Abstract:
Apparatuses, systems, and methods are described for selectively generating an aspiration flow within a surgical instrument. Particularly, the disclosure describes example vitrectomy probes operable to selectively generate an aspiration flow in relation to operation of the cutter of the vitrectomy probe.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates to systems, apparatuses, and methods for traction-limiting vitrectomy probes. Particularly, this disclose relates to systems, apparatuses, and methods for vitrectomy probes having one or more internal valves to create a displacement pump and reduce or eliminate traction on the retina of an eye. 
       BACKGROUND 
       [0002]    Vitrectomy probes are used during vitreoretinal surgery to remove ocular tissues, such as vitreous humor and membranes covering the retina. These probes generally include a port for drawing in and dissecting tissues. The port opens, tissue is drawn into the port, the port closes, severing the tissue, and the tissue is aspirated. This action may be repeated to remove desired tissues. 
       SUMMARY 
       [0003]    According to one aspect, the disclosure describes a surgical instrument that includes a body, a cutter coupled to the body, and a motor. The cutter may include an outer cutting member having a port and an inner cutting assembly. The inner cutting assembly may be slideable within the outer cutting member. The inner cutting assembly may include an inner cutting member; and a valve selectable between an open configuration and a closed configuration. The motor may be operable to reciprocate the inner cutting assembly between an extended position and a retracted position. 
         [0004]    Another aspect of the disclosure encompasses a method of operating a surgical instrument. The method may include forming an occlusion within a portion of an inner cutting member; retracting the inner cutting member within an outer cutting member in a first direction; removing the occlusion within the portion of the inner cutting member; and extending the inner cutting member within an outer cutting member in a second direction opposite the first direction. 
         [0005]    Another aspect of the disclosure encompasses a vitrectomy probe that may include a body and a cutter extending from the body. The cutter may include an outer cutting member and an inner cutting member slideable within the outer cutting member between an extended position and a retracted position. The vitrectomy probe may also include a diaphragm coupled to the inner cutting member and disposed within a chamber formed in the body. The diaphragm may divide the chamber into a first chamber portion and a second chamber portion. The diaphragm may be moveable in a first direction to retract the inner cutting member in response to a first pneumatic pressure introduced into the first chamber portion. The vitrectomy probe may also include a first valve coupled to the inner cutting member. At least a portion of the valve may be disposed in the first chamber portion and adapted to be closed upon introduction of the first pneumatic pressure into the first chamber portion. 
         [0006]    The various aspects may include one or more of the following features. The valve may be configured to close when the inner cutting assembly is in the extended position. The valve may be configured to open when the interior cutting assembly is in the retracted position. The body may include a chamber, and the motor may be at least partially disposed in the chamber. The motor may include a diaphragm, and the diaphragm may be displaced into the retracted position by a first pneumatic pressure. The valve may be configured to close in response to the first pneumatic pressure. The valve may be configured to open upon removal of the first pneumatic pressure. The valve may include a tubular member defining an opening and a resilient member disposed on the tubular member and overlaying the opening. 
         [0007]    The various aspects may include one or more of the following features. Forming an occlusion within a portion of an inner cutting member may include closing a valve coupled to the inner cutting member. Closing a valve coupled to an inner cutting member may include applying a pneumatic pressure to at least a portion of the valve. Removing the occlusion formed within a portion of an inner cutting member may include opening the valve coupled to the inner cutting member. Opening a valve coupled to an inner cutting member may include removing an applied pneumatic pressure from at least a portion of the valve. Retracting an inner cutting member within an outer cutting member in a first direction may include applying a pneumatic pressure to a side of a diaphragm coupled to the inner cutting member. Extending an inner cutting member within an outer cutting member in a second direction opposite the first direction may include applying a pneumatic pressure to a side of a diaphragm coupled to the inner cutting member. 
         [0008]    The various aspects may also include one or more of the following features. An inner cutting assembly may include an inner cutting member, a tubular member, and a first valve. The inner cutting assembly may define a passageway therethrough. The first valve may be operable to form a closure within the passageway. A second valve may be disposed in the body adjacent to an end of the inner cutting assembly opposite the inner cutting member. The second valve may be adapted to close upon introduction of a second pneumatic pressure into the second chamber portion. 
         [0009]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory in nature and are intended to provide an understanding of the present disclosure without limiting the scope of the present disclosure. In that regard, additional aspects, features, and advantages of the present disclosure will be apparent to one skilled in the art from the following detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a cross-sectional view of an example vitrectomy probe. 
           [0011]      FIG. 2  is a detail view, in schematic form, of a portion of the example vitrectomy probe shown in  FIG. 1 . 
           [0012]      FIGS. 3A-3E  shows schematic views of the operation of an example cutting mechanism that includes a valve selectively moveable into an open configuration and a closed configuration. 
           [0013]      FIG. 4  is a cross-sectional view of another example vitrectomy probe. 
           [0014]      FIG. 5  is a detail view, in schematic form, of a portion of the example vitrectomy probe shown in  FIG. 4 . 
           [0015]      FIGS. 6A and 6B  show cross-sectional views of a valve along a longitudinal axis in an open configuration and a closed configuration, respectively. 
           [0016]      FIGS. 6C and 6D  are transverse cross-sectional views of the example valve shown in  FIGS. 6A and 6B  in the open configuration and the closed configuration, respectively. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    The present disclosure relates to systems, apparatuses, and methods to limit traction on a retina during vitreoretinal surgical procedures. Vitreous humor contained within an eye may be adhered to the retina. Traction generally results when the vitreous humor is pulled, such as during a vitrectomy procedure, and, consequently, the retina is pulled. This traction can lead to retinal injury, such a retinal tear or detachment of a portion of the retina from the eye. In some instances, an example vitrectomy probe may include one or more valves to occlude a portion of an aspiration conduit and create a piston effect that can drive the movement of material. In some instances one or more valves may be used to occlude one or more portions of an aspiration conduit. The one or more valves may be selectively closed during a portion of movement of the vitrectomy probe. For example, the one or more valves may be closed during at least a portion of a stroke movement of a cutter of the vitrectomy probe. In some instances, the one or more valves may include a pneumatic pinch valve. However, any type of valve may be used. 
         [0018]      FIG. 1  shows a cross-sectional view of an example vitrectomy probe  10  that includes a body  20 , a cutter  25 , and a motor  50 . The cutter  25  may include an outer cutting member  30  and an inner cutting member  40 . The inner cutting member  40  is slideable within a lumen  60  of the outer cutting member  30 . The inner cutting member  40  may be tubular and define a lumen  65 . The motor  50  is coupled to the inner cutting member  40 . For example, the inner cutting member  40  may be coupled directly to the motor  50 . In other instances, the inner cutting member  40  may form part of an inner cutting assembly  70 . In some instances, the inner cutting assembly  70  may include a tubular member  80 . The tubular member  80  may extend through a central opening  85  formed in the motor  50 . In other instances, the inner cutting member  40  may extend through the central opening  85 . 
         [0019]    The remainder of the description will be made with reference to an implementation of the vitrectomy probe  10  that includes the inner cutting assembly  70  having the inner cutting member  40  and tubular member  80 . However, it is understood that the scope of the disclosure is not so limited. Rather, the scope of the disclosure includes an inner cutting assembly that may include additional or different components than those described as well as implementations in which the inner cutting member  40  extends through the motor  50 . Further, as also explained, implementations of vitrectomy probes within the scope of the disclosure may have an inner cutting member that does not form part of an inner cutting assembly but, rather, that extends from the outer cutting member  30  to the motor  50 . As such, the following description is provided as a non-limiting example. 
         [0020]    The inner cutting assembly  70  defines a passageway  100  extending from a distal end  34  of the outer cutting member  30  to a proximal end  104  of the inner cutting assembly  70 . Thus, the passageway  100  includes the lumen  65  of the inner cutting member  40 . Additionally, the volume of the passageway  100  effectively increases and decreases as the inner cutting member  40  is retracted and extended relative to the outer cutting member  30 . The passageway  100  is operable to conduct aspirated materials through the vitrectomy probe  10 . The outer cutting member  30  defines a port  32  at the distal end  34  of the outer cutting member  30 . The port  32  communicates with the lumen  60 . The inner cutting member  40  includes a distal end  42 . As the inner cutting member  40  reciprocates within the outer cutting member  30 , the distal end  42  passes by the port  32  and severs material entering therethrough. The severed material is aspirated though lumen  60  and passageway  100  and, ultimately, out of the vitrectomy probe  10 . 
         [0021]    In some instances, the motor  50  may be a pneumatically-actuated motor. For example, in some instances, the motor  50  may include a diaphragm  90  disposed in a chamber  110  formed in the body  20 . In some instances, an outer periphery  92  of the diaphragm  90  may be coupled to the body  20 , and an inner periphery  94  of the diaphragm  90  may be coupled to the inner cutting assembly  70 . Seals  112  may be disposed in the chamber  110 . In some instances, one or more of the seals  112  may provide an air-tight seal. The seals  112  may serve to center the inner cutting assembly  70  within chamber  110 . The vitrectomy probe  10  may also include a seal  114  between the inner cutting assembly  70  and the body  20 . The seal  114  may also serve to align the inner cutting assembly  70  within the body  20 . In some instances, the seal  114  may provide an air-tight seal. 
         [0022]    The diaphragm  90  may be oscillated by alternately applying pneumatic pressure to opposite sides of the diaphragm  90 , thereby oscillating the inner cutting member  40  within the outer cutting member  30 . This type of motor may be described as a double-action motor. In some instances, a single-action motor may be used. For example, the vitrectomy probe  10  may include a return spring, or other type of biasing member, disposed between the diaphragm  90  and the housing  20  in the chamber  110 . Pneumatic pressure may be applied to a side of the diaphragm  90 , opposite the spring. The pneumatic pressure displaces the diaphragm  90  in a first direction, compressing the spring. Upon removal of the pneumatic pressure, the diaphragm  90  is biased and displaced in a direction opposite the first direction. However, the motor  50  may be any type of device operable to oscillate the inner cutting member  40 . For example, the motor may be an electric motor, hydraulic, piezoelectric, or any other type of motor. 
         [0023]      FIG. 2  is a detail view, in schematic form, of a portion of the example vitrectomy probe  10 . In this example, the inner cutting assembly  70  includes a valve  120 . The valve  120  is operable to form a barrier or closure in the passageway  100 . In some instances, the barrier may be a fluid-tight barrier that prevents passage of fluid. In other instances the barrier may not be fluid-tight. In some instances, the valve  120  may be a pinch valve. For example, in some instances, the valve  120  may be a pneumatic pinch valve. Thus, valve  120  may operate in response to pneumatic pressure to open or close or constrict a portion of the passageway  100 . The valve  120  may actuate at a selected pressure. 
         [0024]    Other types of valves may be utilized. For example, in other instances, the valve  120  may be an electric, hydraulic, or any other suitable type of valve or device that is selectively operable to form a barrier in the passageway  100 . Therefore, it is within the scope of the disclosure to encompass any device or feature that is selectively operable to open and close the passageway  100 . 
         [0025]    In the example shown, the valve  120  is a pneumatic pinch valve that is actuated in response to pneumatic pressure applied to chamber  110 . Thus, in the example shown, the valve  120  actuates in response to the pneumatic pressure used to actuate diaphragm  90 . In other instances, pneumatic pressure used to actuate valve  120  may be different from pneumatic pressure used to actuate the diaphragm  90 . Still further, in some instances, pneumatic pressure applied to the valve  120  may be applied solely for the purpose of actuating the valve  120  or otherwise independently of actuation of the motor  50 . 
         [0026]    As shown in  FIG. 2 , pneumatic pressure is applied to a first portion  130  of chamber  110  via passageways  140 ,  150 , and  160 . In  FIG. 2 , the applied pneumatic pressure is at or above a pressure needed to close the valve  120 , as illustrated. The pneumatic pressure may also be operable to displace the diaphragm  90  of motor  50  and the inner cutting assembly  70  in the direction of arrow  170 . With the valve  120  in the closed configuration, as the inner cutting assembly  70  is displaced in the direction of arrow  170 , a piston effect drives flow in the passageway  100 . As a result, materials, such as fluids and tissues, are drawn through the port  32  and into the lumen  60  of the outer cutting member  30 . The valve  120  returns to an open configuration upon removal of the pneumatic pressure from the first portion  130  of chamber  110 . Upon application of pneumatic pressure to a second portion  180  of the chamber  110 , the diaphragm  90  and inner cutting assembly  70  are displaced in the direction of arrow  190 . However, it is believed that materials drawn into the passageway  100  substantially remain in a position relative to the housing and are not carried along with the inner cutting assembly  70  in any significant degree. Thus, cycling of the diaphragm  90  and inner cutting assembly  70  not only results in a cutting action of materials entering the port  32  but also in the net movement of materials through the lumen  60  and passageway  100 . 
         [0027]      FIGS. 3A-3E  are schematic views of the outer cutting member  30 , the inner cutting member  40 , and the valve  120  that illustrate the cutting and aspiration action.  FIG. 3A  shows the inner cutting member  40  in a fully extended position such that port  32  is closed. In  FIG. 3B , pneumatic pressure  200  is applied to valve  120  resulting in valve  120  being placed into the closed configuration. As shown, the closed configuration of valve  120  forms a closure in the passageway  100 . The closure may be fluid-tight. In  FIG. 3C , the inner cutting member is displaced in the direction of arrow  170 . In some instances, displacement of the inner cutting member  40  in the direction of arrow  170  may be the result of the pneumatic pressure  200  applied to a diaphragm, such as diaphragm  90 . In other instances, the pneumatic pressure may not be utilized to actuate the motor, such as motor  50 . As the inner cutting member  40  is displaced in the direction of arrow  170 , the material contained in passageway  100  is moved along with the inner cutting member  40 . Generally, the materials contained in the passageway  100  are incompressible (e.g., liquids and tissues), and retraction of the inner cutting member  40  in the direction of arrow  170  generates movement of the material in passageway  100  in a manner similar to the way in which a fluid-filled straw retains the fluid as the straw is withdrawn from the source of fluid. That is, as the inner cutting member  40  is retracted in the direction of arrow  170 , the material within the passageway  100  is retained as a result of fluid continuity and conservation of mass. 
         [0028]    Furthermore, as the inner cutting member  40  is displaced in the direction of arrow  170 , the size of the passageway  100  between the valve  120  and the distal end  34  of outer cutting member  30  increases. As a result of this increase in volume of passageway  100 , additional material enters the outer cutter member  30  through port  32  according to the same physical principles, i.e., fluid continuity and conservation of mass. Thus, the motion of the inner cutting member  40  in the direction of arrow  170  causes materials, for example vitreous humor, fluid, and other ocular tissues, (referred to collectively hereinafter as “vitreous  210 ”) to enter into outer cutting member  30  via port  32 , as shown in  FIG. 3C . 
         [0029]    In  FIG. 3D , the pneumatic pressure  200  applied to valve  120  is removed or reduced below a level required to actuate the valve  120  into the closed configuration. As a result, the valve  120  is actuated into the open configuration such that passageway  100  is no longer obstructed. The pressure at which the valve  120  opens and closes and time to actuate the valve  120  between the open configuration and closed configuration may be selected so that the valve  120  fully or substantially fully closes before or substantially simultaneous with movement of the inner cutting member  40  in the direction of arrow  170  or opens before or substantially simultaneous with movement of the inner cutting member  40  in the direction of arrow  190 . With the valve  120  open the material contained within the passageway  100  is believed to substantially remain in place as the inner cutting member  40  is displaced in the direction of arrow  190 . 
         [0030]    In  FIG. 3E , the inner cutting member  40  is displaced in the direction of arrow  190 , causing a distal end  42  of the inner cutting member  40  to sever the vitreous  210  extending through port  32 . As the cutting and aspiration action illustrated in  FIGS. 3A-3E  is repeated, application of pneumatic pressure  200  to valve  120  and displacement of the inner cutting member  40  in the direction of arrow  170  results in a step-wise movement of the severed vitreous  210  in the direction of arrow  170  and ultimately out of the vitreoretinal probe. 
         [0031]    Consequently, closure of valve  120  and retraction of inner cutting member  40  in the direction of arrow  170  results in step-wise or incremental movement of severed materials. This manner of pumping material eliminates the need for a downstream vacuum source to draw the severed materials out of the vitreoretinal probe  10 . Further, with the movement of material in this incremental way, the amount of vitreous  200  entering the probe  10  is better controlled as compared to a constantly applied vacuum. This control of the amount of vitreous  210  drawn into the port may eliminate or substantially reduce traction on the retina. 
         [0032]    A constant vacuum applied during a vitrectomy procedure may result in a large an amount of vitreous being drawn into the port of the cutter before the inner cutting member has cut the ingested vitreous. The amount of vitreous drawn into the probe is a function of the strength of the applied vacuum and the time the cutter port remains open. The larger amount of vitreous drawn into the probe generally results in a larger amount of traction that may be applied to the retina. This traction on the retina can result in a retinal tear or otherwise damage the retina. 
         [0033]    With the displacement pumping action described herein, the amount of vitreous drawn into the outer cutting member per each cutting cycle is controlled. For example, the amount of vitreous drawn into port  32  of the cutter  25  may be controlled by the length of the stroke of the inner cutting member  40  between its fully retracted position and its fully extended position. A longer stroke may result in a larger amount of vitreous being drawn into the vitreoretinal probe  10 , while a shorter stroke may correspond to smaller amount of vitreous being drawn into the vitreoretinal probe  10 . In some examples, the vitreoretinal probe  10  may include features to adjust the stroke length such that vitreous flow rate can be controlled. Traction applied to the retina is relieved by each cutting event. Therefore, a shorter stroke length results in smaller amounts of vitreous ingested into the vitreoretinal probe  10  between cutting events and, thus, less traction develops between cutting events. 
         [0034]    With the described displacement pumping, the amount of vitreous drawn into port  32  of the cutter  25  is approximately the same per each cutting cycle, independent of the cycle rate of the probe. Thus, the removal rate of vitreous can be controlled by changing the cycle rate of the cutter of the vitreoretinal probe. Moreover, the vitreous removal rate can be changed without increasing the amount of retinal traction. In fact, it is believed that by utilizing this type of displacement pumping, retinal traction may be substantially reduced or eliminated independently of the cycle rate of vitreoretinal probe cutter. For example, increasing the cycle rate of a vitreoretinal probe that utilizes the pumping action described may result in a one-to-one increase in vitreous removal rate. However, any retinal traction may be unchanged because, as explained herein, retinal traction is independent of cycle rate. Rather, it is stroke length that may have an effect on retinal traction. Thus, the material removal rate is dependent on cycle rate, and the amount of traction produced is believed to be independent of both cycle rate and material removal rate. Consequently, with controlled displacement pumping, as described herein, traction applied to the retina of an eye during a vitrectomy may be significantly reduced. 
         [0035]    Although the example illustrated in  FIGS. 3A-3E  is described in the context of a pneumatically-actuated valve, the scope of the disclosure is not so limited. Rather, the valve may be actuated in any manner to form a closure in the aspiration passageway, such as passageway  100 . Therefore, the example illustrated in  FIGS. 3A-3E  is provided as a non-limiting example. 
         [0036]    In implementations in which actuation of the valve  120  is independent of the actuation of the motor  50 , opening and closing of the valve  120  may be timed relative to movement of the inner cutting assembly  70 . For example, with the inner cutting assembly  70  in a fully extended position, the valve  120  may be closed before the inner cutting assembly  70  begins retraction in the direction of arrow  170 . This sequence ensures formation of a closure in the inner cutting assembly  70  before the inner cutting assembly  70  is retracted in the direction of arrow  170 . The valve  120  may then be opened before the inner cutting assembly  70  begins extension in the direction of arrow  190 , providing an unobstructed passageway  100  so that movement of the inner cutting assembly  70  in the direction of arrow  190  minimizes or eliminates movement of the aspirated material within the passageway  100  in the direction of arrow  190 . 
         [0037]      FIG. 4  shows a cross-sectional view of another example vitrectomy probe  400 .  FIG. 5  is a detail view of a portion of vitrectomy probe  400 . This example vitrectomy probe  400  may be similar to the vitrectomy probe  10 , discussed above. However, as shown in  FIG. 5 , the vitrectomy probe  400  includes a second valve  220 . In the illustrated example, the second valve  220  is a pneumatically-actuated pinch valve. However, the scope of the disclosure is not so limited. Rather, the second valve  220  may be an electric, hydraulic, or any other suitable type of valve or device that is selectively operable to form a barrier. 
         [0038]    As shown in  FIG. 5 , the second valve  220  is disposed in a passage  230  formed in the housing  20  of the example vitrectomy probe  400 . The passage  230  may be sized such that proximal end  240  of the inner cutting assembly  70  is received and permitted to move axially therein. The second valve  220  may be actuated by pneumatic pressure applied to displace the diaphragm  90  and inner cutting assembly  70  in the direction of arrow  190 . In the illustrated example, pneumatic pressure applied to second portion  180  of chamber  110  is operable to displace diaphragm  90  and inner cutting assembly  70  in the direction of arrow  190  and cause the second valve  220  to close. 
         [0039]    The second valve  220  may be actuated at a selected pressure. For example, the pneumatic pressure at which the second valve  220  moves between an open configuration and a closed configuration may be different than the pneumatic pressure needed to displace diaphragm  90  within the chamber  110 . In some instances, the second valve  220  may actuate a pneumatic pressure lower than the pneumatic pressure at which the diaphragm  90  actuates in the direction of arrow  190 . In other instances, the second valve  220  and diaphragm  90  may be actuated at the same pneumatic pressure. 
         [0040]    The second valve  220  may be used in cooperation with valve  120 . For example, with the inner cutting assembly  70  fully retracted in the direction of arrow  170 , pneumatic pressure may be applied to a second portion  180  of chamber  110  after the pneumatic pressure applied to the first portion  130  of chamber  110  has been removed. This change in pressure states results in the valve  120  being placed in an open configuration and the second valve  220  being placed in a closed configuration. With the valves  120 ,  220  in these configurations, as the inner cutting assembly  70  moves in the direction of arrow  190 , the closed valve  220  maintains the position of the vitreous presently within the passageway  230  and passageway  100  in the same manner described above. That is, the position of the vitreous is maintained as a result of conservation of mass that prevents the vitreous from moving away from the closed valve  220 . Consequently, the vitreous contained in the passageway  100  is prevented from moving in the direction of arrow  190 . Thus, when closed, the second valve  220  prevents expulsion of vitreous out of the port  32  before the inner cutting member  40  had performed a cut. When the pressure conditions change such that pneumatic pressure is released from the second portion  180  of chamber  110  and pneumatic pressure is added to the first portion  130  of chamber  110 , the configurations of the first and second valves  120 ,  220  reverse. That is, the first valve  120  closes, and the second valve  220  opens. As already explained, in some implementations, the second valve  220  may be eliminated. 
         [0041]      FIGS. 6A and 6B  show an example valve  600  that is within the scope of the present disclosure. Valve  600  includes a resilient member  610  that may be received over an opening  620  formed in a tubular member  630 . In some implementations, the resilient member  610  may be in the form of a tube formed of a flexible material. In some instances, this type of valve may be used for valve  120  or valve  220  or both. In  FIG. 6A , the valve is in an open configuration, such that the passageway  640  is unobstructed. In  FIG. 6B , the valve  600  is in a closed configuration forming an obstruction in the passageway  640 . 
         [0042]    In some instances, the resilient member  610  may be elastomeric. For example, the resilient member  610  may be formed from a rubber material. Any other material that includes a bias to return the material to its original state may also be used. In some implementations, the resilient material  610  may include electromagnetic particles that allow the resilient material  610  to be influenced by applied electromagnetic forces. In some implementations, the resilient material  610  may possess piezoelectric or other properties that enable its shape or position to be influenced by means other than by application of pressure. In some instances, the tubular member  630  may be formed from a metal, plastic material, or any desired material. 
         [0043]    In the open configuration shown in  FIG. 6A , no force is being applied to the resilient member  610 . The resilient member  610  maintains its cylindrical shape. Consequently, the passageway  640  remains unobstructed. In some implementations, the resilient member  610  may have such resilience that it maintains a generally cylindrical shape even when a selected amount of pressure difference is present between the exterior of the valve  600  and the passageway  640 . Above the selected pressure differential, the resilient member  610  may deform and form an obstruction. Thus, in use, aspirated materials may be transported through the passageway  640  even when a pressure differential below the selected pressure differential is present. For example, in some implementations, the resilient member  610  may remain unobstructed notwithstanding application of vacuum to the interior of the passageway  640  by a downstream vacuum source where the applied vacuum is below the selected pressure differential. In the closed configuration, shown in  FIG. 6B , a portion of the resilient member  610  is displaced into the passageway  640  through the opening  620  and contacts an interior surface  650  of the passageway  640  to form a seal. The formed seal may be an air-tight seal. In some instances, the resilient member  610  may be responsive to pneumatic pressure to actuate the valve  600  between the open and closed configurations. Thus, in some implementations, the resilient member  610  may react to a pressure differential between the exterior of the valve  600  and the passageway  640  to open and close the valve  600 . The pressure differential at which the valve  600  opens and closes may be selected as desired. The selected pressure differential at which the valve  600  opens and closes may be such that a vacuum below a selected pressure differential may be applied to the passageway  640  to aspirate material therethrough without causing the valve  600  to close. 
         [0044]    In other implementations, a physical member may be applied to the resilient member  610  to force a portion of the resilient member  610  through the opening  620 . In other implementations, the resilient member  610  may be actuated hydraulically, electromagnetically, piezoelectrically, thermopneumatically, or in any other fashion.  FIG. 6C  is a cross-sectional view of valve  600  taken along I-I showing the passageway  640  in an open, unobstructed condition.  FIG. 6D , on the other hand, is a cross-sectional view of valve  600  taken along II-II showing the passageway  640  in a closed condition. 
         [0045]    The material forming the resilient member  610  may be selected such that the material reacts quickly to an applied closing force. That is, once a force applied to the resilient member  610 , whether pneumatic, hydraulic, electromagnetic, direct contact, or any other manner, that corresponds to the force at which the valve  600  is to close, the material forming the resilient member  610  may be selected to react quickly to fully close the valve. Quick reaction by the valve to open and close relative to the motion of the inner cutting assembly  70  is desirable to promote efficiency of the incremental pumping mechanism. 
         [0046]    Although  FIGS. 6A-6D  show the resilient member  610  forming a tubular member surrounding a portion of the tubular member  630 , in other implementations, the resilient member  610  may be a not be in the form of a tube. For example, in some instances, the resilient member may have a size only large enough to cover the opening  620  in the tubular member  630 . In other instances, the resilient member  620  may be an insert received into the opening  620 . 
         [0047]    Although the example valve  600  is shown as having a circular cross-section, the scope of the disclosure is not so limited. Rather, the valve  600  may have any cross-sectional shape. Also, referring to  FIGS. 6C and 6D , the opening  620  has an angular component, θ, that is approximately 180°. However, the angular size of the opening  620  may be greater or less than 180°. 
         [0048]    Although the disclosure provides numerous examples, the scope of the present disclosure is not so limited. Rather, a wide range of modification, change, and substitution is contemplated in the foregoing disclosure. It is understood that such variations may be made to the foregoing without departing from the scope of the present disclosure.