Surgery – Instruments – Cyrogenic application
Patent
1999-02-12
2000-08-01
Leubecker, John P.
Surgery
Instruments
Cyrogenic application
606 21, 606 22, 606 23, A61B 1818
Patent
active
060960329
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a medical cryo-surgical device.
Warts and other dermatological conditions may be treated by the application of intense cold. This freezing has to be sufficiently sever to form ice crystals within the tissue being treated. At present this cooling is usually accomplished by one of the following methods: will cool down and it will cool down the plug as well. This cooling is known as the Joule-Thompson effect. The gases that are used in practice are either carbon dioxide or nitrous oxide. applied to the tissue to be treated either directly or by using the liquid to cool an applicator. a volatile liquid onto the tissue, either directly or through porous applicator, will cause the tissue to cool down.
In the system using the Joule-Thomson effect a temperature of about -40 degrees C. is reached quite rapidly and there is good thermal contact between the porous plug and the tissue under treatment. It is also possible to limit the cooling to a specific area. The system does have the disadvantage that a heavy carbon dioxide or nitrous oxide cylinder is needed to power the device. The cylinders also need replacing as the gas is used up. Changing cylinders requires a certain amount of skill and strength to ensure that there are no leaks and that the threads are not crossed or damaged.
Liquid nitrogen, although having a very low boiling point (-196 degrees C.) Is difficult to apply only to the tissue to be treated because the liquid can splash onto surrounding areas thereby resulting in frost burns. When the liquid touches the warm skin a thin, insulating layer of gaseous nitrogen is formed which limits its cooling effect. The use of liquid nitrogen is generally limited to hospitals that have a regular supply for other purposes. The liquid nitrogen is also continuously evaporating and cannot be stored for any length of time.
Using an evaporating volatile liquid tends not to cool the tissue sufficiently to destroy it effectively. This method does however have the advantage of being readily available in easily transportable spray canisters.
To extend the availability of cryo-surgery it would be advantageous to have a suitable piece of equipment that would quickly and reliable cool down the treated tissue but have none of the disadvantages of the methods in present use. Obviously a portable device that could be operated from the mains electrical supply, without requiring any consumable supplies, would have very distinct advantages over the present methods. Such a piece of equipment would allow patients to be treated in Family Practitioners' surgeries rather than hospital based facilities.
Thermoelectric devices where two dissimilar metals are joined together to form a circuit and the junctions were maintained at different temperatures to cause a current flow have been known for a considerable number of years. The reverse of this process was discovered by the French physicist Jean Peltier who observed that if a current was passed through two different metal conductors, a temperature difference could be maintained at the junctions. Heat called the Peltier heat, is either absorbed or emitted at the junction depending on the direction of current flow. It was subsequently demonstrated that it was possible to freeze a droplet of water by using a bismuth-antimony junction with a current flowing in one direction and melting the frozen droplet by reversing the current flow.
This so-called Seebeck effect was put to practical use to make the familiar thermocouple thermometer. However, the Peltier effect was of little practical use, as metals, while being good conductors of electricity are also good conductors of heat. Because the Peltier heat was quickly conductor between the junctions, little temperature difference could be maintained. It was not until suitable semiconductor materials were developed that a Peltier cooler could become a practical proposition. In 1963 a junction of N and P type bismuth telluride (Bi.sub.2 Te.sub.2) was found to have large Seebeck coefficient combining good electrical conduct
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Leubecker John P.
Ruddy David M.
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