Abstract:
A system for selectively cooling and warming a cryosurgical instrument using a dual phase cryogen, including: two sources of the cryogen, a first source storing liquid phase cryogen and having a first source heater therein that selectively converts at least some of the liquid phase cryogen into gaseous phase cryogen and a second source storing the gaseous phase cryogen; a cryogen delivery control section selectively delivering cryogen to the tip; a cryogen return path from the tip to the first and second sources; a cryogen return control section that includes a pump that pumps the returning cryogen to the second source; and a pressure control section including a first pressure sensor that senses a pressure in the first source, a second pressure sensor that senses a pressure in the second source, and a pressure regulator that regulates the pressure of the first source based on information from the pressure sensors.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. provisional patent application No. 61/353,375, filed Jun. 10, 2010, the disclosure of which is incorporated by reference. 
    
    
     BACKGROUND 
     1. Technical Field 
     Embodiments of the present invention relate to cryogen flow regulation systems and, more particularly, to devices and systems for regulating pressure in a closed loop in which pressure is at least partially regulated through regulating flow through the system. 
     2. Description of Background Art 
     Various cryosurgical systems that regulate cryogen pressure are known. Further, various approached to cryogen pressure regulation are known. Examples include U.S. Patent Publication Nos. 2009/0270851 and 2007/0149957 and the following U.S. Pat. Nos. 5,520,682, 7,192,426, and 5,334,181. Known systems and approaches, however, have not been entirely successful in providing consistent and smooth pressure regulation. 
     BRIEF SUMMARY 
     The background art does not provide smooth, consistent pressure regulation. 
     The present invention, in at least some embodiments, is an advance over the background art by providing cryosurgical systems and devices that exhibit smooth, constant pressure regulation and in which pressure is at least partially regulated through flow regulation. 
     An aspect of the present invention provides a system for selectively cooling and warming a tip of a cryosurgical instrument using a dual phase cryogen. The system includes: two sources of the cryogen, a first source storing the cryogen in a liquid phase and having a first source heater therein that selectively heats the liquid phase cryogen so as to convert at least some of the liquid phase cryogen stored therein into gaseous phase cryogen and a second source storing the cryogen in a gaseous phase; a first delivery path between the first source and the tip; a second delivery path between the second source and the tip; a cryogen delivery control section that selectively delivers cryogen to the tip from the respective sources; a cryogen return path from the tip to the first and second sources; a cryogen return control section that controls the return of cryogen via the cryogen return path and that includes a pump that pumps the returning cryogen to the second source; and a pressure control section including a first pressure sensor that senses a pressure in the first source, a second pressure sensor that senses a pressure in the second source, and a pressure regulator that regulates the pressure of the first source based on information from the pressure sensors. 
     Another aspect of the present invention provides an apparatus for delivering a phase changing cryogen to a surgical device, including: a first reservoir of the cryogen in a liquid phase; a liquid feed conduit through which cryogen travels from the first reservoir to the surgical device; a second reservoir of the cryogen in a gaseous phase; a gaseous feed conduit through which cryogen travels from the second reservoir to the surgical device; a return conduit through which cryogen that is exhausted from the surgical device returns to the first and/or second reservoir, the exhausted cryogen being in the gaseous phase; a pump disposed in the return conduit, the pump selectively pumping the returning cryogen to the first reservoir and/or the second reservoir; and a logic section that selectively energizes the pump to control an overall pressure in the system, based on information from pressure sensors and flow meters. 
     Still another aspect of the present invention provides a system including: a first cryogen delivery loop including a liquid cryogen storage section in fluid communication with a cryosurgical device via (i) a liquid cryogen delivery path and (ii) a cryogen return path; and a second cryogen delivery loop including a gaseous cryogen storage section in gaseous communication with (i) the cryosurgical device via a gaseous cryogen delivery path and a portion of the return path and (ii) the liquid cryogen storage section via a portion of the cryogen return path. The cryogen return path delivers exhausted, gaseous cryogen from the cryosurgical device to the first and/or the second cryogen storage section, includes a heater that selectively heats the exhausted, gaseous cryogen to maintain a temperature thereof above a boiling temperature of the cryogen, and includes a pump that selectively increases a local pressure in the cryogen return path. When the liquid cryogen heater is energized, liquid cryogen in the liquid cryogen storage section is converted into a gaseous state and delivered to the second cryogen storage section. 
     Yet another aspect of the present invention provides a system for selectively cooling and warming a tip of a cryosurgical instrument using a dual phase cryogen, including: two sources of the cryogen, a first source storing the cryogen in a liquid phase and having a first source heater therein that selectively heats the liquid phase cryogen so as to convert at least some of the liquid phase cryogen stored therein into gaseous phase cryogen and a second source storing the cryogen in a gaseous phase; a first delivery path between the first source and the tip; a second delivery path between the second source and the tip and including a gaseous phase cryogen heater that heats gaseous phase cryogen traveling therein from the second source to the tip; a cryogen delivery control section that selectively delivers cryogen to the tip from the respective sources; a cryogen return path from the tip to the first and second sources; a cryogen return control section that controls the return of cryogen via the cryogen return path and that includes a cryogen heater that selectively heats cryogen in the cryogen return path to maintain a temperature of returning cryogen therein above a boiling temperature thereof, a flow meter that measures a flow rate of the returning cryogen, and a pump that pumps the returning cryogen to the second source; and a pressure control section including a first pressure sensor that senses a pressure in the first source, a second pressure sensor that senses a pressure in the second source, and a pressure regulator that regulates an overall pressure of the system based on information from the pressure sensors and the flow meter. 
     Still another aspect of the present invention provides a system for selectively cooling and warming a tip of a cryosurgical instrument using a dual phase cryogen. The system includes: two sources of the cryogen, a first source storing the cryogen in a liquid phase and having a container contained completely within said first source, said container also containing the cryogen in a liquid phase, said container communicating fluidly with said first source through a check valve, wherein if pressure is greater in said first source than in said container, said check valve opens and cryogen in said liquid phase flows from said first source to said container; a second source storing the cryogen in a gaseous phase; a first delivery path between the first source and the tip; a second delivery path between the second source and the tip; a cryogen delivery control section that selectively delivers cryogen to the tip from the respective sources; a cryogen return path from the tip to the first and second sources; a cryogen return control section that controls the return of cryogen via the cryogen return path and that includes a pump that pumps the returning cryogen to the second source; and a pressure control section including a first pressure sensor that senses a pressure in the first source, a second pressure sensor that senses a pressure in the second source, and a pressure regulator that regulates an overall pressure of the system based on information from the pressure sensors. 
     As used herein, the term “cryoprobe” is provided as a non-limiting example of a cryosurgical instrument. And, although embodiments and/or aspects of the present invention are discussed in the context of a cryoprobe, it is to be understood that other cryosurgical instruments are both contemplated and intended to be included. 
     Without wishing to be limited in any way, and without wishing to provide a closed list, the present invention in at least some embodiments effectively regulates “two-phase flow”, in which the cryogen both flows and boils, thereby controlling the level of the heat flux. 
     These, additional, and/or other aspects and/or advantages of the present invention are: set forth in the detailed description which follows; possibly inferable from the detailed description; and/or learnable by practice of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be more readily understood from the detailed description of embodiments thereof made in conjunction with the accompanying drawings of which: 
         FIG. 1  shows a closed loop system  100  consistent with an embodiment of the present invention; 
         FIG. 2  shows a closed loop system  200  consistent with an embodiment of the present invention featuring a constantly operating pump; 
         FIG. 3  shows a closed loop system  300  consistent with an embodiment of the present invention featuring an additional structure to generate gaseous cryogen; and 
         FIG. 4  shows a partial view of a closed loop system  400  consistent with an embodiment of the present invention featuring additional pressure control structure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice. 
     Before explaining exemplary embodiments of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting. 
     Referring now to  FIG. 1 , there is illustrated a closed loop system  100  for recycling a gaseous cryogen in a pressurized manner, while the pressure and the flow in the system are regulated. The system  100  includes a source of liquid cryogen  104 , a source of gaseous cryogen  102 , a cryoprobe  117 , and structures providing various cryogen flow paths, which are discussed in detail below. 
     The source of liquid cryogen  104  is connected to the cryoprobe  117  via, in series from upstream to downstream, a line  118 , a two-way valve,  121 , and a cryoprobe inlet  116 . 
     The source of gaseous cryogen  102  is connected to the cryoprobe  117  via, in series from upstream to downstream, a line  110 , a two-way valve  113 , a line  115 , a two-way valve  112 , a heater  105 , and a cryoprobe inlet  108 . 
     The cryoprobe  117  is connected to the gaseous cryogen source  102  via, in series from upstream to downstream, a line  119 , a two-way valve  120 , a line  123 , a heater  122 , a line  124 , a pump  134 , a line  132 , and a two-way valve  106 . A flow meter  182  and a relief valve  107  may be connected to line  124  between the heater  122  and the pump  134 . 
     The cryoprobe  117  is connected to the liquid cryogen source  104  via, in series, a line  133  that is connected to line  132  at a point between the pump  134  and the two-way valve  106 , two-way valves  103  and  130 , a line  129 , and a pressure indicator  181 . 
     Also present in the system  100  is a pressure regulator connected to a line  135  that interconnects the two-way valve  130  and the line  115 . 
     A cryoablation procedure may include one or more alternating cooling and active thawing processes, which follow an initialization procedure. 
     Operation of the system  100  is discussed. During a freezing process of the cryoablation procedure, liquid cryogen exits from source  104  through the line  118 . Flow is controlled by either the pressure regulator  101 , or by the two-way valve  121 , although during the freezing process the two-way valve  121  is typically in the open state. The flow of the liquid cryogen is controlled as the liquid cryogen boils, thereby limiting the heat flux to assure smooth operation, as previously described. Cryogen then enters through the inlet  116  and into the cryoprobe  117  where it then cools a tip  124 , which may optionally be solid or hollow. Exhausted cryogen (i.e., cryogen that has cooled the surrounding environment through boiling and has expanded, as the liquid portion of the cryogen is reduced relative to the gaseous portion) then exits through a return tube  106  of the cryoprobe  117  to the line  119 . The exhausted cryogen then passes through the two-way valve  120  and is optionally heated by the heater  122  to ensure that the return line temperature is above the boiling temperature of the cryogen, such that the exhausted cryogen is maintained in a gaseous state. Optionally and alternatively, the cryogen is not heated. The gaseous cryogen then flows through a line  124  and a flow meter  182 , which measures the rate of flow of cryogen through the line  124 . As described in greater detail below, this flow rate information is one component upon which the pressure regulation for system  100  is based. Optionally, if the flow rate is too high for the desired pressure in system  100  to be maintained and/or for effectively cooling tip  124 , gaseous cryogen may be exhausted through a relief valve  107 . 
     The gaseous cryogen, if not exhausted, then passes to the pump  134 , which is controlled to maintain the desired pressure in system  100 . Pump  134  pumps the gaseous cryogen to gaseous cryogen source  102  through the line  132  and then through the two way valve  106 . The desired gaseous state of the cryogen upon entering pump  134  is maintained by the heater  122 , as previously described. Optionally, the gaseous cryogen may be pumped through the two-way valve  103  to the line  131  and hence through the two way valve  130  to the liquid cryogen source  104  through the line  129 . This optional flow path may be advantageous in maintaining the desired pressure differential between the liquid cryogen source  104  and the gaseous cryogen source  102  as described in greater detail below. 
     System pressure is measured at liquid cryogen source  104  by the pressure gauge  181  and at the gaseous cryogen source  102  by the pressure gauge  184 . Preferably, pressure is higher at the source of gaseous cryogen  102  than at the source of liquid cryogen  104 . 
     The pressure regulator  101  and the pump  134  control the overall pressure of system  100 . In more detail, pressure regulator  101  receives information regarding the pressure of system  100  from pressure gauge  181  and flow meter  182  and, based on this received information, the activity of pump  134  may be adjusted through a suitable electronic circuit (not shown) such that the pressure in the gaseous cryogen source  102  is preferably maintained at a higher level than the pressure in the liquid cryogen source  104 . Optionally, in case of excessive systemic pressure, cryogen gas may be exhausted through valve  107 . Also, optionally, in case of excessive pressure at liquid cryogen source  104 , gaseous cryogen may be exhausted through the relief valve  191 . Preferably however, gaseous cryogen is recycled to gaseous cryogen source  102  and the desired pressure is maintained in system  100 . 
     During the active thawing process, the gaseous cryogen flows from gaseous cryogen source  102  through the line  110 , the two-way valve  113 , the line  115 , the two-way valve  112  and is heated by the heater  105 , after which the heated gaseous cryogen enters the cryoprobe  117  through the inlet  108 . This gaseous cryogen continues to flow through the line  119  to the pump  134 . Pump  134  raises the pressure of the gaseous cryogen and returns the gaseous cryogen to the gaseous cryogen source  102 . During this operation valve  107  remains closed and the gaseous cryogen is fully recycled. 
     During an initialization process of the system, when the flow meter  182  indicates that cryogen is not flowing, the pump  134  is first pumping either air or cryogen into source  104 , by opening valves  103  and  130  for line  129 , and also by opening valve  107  to permit entry of air. When the pressure indicator  181  reaches a determined (threshold) value, valve  103  closes and valve  106  opens to deliver the compressed gas to the source  102 , until the pressure at source  102  reaches another determined value, as read by pressure sensor  184 . 
     During the freezing phase of operation, when valves  121  and  120  are open and flow meter  182  indicates flow is occurring, pump  134  is primarily activated to return cryogen to the source  102  through the valve  106 , as long as the pressure as measured by pressure meter  181  is maintained at the desired value or range of values. If the pressure meter  181  indicates that the pressure is below the desired value threshold, then pump  134  forces the cryogen through valves  103  and  130  into the source  104 . During the active thawing phase of operation, pump  134  simply recycles the cryogen through valves  106 ,  113 ,  112  and  120  through lines  110 ,  108  and  119 . 
     Referring now to  FIG. 2 , there is illustrated a system  200  consistent with an embodiment of the present invention. The system  200 , in some respects, operates similarly to system  100  of  FIG. 1 . Thus, for ease of explanation, like components between systems  100  and  200  share corresponding reference numbers and detailed description thereof is omitted. 
     A feature of the system  200  that differentiates it from the system  100  is that pump  234  operates constantly to recycle the cryogen return gas. Furthermore, the pump  234  is preferably able to pump both liquid cryogen and gaseous cryogen. In order to maintain pressure in system  200 , rather than controlling the activity of pump  234 , the pressure regulator  201  preferably controls the exhaust of excess gaseous cryogen through a relief valve  291  at liquid cryogen source  204 . Pressure gauge  292  is preferably located between liquid cryogen source  204  and relief valve  291 , to determine the pressure at liquid cryogen source  204 . In system  200 , where the pump  234  can handle liquid as well as gaseous cryogen, the operation of heater  222  is reserved only for cases when the gaseous cryogen is exhausted through relief valve  207 . 
     Referring now to  FIG. 3 , there is illustrated a system  300  consistent with an embodiment of the present invention. The system  300 , in some respects, operates similarly to system  100  of  FIG. 1 . Thus, for ease of explanation, like components between systems  100  and  300  share corresponding reference numbers and detailed description thereof is omitted. 
     A feature of the system  300  that differentiates it from the system  100  is the presence of additional structure to generate gaseous cryogen in order to fill gaseous cryogen source  302 . In more detail, the sources of cryogen  302  and  304  are connected by line  352 , a two-way valve  353 , and a line  354 , in series from the source  304  to the source  302 . Also present is a heater  351  disposed in the source  304 . 
     In operation, the additional structure generates gaseous cryogen by energizing heater  351  to heat and boil liquid cryogen in the liquid cryogen source  304 . The gaseous cryogen at liquid cryogen source  304  is then preferably directly transferred to gaseous cryogen source  302  through a line  352  and a two-way valve  353 , thereby rapidly increasing the pressure at gaseous cryogen source  302  to the desired pressure and more rapidly enabling system  300  to achieve the desired system pressure. The additional structure is preferably operative during the initiation of the activity of system  300  (i.e., upon initiation of cryotherapy). 
     Referring now to  FIG. 4 , there is illustrated a portion system  400  consistent with an embodiment of the present invention. The system  400 , in some respects, operates similarly to system  100  of  FIG. 3 . Thus, for ease of explanation, like components between systems  100  and  400  share corresponding reference numbers and detailed description thereof is omitted. 
     A feature of the system  400  that differentiates it from the system  100  is additional structure for controlling pressure. In more detail, the pressure control structure includes a closed container  451 , a line  452  extending from one end of the closed container, and a check valve  461  at another end of the closed container. A heater  467  is disposed in the closed container  451  and is controlled by a control circuit  462 . 
     In system  400 , the first source  404  contains liquid cryogen. Inside of the first source  404  there is an additional closed container  453 . The container  451  permits cryogen to flow in through a check valve  461  when the pressure in first source  404  is greater than the pressure in container  453 . When an electrical heater  467  is activated, the pressure in the container  451  is raised and the check valve  461  is closed. As the pressure increases with the boiling that occurs due to the heating, gaseous cryogen flows in the direction  464  which connects container  451  with the second source of gaseous cryogen (not shown), at a pressure set by pressure regulator  463 . During the freezing or cooling mode of operation, liquid cryogen flows through a filter  414 , when valve  421  is open to a cryoprobe (cryosurgical device, not shown) in the direction indicated by the arrow  465 . When the pressure in the first source  404  is lower than desired, pressured gaseous cryogen enters through a line  429 , upstream of which is an additional pressure regulator of in the direction indicated by  466 . 
     During the initialization of the system  400 , the electrical heater  467  is activated and boils the cryogen in container  451 . When the pressure reaches a determined value, the pressure regulator  463  opens and the compressed gaseous cryogen is transferred in the direction  464  to the second source (not shown). During other phases of operation the system  400  operates in a manner at least similar to system  100 . 
     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. 
     The various described embodiments may be selectively combined. 
     Although selected embodiments of the present invention have been shown and described, it is to be understood the present invention is not limited to the described embodiments. Instead, it is to be appreciated that changes may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and the equivalents thereof.