Heat Transfer Issues in Cryogenic Catheters

Published

November 7, 2005

Author(s)

Ray Radebaugh

Abstract

Catheters with diameters of 3 mm or smaller are capable of accessing many internal organs through arteries and veins. They provide the medical community with tools to operate on internal organs without the need to cut through the body to gain access. As a result, the use of catheters greatly speeds recovery times, reduces costs, and often reduces risks. The removal of unwanted tissue, such as cancer tumors or malfunctioning tissue can be carried out through cryoablation with cryogenic catheters. The effectiveness of these catheters depends very much on enhanced heat transfer at the very small tip. Issues to be discussed in this paper include the heat transfer at the boundaries between the working fluid and the catheter tip and between the tip and the tissue. Also of importance is the transient heat transfer within the surrounding tissue. In some cases, a miniature heat exchanger between high and low pressure streams of Joule-Thomson cycle may be required at the cold tip. Hydraulic diameters less than 100 ¿m are required in such miniature heat exchangers to provide high effectiveness and high heat flux densities. Steep temperature gradients are required for the destruction of cancer tumors or other unwanted tissue without excessive damage to surrounding normal tissue. Such a requirement can be met by making the catheter tip as cold as possible. However, achieving lower temperatures with a Joule-Thomson cycle requires higher refrigerant flow rates because the heat of vaporization of lower temperature refrigerants is less than that of refrigerants with high boiling points. The refrigerant flow rate is limited by the catheter diameter. Thus, there is some optimum temperature and associated refrigerant that provides the maximum temperature gradient in the tissue being destroyed. In this paper, we examine the use of mixed refrigerants that can be tailored for any temperature. Factors that influence the lower size limit of cryogenic catheters, such as choice of working fluid, flow rates, tip temperature, and pressures will be covered. An interesting example for cryogenic catheters, which will be discussed here, is the application of freezing locations on the heart that are triggering cardiac arrhythmias or irregular heart beats.

Citation

Microscale Heat Transfer - Fundamental and Applications

Volume

193

Publisher Info

Kluwer Academic Publishers,

Pub Type

Books

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DOI Link

Keywords

catheters, cryoablation, cryocodes, cryogenics, cryosurgery, medical, refrigerants

Citation

Radebaugh, R. (2005), Heat Transfer Issues in Cryogenic Catheters, Kluwer Academic Publishers, , [online], https://doi.org/10.1007/1-4020-3361-3_24 (Accessed October 31, 2024)