EFFECTS OF SURFACE IRRIGATION ON THE THERMAL RESPONSE OF TISSUE DURING LASER IRRADIATION

Effects of surface irrigation on the thermal response of tissue during laser irradiation are investigated. In particular, influence of tempe rature and flow rate of the irrigation fluid on the resulting temperat ure distributions and coagulation depths are studied. Intraluminal Nd: YAG laser irradiation of bovine muscle is performed in vitro for a fix ed value of the irrigation flow rate while the irrigation temperature is varied, and for a fixed irrigation temperature while the irrigation flow rate is kept constant. Thermocouples are used to measure the tem peratures within the tissue for various irradiation and irrigation con ditions. Higher temperatures and deeper coagulation depths are achieve d as the temperature of the irrigation fluid is increased. For suffici ently low values of irradiance and exposure time, the use of cold irri gation is shown to prevent or delay tissue carbonization. Beyond a cri tical irradiance and an exposure time, use of cold irrigation does not prevent tissue carbonization. Coagulation depths and temperature dist ributions are not affected by a change in the flow rate of laminar irr igation. Application of stagnant irrigation, however, results in an in crease in coagulation depth. Results of this study suggest that the do minating mechanism of heat transfer during application of laminar irri gation is thermal diffusion as compared to the bulk motion of the flui d. (C) 1994 Wiley-Liss, Inc.