Automatic and position-sensitive syringe and method for nonaspirating or aspirating obtaining of blood samples
BACKGROUND OF THE INVENTION 
     This is a continuation of application Ser. No. 789,233 filed Oct. 18, 1985, abandoned, for Automatic and Position-Sensitive Syringe and Method for Nonaspirating or Aspirating Obtaining of Blood Samples. 
    
    
     In my prior U.S. Pat. No. 4,448,206 there is disclosed an aspirating syringe having various advantages over the prior art. Such advantages are indicated, for example, in columns 2 and 3 of the patent, as well as columns 5 and 6 thereof. 
     Applicant has now invented an improvement over U.S. Pat. No. 4,448,206, as well as over various other prior-art patents. Such improvement has the advantages described in U.S. Pat. No. 4,448,206 and also has additional important advantages. 
     These advantages include a gravity-responsive and position-responsive ball check valve mounted in the plunger. The ball of the valve is sufficiently heavy to effectively seal with the plunger for aspiration of blood, but sufficiently light that air may vent from the tubular body during taking of an arterial sample under arterial pressure without sealing. Furthermore, the relationships are such that when the syringe is held at an incorrect angle, as by relatively inexperienced personnel, aspiration may not be effected to any substantial extent. The valve is employed in combination with an air-permeable but blood-impermeable filter, such filter preventing blood from reaching the ball. Air can be vented at all times from the tubular body of the syringe, through the filter and past the ball, regardless of the position of the syringe. The only time air does not vent is when aspiration is occurring, while the syringe is in a desired orientation relative to the horizontal, the ball then being seated by gravity and preventing flow of air past the valve seat and through the filter to thereby effect a highly satisfactory aspiration operation as the plunger is moved upwardly. 
     SUMMARY OF THE INVENTION 
     There is seated over an air-venting passage in the plunger of a syringe for single in vitro diagnostic use, a ball that is sufficiently heavy that it will respond to gravity despite frictional, electrostatic or other forces, but sufficiently light that air may vent during taking of an arterial sample without aspiration or aspirating. Because of the ball, there is no need for any lost-motion connection to effect manual closing of the valve when aspiration is desired. 
     The region around the seat for the ball is inclined at a predetermined angle related to the desired angle at which the syringe should be held during drawing of a blood sample. The relationship is such that aspiration may not occur to any substantial degree when the syringe is at an excessively small angle relative to the horizontal. This prevents an inexperienced operator from holding the syringe at an improper angle during aspiration. 
     The plunger has incorporated therein a filter which is permeable to air but not permeable to blood. Preferably, the ball is mounted on the side of the filter remote from the needle, so that no blood ever contacts the ball. The ball and filter collaborate with each other to effect venting of air when desired. 
     The apparatus further comprises a nipple that maintains the ball relatively close to its seat at all times, so that the ball does not rattle around in the syringe to any substantial extent, and so that the ball seats rapidly whereby aspiration may occur. 
     Means are provided to effect a continuous, uninterrupted flow path for air between the forward end of the syringe and the outer end thereof, the only time such flow path is blocked being when the ball is seated, as during aspiration. 
     In accordance with the method, a ball is mounted on the air-venting path through the plunger of a syringe for single in vitro diagnostic use, following which the syringe is held at such an angle that the ball will seat, following which the syringe is operated to withdraw the plunger and thus aspirate blood into the sample chamber. When blood is introduced into the syringe by arterial pressure instead of by aspiration, the ball is lifted by air pressure off of its seat so that air may vent from the blood-sample chamber. Thus, the method comprises a ball that is sufficiently heavy to seat effectively for aspiration purposes, but sufficiently light that it will not interfere with air venting during taking of a sample by arterial pressure. 
     The method further comprises so constructing the region around the ball that the ball will not seat unless the syringe is at a substantial angle to the horizontal, the result being that inexperienced personnel may not operate the syringe improperly during aspiration. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric view of a syringe incorporating the present invention; 
     FIG. 2 is a fragmentary isometric view of only the inner end of the handle of the syringe, and illustrating the air-venting means of the handle; 
     FIG. 3 is an enlarged longitudinal sectional view showing the syringe in a horizontal position and with the handle being pressed inwardly to its limiting position; 
     FIG. 4 corresponds to FIG. 3 but shows the syringe in a horizontal position after the handle has been pulled outwardly to increase the space between the nipple and the ball seat; and 
     FIG. 5 shows the ball in effectively seated condition preparatory to aspirating operation, the syringe being at a proper angle to the horizontal. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The disclosure of my prior U.S. Pat. No. 4,448,206 is hereby incorporated by reference herein. Thus, a description of the materials employed, and other factors and relationships relating to the basic construction of the syringe, will not be repeated in this specification. The present specification will, instead, be directed toward relationships and the material that differs from what is described in the U.S. Pat. No. 4,448,206. 
     Stated generally, the preferred embodiment of the syringe has a tubular body 10 in which a plunger 11 is slidably mounted. The main body of the plunger is formed of a soft elastomeric material, as described in the above-cited patent, and contains an air-permeable and blood-impermeable filter 12. The region between the forward end of the plunger 11 and the forward end of body 11 may be termed a sample chamber, and is numbered 14. 
     Plunger 11 is moved longitudinally of body 10 by a handle 16 which is an extension of the plunger. Stated more specifically, the inner end disc 17 of handle 16 has projecting axially therefrom a cylindrical extension 18. Fixedly mounted on extension 18, at the inner end thereof and concentric therewith, is a disc or nipple 19 the diameter of which is much smaller than that of disc 17. The handle 16 is connected to plunger 11 by inserting the disc 19 through an axial passage at the outer end of plunger 11, the wall 21 of the passage being cylindrical and coaxial with the axis of the syringe. 
     The disc or nipple 19 is disposed in a chamber 22 near the outer end of plunger 11. The chamber 22 is sufficiently large to freely receive the disc 19 and also a ball described subsequently. There is a large clearance between the periphery of disc 19 and the wall of chamber 22, such wall being cylindrical and numbered 23. 
     There is a continuous vent passage from sample chamber 14 to the outer end of body 10, at all times except when aspiration is occurring. Aspiration occurs only when the syringe is at a proper angle relative to the horizontal, the passage then being blocked by a ball as described subsequently. Such passage is through the filter 12, then through an axial passage 24 in plunger body 11, such passage 24 having a cylindrical wall 26 coaxial to the plunger and the body 10, then through the chamber 22, then through passage 21, then through a space between the outer end of plunger body 11 and the disc 17, and then through the body 10 around the X-sectioned handle 16. To ensure that such passage is present, there is a large notch 27 (FIG. 2) in disc or nipple 19, the notch extending inwardly to a region spaced inwardly from wall 21 of the axial passage between chamber 22 and the region of the syringe outwardly of the plunger 11. Furthermore, radial ridges or beads 28 are molded on the inner face of handle disc 17, such ridges or beads serving as spacers that prevent the inner surface of disc 17 from engaging the outer end of plunger body 11 and thereby blocking the passage circumscribed by wall 21. The diameter of disc 17 is substantially smaller than the inner diameter of the tubular body 10 of the syringe. The diameter of extension 18 of the handle is also substantially smaller than is the diameter of passage wall 21 therearound. 
     Extension 18 has a length somewhat greater than that of the passageway 21, to aid in assembly of the apparatus. It is pointed out, however, that no lost-motion connection is required for functional purposes because there need be no valve action except by the ball valve to be described. 
     Disposed in chamber 22 between disc 19 and passage 24 is a ball 31. The ball is adapted to seat on a frustoconical surface 33 of which the innermost end forms an annular seat 32 at the outer end of the cylindrical passage 24. The ball is formed of nonbuoyant material, preferably steel. The ball has a diameter sufficiently large, and a weight sufficiently great, that it will seat effectively on seat 32. On the other hand, it has a weight sufficiently small that it will move off seat 32 and permit venting of air from sample chamber 14 through filter 12 when blood is being introduced into the sample chamber under arterial pressure. Such air, initially within the sample chamber, vents through the above-described air passage through filter 12, passage 24, chamber 22, notch 27 and the region around the periphery of disc 19, the annulus between extension 18 and cylindrical wall 21, the space between the interface of disc 17 and the rear face of the body of the plunger 11, the space between the periphery of disc 17 and the inner wall of tubular body 10, and the region around the X-shaped handle 16. 
     When the handle is in retracted position (FIGS. 4 and 5), the disc or nipple 19 is maintained sufficiently close to valve seat 32 that the ball 31 will not rattle around, and will seat rapidly when desired. When the handle is retracted, the space between disc 19 and valve seat 32 is sufficient that ball 31 may move far enough off the seat for air-flow purposes (as shown in FIG. 4). Conical surface 33, which extends at an angle of about 45 degrees to the syringe axis, forms a guide for the ball to assist the ball in moving between open (FIG. 4) and closed (FIG. 5) positions. Conical surface 33 forms an outwardly-diverging guide surface within the valve chamber 22 that cooperates with the steel ball 31 to enable the ball to be gravity driven onto the valve seat, thereby blocking air flow through the passage 24, whenever the axis of the syringe is at an angle to the vertical that is not greater than a predetermined angle such as about 45 degrees, for example. The frustoconical guide surface 33 also cooperates with the ball and acts to prevent the ball from being gravity driven onto its valve seat when the axis of the syringe is at an angle to the vertical greater than the predetermined angle. 
     The ball will move off its seat when the syringe is used for taking a sample of normal-pressure arterial blood. It will also move off its seat when the syringe axis is at an angle to the vertical of more than about 45 degrees. In the position shown in FIG. 4, with the syringe horizontal, or nearly so, the ball will be gravity displaced from the seat to the extent permitted by the position of the handle disc 19. 
     In a presently-preferred embodiment, the part sizes and configurations are such that even when the handle is pressed inwardly, toward the left as viewed in FIG. 3, to its limiting position (limited by abutment of ridges 28 and disc 17 upon end surface of plunger 11) the ball is not forced to its seated position by the disc 19. As seen in FIG. 3, with the syringe at an angle to the vertical of more than 45 degrees and with the handle in its innermost position, the ball is not seated on the valve seat. 
     The preferred range of diameters of ball 31 is from 0.060 inch to 0.180 inch, and of seat 32 is from 0.040 inch to 0.179 inch, it being understood that the diameter of passage 24 is correlated to the ball diameter in such manner that the ball will seat effectively--the diameter of the ball always being greater than that of the seat 32. (As a specific example, the ball 31 is steel and has a diameter of 0.109 inch. Seat 32 and passage wall 26 have a diameter of 0.105 inch.) 
     It is emphasized that the ball and seat 32 provide an effective check-valve action, being closed during the time when blood is entering the sample chamber 14 by being aspirated into such chamber. Although the ball does not contact the blood because of the interposed filter 12, which is impervious to blood flow, the ball could operate substantially as described if it were placed on the other or inner side of the filter. The specific gravity of the ball is made greater than that of blood, so that the ball will be gravity operated whether or not it is immersed in blood. 
     The ball 31 is sufficiently heavy that gravity and the conical guide surface 33 will effectively guide it onto its seat 32 despite any frictional or electrostatic forces that may be present. Furthermore, the relationships are caused to be such that the ball will not be guided onto its seat unless the axis of the syringe is at a sufficiently-great angle relative to the horizontal. It is correct and proper that blood samples be taken when the syringe axis is at an angle of not more than about 45 degrees to the vertical (it being assumed, for purposes of illustration and description, that the surface of the skin of the patient at the region surrounding the artery is horizontal). Thus, guide means are provided outwardly adjacent to the valve seat 32 to guide the ball onto the seat when the syringe angle, relative the vertical, is not too large. Preferably, such guide means comprise a frustoconical surface 33 extending from valve seat 32 to the inner end of chamber wall 23. Thus, the frustoconical surface 33 diverges toward the outer end of the syringe. The cone angle of surface 33, relative to the axis of the syringe, is about 45 degrees or somewhat less. In the illustrated embodiment, the cone angle is 35 degrees, because such cone angle causes effective seating of ball 31 on seat 32 when the syringe is at an angle of about 45 degrees to the horizontal. However, if the angle of the syringe were substantiallly less than 45 degrees relative to the horizontal, for example 30 degrees relative thereto, the ball would roll off of its seat 32 so that outward pulling of the plunger 11 by handle 16 for aspiration purposes would be ineffective in that air would vent inwardly from the atmosphere through the described flow-passage means in and around the plunger 11 to the sample chamber 14. 
     As described in the cited U.S. Pat. No. 4,448,206, the sample chamber contains, preferably, flake heparin. Liquid heparin may also be employed if desired. 
     DESCRIPTION OF THE METHOD 
     The nurse or other operator pushes on the handle 16 to move the plunger 11 axially along the syringe body 10 to the extreme inner end of the body, the plunger being stopped by the convergent inner end of such body. This operation of the handle, in the present embodiment, moves the ball 31 close to the seat 32 (see FIG. 3) but does not force the ball to its seat. The operator then makes an arterial puncture so that the hollow needle 34 (FIG. 1) of the syringe penetrates an artery. During such arterial puncture, and subsequently, the syringe is held at an angle, relative to the horizontal, that is greater than 45 degrees. 
     Assuming that the blood pressure of the individual is sufficiently great, arterial pressure pumps blood through needle 34 into sample chamber 14. The filter will absorb a small portion of blood after thirty seconds and seal itself if the operator does not manually seal the syringe filter. Sample chamber 14 is thus filled, and the air between the blood and the filter 12 is progressively expelled through filter 12 and passage 24, it being understood that, because of the characteristics of the ball as described above, the ball 31 lifts off of its seat 32 and permits the venting of air through the described flow passages. When all air is vented from the sample chamber 14, the blood engages the inner end of filter 12. Such engagement, and the engagement of the blood with the inner end of the plunger body, causes lifting of the plunger 11 as far as desired. Of course, the tubular body 10 is calibrated and is transparent or translucent so that the level of the plunger may be observed and the operation terminated as soon as the plunger has moved outwardly sufficiently far to enlarge the chamber 14 to desired size. A substantially air-free sample has flowed into the sample chamber. 
     After the needle 34 is withdrawn from the puncture site, the needle end is inserted into a stopper, following which the operator pushes lightly on handle 16. The resulting increased pressure in chamber 14 seals the sample by causing some blood to enter the inner portion of filter 12. Thereafter, the syringe is rotated in order to mix the heparin with the blood. 
     The above-indicated portion of the method may also be performed by initially setting the plunger 11 at the desired position in the tubular body 10, and then allowing blood to fill the chamber under arterial pressure until the plunger starts to rise. At that time, the needle is withdrawn and the above-indicated stopping and sealing steps are performed. 
     When there is insufficient arterial pressure to pump blood into chamber 14, the blood is withdrawn by aspiration. Assuming that the plunger 11 is initially at the extreme inner (forward) end of tubular body 10, that is to say at the bottom of the barrel of the syringe, the nurse or other operator may note that the plunger is not rising and thus realizes that there is insufficient arterial pressure. Then, while the syringe is held at an angle of at least 45 degrees relative to the horizontal, the operator pulls gradually on handle 16 to shift plunger 11 upwardly and outwardly, thereby decreasing pressure within chamber 14. Because the angle of the syringe is at least 45 degrees relative to the horizontal, the ball 31 is effectively seated on seat 32, and remains seated, so no air can flow from the ambient atmosphere through the syringe and into sample chamber 14. It follows that the outward movement of the plunger 11 will aspirate blood from the artery into chamber 14, and such aspiration is continued until sufficient blood is drawn. 
     Thereafter, the syringe is held vertically, with the needle 34 pointing downwardly, after the needle is inserted into a stopper. Then, the handle 16 is again pressed lightly in order to vent air from chamber 14 through the filter and seal the syringe. Then, the syringe is again rotated to mix the heparin as before. 
     It is emphasized that aspiration may not be effected when the axis of the syringe is less than 45 degrees from the horizontal. This is because the ball 31 is then shifted away (by gravity) from seat 32 as illustrated, for example, in FIG. 4, so that outward shifting of the handle and the plunger do not create large suction in chamber 14, there instead being air passed from the ambient atmosphere through the tubular body 10 and the plunger 11 to the chamber 14. On the other hand, when the syringe is properly oriented, as illustrated (for example) in FIG. 5, the ball 31 is firmly seated on seat 32, so that no air can flow in through the syringe body to the chamber 14, and aspiration is effectively achieved. 
     There has thus been described a syringe which is position sensitive relative to the aspirating operation, and which will change automatically from the arterial-pressure mode to an aspirating mode without need for any manual valve closing. Instead, there is a gravity valve that effectively seats at all times when the syringe is held at the desired angle to the horizontal. On the other hand, the valve does not seat when the syringe is held at an undesired angle, which prevents aspirating operation at an undesired angle as by an inexperienced operator. 
     The foregoing detailed description is to be clearly understood as given by way of illustration and example only, the spirit and scope of this invention being limited solely by the appended claims.