Syringe for use in the withdrawal of arterial blood

Claim 1

In apparatus useful for the collection of arterial blood which embodies a tubular body, inclusive of a chamber of relatively large diameter formed therein by an enclosing wall, said tubular body having a forward end and a rearward end, a tubular needle having a dispensing end affixed on the forward end of said tubular body, said needle having an opening therethrough being in communication with said chamber, a plunger having a forward portion and a rearward portion reciprocably fitted within the chamber of said tubular body, the external diameter of the forward portion of which is substantially equal to the internal diameter of the chamber within which the forward portion of said plunger is fitted, the improvement comprising a frusto-conic shaped entry, the included angle formed by the frusto-conic entry ranging from about 45° to about 135°, located in the forward portion of the plunger to provide a permanent opening into the chamber regardless of the position of the plunger, a capillary bore extending from the apex of said frusto-conic shaped entry in the forward portion of said plunger throughout the length of the plunger, and a fast acting valve located within the rearward portion of the plunger, said valve being formed by a lateral opening extending from an outer surface of the plunger to intersect the capillary bore, and a stem slidably movable within said lateral opening for rapidly closing the valve by closure of said capillary bore and thereby creating an obstruction in the bore, or movable within said opening for opening the valve by removing from the bore the obstruction created by the stem, whereby, with the valve open and the plunger positioned to adjust the size of the chamber, the dispensing end of the tubular needle is adapted to be inserted within an artery and arterial blood collected until such time that the chamber is filled, and the valve then closed to trap the arterial blood within the chamber.