fig1 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 . 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 . 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 . 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 . 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 . in fig1 , 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 . 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 fig1 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 . 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 . 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 . 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 . fig2 a and 2b show an embodiment of the invention in a closed and an open position , respectively . in fig2 a , 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 fig2 b , 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 fig2 a and 2b , the end - effector is a basket - type retrieval device , which expands into the form shown in fig2 b when extended out of the distal end of the sheath 102 . fig3 a and 3b illustrate the operation of an embodiment of the medical device of the invention . in fig3 a , 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 fig3 b . 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 . referring now to fig4 a - 4b , another embodiment of the medical device of the invention is shown . in fig4 a , 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 . 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 . as shown in fig4 b , 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 . 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 . 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 . fig5 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 . 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 . 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 fig5 , 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 . fig6 a - 6c show the operation of the biopsy device 500 . in fig6 a , 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 . in fig6 b , 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 fig6 b , the hub 502 has not yet caused the latch 510 to release the cannula 508 . in fig6 c , 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 . fig7 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 fig7 , 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 . in fig7 , 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 . 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 . 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 . 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 . 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 . fig8 a - b illustrate this process . in fig8 a , 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 . in fig8 b , 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 fig8 b , the cannula 704 is fully extended , and further distal movement of the cannula hub 710 is prevented by the cannula stop 714 . in some embodiments , the biopsy end - effectors described with reference to fig5 - 8 may be retracted by application of negative fluid pressure . in other embodiments , the end - effectors of fig5 - 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 . 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 .
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 .