Abstract:
The invention relates to a device for removing body fluid with a puncture element that can puncture the skin of a body part. The device includes a housing structure for body fluids obtained from the skin puncture and a puncture drive for a back and forth movement of the puncture element. The duration of withdrawal movement is longer than the duration of the forward movement. The puncture drive is designed to withdraw the puncture element in a first withdrawal phase of the withdrawal movement with a maximum withdrawal speed of more than 0.02 m/s. A second retraction phase follows the first retraction phase. Body fluid is collected during the second retraction phase, which has a duration of between 0.3 and 0.8 seconds and/or a retraction speed of between 0.6 and 2 mm/s.

Description:
RELATED APPLICATIONS 
     This application is a continuation of PCT/EP2009/051581, filed Feb. 11, 2009, which claims priority to EP08151294.9, filed Feb. 11, 2008, both of which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     The invention concerns a device for withdrawing body fluid with a lancing element that can puncture the skin of a body part and which has a receiving structure for receiving body fluid obtained from the puncture and a lancing drive for a forward and retracting movement of the lancing element, wherein the duration of the retracting movement is longer (preferably many times longer) than the duration of the forward movement. The invention additionally concerns a corresponding method for withdrawing body fluid. 
     For blood sugar tests it has already been proposed that automatic withdrawal of sample from the skin by puncture with a lancing element can be accomplished by carrying out the retraction movement considerably more slowly than the forward movement so that an adequate amount of sample for the test can be reliably collected. In so doing, the position of the transition from rapid to slower movement should be at only such a depth in the tissue that a receiving structure incorporated into the lancing element still makes a reliable contact with the escaping liquid. A lancing system is described in WO 2007/073870 which allows the transition position to be kept constant despite a variable lancing depth but requires considerable technical complexity. 
     SUMMARY 
     The present invention addresses the problems with the systems and methods proposed in the prior art and provides a device for reliable sample collection with limited constructional complexity, and in doing so, also reduces the painfulness of the lancing procedure. 
     These teachings are based on the idea of starting collection at an intermediate position under the skin which can be reached at a very high speed and which is situated at a fixed retraction distance behind the selected deepest puncture position. In this connection, the lancing element is moved in a first retraction phase of the retracting movement at a maximum retraction speed of more than 0.02 m/s. This measure allows the maximum lancing depth to be selected according to the individual skin properties in such a manner that sufficient blood capillaries are opened by the puncture while this particularly pain-intensive phase is reduced to a minimum by the rapid first return movement. The collection process then only takes place in the subsequent second retraction phase, which is designed so that body fluid flows into the receiving structure. For this purpose the duration of the skin puncture should be long enough to enable uptake of the required amount of sample. However, it has surprisingly turned out that an excessively slow movement of the lancing element impedes blood uptake. Furthermore, the collecting phase should be completed within a defined time interval in order to also suffice the boundary conditions for the lancing depth. Accordingly, it is proposed that the lancing drive retracts the lancing element from the skin during a second retraction phase for collecting body fluid into the receiving structure. The second retraction phase follows the first retraction phase in such a manner that the retraction speed is between 0.6 and 2 mm/s and/or the collecting period is in a range between 0.3 and 0.8 s. 
     According to an exemplary embodiment, the lancing element is pulled back during the first retraction phase by a defined first partial distance preferably of up to 0.5 mm from the deepest puncture position into an intermediate position situated under the skin surface. In this connection, the skin surface can be determined by the device by means of an appropriate reference position, for example, by a positioning for the body part or a skin detector or a predetermined lancing depth. Furthermore, the constant first retraction distance enables one to dispense with a technically complicated movement control, thus enabling a harmonious motion sequence in the region where the direction of the needle is reversed without using stop structures at the reversal point that cause unwanted vibrations. 
     The return movement of the lancing element preferably takes place in such a manner that the receiving structure can at least be substantially filled with body fluid during the collecting period while the lancing element still projects into the skin. In this connection it should be noted that an appreciable uptake of body fluid released into the puncture wound does not take place until after the first rapid retraction phase. 
     It is particularly advantageous when the duration of the forward movement and of the first retraction phase is between 0.3 to 3 ms, preferably 0.3 to 0.7 ms, thus enabling a harmonious motion sequence for the initial puncture process. 
     The collection period for taking up body fluid into the receiving structure should advantageously be between 0.4 and 0.5 s. In this connection, it is also particularly advantageous when the mean retraction speed of the lancing element during the second retraction phase is in a range of about 1 to 1.5 mm/s. 
     For a user-related collecting profile it should be possible to adjust the maximum lancing depth between about 1 and 2.5 mm. 
     The speed time course during the return movement of the lancing element is advantageously adapted in accordance with a variable lancing depth in such a manner that the lancing element remains inserted into the skin for a predetermined dwell period. This enables an individual adaptation of the puncture depth without constantly changing the cycle durations. 
     For a simpler movement control it can be advantageous when the speed time course during the retraction movement of the lancing element is preset independently of the lancing depth. 
     Another improvement with regard to sample collection is achieved by the fact that the speed of the lancing element in the second retraction phase is essentially constant. 
     A test element to which body fluid can be applied from the receiving structure is provided for a simplified handling in an integrated system. In order to substantially exclude disadvantageous changes in the samples, the total duration from the start of the retraction movement of the lancing element until loading the test element with the body fluid should be less than 5 s, preferably less than 1 to 2 s. 
     Another supplementary or alternative aspect of these teachings is that a test element designed to detect an analyte in the body fluid is arranged in such a manner that the transfer time for transferring the body fluid from the receiving structure onto the test element is less than 1.5 s, preferably less than 1 s and preferably less than 0.5 s. It has surprisingly turned out that adherence to this time window is particularly important for the test quality. The test element can be directly arranged on the lancing element and optionally be fluidly connected to the receiving structure via a flow path. It is also possible to arrange the test element separately and in particular physically separate from the receiving structure and to transfer the liquid by a suitable actuation, for example, with structure deformation. Reference is made in this connection to WO 2005/084530 and WO 2007/025713 as examples. 
     The lancing element advantageously has a sharp lancing member which penetrates in a low-pain manner into the skin during skin puncture and in particular a single needle tip. 
     In order to take into consideration possible dents in the skin during puncture, it is possible to register the position of the skin surface by a skin detector and/or to define it for the body part by means of a positioning unit. 
     Sample collection is considerably simplified by means of the fact that a channel structure and in particular a groove-shaped or slot-shaped channel structure that can be brought into contact with the body fluid at least at a distal end section during skin puncture, is incorporated into the lancing element. 
     Another advantageous aspect is the fact that the drive mechanism controls the forward movement and retraction movement during a first retraction phase of the lancing element whereas the drive motor retracts the lancing element from the skin in a second retraction phase of the retraction movement. This allows a favorable movement profile to be achieved by simple technical means. This is particularly important for test devices that are required to be produced in large numbers. The drive mechanism can be effectively designed for the rapid movement and the motor provided for the slow remaining movement can be designed to be compact and energy saving. 
     The drive motor advantageously supplies the drive mechanism with mechanical energy for automatic movement control. 
     Another improvement is achieved by means of the fact that the drive motor retracts the drive mechanism together with the lancing element as a combination in the second retraction phase. 
     A constructionally particularly advantageous embodiment provides that the drive mechanism has a cam control driven by means of a spring. 
     Another aspect of this disclosure concerns a method for withdrawing body fluid in which a forward and retraction movement of a lancing element is controlled by a lancing drive in such a manner that the lancing element is retracted in a first retraction phase of the retraction movement at a maximum retraction speed of more than 0.02 m/s and in which the lancing element is retracted from the skin during a second retraction phase for collecting body fluid in the receiving structure which follows the first retraction phase in such a manner that the collection period is in a range between 0.2 and 0.8 s and/or the retraction speed is between 0.8 and 1.5 mm/s. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The above-mentioned aspects of exemplary embodiments will become more apparent and will be better understood by reference to the following description of the embodiments taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  shows a device for blood sugar tests with a multi-stage lancing drive in a simplified sectional diagram; and 
         FIG. 2  shows a lancing profile when using the device according to  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     The embodiments of the present invention described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of the present invention. 
     The device shown in  FIG. 1  enables a user to himself remove a blood sample for analytical purposes and in particular for blood sugar monitoring. The device comprises a hand-held device  10  with a lancing drive  12  for automatically handling a lancing element  14  used as a single-use article for blood withdrawal. 
     The lancing element  14  is designed as a so-called “microsampler” for collecting a small amount of blood from a body part  17  and in particular from a fingertip. As a monolithic one-piece molded part it can consist of thin stainless steel sheet and have a distally shaped tip  16  as a lancing member to produce a puncture wound. A groove-shaped or slot-shaped capillary channel  18  whose distal end section extends into the area of the tip  16 , enables the uptake of body fluid (blood and/or tissue fluid) from the puncture wound. A test element  20  provided with a test chemistry which can be loaded with body fluid from the receiving structure  18  by making a suitable flow connection after the skin puncture can be used to detect the target substance (e.g., glucose) present in the body fluid. Blood glucose detection especially by means of contact-free optical methods is known in the prior art and is therefore not elucidated in more detail here. 
     The lancing drive  12  enables a controlled forward and retraction movement of the lancing element  14  along a lancing axis  22  where the lancing depth can be advantageously selected by the user in a range between 1 and 2.5 mm for adaptation to various skin types by means of an adjusting unit  24 . The position of the skin surface can be optionally predetermined for the body part  17  by means of a positioning unit  26 . 
     For a multiphase motion control the lancing drive  12  comprises an electrical drive motor  28  and a drive mechanism  30  that is pretensioned by the motor and operates purely mechanically. The drive mechanism  30  controls the rapid forward movement and a first rapid phase of the return movement whereas the drive motor  28  slowly retracts the lancing element  14  from the skin via the drive mechanism  30  in a second retraction phase. This allows the collection process to be optimized and made particularly user-friendly. 
     The mechanical drive mechanism  30  has a tensioning rotor  32  and a drive rotor  34  and the rotors are connected together by a pretensioned torsion spring  36 . The drive mechanism  30  additionally comprises a cam drive or sliding gate drive  38  which translates the rotary motion of the drive rotor  34  into a translatory or lancing motion of the coupled lancing element  14  using a control cam  40 . For this purpose the free end of a control arm  42  which extends from the drive rotor  34  engages in the circumferential control cam  40  by means of a cam slider  44 . When the drive rotor  34  rotates, a stroke is generated corresponding to the cam slope whereby the cam drive  38  is guided by a linear guide  46  in the device housing  48 . The relative rotation of the two rotors  32 ,  34  can be mutually limited by stop elements  50 ,  52  in order to take up the pretension of the spring  36  and to stop the drive rotor  34  in a desired rotation angle position. In a preparatory tensioning phase the drive rotor  34  is locked against rotation with respect to the housing  48  so that the spring  36  can be tensioned by the tensioning rotor  32  by rotating the motor  28  until the stop elements  50 ,  52  reach their initial position. The lock on the drive rotor  34  is released at a given angular position of the tensioning rotor  32  by a trigger that is not shown so that the drive rotor  34  instantaneously rotates in a spring-driven manner until the stop member  50  on the drive rotor side strikes against the other end of the stop groove  52  on the tensioning rotor side. In this manner it is possible to travel through an angular range of the control cam  40  in order to very rapidly execute the forward movement and the first retraction phase of the retraction movement. 
     Further details of a suitable drive mechanism are described in U.S. Publication No. 20100168618 which is incorporated herein by reference. 
     As mentioned, the drive side of the drive motor  28  is coupled to the tensioning rotor  32  in order to supply the mechanism  30  with mechanical energy in a preparatory tensioning phase. Another important function of the drive motor  28  is the controlled slow return movement of the lancing element  14  during the second retraction phase. In this process the stop elements  50 ,  52  are held in the end position described above by the remaining spring tension. As a result the drive mechanism  30  can be rotated further as a unit in order to travel through the remaining section of the control cam  40  during which the lancing element  14  is retracted at a defined retraction speed. In this phase the lancing member  16  which is still situated under the skin can take up sufficient blood from the partially vacated puncture wound by means of the collecting structure  18 . The collected blood is subsequently transferred onto the test element  20  by a suitable actuation within preferably 0.5 s in a transfer step. For this purpose the test element  20  is arranged near enough to the receiving structure so that liquid transport takes place in the specified time taking into account the achievable transport rate. 
     The lancing profile shown in  FIG. 2  is particularly advantageous for a blood collection that is as effective and pain-free as possible. In this connection the term “lancing profile” is to be understood as the time course of the lancing movement which is shown as a function of lancing depth over time. 
     In phase v of the forward movement, the tip  16  of the lancing element  14  strikes the skin at t=0 at a high speed and penetrates in one movement down to the desired puncture depth d. This depth must be individually optimized in order to extend through the epidermis to reach the dermis containing the blood capillaries. The duration of the forward movement is preferably between 0.3 and 0.7 ms. 
     Then in the first retraction phase R 1  the tip  16  is pulled back by a predetermined distance Δd of about 0.5 mm to an intermediate position situated under the skin surface. This retraction position is preferably in the stratum corneum of the epidermis. This first retraction phase R 1  should take place as rapidly as possible because the lancing element  14  which has been excited to vibrate by the sharp reversal of direction should not execute too many oscillation periods in the blood-carrying and innervated dermis. Hence, the maximum retraction speed reached shortly after the movement is reversed should be more than 0.02 m/s. Accordingly, the duration of the first retraction phase is limited to a range between 0.3 and 3 ms. As elucidated above, a uniform, harmonious sequence of motions is achieved in phases v and R 1  by means of the drive mechanism  30 . 
     The retraction of the lancing element  14  is considerably slowed at the end of the phase R 1  so that the collection process can take place during the subsequent second retraction phase R 2 . In this connection, it has surprisingly turned out that the retraction speed should not fall below a minimum value and should still be high enough so that the skin tissue readily releases liquid. On the other hand, the collection period should be sufficiently long to allow the receiving structure or capillary  18  to collect the liquid which can take up to 500 ms taking into consideration production tolerances and aging effects. It must also be borne in mind than an excessive dwell period of the lancing element in the inserted state in the skin will be disagreeable to the user. In order to achieve a sufficient uptake of blood into the receiving structure  18 , the speed of the lancing element in the second retraction phase should be substantially constant and a value between 1 and 1.5 mm/s is favorable. Such a relatively slow retraction can be achieved in an energy-saving manner by applying a voltage which is kept constant by simple means to a compact drive motor  28 . 
     The lancing profile can be predefined independently of the lancing depth. In the case of a deeper puncture the curve shown in  FIG. 2  is then, as it were, shifted upwards without alteration. Alternatively it may be of advantage to adapt the speed time course depending on a selectively changed lancing depth in such a manner that a defined dwell time is reached in the punctured state. 
     While exemplary embodiments incorporating the principles of the present invention have been disclosed hereinabove, the present invention is not limited to the disclosed embodiments. Instead, this application is intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.