Experimental Studies And Theoretical Analyses On Liquid Carbon Dioxide Cryoprobe Freeze-thawing Biologic Tissues

The investigation on the theory of heat and mass transfer for cryosurgery has been one of the hot research tasks. It is a significant theory meaning and practical value for people to study the bioheat transfer rules in the process of freezing and thawing.Aiming at the theory of heat and mass transfer of cryosurgery, this paper does some primary experiments and theory analyses. Firstly, the author analyzes the effects of the vacuum acting on blood flow perfusion. It indicates that blood flow perfusion has great impact on the bioheat transfer. According to the experiments, the time that the vacuum acts on tissues has little impact on the engorgement and gore, however the degree of the vacuum plays an important role on the engorgement and gore. The vacuum acting on the biomaterials can not only reduce the blood flow perfusion, but also lessen the pervasion of cancer cells. The probability of successful therapy operation increases. So the author puts forward the notion of vacuum liquid carbon dioxide cryoprobe for the first time.Then the author takes the lead in designing three different structures of cryoprobes: vacuum cryoprobe, heat conductive cryoprobe and spout cryoprobe, and puts up the experimental device. After repeating experiments, dry ice jamming is overcome via adding a mid-heater. Therefore liquid CO₂ avoids of gas-solid multiphase flow, and supplies continuous low temperature gas to the cryoprobe.The experimental research on the 2-dimensional temperature distribution for frozen tissues such as fresh beef and porcine liver is presented in this paper. The temperature distribution trends to symmetry via observing infrared cameras imaging, therefore, the thermocouples are laid on half-plane which is attached to the cryoprobe downwards. As a result, when low temperature CO₂ sprays to the tissue, an extremely small iceball forms near the tip of the cryoprobe. The iceball grows quickly till the heat conduction of tissue is steady. The maximal temperature grad appears at the section start of the phase change. Stopping freezing, the tissue thaws quickly at the initial period, and then slowed down. Generally, it spends about 2 hours to recover to the initial temperature of the tissue. As the diameter of cryoprobe increases, the temperature will descend faster, frozen zone will be broader obviously, and iceball becomes larger. Until it arrives heat conduction balance, the temperature does not keep constant. Single freeze-thawing results in biggish mechanical injury already for loosen tissue such as porcine lung;...