CA1109745A - Syringe - Google Patents

Abstract

SYRINGE
ABSTRACT
Improved disposable syringe for taking arterial blood samples for blood gas testing and for administering epi-dural anaesthesia, wherein the syringe plunger has a compressible elastomeric tip member which has a peripheral annular wiper extending axially forwardly toward the syringe floor and radially outwardly at an acute angle to the longitudinal center line of the barrel and plunger to form an excellent seal with the inner surface of the syringe barrel while at the same time providing only a gentle pressure against such surface and hence an exceptionally low resistance to axial movement of the tip member and plunger.
The tip member and barrel floor are designed so that when the tip member is moved to its furthest point forwardly into engagement with the floor of the syringe barrel, e.g., to eject air and excess liquid anti-coagulant, a sea]. is formed between the forward end of the tip member and the portion of the barrel floor immediately adjacent the needle opening in such floor upon initial contact of the tip member with such floor to prevent further flow of liquid out of such barrel and thereby trap a predetermined amount of the liquid in a space of predetermined volume remaining between the tip member and barrel floor. The trapped liquid acts as a stop to prevent deformation and com-pression of the tip member against the barrel floor The plunger and tip member are also designed so that when the tip member initially engages the barrel floor as aforesaid to seal the needle opening and further forwardly directed axial force on the plunger is substantially restricted to that portion of the tip member which is behind the trapped liquid with a minimum of force being applied to the portion of the tip member located behind the needle opening whereby distortion of such tip member into such opening is minimized. This, in combination with the aforesaid liquid stop minimizes the intake of air upon release of inward force on the plunger after it has been moved to its for-wardmost position against the barrel floor to eject air and excess anti-coagulant prior to taking a blood sample.

Description

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BACKGROUND OF THE INVENTIOM ' ~ - --This invention relates generally to a hypodermic syringe for obtaining a sample of a-body fluid, more particularly for drawing samples from the patient's artery or vein for blood gas analysis or other testing, and for administering fluids, more particularly for administering epidural anaesthesia.
Various syringes and methods for taking blood samples from patients are known. Such samples are normally taken by means of a syringe which includes a generally cylindrical syringe barrel aving a plunger therein which, when pulled axially by an operator, creates a suction force drawing blood into the barrel through a ypodermic needle. Many tests are performed on the blood which is hus obtained from the vein of the patient. However, an increas-ngly important method of determining the medical status of a atient is the obtaining of arterial blood samples for testing the lood for its content of various gases. Such samples are tested or the partial pressure of oxygen, the partial pressure of carbon ioxide, the pH of the hlood, the electrolyte balance, and various ther tests known in the art.
Syringes previously used in obtaining arterial blood amples have generally been glass syringes, in which the ylindrical barrel is made of glass and the plunger is a ground lass rod which closely eits within the cylinder. ~enerally the echnique for taking samples with such devices comprises, as a __~ .. __, " ,, _ _ ................... . _ . . . . , . _. . .
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,", first step, the drawing of an anticoagulant solution, such as ~sodium heparin, Into the syringe to replace the air in the ¦syringe. This solution also acts as a lubricant for the walls ;so that the glass plunger may move relatively freely within ~the cylinder. The syringe is inverted and all air is expelled from the barrel and needle, along with the bulk of the anti-coagulant solution, which is normally far in excess of the amount needed for the blood sample. It is extremely im~ortant that all air be expelled from the syringe, since one of the tests performed is the measurement of the amount of oxygen present in the blood, and even minute contamination with air will prevent accurate meas-urement of that amount. After suitahle preDaration of the patient, the hypodermic needle is inserted into the artery and blood is either forced into the syringe by the pressure of the blood in the artery or is drawn into the syringe barrel by withdrawing the plunger. One advantage of the glass syringe previously used is the ease with which the plunger may be moved within the lubricated barrel. The glass ~lunger is ground to very close tolerances, so that it is sufficiently close to the syringe barrel wall to Prevent leakage but sufficiently far away to allow formation of a thin film of the anticoagulant. Even very low arterial blood pressures are usually sufficient to enter the syringe and force the glass ~lunger ~ackwards without any aid from the person taking the sam~le. Upon entry into the syr;nge the blood mixes with whatever anticoagulant solution remains in the needle, syringe tiP and syringe barrel afte the excess has been expelled.
r~laSs syringes are also conventionally used in epidural anaesthesia em~loying the loss of resistance technique because of ~the 1 resistance to mo~ement of the plunger in the barrel.

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7~5 .Such technique involves loading the syringe with 2-3 ml of normal saline, sterile distilled water or air. The needle (usually 16-18g) is then applied to the syringe. The needle is then inserted into the back towards the spinal area in question, all the while exerting gentle pressure on the plunger. When the needle tip goes through the ligamenta flava into the potential epidural space, the loss of resistance will be immediatelv felt by the thumb because the fluid or air will be pushed into the space. Thereafter the syringe is removed from the inserted needle and is replaced on the needle by a syringe loaded with anaethesia. This "loss of resistance" technique requires a syringe with an exceedingly smooth action and low resistance.
The glass syringes previously used have suffered from a number o disadvantages. They are expensive since the grinding requires close tolerances, in the order of n. oon7 inches clearance etween the ~iston and the cylindrical syringe body. They are easily breakable, which is esDecially costly after the sample as been taken. The glass plunger and the glass barrel of each yringe must commonly be matched during the grinding by the anufacturer, since variations in grinding from one plunger to nother may be sufficient to permit leakage of air or other aterial around the plunger, which will contaminate the sample.
hus the barrels and plungers cannot easily be individually mass roduced since the plungers often cannot be satisfactorily inter-hanged one with another in any given barrel, as pointed out in . S. Patent No. 2,~19,201 to Hinds. Further, because of the asy movement of the glass plunger in the cylinder, the ~lunger alls out of the barrel of its own weight, and normally breaks n the floor, unless the syringe is carried needle end down.

1~3~97~5 Special metal holders for the glass barrel have been used to prevent this problem.
Attempts have been made to avoid these disadvantages by either manufacturing both the barrel and the plunger out of materials other than glass, such as plastics, or by using glass barrels with plastic plungers. In order to prevent leakage around the plunger, these syringes depend upon the use of a compressible and ela~tomeric tip at the end of the plunger, which tip generally has one or more ribs which are slightly larger in diameter than the inside of the barrel ln their uncompre sed state and which, when placed within the barrel, are deformed and compres~ed agalnst the interior wall of the barrel and thereby form a seal. This type of seal, however, has made the movement of the plunger within the barrel difficult, thus normally requirlng manual withdrawal of the plunger to obtain the blood sample, particularly when the patient's arterial pres~ure is low as is often the case. The handline of . the syringe which i9 involved when manual withdrawal of the plunger is required may ¦cause traumatizatlon or collapse of the artery from which the ¦blood ls belng taken. A further major problem has been the fact ¦that when an axial force is applied to the plunger to expel the ¦air and excess anticoagulant solution, the compressible elas-¦tomeric tip at t;he end of the plunger compresses and deforms ¦agalnst the floor of the syrlnge barrel. The initial contact of ¦the compressible and elastomeric tip with the barrel floor is ¦at an area spaced from the central needle opening in the floor.
¦AS force continues to be applied after initial contact the tip ¦is compressed and deformed against the floor to move the contact ¦area radially inwardly toward the needle openin~ When the ¦plunger is released prior to the insertion of the hypodermlc _ . ____ ~ ~L~745 needle into the artery, the pressure on the compressible and elastomeric tip is also released whereby it recover.s its normal shape and in so do~ng moves back slightly from the barrel floor untll its only contact with such floor is its initial contact area thereby drawing a small amount of air into the tip of the hypodermic needle which becomes mixed wi.th the blood sample thereby increasing its ox~gen and nitrogerl content Also, air bubbles tend to collect on the forward face of the elastomeric tip particularly at the area immediately adJacent the point of contact with the syringe barrel wall Since the samples which are drawn to test for the amount of oxygen and carbon dioxide in the blood are very small, e.g., 2, 5 or 10 ml, even minute amounts of oxyeen and carbon dioxide leaked into the sample or ln the form of air bubbles have potentially adverse effects on the re~ults obtained. The compressibillty of the plunger tip also causes non-uniformit~ in the amount of anticoagulant left in the ~yringe barrel, syrin~e tip and hypodermic needle. As can be readily appreciated, the amount left will depend upon the amnunt of pressure used to expel the air and excess anticoagu]ant since ereater pressure will compress and distort the compressible plunger tip to a greater degree, thus expelling more anticoagulant If too little anticoagulant solution remains t;o be mixed with the blood, the blood may coagulate prior to testing and thus adversely affect the results obtained. If, on the other hand, too much antlcoagulant solutlon is left in the syringe, its presence may adversely affect the test, as is known in the art.
OBJECTS OI~ Tl-IE INVENTION
___ Accordingly, an ob~ect of the present invention i8 to provid a simple, inexpensive syringe with compressible and elastomerlc plunger tip, particularl~ one suitable for taking arterlal blood .__. . . _ . _ __ ~ 74S

¦sampl~ and epidural anaesthesia, which avoids the difficulties Ipreviously encountered with the glass syringes but which also ¦avoids the aforesaid difficulties previouslyencountered with ~syringes employing such tips. Thus, the syringe of the present ¦invention, although employing an elastomeric and comPressible ¦plunger tip, avoids air contamination of the sample which will in-¦terfere with the results obtained. It is a further object of the ¦invention to provide such a syringe which is adapted to prevent air Ibeing sucked into the hypodermic needle when the plunger is re-¦leased prior to taking the sample and to reduce the collection of ¦air bubbles on the elastomeric tip surface. It is a further ob~ect . if the invention to provide such a syringe which is adapted so as to supply a uniform and correct amount of anticoagulant solution to jthe blood sample being taken. It is a further object to provide ¦sucha syringe in which the plunger is more easily movable in the ~yringe barrel than conventional plungers with elastomeric tip.
In fact, the ease with which the Dlunger can be moved approaches, and, in some cases, equals the ease with which conventional glass ~lungers can be moved so that it responds to very low arterial ~ressuresand hence minimizes the possibility of traumatization of Ithe patient. On the other hand, an excellent uniform seal is pro-vided between the elastomeric tip and the syringe barrel throughout the distance travelled by the tip to obtain the sam~le. It is a ~till further object to provide such a syringe which limits the lamount of sample taken to a precise, predetermined amount. It is a ~urther ob~ect to avoid any adverse effect on the seal between ~lunger tip and barrel by cantering or bowing of the plunger stem.
~t is a further object to provide a syringe having all of these ad-~antages which is simple and inexpensive to manufacture, and thus 3n ~f low cost and extremely simple to operate in a manner which gives niform and accurate results.

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Other ob~ects and advantages of the present invention will be apparent from thé following description and accompanying drawings.
SU~r~ARY OF THE INVENTION
Certain o~ the aforesaid objects and advantages are achieved i accordance with the present invention by providing a syringe in which the compressible elastomeric tip of the plunger is provided with a peripheral annular wiper lip extending axially forwardly toward the floor of the syringe barrel and radially outwardly at a acute angle to the longitudinal center line of the barrel and lunger. The normal outer diameter of the wiper, i.e., the wiper edge, is slightly greater than the inner diameter of the syringe arrel. By virtue of the fact that the wiper extends at an acute angle to the longitudinal center line of the barrel and plunger it tends to be forced to rock radially inwardly about its base (where it is ~oined to the main part of the plunger tip) against the re-silient resistance offered by the elastomeric material when forced into the syringe barrel, whereby the wiper edge is yieldably presse against the inner wall of the barrel to ~orm an effective seal therebetween which increases in effect with increase in the force tending to move the plunger axially.
Although the seal achieved is excellent, the wiper edge is only lightly pressed against the barrel surface so that the plunger responds to lower pressures as compared to conventional plastic syringes. Accordingly, the syringe fills automatically by even very low arterial pressures with no need for manually withdrawing ¦the plunger and is very sensitive to the touch which makes it highly satisfactory for epidural anaesthesia employing the loss of resistance technique.

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Another aspect of the invention involveq designing the forward end portion of the plunger tip so that when the plunger i8 moved to its forwardmost positlon against the barrel floor, e,g., to e~ect air and excess liquid anti-coagulant before taking a sample, the initial contact of the elastomeric and compressible tip with the barrel floor ls at the area of the floor immediately ad~acent the needle opening in the floor to form a seal between the tip and such area, This prevents the further flow of liquid out of the barrel and needle opening and thereby traps a pre-determined and uniform desired (sufficient to prevent coagulation but not so much as to interfere with the tests~ amount of the llquid anti-coagulant in a sealed space or chamber of predetermin~ d volume remaining between the tip and the barrel floor, The trapped non-compressible liquid act~ as a stop and barrier to prevent deformation and compre~ion of the tip into further contact with the barrel floor upon continued application of forward force on the plunger, i,e,, it prevents the spread of the contact area b,y the continued application of the force, Accordingly, when the force on the plunger i8 released air intake is minimized by recovery of the compressible and elas-tomeric tip back to its initial-contact shape, Preferably the aforesaid space or chamber between the tip ar d floor is formed by an annular trough in the end face of the tip formed on one side b,y the wiper and on the other side by a central _ ly located reduced end portion of the tip extending axially for-wardly from the base of the wiper, It is this end portion which form~ the seal with the barrel floor immediately ad~acent the needle openlng, Preferably the end face of such end portion is convex in shape but it can be of any shape (preferably tapered inwardly as it extends forwardly) which will seal the needle opening on initial contact of the tip with the barrel floor while leaving a space to trap the liquid antl-coagulant, e.g , it may be conical or frusto-conical in shape.
Air intake is further minimized by concentrating and sub-stantially restricting force applied by the plunger stem to the compressible and elastomeric plunger tip in the forward direction after the aforesaid initial contact,at and to that portion of the tip which iB behind the space and liquid trapped therein with a minimum of force (desirably zero) being applied to the portion of the tip member located behind the needle opening, whereby afte the aforesald initlal contact distortlon of the tip member into such opening is minimized. This is preferably achieved by pro-viding lost forward axial motion of the plunger stem relative to the portion of the tip behind the needle openlng, but not relative to the portion of the tip behind the trapped liquid, upon continued application Or axial forward force to the stem after initial contact between tlp and barrel floor. In this way, such contimled force is concentrated at and restricted to the portion of the tip behind the trapped noncompressible liquid to compress such portion between the liquid and the stem and is not applled to the portion of the tip behind the needle opening, In another aspect of the invention, means is provided for mlnimlzing the risk of leakage due to cantering of the annular wlper edge relative to the barrel wall, with consequent reduction in sealing pressure between such edge and such wall, due to cantering of the plunger ~tem by the operator during operation or due to a warped or bowed or otherwise defective plunger stem, Preferably this is achieved by attaching the stem to the tip to permit radial play therebetween, i.e., by the use of a loose radial flt.

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In yet another aspect of the invention, by virtue of the ;reduction in diameter of the aforesaid reduced leading end portion of the plunger tip as compared to the portion of the tip which trails such end portion, as well as the wiper, the solid wall thickness of the tip over most of its length and to which axial forward force is applied lies behind the trough to strengthen the tip.
In yet another aspect of the invention, the wiper is tapered in thickness so that it is wider at its base than at its wiping edge. The wider base strengthens the wiper leaving the thinner edge portion flexible to aoply only a gentle sealing pressure to the wall of the barrel~
In vet another aspect of the invention at least the portion of the syringe barrel traversed by the plunger tip, in taking a sam~le or employing the "loss of resistance" technique in epidural anesthesia, has a constant inside cylindrical diameter, i.e., the inside wall of the barrel does not taper inwardly or outwardly.
This keeps the light sealing pressure o~ the wiper on the barrel wall uniform over its operative range o~ travel in the barrel.

In yet another aspect of the invention the barrel wall is provided with a stop which prevents rearward axial movement, by arterial pressure, of the plunger tip beyond the point where the desired blood sample size has been obtained. Although the stop offers sufficient reslstance to prevent movement of the tip beyond it by virtue of arterial Dressure, such resistance is insufficient to prevent the plunger tip from being pulled out of and Pushed into the barrel by hand. The stop also offers sufficient resis-tance to prevent the plunger from falling out of the barrel hy force of gravity when the syringe is inverted.

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In the present invention there is provided a dis-posable syringe assembly suitable because of the low force requirement for the operation thereof to be used for obtai-ning a blood sam.ple.froma patientcomprising a barrel having a cylindrical inner wall and a plunger comprising a plunger stem and a compressible, elastomeric, generally cylindrical plunger tip of lesser diameter than the inner wall of said barrel, said plunger tip having an integral, annular, elas-tically deformable wiper extending peripherally radially outwardly and axially forwardly from said plunger tip at a forward portion thereof at an acute angle to the longitudinal centre axis of said plunger tip and terminating at the outer edge thereof in a wiping edge having a minimal diameter slightly in excess of the diameter of the inner wall of said barrel, thereby forming a sealing engagement with the inner wall of said barrel, said annular wiper being the sole sea-ling element between said plunger tip and said wall, said plunger being paced from said barrel along the length there-of so that axial movement between said plunger and said bar-rel is substantially free of frictional contact except forthe contact by said sole sealing element, the frictional force of said sealing engagement being of a magnitude that would allow the blood pressure of a patient to move said plunger stem and tip backwardly in said barrel to draw a blood sample from a patient into said barrel.
This invention further provides for a disposable syringe assembly suitable because of the low force require-ment for the operation thereof to be used for obtaining a blood sample from a patient comprising a barrel having a cy-lindrical inner wall and a plunger comprising a plunger stemand a compressible, elastomeric, generally cylindrical plun-ger tip of lesser diameter than the inner wall of said barrel, said plunger tip having an integral, annular elastically -lla-,~"

deformable wiper extending peripherally radially outwardly and axially forwardly from said plunger tip at a forward portion thereof at an acute angle to the longitudinal cen-tre axis of said plunger tip and terminating at the outer edge thereof in a wiping edge having a minimal diameter slightly in excess of the diameter of the inner wall of said barrel, said assembly including means for permitting radial play between said plunger stem and plunger tip, said plunger being spaced from said barrel along the length thereof so that axial movement between said plunger and said barrel is substantially free of frictional contact except for the con-tact by said wiper, the frictional force of said sealing engagement being of a magnitude that would allow the blood pressure of a patient to move said plunger stem and tip back-wardly in said barrel to draw a blood sample from a patient into said barrel.
Further, the present invention provides for a com-pressible and elastomeric syringe plunger tip comprising a generally cylindrical main portion, an integral annular elas-tically deformable wiper extending peripherally radially out-wardly and axially forwardly from a forward portion thereof at an acute angle to the longitudinal centre axis of said tip and terminating at the outer edge thereof in a wiping edge, when used in a syringe assembly said annular wiper being the sole sealing element between said plunger tip and the syringe and providing substantially all frictional contact between the plunger and the barrel of the syringe, the frictional force of said sealing engagement being of a magnitude that would allow the blood pressure of a patient to move said plunger stem and tip backwardly into said barrel to draw a blood sample from a patient into said barrel.

The present invention further provides for a dis-posable syringe assembly suitable because of the low force -llb-. .

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requriement for the operation thereof to be used for obtai-ning a blood sample from a patient comprising a barrel having a cylindrical inner wall and plunger comprising a plunger stem and a compressible elastomeric generally cy-lindrical plunger tip of lesser diameter than the inner wall of said barrel, said plunger tip having an integral annular elastically deformable wiper extending peripherally radially outwardly and axially forwardly from said plunger tip at a forward portion thereof at an acute angle to the longitudinal centre axis of said plunger tip and terminating at the outer edge thereof in a wiping edge having a minimal diameter slightly in excess of the diameter of the inner wall of said barrel thereby forming a sealing engagement with the inner wall of said barrel, said annular wiper being the sole sea-ling element between said plunger tip and said wall, said wiper being tapered from the base thereof to the free end thereof so that it is thicker at its base than at its end, the angle between the leading surface of said wiper and the longitudinal axis being between about 20 and 65 and the angle of taper being between about 4 and 30 and having a wiping edge comprising a plane surface of minor dimension oriented substantially parallel to the longitudinal axis of said plunger tip but extending radially outwardly and axi-ally forwardly relative thereto at a very slight angle of about 2, said plunger being spaced from said barrel along the length thereof so that axial movement between said plun-ger and said barrel is substantially free of frictional con-tact except for the contact by said sole sealing element, the frictional force of said sealing engagement being of a mag-nitude that would allow the blood pressure of a patient tomove said plunger stem and tip backwardly in said barrel to draw said blood sample from a patient into said barrel.
The present invention further provides for a --llc--97~5 disposable syringe assembly suitable because of the low force requirement for the operation thereof to be used for obtaining a blood sample from a patient comprising a barrel having a cylindrical inner wall and a plunger comprising a plunger stem and a compressible, elastomeric, generally cylindrical plunger tip of lesser diameter than the inner wall of said barrel, said plunger tip having an integral, annular, elastically deformable wiper extending peripherally radially outwardly and axially forwardly from ssid plunger tip at a forward portion thereof at an acute angle to the longitudinal centre axis of said plunger tip and terminating at the outer edge thereof in a wiping edge having a minimal diameter slightly in excess of the diameter of the inner wall of said barrel, thereby forming a sealing element with the inner wall of said barrel said annular wiper being the sole sealing element between said plunger tip and said wall, said plunger tip having a plurality of raised portions spa-ced circumferentially around said plunger tip and located at the rearward portion of said plunger tip, said raised por-tion~ engaging said inner wall of said barrel with a minimumof frictional contact to prevent canting of said plunger tip in said barrel, the frictional force of said sealing engage-ment being of a magnitude that would allow the blood pres-sure of a patient to move said plunger stem and tip backward-ly in said barrel to draw said blood sample from a patient into said barrel.

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.- ~ ~ s THE DRAWINGS
For a better understanding of the invention, reference is made to the following detailed description to be read in conjunction with the accompanying drawings, in which Figure 1 is a longitudinal section of the inward or forward part of a commercial prior art blood sampling sysringe with com-pressible and elastomeric plunger tip showing in full lines the initial contact position of the tip with the barrel floor and in broken lines the position of the tip following initial contact upon continued inward or forward force applied to the plunger;
Figure 2 is a planar side view of a preferred embodiment of the syringe of the present invention;
Figure 3 is a longitudinal section of the syringe of Figure 1 with the compressible and elastomeric tip in a position intermedia te its limits of travel;
Figure 4 is an enlarged view of the forward portion of the syringe of Figure 3;
Figure 5 is a view like Figure 4 showing how force applied to the tip forces the wiper edge tighter against the barrel wall to increase sealing effect;
Figure 6 is a view like Figure 4, showing the initial contact position of the plunger tip and barrel floor wherein the needle opening is sealed;
Figure 7 is an inner end view of the plunger tip of Figure 4;
Figure 8 is an enlarged view in section of a part (rotated so that the longitudinal axis is oriented vertically in the illustra-tion) of the wiper of the plunger tip of Figure 4 before it is inserted into the syringe barrel;
Figure 9 is a section taken along the line 9-9 of Figure 4;

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Pig re 10 is a side view of a partial longitudinal section of a preferred embodiment of the syringe of the present invention;
l . Figure 11 is a section ta~en along line 11-11 of Figure 10;
I and Figure 12 is a section taken along line 12-12 of Figure 10.

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DETAILED DESCRIPTION
Referring to the Figures of the drawings, the syringe de-picted has a relatively rigid, generally cylindrical hollow body or barrel 10, preferably made of an inexpensive substantially transparent plastic material, such as polyethylene or polypropy-lene, which is inert to, i.e., does not affect, the sample to be taken, and which is substantially impermeable to oxygen and carbon dioxide. Other suitable materials, such as polystyrenes, acrylic or methacrylic polymers and various glasses, are well known in the art. The cylindrical barrel has a central bore 36 and terminates at one end with finger piece 10a. This finger piece 10a generally has the shape of an annular flange but can be any shape which provides support for two fingers, e.g., hexagonal, or take the form of two tabs. The barrel teminates at the other end in an axially forwardly and radially inwardly tapered end wall 20 which forms the tapered floor 21 of the bore 36 and which extends forwardly into the reduced diameter tapered tip 16 of the barrel. As shown, barrel tip 16 is general'y frusto-conical in shape. Tip 16 is shown as carrying the hypodermic needle 19 through frictional engagement of the tapered periphery thereof wi the tapered end of the internal passage of cylindrical base membe 18 of the needle 19. However, the needle may be secured to the tip 16 by a conventional luer lock arrangement on the base member 18 and tip 16. ~he barrel floor 21 and end wall 20 have a centra located needle opening 22 therein which extends into the internal passage 47 of tip 16.
In a preferred embodiment, the wall of bore 36 of the barrel 10 i.s cylindrical and non-tapered in at least the working area 37 thereof, i.e., the area of the cylinder which is traversed by the compressible and elastomeric plunger tip 28 in taking the sample.

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~ 7~5 Thus, as shown in Figure 3, the inner side wall (bore) of the barrel is straight (cylindrical) in the longitudinal direction and there is no convergence or divergence at ~he area 37 between the end wall 20 and annular rib 39, which extends radially inwardly from the inner side wall of bore 36 and the purpose of which will be described hereinafter. The portion of the inner side wall of bore 36 of the barrel rearward of the rib 39 may be tapered slightly outwardly as it extends rearwardly to aid in molding the barrel but it need not be.
The syringe also comprises a hollow cylindrical plunger 12 having a relatively rigid plunger stem 13 and a compressible and elastomeric plunger tip 28.
The plunger stem 13 is preferably made of an inexpensive plastic material, such as polyethylene or polypropylene, which is also inert to the sample to be taken. Other materials which can be used are the same materials of which the barrel is made. In fact, the plunger stem is preferably made of the same material as the barrel but it need not be. ~t its rearward end, stem 13 term-inates in a thumb supporting flange 13a. THe plunger stem term-inates at the other end in a head portion 12a(Figure 5) to which the compressible and elastomeric plunger tip 28 is secured. Head portion 21a comprises a hollow reduced diameter cylindrical neck portion 23 forming a shoulder 31 with the main part of the plunge~
stem. Neck portion 23 extends axially in a forward direction into square shaped plate portion 24 which forms a shoulder 45 with portion 23 and from which in turn there extends axially in a forward direction a plurality of radially extending fins 25, the peripheral edges of which are tapered radially inwardly at 2G as shown and the forward edges of which are flattened at 27.
Fins 25 run diagonally from opposite corners of the plate portion

2~ through the center thereof.
The hollow compressible and elastomeric plunger tip 28 is ~ 4 5 made up of a main hollow cylindrical portion 30 from the peripher~
of the forward portion of which extends axially forwardly (axiall~
forwardly and axially inwardly mean toward the barrel floor whereas axially rearwardly and axially outward.ly mean away from the barrel floor) and radially outwardly at an acute angle y (see Figures 5, 6 and 8) from the longitudinal center axis of the plunger and plunger ti.p, an annular wiper lip 32, the wiping edge 34 of which is resiliently and yieldably forced into sealing en-gagement with the inner bore or wall 37 o:~ the barrel, The plunger tip extends axially forwardly from the base 64 of wiper 32 into a reduced diameter leading end portion 38, the base 43 of which has an outside frusto-conical shaped taper which terminates in a convex curvilinear end face 43a, ~n annular recess or trough . 41 is formed by the axially forward and radially inner surface 58 f the annular wiper 32 and the radially outer surface 43 of the end portion 38, as ~hown.
The rearward end 56 of plunger tip 28 has an internal socket 42 in which is received the head 21aof the plunger 9tem 12 to secure the plunger tip to the end of the plunger stem, Socket 42 has an enlarged rear cylindrical end portion 44 which extends for-. wardly into a reduced cylindrical portion 46 which then extends forwardly into an enlarged dlameter cyli.ndrical portion 48 (same diameter as 44) which forms a shoulder 29 where it meets with portion 46 and which extends forwardly into a radially inwardly tapered fru~to-conical shaped portion 50, which in turn extends into a curvilinear concave end portion 52, T~le taper of socket wall 50 is slightly sharper than that of outer surface 43 and the curve of soc]cet wall 52 is slightly sharper than that of outer surface 43a, as shown, Preferably~ the c~rcle formed where the frusto-conical outer U7`
face 43 of end porti.on 3~ changes into the curvilinear end surface -- , . . . _ ll ~ f"
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ll ~43a, lies on an imaginary axial extension of cylindrical socket walls 48 and 44.
¦ The cylindrical portion 23 of the head 21aof the plunger stem ¦is located within the rearward portions ~4 and 46 of the plunger 'tip socket and is spaced radially inwardly there~rom as shown.
The square shaped plate portion 24 of the plunger stem is located within the enlarged cylindrical portion 48 of the plunger tip socket and is spaced radially inwardly therefrom as shown. The fins 25 of the plunger stem head are located within the tapered ortion 50 of the socket and are spaced radially inwardly therefron and the ends thereof are spaced axially rearward from the end wall 52 of the socket, all as shown. The annular end 56 of the plunger ti~ i9 held in secure engagement with the shoulder 31 of the Plung stem ~d the shoulder 29 of the socket is held in secure engagement with the shoulder 45 oE the plunger stem head to thereby firmly secure the plunger tip on the end of the Plunger stem 13.
The only part of the plunger which engages the inner ~tall of the barrel is the annular wiping edge 34 which exerts only a slight force on such wall to thereby reduce frictional drag and permit the lunger to be easily moved axially in the barrel.
The acute angle y between the forward or leading wiper sur~ace 58 (Fic3ure 8)of the ~tiper 32 and the longitudinal center axis of the plunger tip is slightly greater than the acute angle x between he rearward or trailing wiper sur~ace h~ of the wiper and the long _ udinal center axis wherehy the wiper is tapered in thickness with he base 64 of the wiper being thicker than the end portion of the iper. The thicker base strengthens the wiper whereas the tapered hinner end portion increases the flexibility of the wiper edge to rovide only gentle sealing pressure on the inner barrel wall to hereby minimize resistance to axial movement of the plunger.

I ~ 74S

In its relaxed state when the plunger tip is removed from the barrel, the wiper edge 34 of the wiper is of slightly greater diam-eter than the inner bore 37 of the barrel so that when the plunger tip is forced into the bore such edge 34 is forced radially in-wardly about the base 64 of the wiper i.e., the wiper is bent or rocked radially inwardly about its base, against the force exerted by the elastic and compressible material, which force yieldably and with only a slight pressure urges such wiper edge into excel-lent sealing engagement with the bore wall 37 with very little fractional drag.
In its relaxed state when the plunger tip is removed from the barrel, the wiper edge surface 3~ preferably extends radially out-wardly and axially forwardly at a slight angle z, e.g., about 2 to the longitudinal center axis of the plunger tip and the barrel bore. The purpose of this is to reduce the chance of leakage whil still achieving gentle sealing pressure. When the plunger tip is forced into the barrel bore, this wiper edge surface 34 is forced to assume a position in which it is parallel to the longitudinal axis of the plunger tip and barrel bore. Without this slight in-clination of the wiper edge surface 34, the undersized barrel may tend to bend the leading end of such wiper edge surface radially inwardly to either reduce the pressure of the wiper edge surface on the bore wall at such leading end or to cause such leading end to move slightly away from the bore wall to provide a slight space or groove therebetween which may result in leakage. The force of the liquid blood sample shown by the arrows in Figure 5 tends to aggravate this since it tends to work into any space or decreased pressure area between such leading end and the barrel bore to force such leading end further away from the bore wall with re-! sulting lea]cage.
By providing this slight angle to the wiper edge surface 34, ~ 5 maximum sealing pressure is applied and concentrated at the lead-ing end of surface 34 where it does the most good and over a rela tively small area, thereby minimizing frictional drag.
The plunger tip can be made of any elastomeric and compress ible material wlth memory, which has a low coefficient of frictior with the barrel wall material and which is inert to the sample material, to the anti-coagulant and to any other substance which is to be located withln the syringe barrel. Natural and synthetic rubbers can be used such as neoprene rubber as well as other elas-tomeric polymers such as polyvinyl chlorlde, polyurethanes, poly-esterc, etc. A preferred material is silicone rubber.
It will be noted that the forward end of the plunger tip is 30 designed that when the plunger tip is moved to its forwardmost position as shown in ~igure 6, the initial contact of the plunger tip with the barrel floor is between the narrow annular area 70 of the barrel floor 21 immediately ad~acent the needle opening 22 and the peripheral part of the curved end surface 43a of the end portion 38 of the plunger tip to thereby seal the needle opening 22 against ~urther flow of fluid out of the syringe through the needle opening. At this time the wiper edge 34 reaches the end of the cyllndrical bore wall 37 and the trough 41 of the wiper forms . with the barrel floor 21 a sealed space or chamber 40 of predeter-mined size, 1 e., sealed by the seal between the plunger tip and the barrel floor at 70 and the 9eal between the tip and the barrel bore at 34. Note that the difference ln taper of the outer and inner surfaces 43 and 50 of the plunger tip increases the wall thickne8s of the tip behind the seal area 70 Conventionally in taking a blood sample, a liquid anti-coagu lant~ e g,, sodium heparin, to prevent coagulation of the blood s~mple is either drawn into the syringe before the blood sample is taken or is located in the syringe as packaged. The excess of suc liquid anti-coagulant and any air in the syringe is then expelled ~. ~ '~ 7~

through the needle opening and needle by forward movement of the plunger and plunger tip.
In accorda-nce with the present invention, the excess anti-coagulant and air are expelled by moving the plunger tip to its forwardmost position as shown in Figure 6. The initi.al sealing contact between the narrow annular area 70 of the barrel floor immediately ad~acent the needle opening and the convex end surfac 43a of end portion 38 seals the syringe barrel against further flow of the liqui.d anti-coagulant out of the syringe and a prede-termined amount of the.anti-coagulant is thereby trapped in the annular 8pace 40. The size of the trough 41 is such that the amount oP anti-coagulant trapped in this space, together with tha filling passage 47 and the needle when the plunger ti.p is in the po9ition shown in Figure 6, is sufficiellt to prevent coagulation of the sample talcen but is less than an amount whicll will inter-fere with the testing of the sample Accordingl~J, the ri.ght amour t . of anti-coagulant is automatically assured Preferably thc volume of the space 40, together with passage 47 and the needle bore, is between .01 and 1.0 milliliters and more preferably between 0 25 and 0.5 mi].li].iters for every 5 mi.l].i _ . llter of blo~d sample taken.
The non-compressible ].iquid trapped in space 40 acts as a no _ ~ieldable stop or barrier to prevent any deformation and compres-sion of the plunger tip again~t the barrel floor radially outwardl f the narrow annular sealing area 70 upon continued application of forward axial force on the plunger.
.. Such conti.nued force by the plunger stem on the plunger tip is cor~centrated and restrlcted to ~ile perip~leral porti.on Or the plunger tip behind the noncompressible trapped liquid in space 40 through shou].der 31 of the stem and the end surface 5~ of the plunger tip to thereb~ compress such peripheral porti.on between shoulder 31 and the trapped liquid. ~lthough, SUc1l force ma~ be ,., ~

~ 9~745 concentrated a1; ar~d rest;ricted to the portion of the tip behind space 40 and sealing area 70, it is highly preferred that it be concentrated at and restricted to the portion behind space 40. At the same time the axial space between the head 21aof the plunger stem and the end 52 of the socket in the plunger tip provides lost motion between such head and tip, i.e,) the head moves axially for wardly with respect to the plunger tip but does not engage the sur-face 52, which is located behind the need~e opening 22. ~ccording ly, the force app]ied to t;he end porti~?n 3~ of the plunger tip behind the needle opening 22 is substantially zero so that there is sùbstantially no deformation of SUCII end portion into the needle opening 70, Therefore, once initial contact is made between the plunger ti.p and the barrel floor. there is substantially no deformatlon Or the end of the plunger tip against the barrel floor or into the needle opening so that when the force on the plunger 1 relea8ed there is sub~tantially no undesirable intake of air into the syringe as compared to a plunger tip of a conventional arteria blood sampling syringe of the type shown in Figure 1 (a plastic syrlnge sold under the name JELC0 by the Jelco Division of Johnson and Johnson) having one or more sealing ribs 72 extending 90 radially outwardly from the periphery of the plunger tip 74 Note in Figure 1 that the end of the plunger tip initially engage8 the barrel floor at its periphery tfull line position) when liquid is expelled therefrom, whereupon continued forward axial force on the plunger causes the end of the tip to be deformed and compressed against the floor radially lnwardly w;th the contact rea expanding from the peripheral portion of the floor radially inwardly toward the needle opening (broken line position). When su h orce i~ released the plunger tip springs back away from the floor o its full line position and in so doing may suck undesired air nto the syringe. ~lso, in most such conventional syringes the end 6 of the plunger 7~ stem exerts axial force on the central portion 0 of the p]unger tip to deform the end of the tip lnto the needle ._ _ _ ~ . .

110~74~

opening, which may draw more air back into the syringe when the force is released.
Also note that in the conventional syringe of Figure 1 with l compressible plunger tip, when the plunger ti~ is forced into the ¦ undersize (compared to the sealing rib or ribs) syringe barrel to deform the edge of the rib or ribs radially inwardly,such defor-¦mation is resisted by the entire thickness of the plunger tip wall including the radial height of the rib or ribs. This causes the ¦ribs to be urged against the bore wall with substantial force ¦thereby creating substantial frictional drag as compared to the ¦syringe of the instant invention where the resistance to the de-¦forming force of the undersize barrel is the relatively gentle ¦resistance to bending of the wiper.
¦ Whereas with a lOcc plastic JELCO syringe and 22 gage needle lS la force of 64 mm/Hg was required to force the plunger back, the ¦force reauired to force the plunger back with a syringe of the ¦same size embodyinq the invention was only 15-18 mm/Hg i.e., only ¦about 1/~ of the force was required. Accordingly, the syringe of ¦the instant invention fills automatically with very low arterial ¦~ressures without manually pulling the plunger outwardly. With a ¦needle of 22 gage, a syringe embodying the instant invention has ¦been found to be as responsive to hydraulic force as a glass ¦syringe.
¦ In spite of the very low pressure required to fill the syringe ¦of the invention and the very gentle sealing pressure of the wiper ¦edge against the syringe barrel, the sealing achieved is excellent ¦by virtue of the design of the wiper. As seen in Figure 5, the force shown hy the arrows apDlied by the blood pressure tends to urge the wiping edge against the barrel wall to increase the sea~ing effect. The plunger tip of the invention has withstood a hydraulic force o~ 30~ mm/Hg without leakinq but such large forces aro not enco-lntered in use.

--" 11~7~5 Note in Fig. 6 that the trapped liquid in space 40 functions a a non-yieldable support for the portion of the highly flexible and sensitive wiper ~ocated radially outwardly as compared to the main portion 30 of the plunger tip to thereby prevent any substanti~l deformation of such portion upon continued application of forward axial force by the plunger stem after initial contact of the tip wit;l the barrel floor. Also note that because such portion of the wiper lies radially outwardly compared to the wall of main ~ortion 30, to which such continued axial force is applied, very little, if any, such force tends to deform such portion in any event. Also the reactive force of the trapped liguid on the wiper tends to force it into greater sealing engagement with the barrel bore.
The loose circumferential fit between the head 21aof the plunge r and the socket 42 of the plunger tip, together ~ith the loose axial fit in the forward direction, prevents cantering of a part of the wiper sealing edge 34 away from the bore by cantering of the plunge by the operator, e.g., by moving the finger piece 13a laterally while operating the syringe, or by virtue of a bowed or warped or uneven plunger. It is difficult to avoid some bowed or warped plungers during manufacture of a lot. ~uch cantering of a ~art of the wiper edge away from the bore wall is apt to reduce the sealing pressure applied by such part to therehy cause leakage.
The optimum angle y of the wiper from the longitudinal center axis of the plunger tip and optimum angle z of the wiper edge sur-face and optimum difference in the angles y and x of the leading and trailing surfaces of the wiper to achieve a thin wiper edge ortion and a thicker base depends in part upon the stiffness of the material oE the plunger tip.
It has been Eound that an angle y of ~3,(preferably it varies etween ahout 20 and 65, more preferably between about 30 and 50)between the leading surface of the wiper and the longitudinal xis of the plunger tip and an angle x of 35 (preferably the dif-ference over angle y may vary between about 10 and 30, more _. .. ~ . .. .. . . .__ . .. ., . .. .. __ _ . _ . . ,__ _ . . _ ~ .

~ 11~?97~S

preferably between about 4 and 15) between the trailing surface and the longitudinal axis gives excellent results.
Excellent results have also been achieved with needle sizes of from 20 to 22 gage. The speed with which the plungertip moves is proportional to the needle gage size.
The rib 39 functions as a stop to limit the outward movement of the plunger tip by engagement of the wiper ed~e 34 therewith tc thereby ensure that a uniform predetermined volumeof sample is ob-tained and also to ensure against the plunger falling out of the barrel.
Although the rib 39 is adequate to resist rearward movement of the plunger due to arterial pressure and due to the weight of the plunger it is inadequate to resist a manual pulling force, which causes deformation of the wiper and consequent movement thereof past the rib to permit the plunger to be inserted and removed fro~
the barrel.
It has been found that air bubbles which in conventional plas tic syringes collect at the leading surface of the plunger ti2 close to the interface ofthe plunger tip and the barrel bore, do not collect on such surface of the plunger tip of this invention.
It is believed that this is due to the particular design of the plunger tip. This is an important advantage since it permits more accurate testing.
The location of the liquid-containing space 40 axially in front of substantially the entire solid axial length of the wall of the plunger tipto which the force is axially applied at 56 greatly strengthens the plunger tip. This is achieved in part by reducing the diameter of the end portion 38 as compared to the main portion of the plunger tip. Although such reduction in diameter strengthens the wiper, it, together with the radially inward taper at 43a, reduces wiper stiffness and thereby increase wiper sensitivity and reduces frictional drag.

` ~ 11997~S

In another preferred embodiment as illustrated in Figure 10, the elastomeri~ plunger tip 130 has a plurality of raised por-tions 135 spaced around the circumference of the rearward sectio of the plunger tip 130 and engaging the inner wall 37 with mini-S mum contact to avoid any significant frictional force. These raised portions 135 of the plunger tip 130 prevent canting of the plunger tip to maintain the plunger tip in a concentric position within the syringe barrel 10 and allow the sole wiping edge 132 of the plunger tip to maintain its most effective sealing en-gagement with the syringe barrel. The raised portions on the rear section of the plunger tip can be of any shape that will accomplish the purpose of preventing canting of the plunger tip.
Generally, a semi-spherical, conical, or frusto-conical shape is preferred to avoid excessive frictional contact with the syringe barrel and for ease of manufacture.
The preferred embodiment illustrated in Figure 10 also show the plunger 110 having a plunger stem comprising two ribs 112 at right angles to each other and having a number of circular discs 116 with a diameter less than that of the syringe barrel positioned along its axis at right angles to the ribs. One of the discs 117 has a greater diameter than the other discs and functions as a stop to limit outward movement of the plunger by engagement with rib 120 at the end of the syringe barrel when drawing a blood sample. The plunger can be withdrawn from the syringe barrel by exerting additional manual force to move disc 117 past rib 120. The plunger stem also has a disc 115 which is larger in diameter than disc 117 and will not move past rib 120 regardless of the force exerted. Disc 115 function as a stop preventihg further inward movement of the plunger and is positioned to prevent such further inward movement at a pre-determined position of said plunger tip to form a chamber or i space between the Plunger tip 130 and the tapered floor 21 of - - ~
114~ 45 Il ¦I the bore 36 of the syringe barrel. The size of the chamber or space thus formed can be predetermined to contain a particular quantity of anti-coagulant. Thus disc 115 effects a positive stop preventing further inward movement and avoiding any compres-sion of the plunger tip.
Disc 117 is positioned along the longitudinal axis of the ~lunger in accord with size of sample to be drawn with the syringe, thus providing an effective preset sample size. Th~s the size of the chamber formed by the plunger ti2 and the floor of the syringe barrel canbe sized to contain the precise amount of anti-coagulant required for the sample size.
The aforesald advantages of the syringe of this invention not only make it highly useful in an improved arterial blood sampling syringe but also for epidural anaesthesia employin~ the 105s of resistance technique and it has been used successfully clinica].ly for that purpose.
~lhile the present syringe is particularly suitable for taking arterial blood samples and for epidural anaesthesia, its suitability for other functions will be readily appreciated in the art. It is disposable and inexpensive. It can be cheaply mass produced out of inexpensive raw materials. There are no breakage problems.
It is not intended that the invention be limited to or by the aforesaid description and accompanying drawings of only one embodiment thereof but only to the subject matter claimed here-inafter and its equivalents.

Claims (36)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A disposable syringe assembly suitable because of the low force requirement for the operation thereof to be used for obtaining a blood sample from a patient comprising a barrel having a cylindrical inner wall and a plunger com-prising a plunger stem and a compressible, elastomeric, generally cylindrical plunger tip of lesser diameter than the inner wall of said barrel, said plunger tip having an integral, annular, elastically deformable wiper extending peripherally radially outwardly and axially forwardly from said plunger tip at a forward portion thereof at an acute angle to the longitudinal centre axis of said plunger tip and terminating at the outer edge thereof in a wiping edge having a minimal diameter slightly in excess of the diameter of the inner wall of said barrel, thereby forming a sealing engagement with the inner wall of said barrel, said annular wiper being the sole sealing element between said plunger tip and said wall, said plunger being spaced from said barrel along the length thereof so that axial movement between said plunger and said barrel is substantially free of frictional contact except for the contact by said sole sealing element, the frictional force of said sealing engagement being of a magnitude that would allow the blood pressure of a patient to move said plunger stem and tip backwardly in said barrel to draw a blood sample from a patient into said barrel.

2. A syringe assembly according to Claim 1, said wiper being tapered from the base thereof to the free end thereof so that it is thicker at its base than at its end.

3. A syringe assembly according to Claim 2, where-in the angle between the leading surface of said wiper and the longitudinal axis is between about 20° and 65° and the angle of the taper is between about 4° and 30°.

4. A syringe assembly according to Claim 2, where-in the angle between the leading surface of said wiper and the longitudinal axis is between about 30° and 50° and the angle of the taper is between about 10° and 15°.

5. A syringe assembly according to Claim l, said wiping edge comprising a plane surface of minor dimension oriented substantially parallel to the longitudinal axis of said plunger tip.

6. A syringe assembly according to Claim 5, where-in said plane surface extends radially outwardly and axially forwardly at a very slight angle.

7. A syringe assembly according to Claim 6, where-in the angle is about 2°.

8. A syringe according to Claim 1, wherein a hy-podermic needle is secured to said barrel for insertion into the artery of a patient to withdraw a blood sample from said patient.

9. A syringe assembly according to Claim l, said assembly further comprising means for securing said tip to said stem so that said tip is propelled axially by said stem, said last mentioned means comprising a head at the forward end of said stem and central socket in the rearward end of said tip in which said head is received, said head having means for providing lost axial forward motion between the stem and socket wall, said stem having a shoulder engaging the peripheral portion of said tip located radially outwardly from said socket to propel said tip axially and forwardly.

10. A disposable syringe assembly suitable because of the low force requirement for the operation thereof to be used for obtaining a blood sample from a patient comprising a barrel having a cylindrical inner wall and a plunger com-prising a plunger stem and a compressible, elastomeric, generally cylindrical plunger tip of lesser diameter than the inner wall of said barrel, said plunger tip having an integral, annular, elastically deformable wiper extending peripherally radially outwardly and axially forwardly from said plunger tip at a forward portion thereof at an acute angle to the longitudinal centre axis of said plunger tip and terminating at the outer edge thereof in a wiping edge having a minimal diameter slightly in excess of the diameter of the inner wall of said barrel, said assembly including means for permitting radial play between said polunger stem and plunger tip, said plunger being spaced from said barrel along the length thereof so that axial movement between said plunger and said barrel is substantially free of frictional contact except for the contact by said wiper, the frictional force of said sealing engagement being of a magnitude that would allow the blood pressure of a patient to move said plunger stem and tip backwardly in said barrel to draw a blood sample from a patient into said barrel.

11. A syringe assembly according to Claim 10, in-cluding means for securing said tip to said stem, said secu-ring means comprising a head on said stem and a socket in said tip, said head being received in said socket, and said head being spaced radially from said socket to permit radial play between said head and socket.

12. A syringe according to Claim 11, said sealing means in sealing engagement with said barrel wall comprising an integral annular elastically deformable wiper extending peripherally radially outwardly and axially forwardly from said plunger tip at a forward portion thereof at an acute angle to the longitudinal axis of said tip and terminating at the outer edge thereof in a wiping edge having a minimal diameter slightly in excess of the diameter of the inner wall of said barrel thereby forming a sealing engagement with said side wall.

13. A syringe according to Claim 12, said trough of said tip forming with said floor a space upon said ini-tial contact, said space being sealed by sealing of said needle opening to thereby trap any fluid contained in said space.

14. A syringe according to Claim 11, said plunger having a plunger stem for axially driving said tip in said bar-rel a portion of said tip lying behind said space and another portion lying behind said needle opening and means for secu-ring said tip to said plunger stem, said means for securing said tip to said plunger stem comprising means for providing lost motion of the plunger stem relative to said portion of said tip behind said needle opening to minimize the applica-tion of substantial tip deforming force by said stem on the portion of the tip located behind said needle opening upon application of forward axial force by said stem on said tip after said initial contact.

15. A syringe according to Claim 11, said plunger having a plunger stem for axially driving said tip in said barrel, a portion of said tip lying behind said space and another portion lying behind said needle opening and means for securing said tip to said plunger stem so that the for-ward force applied by said stem to said tip is substantially restricted to at least the portion of said tip lying behind said space and said initial contact area of said tip to thereby avoid substantial deformation of said tip into said needle opening upon application of an inward force on said tip by said plunger stem after said initial contact.

16. A method of using the syringe of Claim 11 to which a hypodermic needle is attached, comprising moving said plunger tip axially forwardly to expel liquid anti-coagulant and air from said barrel until it reaches its for-ward limit at which there is a predetermined space between said tip and said floor and at which a predetermined amount of said anti-coagulant remains in said space, followed by inserting said needle into a blood vessel of a patient and permitting the blood pressure in said blood vessel to move said plunger tip and plunger axially rearwardly in said barrel to take a sample of blood.

17. A compressible and elastomeric syring plunger tip comprising a generally cylindrical main portion, an in-tegral annular elastically deformable wiper extending peri-pherally radially outwardly and axially forwardly from a forward portion thereof at an acute angle to the longitdui-nal centre axis of said tip and terminating at the outer edge thereof in a wiping edge, when used in a syringe assembly said annular wiper being the sole sealing element between said plunger tip and the syringe and providing substantially all frictional contact between the plunger and the barrel of the syringe, the frictional force of said sealing engagement be-ing of a magnitude that would allow the blood pressure of a patient to move said plunger stem and tip backwardly into said barrel to draw a blood sample from a patient into said barrel.

18. A tip according to Claim 17, said main portion having an end portion of reduced diameter.

19. A tip according to Claim 18, said wiper and reduced diameter portion forming an annular trough in the forward face of said tip.

20. A tip according to Claim 19, the rear end of said tip having a centrally located socket having a tapered end portion, lying behind said end portion of said tip, said trough being located in front of the side wall thickness of said tip.

21. A tip according to Claim 19, said reduced diameter end portion being tapered inwardly as it extends forwardly from said base of said wiper.

22. A tip according to Claim 21, the edge of said wiper comprising a generally cylindrically shaped surface which extends radially outwardly and axially forwardly at a straight acute angle to the longitudinal centre line of said tip.

23. A tip according to Claim 22, the thickness of said wiper being tapered from the base thereof to the free end thereof so it is thicker at its base than at its end.

24. A tip according to Claim 21, said taper of said end portion terminating in a curved surface.

25. A tip according to Claim 17, the thickness of said wiper being tapered from the base thereof to the free end thereof so that it is thicker at its base than at its end.

26. A syringe assembly according to Claim 25, where-in the angle between the leading surface of said wiper and the longitudinal axis is between about 20° and 65° and the angle of taper is between about 4° and 30°.

27. A syringe assembly according to Claim 25, where-in the angle between the leading surface of said wiper and the longitudinal axis is between about 30° and 50° and the angle of the taper is between about 10° and 15°.

28. A tip according to Claim 17, said end portion being of reduced diameter, said reduced diameter end portion being tapered inwardly as it extends forwardly.

29. A tip according to Claim 28, said taper ter-minating in a curved surface.

30. A syringe assembly according to Claim 17, said wiping edge comprising a plane surface of minor dimension oriented substantially parallel to the longitudinal axis of said plunger tip.

31. A syringe assembly according to Claim 30, wherein said plane surface extends radially outwardly and axially forwardly at a very slight angle.

32. A syringe assembly according to Claim 31, wherein the angle is about 2°.

33. A disposable syringe assembly suitable because of the low force requirement for the operation thereof to be used for obtaining a blood sample from a patient comprising a barrel having a cylindrical inner wall and a plunger com-prising a plunger stem and a compressible and elastomeric generally cylindrical plunger tip of lesser diameter than the inner wall of said barrel, said plunger tip having an integral annular elastically deformable wiper extending peri-pherally radially outwardly and axially forwardly from said plunger tip at a forward portion thereof at an acute angle to the longitudinal centre axis of said plunger tip and terminating at the outer edge thereof in a wiping edge having a minimal diameter slightly in excess of the diameter of the inner wall of said barrel thereby forming a sealing engage-ment with the inner wall of said barrel, said annular wiper being the sole sealing element between said plunger tip and and said wall, said wiper being tapered from the base there-of to the free end thereof so that it is thicker at its base than at its end, the angle between the leading surface of said wiper and the longitudinal axis being between about 20°
and 65° and the angle of the taper being between about 4°
and 30° and having a wiping edge comprising a plane surface of minor dimension oriented substantially parallel to the longitudinal axis of said plunger tip but extending radially outwardly and axially forwardly relative thereto at a very slight angle of about 2°, said plunger being spaced from said barrel along the length thereof so that axial movement between said plunger and said barrel is substantially free of frictional contact except for the contact by said sole sealing element, the frictional force of said sealing en-gagement being of a magnitude that would allow the blood pressure of a patient to move said plunger stem and tip backwardly in said barrel to draw said blood sample from a patient into said barrel.

34. A syringe assembly according to Claim 1, wherein said wiper has a leading surface extending axially forwardly and radially outwardly at an acute angle to the longitudinal axis of said tip and a trailing surface exten-ding axially forwardly and radially outwardly at an acute angle to the longitudinal axis of said tip, said wiping edge comprising a generally cylindrical shaped surface which con-nects the ends of said leading and trailing surfaces but which extends radially outwardly and axially forwardly at a slight angle.

35. A disposable syringe assembly suitable because of the low force requirement for the operation thereof to be used for obtaining a blood sample from a patient comprising a barrel having a cylindrical inner wall and a plunger comprising a plunger stem and a compressible, elastomeric, generally cylindrical plunger tip of lesser diameter than the inner wall of said barrel, said plunger tip having an integral, annular, elastically deformable wiper extending peripherally radially outwardly and axially forwardly from said plunger tip at a forward portion thereof at an acute angle to the longitudinal centre axis of said plunger tip and terminating at the outer edge thereof in a wiping edge having a minimal diameter slightly in excess of the diameter of the inner wall of said barrel, thereby forming a sealing engagement with the inner wall of said barrel, said annular wiper being the sole sealing element between said plunger tip and said wall, said plunger tip having a plurality of raised portions spaced circumferentially around said plunger tip and located at the rearward portion of said plunger tip, said raised portions engaging said inner wall of said barrel with a minimum of frictional contact to prevent canting of said plunger tip in said barrel, the frictional force of said sealing engagement being of a magnitude that would allow the blood pressure of a patient to move said plunger stem and tip backwardly in said barrel to draw said blood sample from a patient into said barrel.

36. A syringe assembly according to Claim 35, wherein said raised portions are conical in sahpe.