Blood-gas sampler

Abstract

A syringe comprising a hollow barrel and a coaxial plunger, the plunger having an improved seal at the leading end thereof wherein a minimal resistance to arterial blood aspiration results but increased resistance through pressure-buckling at a thin-wall groove is provided as a result of opposed pressure forces during discharge of blood from the hollow of the barrel. Thus, a material increase in seal resistance against blood leakage across the seal is obtained.

Description

BACKGROUND

1. Field of Invention

The present invention relates generally to blood-gas analysis and more particularly to a blood-gas sampler comprising a syringe having a novel seal at the leading end of the plunger.

2. Prior Art

Prior art blood-gas sampling syringes have utilized relatively unsatisfactory seals between the plunger and barrel of the syringe. Most frequently the syringe barrels are of glass, but occasionally of plastic. The mentioned seals are of a relatively hard elastomer and consist primarily of two or three annularly enlarged rings, each creating a relatively wide high friction sealing contact with the interior surface of the barrel. The same high level of seal-created friction exists both when advancing and when retracting the plunger within the barrel. With such seals it has been impossible for such syringes to self aspirate in receiving a sample of blood following arterial penetration. Manual aspiration has been obligatory. Where constant seal friction is reduced overall aspiration solely under the force of arterial pressure can be achieved but such would be followed by appreciable leakage around the seal as the blood sample is subsequently expelled from the barrel of the syringe under manual pressure applied to advance the plunger.

BRIEF SUMMARY AND OBJECTS OF THE PRESENT INVENTION

In its presently preferred form the present invention comprises a blood-gas arterial syringe comprising a hollow barrel and a plunger situated within the barrel. An improved seal spans between the leading end of the plunger and the interior surface of the barrel. The seal comprises a cup-shaped body which defines an annular wall extending essentially coaxial to but spaced from the inside surface of the intermediate portion of the barrel and also comprises an end closure at the leading end of the seal. The body of the seal is affixed at its trailing end to the leading end of an intermediate section of the plunger. A radially extending annular ring or bead of the seal sealingly engages the interior surface of the barrel creating only limited resistance to plunger extension under force of arterial pressure. An annular groove along the inside of the annular wall of the seal creates a reduced thickness annular buckling region which is forced radially outward into sealing engagement as the plunger is displaced into the barrel by the user causing blood within the barrel to be expelled under substantial pressure through a relatively small diameter port disposed at the forward end of the barrel whereby blood leakage across the seal is greatly alleviated, if not non-existent.

With the foregoing in mind, it is a primary object of the present invention to provide an improved blood-gas arterial sampling syringe.

It is a further paramount object of the present invention to provide, in a blood-gas arterial sampling syringe, an improved seal interposed between the leading end of a plunger and the hollow interior surface of a barrel which creates only limited seal resistance to plunger extension under force of arterial pressure but substantially greater resistance as the plunger is displaced into the barrel and blood is expressed from the small orifice at the leading end of the barrel whereby blood leakage across the seal is greatly alleviated.

These and other objects and features of the present invention will be apparent from the following detailed description, taken with reference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective representation of a presently preferred blood-gas arterial sampling syringe according to the present invention;

FIG. 2 is an enlarged longitudinal cross section of the mentioned syringe taken along line 2--2 of FIG. 1;

FIG. 3 is an enlarged fragmentary cross section showing the seal, which is interposed between the barrel and the plunger in the position assumed during blood aspiration; and

FIG. 4 is a fragmentary cross section similar to FIG. 3 but showing the seal in the position assumed during discharge of blood from a barrel of the syringe.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENT

With reference to the Figures, a presently preferred embodiment of the present invention is illustrated comprising a blood-gas sampling syringe 10 having a barrel 12 and a plunger 14. The barrel is preferably light-transmitting and is made of glass or plastic material, such that gas permeation is negligible. The barrel 12 comprises a forwardly directed converging wall section 16 defining a relatively small diameter port or orifice 18. The projection 16 is adapted to receive an arterial needle in a conventional manner whereby blood from an artery of the patient enters the barrel 12 through the port passage 18.

The barrel 12 also comprises an intermediate portion 20 comprising an annular wall of uniform inside and outside diameter whereby a cylindrical hollow interior 22 consisting of a blood-receiving chamber is defined. The hollow chamber 22 terminates at the trailing end of the barrel 12 at opening 24, the diameter of which is essentially equal to the inside diameter of the chamber 22. A flange 26 projects radially outwardly away from the opening 24 at the trailing end of the barrel 12. The flange 26 provides for finger engagement by the user accommodating advancement of the plunger 14 into the barrel 12 to express blood from the chamber 22 in a manner hereinafter more fully described.

The plunger 14 may be of one-piece molded construction. As illustrated, it comprises a radially enlarged cap or handle 30 bonded at lap joint 32 to an elongated intermediate section comprising a hollow tube 34. A bonded lap joint 36 secures a reduced diameter trailing end portion 38 of an elastomeric head or seal 40 to the leading end of the intermediate tubular section 34.

The elastomeric head or seal 40 is preferably comprised of some highly pliable synthetic resinous material, such as soft vinyl, to facilitate ease of aspiration as hereinafter more fully described. The seal 40 comprises an annular thin wall body 42, said wall having a reduced thickness at an annular groove 44 disposed centrally between the leading end of the tubular intermediate section 34 and a thin wall end closure 46 of the seal 40. An annular bead or ring 48 extends into sealing contact with the interior surface of the intermediate portion 20 of the barrel 12 in such a fashion as to create very little resistance to plunger extension, the bead 48 being situated at or near the interface between the closure end 46 and the annular wall 42 of the seal 40. Thus, the radially extending annular bead for ring 48 creates only a modest seal against the interior surface of the barrel while producing little resistance to the extension of the plunger responsive solely to the force of arterial pressure once needle penetration of an artery has been accomplished. Hence, the sampling syringe 10 is self-aspirating.

The annular wall 42 of the seal 40 is coaxial with the longitudinal axis of the syringe 10 and barrel 12, being spaced therefrom during aspiration as illustrated in FIGS. 2 and 3. However, experimentation has shown that the seal created by the relatively small annular bead 48 is inadequate to prevent blood leakage across the bead 48 as the user of the syringe 10 manually advances the plunger 14 into the barrel 12 to expel blood from the hollow chamber 22 through the small diameter port 18 under substantial pressure. To alleviate or prevent the mentioned blood leakage problem, the annular wall 42 is provided with the mentioned annular groove 44, centrally and radially disposed along the interior surface of the wall portion 42. Because of the indicated configuration, as force is applied to the cap 30 of the plunger 14 as shown at arrow 54 to expel blood from the chamber 22, the relatively yieldable seal 40 buckles radially outwardly along the annular region of the wall 42 at groove 44, under fluid pressure illustrated by arrows 52, into sealing engagement with the interior surface of the barrel 12. See FIG. 4. Thus, an annular bead 50 results which is of substantial thickness and in nearly all situations totally prohibits blood loss across the seal 40.

Thus, the seal 40 accommodates easy self-aspiration of the sampling syringe 10 so that arterial pressure alone will fill the chamber 22 and at the same time creates a major additional sealing bed during those occasions when the plunger is advanced to expel part or all of a blood specimen from the chamber 22. In this way blood leakage across the seal is alleviated or prohibited.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

What is claimed and desired to be secured by United States Letters Patent is:

1. A blood-gas arterial syringe comprising:

a hollow barrel having means at the leading end for receiving an arterial needle, said means comprising a relatively small diameter port whereby blood is communicated from an artery to the hollow of the barrel, the barrel further comprising an intermediate portion having a relatively large essentially uniform inside diameter which opens at the trailing end of the barrel;

a plunger normally extending through the said opening and disposed along the intermediate portion of the barrel, the plunger comprising means at the trailing end for advancing the plunger into the barrel, and an intermediate section having a lateral dimension less than said inside diameter of the intermediate portion of the barrel;

the improvement comprising a seal comprising a cup-shaped body initially defining an essentially annular wall coaxial to but spaced from the inside surface of the intermediate portion of the barrel and an end closure comprising the leading end of the seal, the body being united at its trailing end to the leading end of the intermediate section of the plunger, the seal further comprising at least one radially extending annular seal bead spanning at all times between the annular wall and the inside surface of the intermediate portion of the barrel creating only limited resistance to plunger extension under force of arterial pressure, the seal further comprising a reduced thickness section of the annular wall located forward of said union between said trailing end of the seal and the leading end of the intermediate section of the plunger and creating an annular buckling region which is forced radially outward by fluid pressure creating an additional temporary annulus in sealing contact with the inside surface of the barrel as the plunger is advanced into the barrel causing blood within the barrel to be expelled through the small diameter port whereby blood leakage across the seal is alleviated, the temporary annulus collapsing to the initial configuration when the plunger is no longer advanced.

2. The syringe of claim 1 wherein said annular seal bead is disposed adjacent the interface between the end closure and the annular wall of the seal.

3. The syringe of claim 2 wherein said annular buckling region is disposed essentially midway between the leading end of the intermediate section of the plunger and the annular seal bead.

4. The syringe of claim 1 wherein said barrel is composed of light-transmitting material.

5. The syringe of claim 1 wherein the seal is affixed at its trailing end to the intermediate section of the plunger at a lap joint.

6. The syringe of claim 1 wherein said seal comprises a soft elastomeric material.

7. The syringe of claim 1 wherein said reduced thickness section comprises an annular groove along the inside of the annular wall of the seal, which is free from contact with the intermediate section of the plunger.