Abstract:
An automatic sensor inserter is disclosed for placing a transcutaneous sensor into the skin of a living body. According to aspects of the invention, characteristics of the insertion such as sensor insertion speed may be varied by a user. In some embodiments, insertion speed may be varied by changing an amount of drive spring compression. The amount of spring compression may be selected from a continuous range of settings and/or it may be selected from a finite number of discrete settings. Methods associated with the use of the automatic inserter are also covered.

Description:
FIELD OF THE INVENTION 
     The present invention relates to medical devices for monitoring analytes in a living body, such as monitoring glucose levels in people with diabetes. More particularly, the invention relates to automatic devices for inserting analyte sensors into the skin of a patient. 
     BACKGROUND OF THE INVENTION 
     In recent years, people with diabetes have typically measured their blood glucose level by lancing a fingertip or other body location to draw blood, applying the blood to a disposable test strip in a hand-held meter and allowing the meter and strip to perform an electrochemical test of the blood to determine the current glucose concentration. Such discrete, in vitro testing is typically conducted at least several times per day. Continuous in vivo glucose monitoring devices are currently being developed to replace in vitro devices. Some of these continuous systems employ a disposable, transcutaneous sensor that is inserted into the skin to measure glucose concentrations in interstitial fluid. A portion of the sensor protrudes from the skin and is coupled with a durable controller and transmitter unit that is attached to the skin with adhesive. A wireless handheld unit is used in combination with the skin-mounted transmitter and sensor to receive glucose readings periodically, such as once a minute. Every three, five or seven days, the disposable sensor is removed and replaced with a fresh sensor which is again coupled to the reusable controller and transmitter unit. With this arrangement, a person with diabetes may continuously monitor their glucose level with the handheld unit. Detailed descriptions of such a continuous glucose monitoring system and its use are provided in U.S. Pat. No. 6,175,752, issued to Abbott Diabetes Care Inc., formerly known as TheraSense, Inc. on Jan. 16, 2001, which is incorporated by reference herein in its entirety. 
     Transcutaneous analyte sensors may be inserted into the user&#39;s skin using an automatic introducer or inserter device, such as those described in U.S. patent application Ser. No. 10/703,214, published Jul. 8, 2004 under publication number 20040133164, now U.S. Pat. No. 7,381,184, incorporated herein by reference in its entirety. Most sensor inserter devices described in the above published patent application have two springs, one for driving an introducer sharp and a sensor into the skin of a patient, and another for retracting the introducer sharp, leaving the sensor behind in the patient&#39;s skin. The spring arrangements are chosen to provide an introducer sharp and sensor speed optimized to insert the sensor into a typical patient. 
     SUMMARY OF THE INVENTION 
     According to aspects of some embodiments of the present invention, it is recognized that a sensor introducer having variable insertion speeds, insertion forces, travel distances, accelerations and/or other characteristics of sensor insertion that may be adjusted for different situations and/or different patients may be desirable. For example, due to physiological factors and trauma that may result from high speed automatic insertion of an analyte sensor, there may be a need to slow down and control the velocity of the puncturing apparatus. In other situations, such as for patients with different skin characteristics such as higher than average skin thickness and/or skin density, it may be desirable to speed up the velocity of the puncturing device. Alternatively, situations involving inserting sensors into different locations on a patient, such as the arm, torso or thigh, may benefit from the use of a single inserter or single inserter type with a sensor insertion velocity that may be sped up or slowed down. According to other aspects of the invention, a single inserter type may be configured to alternately insert different types of sensors and/or other devices, in which case an insertion setting may be set depending on which type of sensor or device is currently being inserted. 
     According to other aspects of the invention, a sensor insertion device may be provided with an adjustable feature allowing a user to adjust the sensor insertion speed prior to use. 
     According to other aspects of the invention, a sensor insertion device may be provided with an adjustment feature allowing the insertion speed to be variably adjusted over a range of velocities. 
     According to other aspects of the invention, a sensor insertion device may be provided with an adjustment feature allowing the insertion speed to be selected from among a finite number of discrete settings. 
     According to other aspects of the invention, a sensor insertion device may be provided with an adjustment feature allowing the insertion speed to be adjusted by changing the amount of compression of a drive spring. In one embodiment, a spring compression may be adjusted by using a knob. In another embodiment, a spring compression may be adjusted by turning a thumbwheel. In another embodiment, a spring compression may be adjusted by changing the orientation of a component of the inserter. In another embodiment, a spring compression may be adjusted by using one or more magnets. 
     Various analytes may be monitored by sensors inserted into a patient according to aspects of the present invention. These analytes may include, but are not limited to, lactate, acetyl choline, amylase, bilirubin, cholesterol, chorionic gonadotropin, creatine kinase (e.g., CK-MB), creatine, DNA, fructosamine, glucose, glutamine, growth hormones, hematocrit, hemoglobin (e.g. HbA1c), hormones, ketones, lactate, oxygen, peroxide, prostate-specific antigen, prothrombin, RNA, thyroid stimulating hormone, and troponin, in samples of body fluid. Monitoring systems may also be configured to determine the concentration of drugs, such as, for example, antibiotics (e.g., gentamicin, vancomycin, and the like), digitoxin, digoxin, drugs of abuse, theophylline, warfarin and the like. Such analytes may be monitored in blood, interstitial fluid and other bodily fluids. 
     In certain embodiments, other types of sensors may be inserted into a body using an inserter constructed according to aspects of the present invention. Such sensors may include, but are not limited to, devices for measuring physiologic parameters such as temperatures, pressures, respiration, pulse, movement and electrical signals, through means such as mechanical, chemical, electrical, optical or otherwise. In addition to or instead of inserting a sensor(s) into a body, an inserter constructed according to aspects of the present invention may insert medicine, fluid delivery devices such as infusion sets, cannulas or needles, or other medical devices. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Each of the figures diagrammatically illustrates aspects of the invention. Of these: 
         FIG. 1  is a perspective view showing an exemplary embodiment of a sensor inserter and adhesive mount constructed according to aspects of the present invention. 
         FIG. 2  is a perspective view of an adhesive mount and sensor attached to a patient&#39;s skin. 
         FIG. 3  is a perspective view of a transmitter attached to an adhesive mount and transmitting to a handheld receiver. 
         FIG. 4  is an exploded perspective view of the embodiment shown in  FIG. 1 . 
         FIG. 5  is a side elevation view of the embodiment shown in  FIG. 1 . 
         FIG. 6  is an end elevation view of the embodiment shown in  FIG. 1 . 
         FIG. 7  is a cross-sectional view taken along line  7 - 7  in  FIG. 6 . 
         FIG. 8  is a cross-sectional view taken along line  8 - 8  in  FIG. 5 . 
         FIG. 9  is a broken away view similar to  FIG. 8 , showing a shuttle in a neutral position. 
         FIG. 10  is a broken away view similar to  FIG. 8 , showing a shuttle in a cocked position. 
         FIG. 11  is a broken away view similar to  FIG. 8 , showing a shuttle in an insertion position. 
         FIG. 12  is a cross-sectional view taken along line  12 - 12  in  FIG. 5 . 
         FIG. 13  is a perspective view of a transcutaneously implantable sensor. 
         FIG. 14A  is a perspective view of a sensor introducer. 
         FIG. 14B  is a bottom view of the introducer shown in  FIG. 14A . 
         FIG. 15  is a perspective view of a shuttle member. 
         FIG. 16A  is a perspective view of an alternative embodiment of a sensor inserter kit. 
         FIG. 16B  is an exploded view of some of the components shown assembled in  FIG. 16A . 
         FIG. 17  is a side elevation view schematically showing an alternative embodiment of a sensor inserter. 
         FIG. 18A  is a side elevation view schematically showing an alternative embodiment of a sensor inserter. 
         FIG. 18B  is a top view schematically showing the sensor inserter of  FIG. 18A . 
         FIG. 19A  is a side elevation view schematically showing an alternative embodiment of a sensor inserter. 
         FIG. 19B  is a top view schematically showing the sensor inserter of  FIG. 19A . 
         FIG. 20A  is a side elevation view schematically showing an alternative embodiment of a sensor inserter. 
         FIG. 20B  is a top view schematically showing the sensor inserter of  FIG. 20A . 
     
    
    
     Variation of the invention from that shown in the figures is contemplated. 
     DETAILED DESCRIPTION 
     The following description focuses on several variations of the present invention. The variations of the invention are to be taken as non-limiting examples. It is to be understood that the invention is not limited to particular variation(s) set forth and may, of course, vary. Changes may be made to the invention described and equivalents may be substituted (both presently known and future-developed) without departing from the true spirit and scope of the invention. In addition, modifications may be made to adapt a particular situation, material, composition of matter, process, process act(s) or step(s) to the objective(s), spirit or scope of the present invention. 
     Referring to  FIGS. 1-20 , exemplary embodiments of a sensor inserter constructed according to some aspects of the invention will be described.  FIG. 1  shows an overall perspective view of a sensor inserter kit  300  comprising a single-use sensor inserter  310  and a single-use adhesive mount  312  removably attached to the bottom thereof. 
     As an overview of the operation of this embodiment of an inserter kit  300 , the kit may come packaged generally as shown in  FIG. 1  with a sensor  314  (best seen in  FIGS. 4 and 13 ) preloaded within inserter  310  and with inserter  310  in a “cocked” state. After preparing an insertion site on the skin, typically in the abdominal region, the patient may remove an upper liner  316  and a lower liner  318  from adhesive mount  312  to expose the bottom surface and a portion of the top surface of an adhesive tape  320  (best seen in  FIG. 4 ) located beneath mount  312 . Mount  312 , with inserter  310  attached, may then be applied to the patient&#39;s skin at the insertion site. Safety lock tabs  322  may be squeezed together to allow actuator button  324  to be pressed causing inserter  310  to fire, thereby inserting sensor  314  into the patient&#39;s skin with a predetermined velocity and force. Once sensor  314  has been inserted into the skin, the patient may remove inserter  310  from mount  312  by pressing release tabs  326  on opposite sides of inserter  310  and lifting inserter  310  away from mount  312 . 
     Referring to  FIGS. 2 and 3 , mount  312  is shown adhered to a patient&#39;s skin  328  with sensor  314  already inserted, according to this exemplary embodiment. Once inserter  310  is removed from mount  312 , transmitter  330  may be slid into place. The circuitry  442  of transmitter  330  may then make electrical contact with the contact pads on sensor  314  after transmitter  330  is fully seated on mount  312 . Once initialization and synchronization procedures are completed, electrochemical measurements from sensor  314  may be sent wirelessly from transmitter  330  to a portable receiver  332 , as shown in  FIG. 3 . Sensor  314 , mount  312  and transmitter  330  may remain in place on the patient for a predetermined period, such as three, five or seven days. These components may then be removed so that sensor  314  and mount  312  may be properly discarded. The entire procedure above may then be repeated with a new inserter  310 , sensor  314  and mount  312 , reusing transmitter  330  and receiver  332 . 
     Referring to  FIG. 4 , inserter kit  300  may be assembled as shown from the following components: housing  334 , actuator button  324 , drive spring  336 , shuttle  338 , introducer sharp  340 , sensor  314 , retraction spring  342 , inserter base  344 , upper liner  316 , adhesive mount  312 , adhesive tape  320 , and lower liner  318 . 
     Sensor  314  may have a main surface  346  slidably mounted between U-shaped rails  348  of introducer sharp  340  and releasably retained there by sensor dimple  350  which engages introducer dimple  352 . Introducer sharp  340  may be mounted to face  354  of shuttle  338 , such as with adhesive, heat stake or ultrasonic weld. Sensor  314  may also have a surface  356  that extends orthogonally from main surface  346  and just beneath a driving surface  358  of shuttle  338  when mounted thereon (details of these features are better shown in  FIGS. 7 and 13-15 .) 
     Shuttle  338  may be slidably and non-rotatably constrained on base  344  by arcuate guides  360 . As best seen in  FIGS. 7, 12 and 15 , shuttle  338  may be generally formed by an outer ring  362  and an inner cup-shaped post  364  connected by two bridges  366 . Bridges  366  slide between the two slots  368  formed between guides  360  and allow shuttle  338  to travel along guides  360  without rotating. Retraction spring  342  may be captivated at its outer circumference by guides  360 , at its bottom by the floor  370  of base  344 , at its top by bridges  366 , and/or at its inner circumference by the outer surface of shuttle post  364 . Drive spring  336  may be captivated at its bottom and outer circumference by the inside surface of shuttle post  364 , at its top by the ceiling  372  inside actuator button  324 , and/or at its inner circumference by stem  374  depending from ceiling  372 . When drive spring  336  is compressed between actuator button  324  and shuttle  338  it urges shuttle  338  towards base  344 . When retraction spring  342  is compressed between shuttle  338  and base  344 , it urges shuttle  338  towards actuator button  324 . 
     Actuator button  324  may be slidably received within housing  334  from below and reside in opening  376  at the top of housing  334  with limited longitudinal movement. Arms  378  on each side of actuator button  324  may travel in channels  380  along the inside walls of housing  334 , as best seen in  FIG. 8 . Longitudinal movement of actuator button  324  may be limited in one direction by the base of arms  378  contacting the edge of opening  376  at the top of housing  334 , and in the other direction by the distal ends  384  of arms  378  contacting stops  386  in channels  380 . In this embodiment, slots  388  are provided in the top of housing  334  for ease of housing manufacture and so tools may be inserted to inwardly compress areas  378  beyond stops  386  to allow actuator button  324  to be removed from housing  334  if needed. 
     When sensor  314 , introducer  340 , shuttle  338 , retraction spring  342 , drive spring  336  and actuator button  324  are assembled between base  344  and housing  334  as shown in  FIG. 4  and described above, housing  334  may be snapped into place on base  344 . Base  344  may be held onto housing  334  by upper base barbs  390  that engage upper openings  392  in housing  334 , and lower base barbs  394  (best seen in  FIG. 5 ) that engage lower openings  396  in housing  334 . In this embodiment, slots  398  and  400  are provided for ease of manufacture of housing  334 , and base  344  is removable from housing  334  with tools if needed. 
     Referring to  FIG. 7 , actuator button  324  may be provided with safety lock tabs  322  hingedly formed on opposite ends. Tabs  322  may be urged from a relaxed outward position to a flexed inward position. When in the normal outward position, shoulders  402  on the outer surfaces of tabs  322  engage the rim  404  of opening  376  to prevent the actuator button  324  from being depressed, thereby avoiding accidental firing of inserter  310 . Tabs  322  may be squeezed inward just enough to clear the rim  404  of opening  376  while pressing the actuator button  324  down to fire the inserter. Alternatively, tabs  322  may be squeezed further inward so that barbs  406  on the inside edges engage catches  408  located on a center portion of actuator button  324 , thereby defeating the safety lock to allow later firing by simply pressing down on the actuator button  324 . In this embodiment, upwardly extending grips are provided on tabs  322  for better visual indication of safety lock status and actuation control. 
     Referring to  FIG. 8 , shuttle  338  may be provided with laterally extending barbed fingers  412  which travel in channels  380  along the inside walls of housing  334 . When shuttle  338  is inserted up into housing  334  far enough in this embodiment, barbed fingers  412  momentarily deflect inward and then snap outward again to catch on stops  386 . In this “cocked” position as shown, drive spring  336  may be compressed and urging shuttle  338  towards base  344 , but barbed fingers  412  catching on stops  386  prevent such travel. 
     Referring to  FIGS. 9-11 , the sequence of loading, cocking, arming, firing, and automatic retraction of exemplary inserter  310  will be described. According to aspects of the invention, during production inserters  310  may be fabricated and fully assembled by one vendor, except for sensor  314 , which may be supplied and installed by a second vendor in a sterile environment. Accordingly, inserter  310  may be manufactured and shipped to the sensor vendor in a neutral state, as shown in  FIG. 9 . A hole  414  provided through the center of actuator button  324  allows the sensor vendor to insert a pin (manually or by automated machinery, not shown) through hole  414  to drive shuttle  338  towards base  344  in a controlled fashion and hold it there against the force of retraction spring  342 . This will allow introducer sharp  340  to be extended through base  344  (as shown in  FIG. 11 ) so that sensor  314  may be loaded into introducer  340 . When the pin is removed, shuttle  338 , introducer  340  and sensor  314  may be allowed to retract to the neutral position. The sensor vendor may then cock the loaded inserter  310  before shipment by pushing another pin (not shown) from the opposite direction through a central hole  416  in base  344  (with mount  312  removed) until the pin contacts dimple  418  formed in the bottom of shuttle  338 . By pushing shuttle  338  towards actuator button  324  until barbed fingers  412  clear stops  386 , the inserter  310  may be cocked (as shown in  FIG. 10 .) 
     Referring to  FIG. 10 , inserter  310  may be received by the patient in the cocked position as shown. To use inserter  310 , the patient may apply mount  312  to the mounting site and may disable the safety mechanism as previously described, and may then push actuator button  324  against the force of drive spring  336 . As actuator button  324  travels toward base  344 , drive cam surfaces  420  on arms  378  contact ramped surfaces  422  of barbed fingers  412  and urge them inward. When fingers  412  are driven inward enough to clear stops  386 , shuttle  338  may be driven by drive spring  336  with a predetermined speed and force to an insertion position, as shown in  FIG. 11 . 
     Referring to  FIG. 11 , exemplary inserter  310  is shown in the insertion position with the tail  424  of introducer sharp  340  extending through base  344  and mount  312  into the skin of the patient.  FIG. 11  shows shuttle  338  in a fully extended position with its lower surface  426  (see  FIG. 15 ) bottomed out on base  344 . However, in this embodiment, the lower orthogonal surface  356  of sensor  314  will contact an exposed sensor contact portion  428  (best seen in  FIGS. 2 and 4 ) on top of adhesive tape  320  supported from below by the patient&#39;s skin, and therefore will typically stop traveling before reaching the fully bottomed out position shown. Tail  424  of introducer sharp  340  may provide rigidity and a skin piercing edge  430  for allowing the flexible tail  431  ( FIG. 13 ) of sensor  314  to be implanted in the patient&#39;s skin. After providing this function, introducer sharp  340  may be immediately removed from the patient and retracted into a safe position inside housing  334  as retraction spring  342  (which has been compressed by the travel of the shuttle) pushes shuttle  338  back towards actuator cap. Sensor  314  may be pulled from introducer  340  and held in place by the sensor contact portion  428  on top of adhesive tape  320  adhering to orthogonal surface  356  of sensor  314 . The geometries of sensor dimple  350  ( FIG. 13 ) and mating introducer dimple  352  ( FIG. 14A ) may be chosen to create a separation force between them that is less than the adhesion force of tape  320  on orthogonal surface  356 , but great enough to retain sensor  314  in introducer  340  during typical shipping and product handling shock loads. Driving surface  358  beneath shuttle  338  may press down on top of orthogonal surface  356  to ensure good contact with adhesive tape  320  before shuttle  338  retracts within introducer  340 . Barb(s) on sensor tail  431  may be employed to further anchor the sensor in its operating position. 
     Referring again to  FIG. 9 , in this embodiment retraction spring  342  will return shuttle  338  to the neutral position as shown after firing, but without sensor  314  which remains inserted in patient&#39;s skin (not still in introducer  340  as shown here), Drive spring  336  may be designed to be stiffer than retraction spring  342  so that shuttle  338  oscillations are quickly dampened out, and so introducer sharp  340  does not return to sensor  314  or the patient to cause injury. With sensor  314  now inserted in the patient&#39;s skin, inserter  310  may be removed from mount  312  by inwardly flexing release tabs  326  on opposite sides of inserter  310  to remove latch hooks  432  (see  FIG. 8 ) from mount channels  434  ( FIG. 8 ) and then lifting inserter  310  away from mount  312 . Introducer sharp  340  remains protected inside housing  334  during disposal of inserter  310 . Transmitter  330  may now be slid into place on mount  312  as previously described. 
     In one embodiment, sensor  314  may be made from a 0.005 inch thick Mylar substrate, such as Dupont Melinex ST-505, print treated both sides, heat stabilized and bi-axially oriented. In this embodiment, main surface  346  is 0.315 inches tall by 0.512 inches wide, and orthogonal surface  356  is 0.374 inches wide by 0.202 inches deep. Sensor tail  431  is 0.230 inches long by 0.023 inches wide. Semispherical sensor dimple  350  is 0.050 inches wide and 0.026 inches deep. Introducer  340  is made from SUS 301 medical grade stainless steel, 0.004 inches thick, having a surface roughness less than or equal to 0.5 micrometers. The height of the main portion of introducer  340  is 0.614 inches, and the inside width is 0.513 inches. The overall thickness of rolled rails  348  is 0.026 inches. The length and width of introducer tail  424  are 0.354 and 0.036 inches, respectively. The preferred angle of the sharp  340  is 21 degrees. Semispherical introducer dimple  352  has a radius of 0.024 inches. Also, in this embodiment, shuttle  338  has an average speed of at least 1 meter/second, and has a momentum at its end of travel of about 2.65 lb-m/sec. 
     In the above exemplary embodiment, housing  334 , button  324 , shuttle  338 , base  344  and mount  312  are all injection molded from G.E. Lexan PC. Inside and outside working surfaces of arms  378  on button  324  are lubricated with Dow Corning 360 Medical Fluid. Drive spring  336  has a free length of 1.25 inches, a working length of 1.00 inch, and a rate between 20 and 30 pounds per inch. Retraction spring  342  has a free length of 1.5 inches, a working length of 0.35 inches, and a rate between 0.15 and 0.35 pounds per inch. Adhesive tape  320  is medical grade acrylic adhesive on polyester film (such as Acutek 0396013) with a semi-bleached kraft liner having silicon release. 
     The following enhancements may be added to the inserter kit  300  described above in an effort to increase the reliability of sensor insertion. First, a sensor flap, may be formed along the top edge of sensor  314  ( FIG. 13 ). When sensor  314  reaches the extended, delivered position as shown in  FIG. 11 , the sensor flap catches on a bottom edge of base  344  to ensure that sensor  314  separates from introducer  340  as shuttle  338  returns upward to the retracted position. Adhesive may also be located on the bottom of orthogonal sensor surface  356  to ensure that sensor  314  adheres to the sensor contact portion  428  on the top of adhesive mount tape  320 , as shown in  FIG. 4 . 
     Referring to  FIGS. 16A and 16B , an alternative embodiment of inserter kit  300 ′ is shown. Actuator button  324 ′ may be made easier for elderly patients to push by anchoring the upper end of drive spring  336  on a housing bridge  470  instead of button  324 . This option may also make the insertion force of inserter  310  more consistent, and may allow stronger spring forces to be used if desired. Bridge  470  may span across opening  376 ′ and divide it into two openings  472  in the top of housing  334 ′. The top portion of button  324 ′ may be bifurcated into two protrusions  474  that each extend through an opening  472 . A clearance hole (not shown) may be provided through the center of button  324 ′ to allow drive spring  336  to pass through and secure around a post (not shown) depending from the bottom center of bridge  470 . 
     Safety lock key  476  may be provided to prevent actuator button  324 ′ from being pressed until key  476  is removed. Aperture  478  may be provided in the top center of bridge  470  for receiving boss  480  located at the bottom of key  476 , thereby allowing key  476  to rotate. When key handle  482  is rotated perpendicular to button protrusions  474  in the embodiment shown in  FIGS. 16A and 16B , two opposing perpendicular fins  484  on key  476  swing into inwardly facing slots (not shown) on the inside of protrusions  474  and prevent button  324 ′ from being actuated. When key handle  482  and fins  484  are rotated parallel to button protrusions  474  such that fins  484  disengage therefrom, key  476  may be removed and button  324 ′ may then be actuated. Other than these modifications, this alternative embodiment inserter kit  300 ′ functions the same as the embodiments previously described. 
     In another embodiment, less aggressive finger engagement with stops  386  may be employed to provide an easier and more consistent release of shuttle  338  by actuator button  324  or  324 ′. Alternatively, the above designs may be modified to have a single, more centrally located shuttle release finger (not shown) instead of the two outboard fingers  412  shown. 
     Referring to  FIGS. 17-20 , various alternative embodiments are shown comprising features which allow the sensor insertion velocity to be changed. Referring first to  FIG. 17 , an inserter  500  embodiment having a micrometer style head or knob  502  is shown, similar in arrangement to inserter embodiments described above. Knob  502  may be attached to a threaded rod  504 . Threaded rod  504  may be received through a threaded hole or inserted in fixed housing cross member  506 . A distal end of threaded rod  504  may be rotatably or fixedly attached to compression member  508 . Compression member  508  may be movable with respect to carrier or shuttle  510  for compressing drive spring  512  therebetween. 
     Shuttle  510  may be provided with barbed fingers  514  for engaging stops  516  within housing  518  to releasably retain shuttle  510  in a cocked position, similar to the arrangements of embodiments described above. Inserter  500  may be provided with an actuator button (such as  324  shown in  FIG. 1 ) for releasing barbed fingers  514  from stops  516  as also previously described, allowing drive spring  512  to drive shuttle  510  downward with introducer sharp and/or sensor  520  to be inserted into the patient&#39;s skin. A return spring  522  may also be provided to retract shuttle  510  into housing  518  after sensor insertion. 
     The driving force, travel distance, velocity, acceleration and/or other characteristics of sensor insertion may be adjusted according to aspects of the present invention. In this embodiment, the user may turn knob  502  causing threaded rod  504  to rotate within the threaded hole or insert in housing cross member  506 . Turning knob  502  in one direction causes knob  502 , rod  504  and compression member  508  to move downward, thereby further compressing drive spring  512  against shuttle  510 . Turning knob  502  in the opposite direction reduces the compression of drive spring  512 . By turning knob  502  prior to firing inserter  500 , a user may increase or decrease the insertion speed and/or other characteristics of sensor insertion. 
     Knob  502 , rod  504  and/or housing  518  may be provided with numbers, lines, pointers or other indicia to aid a user in setting knob  502  in a desired location. In this particular embodiment, a user may adjust knob  502  prior to cocking inserter  500  to reduce the amount of force needed to turn knob  502 , since drive spring  512  may not be compressed or as compressed in an uncocked state. Alternatively, knob  502  may be turned after inserter  500  has been cocked. This scenario may provide the user with feedback during adjustment, as inserter  500  may be designed to allow the user to feel more resistance in turning knob  502  as drive spring  512  is further compressed. It should be noted that in this embodiment, a user is allowed to variably adjust an insertion characteristic such as insertion speed across a range of speeds by turning knob  502  through a range of positions. In one embodiment, inserter  500  is provided to a user with knob  502  set in a middle of a range so that the user may either increase or decrease the insertion speed, or leave it at its default setting. 
     In an alternative embodiment (not shown), which is a variation of the embodiment shown in  FIG. 17 , knob  502  may be arranged so that it remains in a fixed location while being free to turn. In this embodiment, a threaded hole or insert may be provided within either knob  502  or compression plate  508 , and threaded rod  504  may be fixed attached to the other. This arrangement may operate in a similar fashion to the embodiment shown in  FIG. 17  and allow fixed housing cross member  506  to be eliminated. 
     In another alternative embodiment (not shown), which is another variation of the embodiment shown in  FIG. 17 , knob  502 , threaded rod  504  and compression member  508  may be replaced with a housing cap that rotably engages with the main housing, such as with a threaded coupling. The drive spring may be captured between the cap and shuttle  510 . As the cap is threaded into further engagement with the main housing, the drive spring is further compressed. Conversely, the cap may be backed away from the main housing to reduce the compression of the drive spring. As before, the compression setting of the drive spring may affect characteristics of sensor insertion, such as sensor delivery speed. 
     Referring now to  FIGS. 18A and 18B , another alternative inserter  600  embodiment is shown. Inserter  600  may include a thumbwheel  602 . Thumbwheel  602  may protrude from housing  604  as shown to allow a user to easily turn it for adjusting a parameter(s) of sensor insertion. Thumbwheel  602  may drive threaded rod  606  directly, or indirectly by rotably engaging pinion  608 . Pinion  608  or compression member  610  may include a threaded hole or insert for receiving threaded rod  606 . With this arrangement, rotation of thumbwheel  602  causes threaded rod  606  to lower or raise compression plate  610 , thereby further compressing or decompressing drive spring  612 , respectively. Thumbwheel  602  and/or housing  604  may be provided with numbers, lines, pointers or other indicia to aid a user in setting thumbwheel  602  in a desired position. A window may be provided atop housing  604  to allow one or more indicia on thumbwheel  602  to be viewed. In all other respects, inserter  600  shown in  FIGS. 18A and 18B  may operate in a similar manner to that of inserter  500  shown in  FIG. 17 . 
     Referring now to  FIGS. 19A and 19B , another alternative inserter  700  embodiment is shown. Inserter  700  includes a shuttle  702  that may be rotated to affect compression of drive spring  704 . As seen in  FIG. 19A , barbed fingers  706  may engage with a first pair of stops  708  to hold shuttle  702  in a cocked position at a first height. As seen in  FIG. 19B , inserter  700  may be provided with a second pair of stops  710 . The second pair of stops  710  may be located within housing  712  at a second height which is lower than the first height. Inserter may be provided with provisions to allow shuttle  702  to be rotated 90 degrees so that barbed fingers  706  may engage with either the first pair of stops  708  or the second pair of stops  710  when shuttle  702  is cocked. In this embodiment, when barbed fingers  706  are engaged with the higher first pair of stops  708  as shown in  FIGS. 19A and 19B , drive spring  704  is compressed more than when barbed fingers  706  are engaged with the lower second pair of stops  710 , which may result in a higher sensor velocity when inserter  700  is actuated. It should be noted that this embodiment may provide the user with individual, discrete adjustment settings as opposed to a continuously variable range of settings as may be provided with the previously described embodiments. 
     In alternative embodiments (not shown), more than two pairs of stops may be provided to provide additional positions of drive spring compression. Such arrangements may be used with square, round or other shapes of housings. In other embodiments, one pair of stops  708  may be provided on housing  712 , and multiple pairs of barbed fingers  706  may be located at different heights on shuttle  702  for alternating engagement with the pair of stops  708 . Alternatively or in conjunction with this embodiment, stop(s)  708  may be located on shuttle  702  while barbed finger(s)  706  may be located on housing  712 . Other variations of these embodiments may occur to those skilled in the art without departing from the scope of the present invention. 
     Referring now to  FIGS. 20A and 20B , another alternative inserter  800  embodiment is shown. Inserter  800  includes at least one magnet  802  which may affect the compression of drive spring  804 . Drive spring  804  may be located between shuttle  806  and a top portion  808  of housing  810 . Shuttle  806  may include a ferrous material and/or one or more magnets (not shown) for attracting shuttle  806  to magnet  802 . Magnet  802  may be located above shuttle  806  on pivot arm  812 , which may pivot about hinge  814 . In this embodiment, a magnetic attraction between magnet  802  and shuttle  806  compresses drive spring  804  and holds shuttle  806  in a cocked position. Pressing on firing tab  816  causes arm  812  to pivot about hinge  814  in the direction shown by Arrow A and raises magnet  802  away from shuttle  806 . The increased separation between magnet  802  and shuttle  806  decreases the magnetic attraction between the two until the force of compressed drive spring  804  exceeds the force of magnetic attraction. At this point, drive spring  804  is allowed to extend, firing sensor  818  into the user&#39;s skin. 
     The degree of magnetic attraction between shuttle  806  and magnet(s)  802  may be varied by the size, number, location and/or polarity of magnet(s)  802 . For example, a user may place additional magnets  802  on top of pivot arm  812  to further compress drive spring  804 . This in turn may provide a higher sensor insertion velocity. In alternative embodiments, magnet(s) may be used in conjunction with previously described embodiments to affect spring compression. In such embodiments, no magnet may be used for a low speed setting, and one or more magnets may be used for higher speed setting(s). 
     In other embodiments (not shown), separate cartridges may alternately be installed by a user, each cartridge having a different spring rate for providing different insertion characteristics. Alternatively, a wind-up type constant force spring may be utilized to vary the spring force. Such an arrangement may also use a ratchet and lock type mechanism to affect the winding. In yet other embodiments, internal dampeners or other features may be used to allow adjustment of the firing characteristics of the inserter. For example, air bladders, movable walls or contact areas can be employed to increase, decrease or remove friction, thereby allowing sensor shuttle speed to be varied. 
     In the embodiments described above, a force or forces to drive a sensor or other object into a body may come from a compression spring, an extension spring, a torsion spring, a pneumatic or hydraulic cylinder or bladder, a magnet, an electromagnet or other prime mover or device for storing potential energy known to those skilled in the art. 
     In the embodiments described above, the entire insertion device or portions thereof can be either disposable or reusable. 
     As for additional details pertinent to the present invention, materials and manufacturing techniques may be employed as within the level of those with skill in the relevant art. The same may hold true with respect to method-based aspects of the invention in terms of additional acts commonly or logically employed. Also, it is contemplated that any optional feature of the inventive variations described may be set forth and claimed independently, or in combination with any one or more of the features described herein. Likewise, reference to a singular item, includes the possibility that there are plural of the same items present. More specifically, as used herein and in the appended claims, the singular forms “a,” “and,” “said,” and “the” include plural referents unless the context clearly dictates otherwise. It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely,” “only” and the like in connection with the recitation of claim elements, or use of a “negative” limitation. Unless defined otherwise herein, 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. The breadth of the present invention is not to be limited by the subject specification, but rather only by the plain meaning of the claim terms employed.