Abstract:
The present invention is directed to a measuring unit, for measuring characteristics of a sample liquid, comprising a support member, having at least one upper bearing arm, with an upper bearing unit, at least one lower bearing arm, with a lower bearing unit, and a base, for being attachable to a respective measuring system; a shaft, having shaft toes and being rotatably supported about a rotation axis, by said upper bearing unit, and said lower bearing unit, wherein said upper bearing unit, said lower bearing unit, and said shaft toes form toe bearings, respectively; an interface member, having a detecting element, and a drive element, said interface member, being fixed on said shaft, and being connected to a coupling shaft, with a probe connector section, for measuring characteristics of said sample liquid; wherein said interface member, and the coupling shaft, are coaxially aligned with said shaft.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/145,270, filed Jan. 16, 2009, the entire disclosure of which is herein incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a measuring unit for measuring characteristics of a sample liquid, in particular viscoelastic characteristics of a blood sample. The present invention also relates to a corresponding measuring system. 
         [0003]    It is essential for survival that a wound stops bleeding, i.e. that the body possesses an adequate mechanism for haemostasis. The process of blood clotting can be activated in the case of injuries or inflammations by either extrinsic or intrinsic factors, e.g. tissue factor (TF) or Hagemann factor (F XII), respectively. 
         [0004]    The other main constituent of the final blood clot are the thrombocytes which are interconnected by the fibrin fibres and undergo a number of physiological changes during the process of coagulation. 
         [0005]    Various methods have been introduced to assess the potential of blood to form an adequate clot and to determine the blood clots stability. Common laboratory tests such as thrombocyte counts or the determination of fibrin concentration provide information on whether the tested component is available in sufficient amount but lack in answering the question whether the tested component works properly under physiological conditions (e.g. the polymerisation activity of fibrinogen under physiological conditions can not be assessed by common optical methods). Besides that, most laboratory tests work on blood-plasma and therefore require an additional step for preparation and additional time which is unfavourable especially under POC (point of care) conditions. 
         [0006]    Another group of tests which overcomes these problems is summarized by the term “viscoelastic methods”. The common feature of these methods is that the blood clot firmness (or other parameters dependent thereon) is continuously determined, from the formation of the first fibrin fibres until the dissolution of the blood clot by fibrinolysis. Blood clot firmness is a functional parameter, which is important for haemostasis in vivo, as a clot must resist blood pressure and shear stress at the site of vascular injury. Clot firmness results from multiple interlinked processes: coagulation activation, thrombin formation, fibrin formation and polymerization, platelet activation and fibrin-platelet interaction and can be compromised by fibrinolysis. Thus, by the use of viscoelastic monitoring all these mechanisms of the coagulation system can be assessed. 
         [0007]    A common feature of all these methods used for coagulation diagnosis is that the blood clot is placed in the space between a cylindrical pin and an axially symmetric cup and the ability of the blood clot to couple those two bodies is determined. 
         [0008]    The first viscoelastometric method was called “thrombelastography” (Hartert H: Blutgerinnungsstudien mit der Thrombelastographie, einem neuen Untersuchungsverfahren. Klin Wochenschrift 26:577-583, 1948). In the thromboelastography, the sample as a sample liquid is placed in a cup that is periodically rotated to the left and to the right by about 5°, respectively. A probe pin is freely suspended by a torsion wire. When a clot is formed it starts to transfer the movement of the cup to the probe pin against the reverse momentum of the torsion wire. The movement of the probe pin as a measure for the clot firmness is continuously recorded and plotted against time. For historical reasons the firmness is measured in millimetres. 
         [0009]    A common feature of all these methods used for coagulation diagnosis is that the blood clot is placed in the space between a cylindrical pin and an axially symmetric cup and the ability of the blood clot to couple those two bodies is determined. 
         [0010]    Calatzis et al. (U.S. Pat. No. 5,777,215) describe a measuring illustrated in  FIG. 1  which is known under the term thromboelastometry. Contrary to the modifications mentioned above, thromboelastometry is based on a cup  43  fixed in a cup holder  48  while a probe element  42  is actively rotated. For this purpose the probe element  42  is attached to a coupling shaft  35 ′ which is suspended by a ball bearing  49  in a base plate  39  and has a drive element  32  connected to it. An oscillating motion perpendicular to the drawing plane induced at the opposite end of the drive element  32  is transformed into a periodically rotation of the coupling shaft  35 ′ and the connected cup  43  around a rotation axis  20  by about 5° in each direction. As the sample liquid  44  begins to coagulate the motion amplitude of the coupling shaft  35 ′ which is detected by e.g. the deflection of a light beam from detecting means  41  and a detecting element  31 , e.g. a mirror, starts to decrease. 
         [0011]    During coagulation the fibrin backbone creates a mechanical elastic linkage between the surfaces of the blood-containing cup  43  and the probe element  42  plunged therein. A proceeding coagulation process induced by adding one or more activating factor(s) can thus be observed. In this way, various deficiencies of a patient&#39;s haemostatic status can be revealed and can be interpreted for proper medical intervention. 
         [0012]    A general advantage of viscoelastometric, e.g. thromboelastometric, techniques compared to other laboratory methods in this field therefore is that the coagulation process and the change of mechanical properties of the sample are monitored as a whole. This means that thromboelastometry does not only indicate if all components of the coagulation pathways are available in sufficient amounts but also if each component works properly. 
         [0013]    Compared with the device mentioned above using a torsion wire thromboelastometry as shown in  FIG. 1  has the advantage that a ball bearing provides a certain stability of the measuring device, e.g. the measuring device can be configured as a transportable device and used under POC (point of care) conditions. 
       SUMMARY OF THE INVENTION 
       [0014]    It is a problem underlying the presented invention to provide an improved measuring unit for measuring characteristics of a sample liquid, in particular viscoelastic characteristics of a blood sample. 
         [0015]    Directly connected to this invention is the problem to provide a corresponding improved measuring system for measuring viscoelastic characteristics of a sample liquid, in particular the coagulation characteristics of a blood sample liquid. 
         [0016]    These problems are solved by the subject-matter of the independent claims. Preferred embodiments are set forth in the dependent claims. 
         [0017]    In a first aspect, the present invention provides measuring unit for measuring characteristics of a sample liquid, in particular viscoelastic characteristics of a blood sample, comprising a support member having at least one upper bearing arm with an upper bearing unit, at least one lower bearing arm with a lower bearing unit and a base for being attachable to a respective measuring system; a shaft having shaft toes and being rotatably supported about a rotation axis by said upper bearing unit and said lower bearing unit, wherein said upper bearing unit, said lower bearing unit and said shaft toes form toe bearings, respectively; an interface member having a detecting element and a drive element, said interface member being fixed on said shaft and being connected to a coupling shaft with a probe connector section for measuring characteristics of said sample liquid; wherein said interface member and the coupling shaft are coaxially aligned with said shaft. 
         [0018]    In a second aspect, the present invention provides a measuring system for measuring characteristics of a sample liquid, in particular viscoelastic characteristics of a blood sample, comprising at least one measuring unit according to the invention. 
         [0019]    Toe bearings have clearances and friction losses which are decreased in relation to ball bearings. In particular it is advantageous that toe bearings have smaller clearances regarding tilting as well. The measuring device according to the invention also has the advantage to provide a unit which does not need a basement being aligned horizontally with high precision. Thus it is highly suitable for use in POC conditions and the like. Moreover the measuring unit according to the invention is more unsusceptible in case of vibrations than that one of the state of the art. Another advantage is the miniaturized shape of toe bearings. 
         [0020]    The support member forms a structural rigid component of the measuring unit and supports the shaft by the toe bearings. The shaft is coupled to a coupling shaft by an interface member being a component with several functions. 
         [0021]    Said upper bearing unit and said lower bearing unit are removable inserts each being fixed in said respective bearing arm of said support member. Thus it is possible to remove the bearing units together with the shaft in case of maintenance without changing the support member. 
         [0022]    Said lower bearing unit is a thrust bearing and said upper bearing unit is a moveable bearing. The moveable bearing is configured to be adjustable by adjusting means to achieve optimal friction and clearances. 
         [0023]    The bearing units are equipped with bearing plates made of e.g. kind of jewel, e.g. sapphire or/and ceramic. 
         [0024]    The interface member comprises an upper connector section connected to said shaft. This forms a simple connection to the shaft. 
         [0025]    Furthermore said interface member has a frame having an opening for a passage of said lower bearing arm of said support member, which allows for a compact assembly of the measuring unit and a connection to the coupling shaft. 
         [0026]    Moreover a lower connector section for a connection to said coupling shaft forms another portion of the interface member. 
         [0027]    Eventually the interface member has a front for securing that said detecting element thereon; and moreover a receptacle for securing that said drive element therein. 
         [0028]    The interface member further comprises a fixing unit for fixing said interface member to said shaft. It is preferred that said fixing unit is at least one screw to achieve a simple fixing. 
         [0029]    In an alternative embodiment said fixing unit is formed having clip means cooperating with corresponding clip means of said shaft. 
         [0030]    It is preferred that said lower connector section is formed having clip means cooperating with corresponding clip means of an interface section of said coupling shaft for easy and fast connection without any tool. 
         [0031]    It is also preferred that said probe connector section of said coupling shaft is formed having clip means cooperating with corresponding clip means of a probe element being detachably fixed onto said probe connector section. Thus an easy assembly and disassembly of different probe elements can be done. 
         [0032]    In another preferred embodiment said detecting element can be a mirror. 
         [0033]    When, in case of inserting the coupling shaft and/or a probe element onto the coupling shaft, an axial force can be exerted on the shaft and the interface member and cause an axial movement of the shaft in direction to the upper movable bearing. To limit said axial movement of the shaft and the interface member and a possible damage of the upper movable bearing the measuring unit can comprise axial stop means. Said stop means can be formed e.g. by a shoulder of the interface member or/and a shoulder of the shaft, said shoulder pointing to the upper bearing arm and co-operating with a corresponding shoulder of the upper bearing arm and/or the upper bearing unit. 
         [0034]    In another embodiment at least one of said upper bearing unit and said lower bearing unit can comprises at least one bearing cover plate. Said bearing cover plate serves as a sealing and/or as a centre means for the shaft. 
         [0035]    And in another embodiment it is preferred that the drive element is a spring wire. 
         [0036]    Further features and advantages of the present invention will be evident from a description of embodiments with reference to the figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0037]    The figures are showing the following: 
           [0038]      FIG. 1  is a schematic drawing of an example of thromboelastometry according to the state of the art. 
           [0039]      FIG. 2  is a perspective exploded view of an exemplary embodiment of a measuring unit according to the invention. 
           [0040]      FIG. 3  is a schematic view along y-direction of a sectional view along a rotation axis  20  of the assembled measuring unit of  FIG. 1   
           [0041]      FIG. 4  is a perspective view of an exemplary embodiment of a measuring device according to the invention. 
           [0042]      FIG. 5  is a top view of the measuring device of  FIG. 4 . 
           [0043]      FIG. 6  is a view along y-direction of the measuring device of  FIG. 4 . 
           [0044]      FIG. 7  is a perspective view in x-direction of the measuring device of  FIG. 4 . 
       
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0045]    Parts and components having same functions are depicted with same references. Coordinate systems indicating x-, y- and z-direction in the figures allow for better orientation. 
         [0046]    An exemplary embodiment of a measuring unit  1  according to the invention will now be described with regard to  FIG. 2  and to  FIG. 3 . 
         [0047]      FIG. 2  is a perspective exploded view of an exemplary embodiment of the measuring unit  1  according to the invention and  FIG. 3  is a schematic view along y-direction of a sectional view along a rotation axis  20  of the assembled measuring unit  1  of  FIG. 1 . 
         [0048]    The measuring unit comprises a support member  2  with a body  6  extending in z-direction. The body  6  connects an upper bearing arm  3  and a lower bearing arm  4 . The bearing arms  3  and  4  extending in x-direction are parallel to each other spaced with a distance. Body  6  and said bearing arms  3  and  4  form a U-shaped block having with a recess  7  with the distance defined by the bearing arms  3  and  4 . 
         [0049]    The body  6  and the lower bearing arm  4  are fixed onto a base  5  extending in x-direction. The base  5  comprises fixing holes (see  FIG. 4  for mounting elements  38 ). 
         [0050]    The upper bearing arm  3  is formed with a through hole for an upper bearing unit  14  and the lower bearing arm  4  has a through hole for a lower bearing unit  21 , the through holes being aligned along a rotation axis  20 . 
         [0051]    The upper bearing unit  14  and the lower bearing unit  21  are formed as inserts to be inserted into said through holes. An upper fixing passage  8  extending from the side of the body  6  in the upper bearing arm  3  in y-direction allows for fixing the inserted upper bearing unit  14  by a fixing element  34 , e.g. a screw. The inserted lower bearing unit  21  can be fixed similarly by a fixing element  34  via a lower fixing passage  9  extending in the lower bearing arm  4 . 
         [0052]    A shaft  10  with a shaft body  13  having an upper shaft toe  11  and a lower shaft toe  12  is provided to be supported by the bearing units  14  and  21 . Said bearing units  14  and  21  are configured together with the shaft  10  having said upper shaft toe  11  and said lower shaft toe  12  to form a toe bearing, respectively. A groove  51  for a circlip  50  is formed in the shaft body  13 . 
         [0053]    The upper bearing unit  14  comprises a fixing section  15  and a bearing section  16 . As can be seen from  FIG. 3  the bearing section  16  is inserted into a through hole of the upper bearing arm  3 . The upper bearing unit  14  is designed as a movable bearing with a movable bearing plate  46 , e.g. made of a kind of jewel or ceramic, arranged in a through hole of the bearing unit  14 . The upper shaft toe  11  of the shaft  10  rests on the movable bearing plate  46 . The movable bearing plate  46  is movable along the rotation axis, i.e. in z-direction. A spring  45  is arranged in the fixing section  15  and can be adjusted by adjusting means  17 , e.g. a screw, the adjusting means  17  being fixable by a fixing means  18 , e.g. a screw through a fixing passage  19  in the fixing section  15 . 
         [0054]    The lower bearing unit  21  comprises a collar  22  and a bearing section  23 . The bearing section  23  is inserted into a through hole of the lower bearing arm  4 , wherein the collar  22  rests on the lower bearing arm  4 . A thrust bearing plate  47  is arranged within a through hole of the lower bearing unit  21  and fixed therein. The trust bearing plate  47  is made of the material as the movable bearing plate, wherein the lower shaft toe  12  of the shaft  10  rests on the thrust bearing plate  47 . 
         [0055]    A pretension of the bearing units  14 ,  21  and the shaft  10  can be adjusted by the adjusting means  17 . 
         [0056]    The measuring unit  1  further comprises an interface member  24  having an upper connector section  25 , a frame  26  and a lower connector section  27 . An opening  28  is formed in the frame to form a passage having a cross-section greater than the cross-section of the lower bearing arm  4  (see also  FIG. 3 ). 
         [0057]    The upper connector section  25  is designed with a bore to be connected to the shaft  10  as can be seen from  FIG. 3 , wherein the shaft  10  is fixed by a fixing unit  29 , e.g. a screw, to connect the interface member  24  to the shaft  10 . 
         [0058]    The lower connector section  27  is also provided with a bore to be connected to a coupling shaft  35 . To this end the coupling shaft  35  is formed with an interface section  36  which is preferably designed as a clip means. Other fixing means can be possible. The coupling shaft  35  further comprises a probe connector section  37  which is provided to be connected to a probe element  42  (see  FIG. 1 ). 
         [0059]    Furthermore the interface member  24  has a front  30  on which a detecting element  31 , e.g. a mirror (see also  FIG. 1  and  FIG. 2 ), is fixed, e.g. by glue. The interface member  24  also comprises a receptacle  33  on the side of the front at the lower portion of the frame  26 . A drive element  32 , e.g. a spring wire, as already shown in  FIG. 1  can be inserted into this receptacle  33 . 
         [0060]    In this example the upper bearing unit  14  and the lower bearing unit  21  are equipped with bearing cover plates  52 . Said bearing cover plates  52  are disc-shaped and inserted into the through holes of the bearing units  14  and  21  in such a way that they surround portions of the shaft  10  which extends through passage holes of the bearing cover plates  52 . These passage holes have an inner diameter which is a little bit greater than that of the outer diameter of the corresponding shaft portion. So the bearing cover plates  52  provide a certain sealing function. On the other hand the bearing cover plates  52  can centre the shaft  10 . In use there is no friction between the bearing cover plates  52  and the corresponding shaft portions. In the example of  FIG. 3  the bearing cover plate  52  of the upper bearing unit  14  is inserted into the lowest part of the bearing section  16  and co-operates with a cylindrical portion of the upper shaft toe  11  of the shaft  10 . The bearing cover plate  52  of the lower bearing unit  21  is inserted into the upper part of the collar  22  and co-operates with a cylindrical portion of the shaft body  13  of the shaft  10 . 
         [0061]    An assembly of the measuring unit  1  can be done as following to achieve the assembled unit (see  FIGS. 2 and 3 ). 
         [0062]    First the lower bearing unit  21  is inserted into the lower bearing arm  4  and fixed as mentioned above. Then the interface member  24  is inserted into the recess  7  between upper bearing arm  3  and lower bearing arm  4  in such a way that the lower bearing  4  extends and protrudes through the opening  28  of the frame  26  of the interface member  24 . The interface member  24  should be aligned with its bores to the rotation axis  20 . Now the shaft  10  is inserted along the rotation axis  20  through the through hole in the upper bearing arm  3 , through the bore of the upper connector section  25  of the interface member  24  into the lower bearing unit  21  so that the lower shaft toe  12  rests on the thrust plate  47  of the lower bearing unit. 
         [0063]    Now the upper bearing unit  14  is inserted into the through hole of the upper bearing arm  3  and fixed as mentioned above, the movable bearing plate  46  resting on the upper shaft toe  11 . Then the adjusting means  17  can be adjusted for a predefined pretension now or later. 
         [0064]    The interface member  24  is shifted upwards on the shaft body  13  until the groove  51  can be fitted with a circlip  50 . Then the interface member  24  is shifted downwards to rest on the circlip  50  to maintain a predefined axial position along the rotation axis  20 . Now the interface member  24  can be fixed on the shaft body  13  by said fixing unit  29 . 
         [0065]    Thrust plate  47  and movable plate  46  comprise a dimple, respectively. The dimple will align the shaft  10  together with the interface member  24  and the coupling shaft  35 . 
         [0066]    Finally the coupling shaft  35 , the detecting element  31  and the drive element  32  can be connected to the interface member  24 . 
         [0067]    When, in case of inserting the coupling shaft  35  and/or a probe element  42  (see  FIG. 1 ) onto the coupling shaft  35 , an axial force can be exerted via the interface member  24  on the shaft  10  and cause an axial movement of the shaft  10  in direction of the rotation axis  20  to the upper movable bearing  14 . To limit said axial movement of the shaft  10  and the interface member  24  and a possible damage of the upper movable bearing  14  the measuring unit  1  can comprise axial stop means. Said stop means can be formed in the shown embodiment e.g. by an upper shoulder of the interface member  24  or/and a shoulder of the shaft  10 , said shoulder pointing to the upper bearing arm  3  and co-operating with a corresponding shoulder of the upper bearing arm  3  and/or the upper bearing unit  14 . 
         [0068]    The assembled measuring unit  1  is shown in  FIG. 3  and can be mounted on a base plate  39  of a measuring device  40  as shown in  FIG. 4 , which is a perspective view of an exemplary embodiment of a measuring device  40  according to the invention. 
         [0069]    In the shown embodiment the measuring device  40  comprises four measuring units  1 . The measuring units  1  are fixed on the base plate  39  by mounting elements, e.g. screws or clip fixing means, the coupling shafts  35  extending through corresponding openings in the base plate  39 . The drive elements  32  extend in y-direction and can be driven by a not shown driving device to oscillate the respective interface members  24  with the thereto connected respective coupling shafts  35  (and corresponding parts as mentioned above) around the respective rotation axis  20 . 
         [0070]      FIG. 5  is a top view of the measuring device  40  of  FIG. 4 . Here it is shown that the drive elements  32  and the connected interface members  24  are arranged in a specific angle to the y-direction. 
         [0071]      FIG. 6  is a view along y-direction of the measuring device of  FIG. 4 , wherein the detecting elements  31  can be seen from a front view. 
         [0072]    Finally  FIG. 7  is a perspective view in x-direction of the measuring device  40  of  FIG. 4 . 
         [0073]    It will be apparent to those skilled in the art that changes and modifications can be made to the embodiments described above without departing from the spirit and scope of the present invention as defined by the appended claims. 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           1  Measuring unit 
           2  Support member 
           3  Upper bearing arm 
           4  Lower bearing arm 
           5  Base 
           6  Body 
           7  Recess 
           8  Upper fixing passage 
           9  Lower fixing passage 
           10  Shaft 
           11  Upper shaft toe 
           12  Lower shaft toe 
           13  Shaft body 
           14  Upper bearing unit 
           15  Fixing section 
           16  Bearing section 
           17  Adjusting means 
           18  Fixing means 
           19  Fixing passage 
           20  Rotation axis 
           21  Lower bearing unit 
           22  Collar 
           23  Bearing section 
           24  Interface member 
           25  Upper connector section 
           26  Frame 
           27  Lower connector section 
           28  Opening 
           29  Fixing unit 
           30  Front 
           31  Detecting element 
           32  Drive element 
           33  Receptacle 
           34  Fixing element 
           35 ,  35 ′ Coupling shaft 
           36  Interface section 
           37  Probe connector section 
           38  Mounting element 
           39  Base plate 
           40  Measuring device 
           41  Detecting means 
           42  Probe element 
           43  Cup 
           44  Sample liquid 
           45  Spring 
           46  Movable bearing plate 
           47  Thrust bearing plate 
           48  Cup holder 
           49  Ball bearing 
           50  Groove 
           51  Circlip 
           52  Bearing cover plate