefficients are sufficient. The rate process models apply well to the prediction of damage thresholds and less well as the damage becomes complete, since several of the fundamental assumptions are violated. In order to be useful in evaluating laser dosimetry, the kinetic model must be coupled to quantitative pathological analysis. This chapter describes quantitative markers of thermal damage and experimental methods for estimating relevant kinetic coefficients in both constant-temperature and transient thermal history experiments. As expected, transient in vivo thermal history data yield a noisy kinetic plot; however, estimates of the appropriate rate coefficients often can be made.

Rate Process Analysis of Thermal Damage

A hyperstable collagen mimic.

Tissue welding is a potentially important biomedical application of laser technology. The structural alterations basic to this phenomenon were studied in experimental repair of lesions of the rat carotid artery and sciatic nerve. A modified neodymiumdoped yttrium-aluminum-garnet laser operating at a wavelength of 1.319 micrometers was used in conjunction with conventional suture techniques. Histological and fine-structural analysis revealed a homogenizing change in collagen with interdigitation of altered individual fibrils that appeared to be the structural basis of the welding effect.

http://science.sciencemag.org/content/sci/232/4756/1421.full.pdf

Laser-Induced Alteration of Collagen Substructure Allows Microsurgical Tissue Welding

Laser-assisted nerve anastomoses (LANA) of the left sciatic nerve of 30 adult albino rats were carried out with the 1,318 µm Nd:YAG laser in the following way: The nerves are cut through with microscissors. The proximal and the distal nerve stumps are adapted by two lateral epineural sutures. The epineurium, adapted by means of tweezers, is welded together on the upper side and the lower side by a few laser fusion points (12,5 W; 0,1 sec; 0,2 mm diameter) and then the epineural tube is closed.

Laser-Assisted Nerve Anastomoses Using a 1,3 µm Nd: YAG Laser with Long-Term Observations

Various types of lasers have already been tested as a substitute for sutures in microsurgical peripheral nerve anastomoses (Almquist et al. 1984; Fischer et al. 1985; Ulrich et al. 1986). In a histological evaluation of experiments using this technique, the 1.32 μm Nd:YAG laser has been found to be suitable but not appreciably superior to epineurial suture alone (Schober et al. 1988). It was advocated to use the 1.32 μm Nd:YAG laser with its inherent property of precise coagulation in peripheral nerve transplantation, a procedure where so far laser application has been restricted to the milliwatt CO2 laser (Richmond 1986). In this report we give an account of some ultrastructural features pertinent to the outcome of regeneration in such an experimental design. A final evaluation must await the conclusion of a larger experimental series, technical details of which are described in another contribution to this volume (Ulrich et al.).

T. Sander

Papers

Laser-Induced Alteration of Collagen Substructure Allows Microsurgical Tissue Welding

Laser-Assisted Nerve Anastomoses Using a 1,3 µm Nd: YAG Laser with Long-Term Observations

Some Ultrastructural Aspects of Regeneration in 1.32 μm Nd:YAG Laser-Assisted Peripheral Nerve Transplantation