Blood-gas sampler

Claim 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.