Abstract:
An apparatus and method are described for actuating a minimally invasive medical device using fluid pressure. The invention involves a medical device that includes a fluid source, such as a compressible bladder that may apply positive fluid pressure into a sheath to controllably deploy an end-effector from a distal end of the sheath. In some embodiments, the fluid source may apply negative fluid pressure into the sheath to controllably retract the end-effector into the distal end of the sheath. Typical end-effectors for use with the medical device of the invention include biopsy devices and retrieval devices, including basket-type retrieval devices and grasper retrieval devices. Generally, the fluid that is used to actuate the device may be a liquid or a gas, including air.

Description:
TECHNICAL FIELD  
         [0001]    The invention generally relates to a minimally invasive medical device for use in procedures such as retrieval or biopsy. More particularly, the invention relates to a minimally invasive medical device that is actuated through application of fluid or air pressure.  
         BACKGROUND  
         [0002]    Current minimally invasive medical devices for use in operations such as retrieval or biopsy are typically operated by mechanical means, using a pull wire. Typically, a distal end of the pull wire connects to an end-effector, such as a basket-type retrieval device, a grasper, a biopsy device, etc. Generally, the proximal end of the pull wire is connected to a control or actuation mechanism in the handle of the medical device.  
           [0003]    The pull wire typically transmits movement in a control or actuation mechanism in the handle of the device to the end-effector. Through use of such a pull wire, or a series of pull wires, the end-effector can be controlled to extend from the end of a sheath, retract into the sheath, cut away a sample for a biopsy, or to take other actions that are typically performed by devices such as graspers, basket-type retrieval devices or biopsy devices.  
           [0004]    The pull wire in these devices is typically made of metal, and is often somewhat rigid. This rigidity can make it more difficult to maneuver the medical device within the body.  
           [0005]    Additionally, use of a pull wire and actuation mechanisms associated with the pull wire add substantially to the number of component parts of a minimally invasive medical device. This increases the cost and complexity of the device, and increases the chance of failure of the device.  
           [0006]    Minimally invasive medical devices that use actuation means other than a pull wire have been developed. For example, some devices use compressed gas to propel a needle, biopsy device, or other medical device. Such pneumatically-actuated medical devices typically use a “firing trigger” mechanism to trigger the release of the compressed gas. Such mechanisms provide very little control, and are typically only able to perform the single action of rapidly propelling a device such as a needle.  
           [0007]    While this lack of control may be acceptable for some procedures, many medical procedures require fine control over the rate, timing, and precise positioning of a device. Other applications for minimally invasive medical devices require more varied action than simply propelling a portion of the device forward. For example, many procedures require a medical device that can be controllably extended and retracted. Devices that use compressed gas and “firing triggers” typically do not provide such fine control or varied actions.  
         SUMMARY OF THE INVENTION  
         [0008]    In view of the foregoing, a minimally invasive medical device that provides a high degree of controllability, but does not use pull wires or other actuation mechanisms that may substantially reduce the flexibility of the device is desirable. The present invention, in one embodiment, provides a minimally invasive medical device in which an end-effector, such as a retrieval device or biopsy device, may be extended or retracted through controlled use of fluid pressure. Because no pull wire is needed to control the device, a medical device in accordance with this embodiment of the invention provides increased flexibility relative to known devices that perform similar operations. Additionally, medical devices constructed in accordance with this embodiment of the invention require fewer parts than other devices that perform similar functions, thereby decreasing manufacturing costs and increasing reliability.  
           [0009]    In one aspect, the invention provides a medical device that includes a sheath, and an operator-controlled fluid source adapted to apply positive fluid pressure into the sheath to deploy at least a portion of an end-effector from a distal end of the sheath in a controlled fashion. In some embodiments, the fluid source is adapted to apply negative fluid pressure into the sheath to controllably retract at least a portion of the end-effector into the sheath. Typical end-effectors for use with the medical device of the invention include biopsy devices and retrieval devices, including basket-type retrieval devices and grasper retrieval devices, and the like. In one embodiment, the fluid that is used to actuate the device may be a liquid. In another embodiment, the actuating fluid is a gas, such as air. In another embodiment, the actuating fluid is a gel. According to other embodiments, any suitable actuating fluid may be employed.  
           [0010]    In some embodiments, the end-effector includes a first hub, disposed within the sheath in a manner that permits it to slide within the sheath. According to one feature, the first hub is adapted to substantially form a seal with the sheath. Applying a positive fluid pressure within the sheath causes the first hub to move in a distal direction within the sheath. In some embodiments, applying a negative fluid pressure within the sheath causes the first hub to move in a proximal direction within the sheath. With the end-effector connected to the first hub, this movement of the hub causes the end-effector to be moved from a “closed” position within the sheath, to an “open” position, in which a portion of the end-effector extends from the distal end of the sheath.  
           [0011]    In some embodiments, a stop, located within the sheath, prevents the first hub from moving in a distal direction past the stop. Some embodiments, particularly those in which a negative fluid pressure may be applied, also include a second stop that prevents the hub from moving in a proximal direction past the second stop.  
           [0012]    In some embodiments, the operator-controlled fluid source is a bladder that is in fluid communication with the sheath. When pressure is applied to the bladder, the bladder pushes fluid into the sheath, thereby applying positive fluid pressure. When pressure is released from the bladder, the bladder pulls fluid from the sheath, applying negative fluid pressure.  
           [0013]    In one embodiment, the bladder is placed on a handle that is located at a proximal end of the sheath. In some embodiments, the bladder may be placed at a location on the handle that permits an operator to operate the bladder using his or her thumb. According to one feature, the handle and bladder have an ergonomic design, which provides easy and comfortable operation of the medical device.  
           [0014]    In some embodiments, an elastic member, such as a spring is used to retract the end-effector. In some such embodiments, the elastic member is compressed when the end-effector is deployed, while in other embodiments, the elastic member is stretched when the end-effector is deployed. In these embodiments, the elastic member retracts at least a portion of the end-effector into the sheath when the positive fluid pressure is insufficient to overcome the force applied by the stretched or compressed elastic member.  
           [0015]    Some devices for use with the medical device of the invention may require actuation of more than one portion of the device. For example, in some biopsy devices, multiple steps may be used to take a sample. In one such biopsy device, a stylet is extended from the distal end of a sheath. Once the stylet is fully extended, a cannula is extended over the stylet to capture a tissue sample. In one embodiment, the invention provides a mechanism for controlling or actuating such devices by using multiple slidable hubs. In an alternative embodiment, the invention employs an elastic member, such as a spring, and a latch for control and actuation.  
           [0016]    In some embodiments, the end-effector includes a second hub that is disposed within the sheath at a position distal of the stop, and that is able to slide within the sheath. In some embodiments, a second stop disposed within the sheath prevents the second hub from moving in a distal direction past the second stop.  
           [0017]    In some embodiments, the first hub includes an opening that permits a limited flow of fluid through the first hub. When the first hub is prevented from further distal movement by the first stop, this opening permits fluid pressure to move the second hub in a distal direction.  
           [0018]    In some such embodiments, the end-effector comprises a biopsy device, the first hub is connected to a stylet portion of the biopsy device, and the second hub is connected to a cannula portion of the biopsy device. When the first hub is moved in a distal direction, the stylet portion of the biopsy device is extended from the distal end of the sheath. When the second hub is moved in a distal direction, the cannula portion of the biopsy device is extended from the distal end of the sheath.  
           [0019]    In some embodiments, a notch is formed in the stylet portion of the biopsy device, and the cannula portion of the biopsy device has a sharp edge. When the cannula portion of the biopsy device is extended from the distal end of the sheath, the cannula portion of the biopsy device slides over the stylet portion of the biopsy device. This permits the cannula to cut tissue, and to capture a tissue sample within the notch formed in the stylet portion of the biopsy device.  
           [0020]    Instead of using two (or more) sliding hubs to control end-effectors with multiple moving portions, elastic members and latches may be used. In some embodiments, the end-effector includes a first portion, connected to the first hub, and a second portion. A proximal end of an elastic member, such as a spring, connects to the first hub, and a distal end of the elastic member connects to the second portion of the end-effector. Additionally, the medical device includes a latch that holds the second portion of the end-effector in a stationary position relative to the sheath until the latch is released.  
           [0021]    In one embodiment, the elastic member compresses when the first hub moves in a distal direction. In some embodiments, the elastic member propels the second portion of the end-effector in a distal direction when the latch is released.  
           [0022]    For example, if the end-effector is a biopsy device, the first portion of the end-effector may be a stylet, and the second portion may be a cannula. When positive fluid pressure is applied, the stylet extends from the distal end of the sheath, and the elastic member compresses. When the latch is released, the cannula is propelled in a distal direction by the elastic member, extending from the distal end of the sheath, and sliding over the stylet, capturing a tissue sample in a notch formed in the stylet.  
           [0023]    In another aspect, the invention provides a method for controlling an end-effector, in which positive fluid pressure is applied to controllably deploy the end-effector from the distal end of a sheath. In some embodiments, applying positive fluid pressure is accomplished by applying pressure to a bladder in fluid communication with the sheath. Some embodiments use negative fluid pressure to controllably retract the end-effector into the sheath. In one embodiment, releasing pressure from a bladder in fluid communication with the sheath applies negative fluid pressure.  
           [0024]    These and other objects, advantages, and features of the invention will become apparent through reference to the following description, the accompanying drawings, and the claims. Furthermore, it will be understood that the features of the various embodiments described herein are not mutually exclusive, and can exist in various combinations and permutations. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the invention are described with reference to the following drawings, in which:  
         [0026]    [0026]FIG. 1 shows an illustrative embodiment of a medical device in accordance with the invention;  
         [0027]    FIGS.  2 A-B show an embodiment of a retrieval end-effector for use with a medical device in accordance with the invention;  
         [0028]    FIGS.  3 A-B illustrate the operation of an embodiment of a medical device in accordance with the invention;  
         [0029]    FIGS.  4 A-B show an embodiment of a retrieval end-effector for use with a medical device in accordance with the invention;  
         [0030]    [0030]FIG. 5 shows an embodiment of a biopsy end-effector for use with a medical device in accordance with the invention;  
         [0031]    FIGS.  6 A-C illustrate operation of the biopsy end-effector of FIG. 5;  
         [0032]    [0032]FIG. 7 shows an embodiment of a biopsy end-effector for use with a medical device in accordance with the invention; and  
         [0033]    FIGS.  8 A-B illustrate the operation of the biopsy end-effector of FIG. 7.  
     
    
     DESCRIPTION  
       [0034]    [0034]FIG. 1 shows a view of a medical device  100  in accordance with an illustrative embodiment of the present invention. The medical retrieval device  100  includes a sheath  102 , an end-effector  104  (in this case, a basket-type retrieval device), disposed at a distal end  112  of the sheath  102 , and a handle  106 , disposed at a proximal end  114  of the sheath  102 .  
         [0035]    The handle  106  includes a bladder  108 , which is connected through the handle  106  to the sheath  102  so that it is in fluid communication with the sheath  102 . The bladder  108  and the sheath  102  are filled with a fluid, such as air, water, a saline solution, or other liquids, gels, or gasses.  
         [0036]    The end-effector  104  is connected to an inner hub  110 , which is disposed within the sheath  102  in a manner that permits it to slide between a proximal stop  118  and a distal stop  116 . Preferably, a substantially effective seal is created between the inner hub  110  and the sheath  102 , inhibiting the escape of fluid from sheath the  102  past the inner hub  110 .  
         [0037]    Pressure applied to the bladder  108  forces fluid out of the bladder  108 , and into the sheath  102 , causing positive fluid or air pressure in the sheath  102 , and pushing the inner hub  110  towards the distal end  112  of the sheath  102 . This extends the end-effector  104 , which is connected to the inner hub  110 , into an “open” position, thereby deploying the end-effector  104 . The movement of the inner hub  110  is limited by the distal stop  116 , which prevents the inner hub  110  from sliding distally any farther than the distal stop  116 .  
         [0038]    Releasing pressure from the bladder  108 , fluid in the sheath  102  draws back into the bladder  108 , causing negative fluid pressure in the sheath  102 . This negative pressure pulls the inner hub  110  and the end-effector  104  towards the proximal end  114  of the sheath  102 , retracting the end-effector  104  into a “closed” position within the sheath  102 . The proximal movement of the inner hub  110  is limited by the proximal stop  118 , which prevents the inner hub  110  from sliding proximally farther than the proximal stop  118 .  
         [0039]    In FIG. 1, the medical device is shown with the end-effector  104  fully extended, and the inner hub  110  abutting the distal stop  116 . This is the configuration that the medical device would have if sufficient pressure were applied to the bladder  108  to completely extend the end-effector  104 .  
         [0040]    The sheath  102 , the end-effector  104 , the handle  106 , the bladder  108 , the inner hub  110 , the proximal stop  118 , and the distal stop  116  as illustrated in FIG. 1 are not necessarily shown in their correct size or proportion to each other. Preferably, the sheath  102  is dimensioned to fit the requirements of its application in the body. For example, for urological applications, the outside diameter of the sheath  102  is typically between 1.7 and 8.0 french, though some applications may call for larger or smaller sizes.  
         [0041]    The handle  106  is preferably sized to fit easily in an operator&#39;s hand, and the bladder  108  is preferably sized and placed on the handle  106  in a position that permits an operator to use his or her thumb to depress the bladder  108 . In preferred embodiments of the invention, the handle  106  and the bladder  108  are ergonomically sized and placed, providing a medical device that is comfortable and easy to use. However, other sizes and shapes for the handle  106  are within the scope of the invention. Additionally, excluding the handle  106  from the device entirely, so that the bladder  108  is directly connected to the sheath  102  is within the scope of the invention. Similarly, alternative placements of the bladder  108 , including separating the bladder  108  from the handle  106  are also within the scope of the invention.  
         [0042]    Advantageously, since the end-effector  104  of the medical device  100  is operated using fluid pressure, there is no need for a pull wire to be used to operate the end-effector  104 . Since there is no pull wire, the flexibility of the medical device  100  is increased. Additionally, fewer mechanical components are needed to construct the medical device  100 , potentially decreasing the manufacturing cost and likelihood of failure of the medical device  100 .  
         [0043]    A high degree of control is achieved by use of an operator-controlled fluid source, such as the bladder  108 . For example, in some embodiments, by compressing the bladder  108  to varying degrees, an operator may determine the degree to which the end-effector  104  extends from the distal end of the sheath  102 . In some embodiments, by releasing pressure from the bladder  108 , the operator may retract the end-effector  104  into the sheath  102 . In various embodiments, an operator-controlled fluid source, such as the bladder  108 , can control the rate or speed of deployment, the degree of deployment, the position, or other operational aspects of the medical device  100  and end-effector  104 .  
         [0044]    [0044]FIGS. 2A and 2B show an embodiment of the invention in a closed and an open position, respectively. In FIG. 2A, the end-effector  104  is in the closed position, collapsed within the sheath  102 . As can be seen, the inner hub  110  is positioned near the proximal stop  118 . As shown in FIG. 2B, applying positive fluid pressure within the sheath  102  pushes the inner hub  110  into a position adjacent to the distal stop  116 , and pushes the end-effector  104  out of the end of the sheath  102 , into an open position. In the illustrative embodiment shown in FIGS. 2A and 2B, the end-effector is a basket-type retrieval device, which expands into the form shown in FIG. 2B when extended out of the distal end of the sheath  102 .  
         [0045]    [0045]FIGS. 3A and 3B illustrate the operation of an embodiment of the medical device of the invention. In FIG. 3A, an operator applies no pressure to the bladder  108 , so the end-effector (not shown) remains in the closed position, collapsed within the sheath  102 . In FIG. 3B. the operator depresses the bladder  108 , forcing fluid from the bladder  108  into the sheath  102 , causing positive fluid pressure in the sheath  102 . This positive pressure pushes the end-effector out of the distal end of the sheath  102 , into its open position. The operator may return the end-effector to the closed position by ceasing the application of pressure on the bladder  108 . This causes negative fluid pressure in the sheath  102 , which pulls the end-effector back into the closed position. The operator can extend the end-effector out of the distal end of the sheath  102  to varying degrees by varying the amount of pressure applied to the bladder  108 .  
         [0046]    Referring now to FIGS.  4 A- 4 B, another embodiment of the medical device of the invention is shown. In FIG. 4A, a medical device  400 , of which only a distal portion is shown, is in its closed position. As in previous embodiments, an end-effector  402  (a basket-type retrieval device, in this embodiment) connects to an internal hub  404 . The internal hub  404  slides within a sheath  406 , and preferably forms a seal with the sheath  406 . A proximal stop  408  and a distal stop  410  limit the range of movement of the internal hub  404 . As in previously discussed embodiments, application of positive fluid pressure pushes the internal hub  404  and the end-effector  402  in a distal direction, extending the end-effector  402  into its open position.  
         [0047]    The medical device  400  includes an elastic member, such as a spring  412 , which provides a positive closure mechanism for the medical device  400 . When the medical device  400  is in the closed position, with the end-effector  402  collapsed within the sheath  406 , and the internal hub  404  adjacent to the proximal stop  408 , the spring  412  is in an equilibrium position, and does not exert force on the internal hub  406 .  
         [0048]    As shown in FIG. 4B, when sufficient fluid pressure pushes the inner hub  404  towards the distal stop  410 , the end-effector  402  extends from the sheath  406 , into its open position. In the open position, the spring  412  is compressed, and exerts a force on the internal hub  404  to push the internal hub  404  towards the proximal stop  408 . The force exerted by the spring  412  assists in placing the medical device  400  into the closed position when the fluid pressure is released or becomes insufficient to compress the spring  412 .  
         [0049]    Other elastic members, such as elastic materials may be used in place of the spring  412 . Additionally, instead of compressing the elastic member, in some embodiments, extending the end-effector stretches the elastic member. When the elastic member is stretched in this manner, it exerts a force to assist in retracting the end-effector.  
         [0050]    As mentioned above, numerous types of end-effectors may be used in conjunction with the fluid pressure-actuated medical device of the present invention. For example, instead of using a basket-type retrieval device as the end-effector, a grasper retrieval device, cutting device or any other device previously deployed using a pull wire may be used.  
         [0051]    [0051]FIG. 5 shows a biopsy device end-effector for use with an embodiment of a medical device in accordance with the principles of the invention. A biopsy device  500  includes a hub  502 , to which a stylet  504  is rigidly attached. An elastic member, such as a spring  506  surrounds a proximal portion of the stylet  504 , and connects at its proximal end to the hub  502 , and at its distal end to a cannula  508 .  
         [0052]    A latch  510 , which is preferably connected to a sheath  512 , holds the cannula  508  in place. The latch  510  holds the cannula  508  at a fixed position within the sheath  512 , while permitting the hub  502  and the stylet  504  to be pushed forward by fluid pressure. As the fluid pressure pushes the hub  502  forward, the stylet  504  extends out of the distal end of the sheath  512 , and the cannula  508  remains stationary, causing the spring  506  to compress. When the stylet  504  fully extends, the hub  502  causes the latch  510  to release, propelling the cannula  508  forward, to enclose the stylet  504 . The cannula  508  includes a sharp edge  514 , that cuts tissue when propelled forward, capturing a sample of the tissue within a notch formed in the stylet  504 .  
         [0053]    The biopsy device  500  fits within the sheath  512 . Preferably, the hub  502  forms a substantially effective seal with the sheath  512  so that it can be propelled forward by positive fluid or air pressure in the sheath  512 . In the embodiment shown in FIG. 5, the latch  510  acts as a stop, preventing the hub  502  from being propelled past the latch  510 . In other embodiments, stops (not shown), such as the proximal and distal stops shown in previously embodiments may be used.  
         [0054]    FIGS.  6 A- 6 C show the operation of the biopsy device  500 . In FIG. 6A, the biopsy device  500  is within the sheath  512 , with the spring  506  in an equilibrium position, and the cannula  508  held in place by the latch  510 .  
         [0055]    In FIG. 6B, an operator has started to apply pressure to a fluid filled bladder (not shown) in fluid communication with the sheath  512 , causing positive fluid pressure within the sheath  512  to propel the hub  502  towards the distal end of the sheath  512 , thereby extending the stylet  504 . Because the hub  502  is being pushed towards the distal end of the sheath  512 , and the cannula  508  is being held in place, the spring  506  compresses. In FIG. 6B, the hub  502  has not yet caused the latch  510  to release the cannula  508 .  
         [0056]    In FIG. 6C, the latch  510  has been released, causing the spring  506 , which was compressed, to propel the cannula  508  forward over the stylet  504 . When the cannula  508  is propelled forward, it cuts tissue, capturing a tissue sample  602  within a slot formed in the stylet  504 .  
         [0057]    [0057]FIG. 7 shows another embodiment of a biopsy device for use as an end-effector in a medical device according to the invention. In the embodiment shown in FIG. 7, no spring is needed to propel the cannula forward to cut tissue, as in the previous embodiment. Instead, fluid pressure is used to propel both the stylet and the cannula.  
         [0058]    In FIG. 7, a biopsy device  700  is shown in a fully extended position, with a stylet  702  and a cannula  704  fully extended from the distal end of a sheath  706 . The stylet  702  attaches to a stylet hub  708 , and the cannula  704  attaches to a cannula hub  710 . Preferably, the stylet hub  708  and the cannula hub  710  form seals with the sheath  706 .  
         [0059]    A stylet stop  712  limits the distal movement of the stylet hub  708  (and, therefore, of the stylet  702 ). The stylet stop  712  prevents the stylet hub  708  from advancing in a distal direction past the stylet stop  712 . Note that the stylet stop  712  may also prevent the cannula hub  710  from moving in a proximal direction past the stylet stop  712 . Optionally, an additional proximal stop (not shown) may be included to limit the proximal movement of the stylet hub  708 .  
         [0060]    A cannula stop  714  limits the distal movement of the cannula hub  710  (and the cannula  704 ). The cannula stop  714 , which may be integrated into a distal tip of the sheath  706 , prevents the cannula hub  710  from advancing in a distal direction past the cannula stop  714 . As noted above, the stylet stop  712  may limit the proximal movement of the cannula hub  710 .  
         [0061]    The stylet hub  708  includes a small hole  718  which permits a limited amount of fluid to pass through the stylet hub  708  into the area between the stylet hub  708  and the cannula hub  710 . In operation, positive fluid pressure first pushes the stylet hub  708  in a distal direction, extending the stylet  702  from the distal end of the sheath  706 . When the stylet  702  is fully extended, the stylet stop  708  prevents further distal movement of the stylet hub  708 .  
         [0062]    At this point, fluid forced through the hole  718  in the stylet hub  708  causes positive fluid pressure to push the cannula hub  710  (and the cannula  704 ) in a distal direction, extending the cannula  704  out of the distal end of the sheath  706 . As the cannula  704  extends over the stylet  702 , a sharp edge  716  of the cannula  704  cuts tissue, capturing a tissue sample within a notch formed in the stylet  702 . When the cannula  704  is fully extended, the cannula stop  714  prevents further distal movement of the cannula hub  710 .  
         [0063]    FIGS.  8 A-B illustrate this process. In FIG. 8A, positive fluid pressure has propelled the stylet  702  out of the distal end of the sheath  706 . The stylet stop  712  is preventing the stylet hub  708  from further movement in a distal direction. The cannula hub  714  has not yet been pushed in a distal direction by a substantial amount, and the cannula  704  is still within the sheath  706 .  
         [0064]    In FIG. 8B, when the stylet hub  708  is prevented from further distal movement by the stylet stop  712 , fluid forced through the hole  718  in the stylet hub  708  propels the cannula  704  out of the distal end of the sheath  706 . In FIG. 8B, the cannula  704  is fully extended, and further distal movement of the cannula hub  710  is prevented by the cannula stop  714 .  
         [0065]    In some embodiments, the biopsy end-effectors described with reference to FIGS.  5 - 8  may be retracted by application of negative fluid pressure. In other embodiments, the end-effectors of FIGS.  5 - 8  may not require retraction. In addition, such biopsy devices may be operated through application of short bursts of fluid pressure, rather than through substantially continuous application of pressure to a fluid filled bladder in fluid communication with a sheath.  
         [0066]    Other embodiments incorporating the concepts disclosed herein are within the spirit and scope of the invention. The described embodiments are illustrative of the invention and not restrictive.