Medical instrument for measuring fluid pressure

Claim 1

A medical instrument useable in conjunction with an intravascular infusion system having a fluid source and adapted selectively to effect normal intravascular infusion or to measure intravascular fluid pressure; said instrument comprising: A. an instrument body having formed therein a through-passage, one end of which includes means connectable to said fluid source and the other end of which includes means connectable to a patient to provide a feed path for the infusion system, a closed air cavity, a capillary tube, one end of which communicates with the cavity to define therewith a pressure gauge means, a valve chamber defining a conduit extending between said through-passage and the other end of said capillary tube, and an air vent connecting said chamber to the atmosphere, and B. valve means movable within said valve chamber from a first position blocking flow between said through-passage and said valve chamber to permit normal infusion, to a second position blocking flow between said fluid source and said throughpassage to interrupt infusion and to admit a return flow of pressurized fluid from the patient into said valve chamber without blocking said vent, to a third position blocking flow between said fluid source and said through-passage to interrupt infusion and to admit a return flow of pressurized fluid from the patient into said valve chamber while blocking said vent, thereby causing the pressurized fluid to flow into said capillary tube to be measured by said gauge.