Abstract:
A constant speed fluid sample collection system for use with a catheter, needle, or the like in communication with a patient&#39;s vein is useful to extract a blood sample. The system uses a constant force system to not disrupt the components of the fluid, such as platelets found in blood. The system includes a syringe device and moves a plunger at a constant velocity. The device includes a housing, a piston rod movably mounted within the housing, and a brake mechanism for controlling the movement of the piston with respect to a syringe positioned within the housing. The plunger retracts into the drive device as it is being withdrawn.

Description:
[0001]    This application is related and claims priority under 35 U.S.C. § 119 and/or § 120 to U.S. application Ser. No. 60/170,569, “Constant Speed Sample Collection System”, filed Dec. 13, 1999, by Joel S. Douglas, the entire contents of which are incorporated by reference herein. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a fluid sample collection device which extracts a sample of body fluid, such as blood, from a patient and uses a constant force or speed control to limit the disturbance of the sample to permit analysis of the sample.  
           [0004]    2. Brief Description of the Related Art  
           [0005]    Many medical procedures in use today require a relatively small sample of blood, in the range of 50-500 milliliters. It is typically more cost effective and less traumatic to the patient to obtain such a sample by lancing or piercing the skin at a selected location, using a catheter to open a wound in a vein, to enable the collection of blood. The phlebotomist can draw then venous blood into a device which is useable in the analysis mechanism and does not overly disturb the sample.  
           [0006]    Blood collection tubes are commonly used by doctors, nurses and other persons to draw a sample of a body fluid from a patient or to receive a fluid sample from another vessel. Such tubes are ordinarily evacuated, and include a pierceable closure. During one typical use of a blood collection tube, one end of a double-ended needle assembly is used to pierce a vein. The evacuated blood collection tube is then urged towards the second end of the double-ended needle assembly until its closure is pierced. Blood is thereby drawn into the tube. The double-ended needle assembly is ordinarily mounted to a holder having a tubular body. The blood collection tube is inserted within the holder&#39;s tubular body in order to engage the second end of the double-ended needle assembly.  
           [0007]    The maintenance of a vacuum within the blood collection tube is important for the proper operation of such devices. Blood collection tubes may be stored for considerable lengths of time before they are used, yet loss of vacuum during storage or at any time can render the collection tube less effective or useless. Furthermore, the vacuum is such collection tubes can cause activation of the platelets due to turbulence in the blood caused by the vacuum.  
           [0008]    In institutional settings, it is often desirable to collect the sample from the patient and then introduce the sample to a test device in a controlled fashion. Some blood glucose monitoring systems, for example, require that the blood sample be applied to a test device which is in contact with a test instrument. In such situations, bringing the finger of a patient directly to the test device poses some risk of contamination from blood of a previous patient. With such systems, particularly in hospital settings, it is common to lance a patient, collect a sample in a micropipette via capillary action, and then deliver the sample from the pipette to the test device.  
         SUMMARY OF THE INVENTION  
         [0009]    According to a first exemplary embodiment, a fluid sample collection device comprises a housing having a hollow interior, a plunger positioned at least partially within said housing interior and movable within said housing, a piston attached to the plunger and extending from the housing, a spring positioned to move the plunger in a first direction, a wall surrounding and engaging a portion of the plunger to generate a friction force when the plunger moves relative to the wall, and a brake mechanism in the plunger which adjusts the friction force.  
           [0010]    Still other objects, features, and attendant advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed description of embodiments constructed in accordance therewith, taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The invention of the present application will now be described in more detail with reference to preferred embodiments of the apparatus and method, given only by way of example, and with reference to the accompanying drawings, in which:  
         [0012]    [0012]FIG. 1 illustrates an exploded perspective view of an exemplary embodiment in accordance with the present invention;  
         [0013]    [0013]FIG. 2 illustrates a longitudinal cross-sectional view of the device illustrated in FIG. 1, with the device oriented to withdraw a sample of a fluid;  
         [0014]    [0014]FIG. 3 illustrates a view similar to that illustrated in FIG. 2, with the device oriented after having withdrawn a sample of fluid; and  
         [0015]    [0015]FIG. 4 illustrates an enlarged cross-sectional view, with portions broken away, of interior portions of the device illustrated in FIGS.  1 - 3  in two different orientations.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]    In general, the present invention assists in ensuring that a sufficiently large sample of body fluid or blood can be drawn and used in an analysis machine without having to be transferred to another device. The sample is not disturbed by excess turbulence, as in prior devices, so that the sample can be properly analyzed. By controlling the speed of the collection of the body fluid, the sample is not disturbed as in prior collection devices.  
         [0017]    Exemplary embodiments of a collection device and system in accordance with the present invention may be used with a catheter, needle, or other body-indwelling device for collecting fluids, such as blood, from the body. Exemplary devices includes a housing, a piston rod movably mounted within the housing, and a control mechanism which controls the movement of the piston with respect to a fluid containing syringe cartridge removably positioned within the housing. The piston rod includes a plunger and a shaft in communication with the collection mechanism. The plunger and collection mechanism are connected by a holder. The system includes one or more latches to hold the device in an extended position until the device is to collect the body fluid sample.  
         [0018]    The sample is collected by attaching the device to a catheter, needle, vacuum-filled vial, or the like, and releasing the latch(es) once body fluid has filled and is in communication with the device. The latches when released allow the plunger be moved inside the housing by a spring and the friction between the walls of the housing and the plunger is such that the friction provides a resistance force proportional to the spring force driving the plunger cylinder, so that a constant speed of the plunger is attained by the system. This provides a low shear force in the fluid being collected, which contributes to lower degradation of the sample, so that the fluid sample can be used directly in the testing system. The low shear force extraction also has a second benefit for people with fragile veins because it extracts at a slow and constant rate to avoid collapsing their veins. The system can alternatively be used with a needle or other hollow cannula if the patient does not want to use a catheter. Additionally, provision is made to expel the collected fluid from the system.  
         [0019]    Referring to the drawing figures, like reference numerals designate identical or corresponding elements throughout the several figures.  
         [0020]    [0020]FIG. 1 illustrates an exemplary embodiment of an apparatus in accordance with the present invention. Fluid collection and dispensing device  100  includes an elongate and hollow housing  102 , a spring  104 , a cylindrical and hollow plunger  106 , and a distal cannula  108 . A piston  110  is slidably received in the hollow interior of the cannula  108 , and includes a distal seal  112  which engages with the interior wall of the cannula (see FIGS. 2 and 3) sufficiently to pull a vacuum when retracted proximally. The piston includes a proximal end  114  which is configured to attach to a coupling inside the housing, described in greater detail below.  
         [0021]    The housing  102  includes at least one movable or pivotable latch  116 , and preferably a second latch  118 , disposed on opposite sides of the exterior of the housing. The housing itself includes a hole  120  which leads into the interior of the housing through which portions of the latch extend and engage the plunger  106  (see, again, FIGS. 2 and 3), and from which these same portions can be moved to permit the plunger to move. A flanged coupling  122  is mounted around a distal opening  123  in the housing, and provides a mount for the proximal end of the cannula  108 . According to yet another aspect of the present invention, the plunger  106  can be made longer so that the user of the device  100  can pull on the plunger to release it.  
         [0022]    The plunger  106  includes a cylindrical barrel  124  from which a distal cylindrical extension piece  126  extends. Piece  126  is sized and shaped to receive therein or thereon the proximal end  114  of the piston  110 . When the plunger  106  is in a proximal, retracted orientation, the piston  110  extends through the coupling  122 , distal opening  123 , spring  104 , and into a first hollow interior space  150  (see FIG. 3) of the housing  102 . The plunger  106  includes at least one, preferably at least two, outwardly extending spring tabs  128  which are separated by slots  129  through the barrel  124 . Each tab  128  includes an outer friction surface  130  which is oriented to bear against an inner surface of the housing  102 , described in greater detail below. As discussed generally above, the friction force generated between surface(s)  130  and the inner surface of the housing  102  is used to counterbalance the spring force generated by the spring  104  to result in a substantially constant velocity of the piston  110  relative to the cannula  108 .  
         [0023]    A split nut  132  having an at least partially threaded interior bore  133  (see FIG. 2) is permanently mounted in the hollow interior of the plunger  106 . A distal interior threaded portion  134  receives the distal end of a screw  140 , which extends proximally. At least two, and preferably a plurality of proximal slots  136  extend through the nut  132  and define at least one, and preferably a plurality of outwardly deflectable fingers  138 . The screw  140  acts as a speed adjustment device as described in greater detail below.  
         [0024]    A coupling disc  152  is positioned in the interior of the plunger  106  and is secured, either permanently or releasably, to the proximal end  114  of the piston  110 , and thus secures the piston to the plunger so that the two elements move longitudinally together. A proximal end plate  142  including an access hole  144  is secured to the proximal end of the housing. The access hole is sized to permit an appropriately shaped driving tool (not illustrated), such as a screwdriver or the like, to be inserted through the plate  142  to turn the screw  140 .  
         [0025]    [0025]FIG. 4 illustrates the balancing of forces to result in a substantially constant piston-and-plunger retraction velocity. In FIG. 4, two exemplary positions of the split nut  132  relative to the plunger  106  are illustrated, an upper and a lower example. In FIG. 4, the tapers of several of the elements have been exaggerated to be easier to visualize, and one of ordinary skill in the art will appreciate that a much less severe taper is also within the scope of the present invention. In FIG. 4:  
         [0026]    F A =Force of friction, lower example  
         [0027]    F B =Force of friction, upper example  
         [0028]    F 1 =Normal force of wall  148  against tabs  128 , lower example  
         [0029]    F 2 =Normal force of wall  148  against tabs  128 , upper example  
         [0030]    F S =Spring force from spring  104   
         [0031]    In the upper example, the screw  140  is relatively proximally located, so that the screw head  154  does not bear against the proximal portions of the split nut  132 . Thus, the deflectable fingers  138  do not bear on, or bear less on, the inner surface(s) of the plunger  106 . Thus, there is less normal force F 2  generated between the surface(s)  132  and the inner surface  148  of the housing, and therefore there is less frictional force to counteract the spring force F S .  
         [0032]    The lower example illustrates when the speed adjustment screw  140  is adjusted to push the deflectable fingers  138  outward. The fingers  138  thus bear, or bear more than in the upper example, on the inner surface of the plunger  106 , which in turn generates a greater normal force F 1  between the surface(s)  130  and the surface  148 . This generates a greater frictional force F A  to counteract the spring force F S . By thus simply turning the screw  140 , the device  100  can be adjusted to achieve a nearly constant piston velocity. Additionally advantageous, as the surfaces  130  and  148  begin to wear with use, the device  100  can be readjusted to achieve constant velocity piston motion.  
         [0033]    Turning now to FIGS. 2 and 3, in which longitudinal cross-sectional views of the assembled device  100  are illustrated, the operation of the device will now be described with reference to the drawing figures. In FIG. 2, the device  100  is in an extended position with the piston  110  positioned distally in the cannula  108  and the plunger  106  positioned in the distal portions of cavity  150 . The tabs  128  are engaged and held by the latches  116 ,  118 , through the holes  120 . The spring  104  is thus compressed between the tabs  128  and the distal interior wall of the housing  102 . In this orientation, the device  100  is ready to take a fluid sample.  
         [0034]    When it is desired to gather a fluid sample, the distal tip  156  of the cannula  108  is placed in fluid communication with the fluid, such as by inserting it into the hub of a catheter or needle, or into a drop of fluid from a puncture. The latches  116 ,  118  are then released, which releases the plunger  106 . The spring  104  is therefore unrestrained, and pushes the plunger  106  proximally. The friction surfaces  130  of the tabs  128  bear against the outwardly tapered interior wall  148  of the housing  102 , and generate a frictional force therewith that counteracts the spring force and results is the plunger moving proximally at a substantially constant speed. As will be readily appreciated by one of ordinary skill in the art, the interior wall  148  of the housing  102  is tapered outwardly from the distal end of the cavity  146  to the proximal end, so that the friction force tapers off at substantially the same rate that the spring force diminishes. Thus, the plunger is made to move proximally at a substantially constant speed over the length of its travel in the housing  102 , with the tabs  128  and housing  102  together cooperating as a brake mechanism.  
         [0035]    When the plunger reaches the end plate  142 , it stops its proximal motion, and the piston  110  has been withdrawn relative to the cannula  108 , drawing a fluid sample into the interior of the cannula distal of the seal  112 . When it is desired to dispense the fluid thus collected, the plunger  106  is pushed distally, as by inserting a pushrod or the like (not illustrated) through the hole  144  and pushing the plunger.  
         [0036]    According to other aspects of the present invention, the coil spring  104  can be alternatively replaced with an air spring, for which appropriate seals are provided between the outer surface of the piston  110  and the inner surface of the housing  102 , such as at the distal opening  123 , and between the outer surface of the plunger  106  and the inner surface of the housing  102  in the region of cavity  150 .  
         [0037]    While the invention has been described in detail with reference to preferred embodiments thereof, it will be apparent to one skilled in the art that various changes can be made, and equivalents employed, without departing from the scope of the invention.