Abstract:
A cryogenic medical device for delivery of subcooled liquid cryogen to various configurations of cryoprobes is designed for the treatment of damaged, diseased, cancerous or other unwanted tissues. The device is a closed or semi-closed system in which the liquid cryogen is contained in both the supply and return stages. The device comprises a number of parts including a vacuum insulated outer dewar, submersible cryogen pump, baffled linear heat exchanger, return chamber, and a series of valves to control the flow of the liquid cryogen. The cryogenic medical device promotes the subcooling to any external cryogenic probe.

Description:
RELATED APPLICATIONS 
       [0001]    The present application claims priority to U.S. Provisional Patent Application Ser. No. 61/093,904 filed on Sep. 3, 2008 and titled Medical Device for the Transport of Subcooled Cryogenic Fluid through a Linear Heat Exchanger, which is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to the medical technology field and, in particular, to a medical device for use in a cryogenic system. 
       BACKGROUND OF THE INVENTION 
       [0003]    Over a recent number of years, there has been a strong movement within the surgical community toward minimally invasive therapies. The main goals of the minimally invasive therapies include: 1) eradication of targeted tissue, 2) decreased hospitalization time, 3) limited postoperative morbidities, 4) shortened return interval to daily functions and work, and 5) reduced overall treatment cost. Cryotherapy is a minimally invasive method of treating a disease state through tissue freezing with thousands of patients now receiving the procedure annually. Currently, cryotherapy is used to treat numerous disease states including organ confined tumors such as prostate, kidney, liver, as well as cardiovascular disease, retinal detachment, pain management, and other illness/disease states. 
         [0004]    Cryotherapy is an effective yet minimally invasive alternative to radical surgery and radiation therapy. The procedure is done under either general or epidural anesthesia. Since it is minimally invasive, it offers patients a quicker recovery and reduced severity of potential side effects. Without the expense associated with major surgery or an extended hospital stay, cryotherapy is a cost-effective treatment option. 
         [0005]    The approaches utilized to date have focused on the delivery of liquid cryogen through the use of moderate to high pressure on the entire system or piston/bellows compression to drive fluid movement. Further, the use of heat exchangers have been limited to coils placed into a bath of cryogen to allow for time consuming, inefficient passive subcooling of the cryogen in which activation of these devices circulate a cryogen (such as liquid nitrogen) to a probe to create a heat sink, thus resulting in tissue freezing. 
         [0006]    There exists a need for improvements in cryotherapy, and medical devices or components associated with the treatment to better circulate liquid cryogen to a cryoprobe and facilitate improved measures for treatment and cost. The medical device of the present invention will allow for the circulation (cooling, delivery, and return) of liquid cryogen to a cryoprobe for the freezing of targeted tissue. The invention will facilitate the eradication of tissue, decrease hospitalization time, limit postoperative morbidities, shorten return to daily functions and work, and further reduce the overall treatment cost. Desirably, these improvements to device design and application will also increase its utilization for the treatment of multiple disease states. 
       SUMMARY OF THE INVENTION 
       [0007]    The following invention is a cryogenic medical device designed to deliver subcooled liquid cryogen to various configurations of cryoprobes for the treatment of damaged, diseased, cancerous or other unwanted tissues. The device is a closed or semi-closed system in which the liquid cryogen is contained in both the supply and return stages. The device is vented to the surrounding atmosphere through an adjustable pressure vent to prevent excess pressure buildup while in operation. The device comprises a number of parts including a vacuum insulated outer dewar, submersible cryogen pump, baffled linear heat exchanger, return chamber, and a series of valves to control the flow of the liquid cryogen. In general terms, the outer dewar comprises a submersible rotary pump to drive liquid cryogen through the baffled linear heat exchanger. The linear heat exchanger comprises a tube-within-a-tube whereby a vacuum is applied to the outer chamber to subcool an isolated reservoir of liquid cryogen. The inner chamber comprises a series of baffles and a central spiral to increase the flow path of the liquid cryogen while providing for increased contact based surface area with the outer chamber to allow for more effective heat transfer and subcooling of the cryogen being delivered to the probe. Following circulation to the cryoprobe, cryogen (liquid and gas) is returned to the device into a return chamber which surrounds the supply chamber thereby providing for a staged secondary subcooling chamber for the cryogen in the supply tube. The return chamber is open to the main dewar tank thereby allowing for exchange of liquid and gas between the supply and return chambers. Device operation is controlled and monitored by a series of pressure and vacuum valves designed to control the flow, cooling, pressurization, etc. of the liquid cryogen. This control is achieved through various configurations of manual and computer controlled systems. 
         [0008]    One embodiment of the cryogenic system described herein comprises a container filled with liquid cryogen, at least one cryoprobe outside said container for use in cryotherapeutic procedures, a heat exchanger surrounded by said container or a subcooling chamber, a pump which delivers the liquid cryogen to said heat exchanger to subcool the cryogen, an exit port where one or more of said cryoprobes are attached, at least one supply line connected to said heat exchanger and to said exit port, said supply line directing the liquid cryogen to said cryoprobe, and at least one return line which returns liquid cryogen to the container, wherein said container integrates said supply line and said return line with said heat exchanger to form a closed system, said return line configured to redirect the liquid cryogen back into said container. In one embodiment, the cryogenic system is an electronically controlled system and monitored by computer systems. 
         [0009]    In one embodiment, the heat exchanger is baffled and provides an interior central component within the interior lumen of the inner chamber that circulates the flow of the liquid cryogen. The cryogenic system further comprises a return chamber surrounding the supply line between an exit opening of the heat exchanger and the exit port such that the return chamber receives the liquid cryogen returned from the cryoprobe by way of the return line. In one aspect, the return chamber includes a secondary heat exchanger so that the return line passes through the secondary heat exchanger to subcool the liquid cryogen in the return line. In another aspect, the cryogenic system uses the container to receive the liquid cryogen returned from the cryoprobe, the container of which insulates the supply line and the return line. 
         [0010]    One method of delivering liquid cryogen to a cryoprobe, comprises the steps of (a) providing a device for containing liquid cryogen, said device having one or more openings to allow excess gas or liquid overflow to exit and at least one exit port where one or more cryoprobes is attached; a submersible pump positioned within said device; a heat exchanger positioned within said device; one or more supply lines connecting said submersible pump to said heat exchanger and exiting said heat exchanger to said exit port; a return chamber surrounding said one or more supply lines; and one or more return lines exiting said return chamber and connected to said one or more cryoprobes through said exit port; wherein said one or more supply lines and said one or more return lines form a closed system; (b) filling said device with the liquid cryogen; (c) pumping the liquid cryogen through said submersible pump and into said heat exchanger; (d) subcooling the liquid cryogen within said linear heat exchanger; (e) delivering the liquid cryogen through said one or more supply lines to said exit port which attaches to said one or more cryoprobes; (f) returning the liquid cryogen through said one or more return lines into a return chamber of said device; and (g) recirculating the liquid cryogen through said device for reuse in delivering liquid cryogen to said one or more cryoprobes. 
         [0011]    In one embodiment, the method includes a step of subcooling the liquid cryogen within the heat exchanger in which the flow path of the liquid cryogen increases within said heat exchanger. In one aspect, an internal component within the heat exchanger circulates the liquid cryogen. In another aspect, a series of baffles within the heat exchanger emanate into the flow path of the liquid cryogen and provide an enhanced surface area for reducing the temperature of the liquid cryogen within said heat exchanger. 
         [0012]    Although pressurization of the liquid cryogen may not be included within the method described above, an additional step of pressurizing the liquid cryogen within the closed system may be advantageous. In one aspect, one or more control valves positioned therein are capable of being electronically manipulated. The control valves may have control over supply of the liquid cryogen, temperature, pressure, and other metrics to allow the safe operation of the cryogenic system. 
         [0013]    One embodiment of a device for use in a cryogenic system comprises: one or more walls providing an internal lumen for containing liquid cryogen, said walls having one or more openings which allow for venting of excess gas or liquid overflow, and at least one opening providing an exit port where one or more external cryoprobes are attached; a submersible pump positioned within said internal lumen; a heat exchanger positioned within said internal lumen and capable of integrating a subcooling chamber; one or more supply lines connecting said submersible pump to said heat exchanger and exiting said heat exchanger to said exit port; a return chamber surrounding said one or more supply lines; and one or more return lines exiting said return chamber and connected to said one or more external cryoprobes through said exit port; wherein said one or more supply lines and said one or more return lines form a closed system that provides for supply and return of the liquid cryogen to said heat exchanger within said internal lumen, said heat exchanger providing an enhanced surface area for reducing temperature of the liquid cryogen. In one aspect, the device comprises an inner tubular unit or internal structure which circulates the flow of liquid cryogen through the interior lumen of the chamber. In another aspect, the heat exchanger of the device comprises a series of baffles emanating into the flow path of the liquid cryogen, said series of baffles increasing the surface area within the heat exchanger and thereby further reducing the temperature of the liquid cryogen. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The invention is best understood from the following detailed description when read with the accompanying drawing figures. It is emphasized that the various features are not necessarily drawn to scale. In fact, the dimensions may be arbitrarily increased or decreased for clarity of discussion. 
           [0015]      FIG. 1  is a side view of an illustrative embodiment of the device of the present invention. 
           [0016]      FIG. 2A  is a side view of one embodiment of a heat exchanger of the present invention. 
           [0017]      FIG. 2B  is a cross-sectional view of  FIG. 2A , a front view of one embodiment of a device of the present invention. 
           [0018]      FIG. 3A  illustrates a side view of one embodiment of a heat exchanger of the present invention. 
           [0019]      FIG. 3B  is a cross-sectional view of  FIG. 3A , one aspect of fluid flow through one embodiment of a heat exchanger of the device. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    In the following detailed description, for purposes of explanation and not limitation, exemplary embodiments disclosing specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one having ordinary skill in the art that the present invention may be practiced in other embodiments that depart from the specific details disclosed herein. In other instances, detailed descriptions of well-known devices and methods may be omitted so as not to obscure the description of the present invention. 
         [0021]    An external view of a device and system  10  in accordance with one embodiment of the present invention is shown in  FIG. 1 . The cryogenic system or device  10  has side walls  17  enclosing an internal area, or lumen  15 . The device  10  in this embodiment takes the form of a vacuum insulated dewar  6  which stores liquid cryogen in connection with a supply line  11  and return line  12  to a probe or catheter (not shown) to form a closed system  10 . The dewar  6  may be made of material such as stainless steel or any other material known for providing a vacuum insulated vessel. The dewar  6  is filled with liquid nitrogen or other liquefied gas (here, discussing as cryogen) to a maximum level  13 . Internal to the dewar is a submersible pump  1  which delivers the liquid cryogen to a linear heat exchanger  4  to subcool the cryogen. A subcooling vacuum chamber  3  may surround a heat exchanger  4  facilitating the delivery of subcooled cryogen to an attached cryprobe (also referred to as probe or catheter). The subcooling chamber  3  in connection with the heat exchanger  4  at an entrance and an exit opening form an integral unit for supplying subcooled liquid cryogen. From the heat exchanger, then, the subcooled cryogen passes into a supply line  11  and continues out through an exit port  14  where various configurations of cryoprobes are attached. 
         [0022]    The cryogen is returned (as demonstrated by the arrows in  FIG. 1 ) from the cryoprobe via a return tube  12  into a return chamber/cylinder  5  of the dewar  6 . The return tube  12  connects into the return cylinder  5  which also surrounds the supply tube  11  that exits the heat exchanger  4 . One or more exit ports  14  may be included in a side wall  17  of the dewar  6  or may be a separate unit  14  to incorporate various control valves. 
         [0023]    In operation, the device  10  is a closed system allowing for the supply, return, collection, and re-utilization of liquid cryogen during its utilization in the medical/surgical field. The device  10  may or may not be pressurized during operation. The device may also be vented to the surrounding environment to prevent excess pressure buildup during operation. 
         [0024]    In one aspect, the returning cryogen empties into the return cylinder or chamber  5 . In another aspect, the returning cryogen may empty as bulk fluid into the internal lumen  15  within the dewar  6 . 
         [0025]    In one embodiment of the present invention, the linear heat exchanger  4  subcools the liquid cryogen prior to delivery to tissue. The heat exchanger  4  comprises a chamber within a chamber configuration such that a vacuum chamber  3  is a subcooling chamber  3 , a sealed cylinder  3  filled with liquid cryogen upon which a vacuum is drawn to reduce the atmospheric pressure on the cryogen, in which the temperature of the cryogen within the subcooling chamber  3  is reduced even further. The subcooling chamber  3  further comprises valve controlled ports  8  external to the maximum liquid cryogen level. In one aspect, a vacuum  18  can be drawn on connecting line  16  at a controlled internal valve  7  or external valve  9 . The vacuum  18  can also be utilized for attachment to the cryoprobe. In another aspect, valve controlled ports  8  may be accessible for delivery of liquid cryogen to the subcooling chamber  3  by way of a supply line  19  or as a vent  8  for any excessive gas coming from the subcooling chamber  3 . 
         [0026]    In this embodiment, the linear heat exchanger  4  is an inner chamber  4  which passes through subcooling chamber  3  and connected via the entrance and exit openings. Liquid cryogen passing through the inner chamber  4  is reduced in temperature to a subcooling degree by the outer subcooling chamber  3 . 
         [0027]    Aspects of the linear heat exchanger  4  are illustrated in  FIGS. 2A ,  2 B and  FIGS. 3A ,  3 B.  FIG. 2A  illustrates a side view of a linear baffled heat exchanger  4 .  FIG. 2B  depicts a cross-sectional of  FIG. 2A , a front view of the linear baffled heat exchanger  4  when looking into the inner chamber  4 . An interior central component  20 , a spiral  20 , within the interior lumen of the chamber  4  operates like a corkscrew to increase the flow path  25  of the liquid cryogen. An outer wall  22  of the inner chamber  4  also comprises baffles  24  which increase the surface area in the heat exchanger for quicker and reduced cooling of the liquid cryogen. As illustrated, a series of baffles  24  emanate into the flow path  25  (as illustrated by arrows) of the cryogen in the inner lumen, thereby increasing the surface area in the heat exchanger  4 . The spiral component, however, may be any size and shape as to efficiently increase the flow of liquid cryogen. Planar structures, as described below, or any additional features included to increase surface area may further be incorporated. 
         [0028]      FIG. 3A  illustrates another embodiment of a linear heat exchanger  4  such that the internal component or structure  20  has a planar configuration and also operates in a circular motion to increase the flow  25  of the liquid cryogen.  FIG. 3B  depicts a cross-section of  FIG. 3A  such that the inner tubular unit  21  assists the internal structure  20  in circulating the flow of liquid cryogen through the interior lumen of the chamber  4 . 
         [0029]    One embodiment of the medical device comprises a return chamber  5  which is illustrated as a return cylinder  5  in  FIG. 1  such that the return chamber  5  surrounds the supply line  11  coming from the heat exchanger  4 . The return chamber  5  and the surrounded supply line may then provide a secondary heat exchanger for the system/medical device  10 . Cryogen return is vented into the return chamber  5 . In one aspect, the return chamber  5  comprises a series of vent holes  26  near the top of the return chamber  5  to allow for the venting of gas and/or liquid overflow into the main dewar  6 . Vent holes  26  allow for the reutilization of cryogen and thus extend the operation time for the medical device  10 . In another aspect, the return tube  12  is vented into the main dewar  6  either directly or by first passing through a linear heat exchanger (similar to the combination of heat exchanger  4  and subcooling chamber  3 ) to subcool the return cryogen prior to venting into the main dewar  6 . Return of the cryogen to the main dewar  6  allows the cryogen to return through a heat exchanger such that the cryogen is reutilized and extends the operation time even longer. 
         [0030]    In another embodiment, the medical device  10  may provide a system which is controlled electronically or through a series of computer controlled valves including any heaters, sensors, motors, or gauges. The sensors monitor pressure, temperature, fluid level in the dewar and can measure any metric as may be desired. In one aspect, the sensors monitor pressure levels within defined safety ranges. In another aspect, the sensors may control the pressurization of one or more components internal to the dewar. Any of the valves  2 ,  7 ,  8 ,  9 , including exit portal valve  14 , may be automated to enable a controlled and consistent operation of the cryogenic system. 
         [0031]    In utilizing the medical device of the present invention, various methods in the industry may be employed in accordance with accepted cryogenic applications. As discussed, the embodiments of the present invention are for exemplary purposes only and not limitation. Advantageously, this device represents an important step in targeted thermal therapies. Various cryosurgical devices and procedures to apply freezing temperatures to a target tissue may be employed for use with the medical device of the present invention. The medical device of the present invention has been developed to enable and improve some of the approaches used to target or ablate tissue. Furthermore, the medical device can couple controlled pumping of a liquid cryogen through a baffled linear heat exchanger to decrease the overall temperature of the cryogen providing a greater heat capacity of the fluid and thereby resulting in an increased cooling potential in a cryoprobe. 
         [0032]    Thus, the invention facilitates other improvements in cryotherapy, and medical devices or components associated with the treatment. The medical device of the invention allows for the circulation (cooling, delivery, and return) of liquid cryogen to a cryoprobe for the freezing of targeted tissue. The invention facilitates the eradication of tissue and can thereby decrease hospitalization time; and further limit postoperative morbidities, shorten return to daily functions and work, and further reduce the overall treatment cost. These improvements to device design and application can also increase utilization of the device for the treatment of multiple disease states. 
         [0033]    The current device represents an improved development of cryosurgical devices by allowing for controlled linear flow of a cryogen without the need for high pressure or compression based bellows or piston systems. Further, the device contains a novel baffled linear heat exchanger designed for cryogen flow through a specialized subcooling chamber. 
         [0034]    The embodiments of the present invention may be modified to take the shape of any device, container, apparatus, or vessel currently used in industry. Specifically, cylindrical or alternative vessels may provide containers for the cryogenic system for improved cryogenic supply and delivery. Further, any compartmental arrangement in combination with the components of the above system may take many forms and be of any size, shape, or passageway. Any number of vents may also be utilized to facilitate operation of the system. The system may also be a partially closed or completely closed system. 
         [0035]    In one embodiment of the system, the device is contained within a shell or enclosure that allows the system to be easily transported. The enclosure may then include any mobile feature such as wheels, handles, and fixtures (or allow placement onto a cart having these features) so that the system can be transported to and from the location of treatment. Such mobility allows the system to be easily moved to and from an operating room or site of therapeutic treatment. It is also noted that the system is readily separable from the cryogen fill tanks and fill lines that initially supply the system with the liquid nitrogen or other such cryogenic fluid. This improved feature eliminates the bulkiness of standard cryogenic medical devices. 
         [0036]    As presented, the multiple embodiments of the present invention offer several improvements over standard medical devices currently used in cryogenic industry. The improved cryogenic medical devices remarkably enhance its utilization for the cooling, delivery and return of a liquid cryogen to a cryoprobe for the freezing of targeted tissue. The present invention provides cost savings and significantly reduced treatment times which further reduce expenditures in the healthcare setting. The previously unforeseen benefits have been realized and conveniently offer advantages for the treatment of multiple disease states. In addition, the improvements enable construction of the device as designed to enable easy handling, storage, and accessibility. Further uses of the system outside of the healthcare setting are foreseeable. Potential uses in the space industry, defense systems or any industry requiring rapid cooling may incorporate the cryogenic system as thus described. 
         [0037]    As exemplified, the device may include any unitary structure, vessel, device or flask with the capacity to integrally incorporate any combination of such structures. The invention being thus described, it would be obvious that the same may be varied in many ways by one of ordinary skill in the art having had the benefit of the present disclosure. Such variations are not regarded as a departure from the spirit and scope of the invention, and such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims and their legal equivalents.