Patent Application
20070149958
The inventions described below relate to the field of cryoprobes and more specifically to cryoprobes used in surgical procedures.
Cryosurgical probes are used to treat a variety of diseases. The cryosurgical probes quickly freeze diseased body tissue masses, causing the tissue to die after which it will be absorbed by the body, expelled by the body or sloughed off. Cryothermal treatment is currently used to treat prostate cancer and benign prostate disease, breast tumors and breast cancer, liver tumors and cancer, glaucoma and other eye diseases. Cryosurgery is also proposed for the treatment of a number of other diseases.
A variety of cryosurgical instruments, referred to as cryoprobes, cryosurgical ablation devices, and cryostats and cryocoolers, have been available for cryosurgery. The preferred device uses Joule-Thomson cooling in devices known as Joule-Thomson cryostats. These devices take advantage of the fact that most gases, when rapidly expanded, become extremely cold. In these devices, a high pressure gas such as gaseous argon or gaseous nitrogen is expanded through a nozzle inside a small cylindrical sheath made of steel, and the Joule-Thomson expansion cools the steel sheath to sub-freezing cryogenic temperature very rapidly. Instead of gas, other cryosurgical instruments use liquid cryogen to quickly freeze diseased body tissue.
In cryosurgical instruments, it is important to prevent exhaust fluid from transferring heat to the inlet fluid as much as practical. Some cryosurgical instruments have exhaust cryogen fluid lines running in close proximity to inlet fluid lines. Current solutions to this heat transfer problem in cryosurgical instruments have been to flow the exhaust fluid in a separate tube or con-annularly with the inlet fluid for the length of the outer rigid tube to the handle in a cryprobe and then have the exhaust fluid flow back to the cryoprobe console in a separate line to be vented to the atmosphere. This solution, however, results in the cryoprobe having two bulky super-insulated lines, one for inlet fluid and the other for exhaust fluid. What is needed is a cryosurgical instrument system and method of use that prevents exhaust fluid from transferring heat to the inlet fluid as much as practical while also allowing exhaust fluid to be vented to the atmosphere without a second bulky exhaust line.
The cryoprobes and method their use described below prevent exhaust fluid from transferring heat to the inlet fluid as much as practical while also allowing exhaust fluid to be vented to the atmosphere. in an efficient manner. The cryoprobes include a probe with structures that permit the surgeon to secure and form an ice mass of a suspect mass or tumor. The probe is provided with a rigid outer tube, an inlet tube and a sharp distal segment. To secure the tumor to the probe, the surgeon pierces the tumor with the distal segment. Inlet tubing extending within the rigid outer tube directs coolant to the distal tip to cool the tip. A handle comprising an exhaust heater for heating exhaust fluid is disposed about the proximal end of the rigid outer tube. The exhaust heater is placed in fluid communication with exhausting cryogen is heated prior to being vented to atmosphere.
The outer tube has an outer diameter of about 2.7 mm, an internal diameter of about 2.4 mm, and a length of about 40 mm. The inlet tube 13 has an outer diameter of about 0.76 mm and an inner diameter of about 0.64 mm. These dimensions may vary depending on the materials used and the application for the cryoprobe. The penetrating segment comprises a sharp distal tip 17. As can be seen from the sectional view, the sharp distal tip is solid and adapted for piercing through a tumor. The length of the penetrating segment is chosen to be approximately the same size as the target tissue mass to be treated. This penetrating segment is forced into a lesion or tumor. An annular cavity 18 or lumen is created by the outer surface of the inlet tube and the inner surface of the rigid outer tube.
The liquid exiting the orifice of the inlet tube 13 counterflows along the annular cavity to an exhaust manifold 19 in fluid communication with the outer tube. The exhaust manifold isolates the cryogen exhaust from the annular cavity and directs the exhaust fluid through an exhaust line 20 into an exhaust heating chamber. The exhaust heating chamber is bounded on its distal end and proximal end by plugs 21. A heating element 22 in electrical communication with a power source is placed in thermal communication with the heating chamber allowing the exhaust heater to warm exhausting cryogen. Insulation 23 is disposed between the heating element and the outer surface of the handle in order to prevent the surface of the handle from becoming hot. An exhaust port 24 or vent is disposed on the proximal end of the heating chamber in fluid communication with the heating chamber allowing heated cryogen to safely vent to the atmosphere from the chamber.
The heating element may comprise resistance wire such as nichrome, self-regulating resistive polymers or other electrical restive materials. A console is provided and placed in electrical communication with the power source and placed in fluid communication with a cryogen source. The console has a control system that is able to regulate the use of power, the temperature of the probe, the temperature of the exhaust heater and the flow of cryogen to the cryoprobe.
When the cryoprobe is in use, the inlet tube 13 is placed in fluid communication with a lightly pressurized cryogen source by means of an inlet fitting. The cryogen is supplied to the assembly through a pressure fitting 31, flows through a fluid supply line, flows through the inlet tube and exits the distal end of the inlet tube 13. The distal end of the inlet tube 13 is exposed to a cavity at the distal end of the outer tube closed by the rigid penetrating segment. After expanding in the chamber, the fluid is at lower pressure and exhausts over the exhaust pathway which includes flow over outside of the inlet tube. The liquid nitrogen cools the distal tip of the probe to temperatures as low as −196° C. when steady flow has been established. The cryogen cools the inner surface of the rigid penetrating segment, thereby cooling the outer surface of the segment. The outer surface of the penetrating segment is placed against the targeted tissue to be cooled by the physician and the targeted tissue becomes an ice mass. Fluid flowing past the outer surface of the inlet tube is placed in contact with the helical-shaped baffle creating a turbulent helical flow path and forcing the cryogen torwards the inner surface of the outer tube. Turbulent fluid flow provides for improved heat transfer between the cryoprobe and targeted tissue. As the liquid nitrogen boils, the exhaust gas flows through the remainder of the exhaust gas pathway. Depending on the flow rates of the nitrogen, boiling can occur once the nitrogen flows past the baffle. In order to minimize cryogen consumption, flow rates can be reduced to a level where the nitrogen is about 90% vapor by the time it reaches the handle.
Once the exhaust fluid enters the handle of the cryoprobe, it is diverted away from the inlet tube to the heating chamber by the manifold. When the cryogen reaches the heating chamber, the exhaust heater heats the cryogen to a safe temperature that does not cause injury to a user of the cryoprobe when the cryogen is vented out of the handle. Safe temperatures may include temperatures ranging between about 32° F. to about 110° F. For example, a 150 watt heating element would be needed to heat the exhausting cryogen to a temperature of about 50° F. Once the cryogen is heated to a safe temperature, the cryogen is then vented to the atmosphere through the exhaust port.
While the preferred embodiments of the devices and methods have been described in reference to the environment in which they were developed, they are merely illustrative of the principles of the inventions. other embodiments and configurations may be devised without departing from the spirit of the inventions and the scope of the appended claims.
