Apparatus for measuring blood pressure

Abstract

The open end of a catheter is inserted in the blood vessel of a patient. The catheter is connected by hollow tubing to a physiologic pressure transducer. The tube is filled with an intermediate pressure-transmitting fluid such as a physiologic saline solution. An infusion device between the patient and the transducer constantly flushes the system with a slow flow of fluid. Blood pressure variations are transmitted through the fluid to the transducer, which converts the pressure to electronic information and transmits the information to a monitor for display. Between the infusion device and the transducer is a variable restrictor which damps the pressure waves in the fluid. This restrictor is used to tune the system to eliminate resonant waves, which distort the monitoring reading. In one form, the variable restrictor includes a valve having an orifice, the effective size of which is reduced or enlarged by compressing and releasing a deformable, flexible ring. In another form, the variable restrictor includes a valve which has a valve seat with a flow opening through which the fluid pressure wave passes. To control pressure wave flow through the valve, a valve needle is moved toward and away from a valve seat, which reduces and increases the size of the flow opening.