A NEW CRYOSURGICAL DEVICE FOR CONTROLLED FREEZING .2. IN-VIVO EXPERIMENTS ON SKELETAL-MUSCLE OF RABBIT HINDLIMBS

A new cryosurgical device was developed in this study to facilitate ex amination of factors affecting the outcome of cryotreatment. Special e mphasis was placed on the control of the cooling rate at the freezing front. In the new computer-controlled cryosurgical device, the control ling variable is the cryoprobe temperature, which is calculated to ens ure prespecified cooling rates at the freezing front. Details of the n ew cryodevice, results of a validation test, and the system characteri stics are presented in Part I of this study. In this part of the study initial results of 13 in vivo experimental cryotreatments, including histological observations, are presented. The in vivo pilot investigat ions include the normal, healthy skin and the underlying skeletal musc le of the thighs in rabbits. Using low cooling rate-controlled freezin g, the new cryosurgical device is demonstrated here as an effective su rgical tool. An in vivo temperature measurement technique is employed based on miniature thermocouples and X-ray images. Thermal analysis of the heat transfer in the cryotreated tissue is presented, based on th e temperature measurements and on numerical heat transfer simulations. Cryotreated tissue was extracted either immediately or 4 or 7 days fo llowing the procedure. The histological observations on the skeletal m uscle of the 4- and 7-day postcryoinjury were not substantially differ ent. The effective penetration depth of the cryolesion was in the rang e of 5-15 mm, possibly extending up to 25 mm, depending on the specifi c area treated and operating parameters. The cryotreatment resulted in complete destruction of cells in the skin followed by rapid replaceme nt by epithelial cells. Histological responses to cryotreatment of ske letal muscle were similar to those resulting from a range of traumatic episodes, e.g., crash damage. It was also found that most of the bloo d vessels in the cryotreated region remained intact without histologic al evidence of extravasation of erythrocytes. (C) 1996 Academic Press, Inc.