Pressure transducer assembly

The pressure transducer assembly herein can be used in any fluid line for which the fluid pressure within the line is to be determined. The pressure transducer assembly herein has particular utility for the invasive monitoring of blood pressure. In a particular application, the pressure transducer assembly provides a disposable pressure transducer assembly which can be used for a single patient use and then discarded.

Invasive blood pressure monitoring as a system which provides an accurate method for monitoring the blood pressure of a patient. Frequently, invasive blood pressure monitoring is performed for critically infirmed patients. Invasive blood pressure monitoring is also performed during critical surgeries and on patients in intensive care units and critical care units. Invasive blood pressure monitoring is gaining acceptance in conjunction with the care and treatment of cardiac .[.pateints.]. .Iadd.patients .Iaddend.and for providing a technique for the constant, accurate determination of blood pressures for such patients. Invasive blood pressure monitoring is used with cardiac catheterization to provide bedside cardiac and blood pressure monitoring. In invasive blood pressure monitoring, a catheter is inserted into a patient's circulatory system with the end of the catheter having an opening which is open to the blood stream. In many instances, the catheter is inserted into the circulatory system such that the proximal end of the catheter reaches the heart in order to provide monitoring of atrial and venous pressures. An I.V. set is generally attached to the distal end of the catheter protruding from the patient. An I.V. solution bag in the I.V. set assembly contains a solution which is permitted to flow through the catheter and into the patient. The I.V. solution extending through the catheter and into the patient provides a fluid pathway for pressure in the patient's circulatory system. By positioning a pressure transducer along the fluid pathway, the blood pressure in the patient's circulatory system can be monitored. Generally, such a pressure transducer consists of a dome which functions as a reservoir for the I.V. fluid. The dome includes a resilient diaphragm which attaches to an electrical transducer. The transducer senses pressure fluctuations in the diaphragm and converts such pressure fluctuations into electrical impulses which are transmitted to a monitor.

The pressure transducers that are currently used in invasive monitoring systems are relatively expensive and are generally constructed to be reusable following sterilization. Some pressure transducers can be reused as they are not in direct contact with the fluid being administered but rather are adapted to be connected to fluid reservoir domes which can be either disposable or reusable.

It would be desirable to provide a pressure transducer in a single integrated assembly which can provide an accurate monitoring of fluid pressure while being inexpensive and disposable. It would also be desirable to provide such a pressure transducer such that the pressure in the fluid pathway is determined and converted to electrical impulses such that the transducer need only be electrically connected to a readout monitor or display unit for such determined pressures.

The invention herein is directed to a pressure transducer assembly for directly monitoring pressure in a fluid which flows through the assembly. The assembly includes a housing defining a chamber therewithin and having an inlet port and an outlet port in fluid-flow communication with the chamber. An electrically insulated body element is sealed within the chamber dividing the chamber into a first chamber and a second chamber within the housing. The first chamber is in fluid-flow communication with the inlet and outlet ports. The second chamber is separated from the first chamber by a fluid-tight seal such that any fluid present in the first chamber cannot enter the second chamber. A pressure transducer sensor is secured in the insulated body and exposed to the first chamber such that the pressure transducer sensor can determine the fluid pressure in a fluid in the first chamber and convert the sensed fluid pressure into electric impulses. The pressure transducer sensor is separated from the fluid in the first chamber by an insulating medium across which fluid pressure can be determined but electrical current cross. Connected to the pressure transducer sensor are electrical conductors which extend through the insulated body and into the second chamber. The second chamber provides an engagement site for an electrical connector which can interconnect with the electrical conductors and provide an electrical path through which the electric impulses generated by the pressure transducer sensor can be transferred to a monitor for monitoring the fluid pressure within the fluid in the first chamber.

FIG. 1 is a top plan view of the pressure transducer assembly herein connected to an electrical connector which can form a part of the assembly herein;

FIG. 2 is a lateral cross-sectional view of the embodiment shown in FIG. 1 taken along lines 2--2;

FIG. 3 is a side elevational view of the pressure transducer assembly shown in FIG. 1;

FIG. 4 is an end elevational view of the electrical connector which connects to the pressure transducer housing assembly.

FIG. 5 is an exploded view of the pressure transducer housing assembly and the electrical connector assembly; and

FIG. 6 is a schematic representation of a pressure transducer assembly illustrating its utility in a technique for the invasive monitoring of blood pressure.

The pressure transducer assembly herein will be described with regard to the accompanying drawings wherein the overall assembly and utility for the assembly is illustrated in FIG. 6. FIG. 6 schematically represents the use of the pressure transducer assembly herein for invasive blood pressure monitoring.

In particular, the invention herein resides in the pressure transducer housing assembly 12 shown in FIG. 1. With regard to FIG. 1, the pressure transducer assembly 10 is shown in part by the pressure transducer housing assembly 12 which is connected to an electrical connector assembly 14. The electrical connector assembly is structured to enable electrical connection with the pressure transducer assembly so as to provide power to the pressure transducer assembly and to provide a route for electrical impulses generated by the pressure transducer assembly.

The pressure transducer housing assembly comprises a housing 16 which defines a chamber 15 therein. The chamber 15 is divided into a first chamber 20 and a second chamber 22 by an insulated body 24 which is sealed to the housing within the chamber 15. The insulated body 24 is nonconductive of electricity and is constructed of a suitable material that is compatible with the material of the housing, which is biocompatible with the human physiology, and which will not react with the fluid being administered to a patient through the pressure transducer assembly. The material of the insulated body is selected from a material which can be sealed to the housing to provide a fluid-tight seal between the first and second chambers. The housing can be constructed of any suitable material which is biocompatible with the human physiology including materials such as polycarbonate, polypropylene, polyethylene, polysulfone and the like. A suitable material for the insulated body member is polysulfone. The insulated body member can be sonically welded to seal the body member within the chamber 15 and to form and separate the first chamber 20 and the second chamber 22. Constructing the housing and presure transducer assembly of the plastic materials described makes the assembly disposable so that it can be discarded after a single patient use. Such materials are inexpensive and easy to mold, such as by injection molding in large volumes.

The first chamber 21 is in fluid-flow communication with an inlet port 26 provided on the housing. The first chamber is also in fluid-flow communication with an outlet port 28 provided on the housing. The inlet and outlet ports can be hollow, cylindrically extending portions of the housing which project from the housing to enable the affixing of tubing (shown in FIG. 6) to the housing. Preferably, the inlet and outlet ports are axially aligned to provide a substantially unimpeded flow path through the housing. The inlet port, outlet port and first chamber provide a fluid-flow pathway through which fluid can be administered to a patient while simultaneously permitting the monitoring of pressure waves along the fluid pathway. The inlet port can be provided with a rotating adapter 27 or other similar attachment means such as Linden fittings, Luer fittings and the like whereby a catheter or tubing can be attached to the housing in a fluid-tight seal. Similarly, the outlet port can be provided with a rotating adapter 29 to connect a catheter or tubing to the outlet side of the housing.

The housing can include a dome 30 which is a portion of the housing that is structured in a dome which extends over the first chamber. The dome is preferably constructed of a clear material such that any fluid within the first chamber can be observed. The dome functions as a clear lens which permits the observation of the fluid and any bubbles which can be present in the fluid. The dome can also function to trap, or momentarily trap, any air bubbles which can be present in the fluid. The presence of air bubbles is undesirable as it can provide erroneous pressure readings and it is undesirable to introduce air bubbles to the patient.

Positioned within the first chamber is a pressure sensor such as a silicon pressure sensor 32. In the preferred embodiment, the pressure sensor is positioned in a depression on the insulated body as can be readily seen from the cross-sectional view of FIG. 2. The silicon pressure sensor is a pressure transducer which is capable of sensing or determining a pressure in any fluid present in the first chamber and converting such pressure to an electric impulse. Preferably, the pressure transducer is a monolithic silicon pressure sensor employing a four-terminal resistive element formed in a thin monocrystalline silicon diaphragm. Acceptable silicon pressure sensors are commercially available from Motorola, Inc., Sensors which can be used in the pressure transducer assembly herein include the sensors that are disclosed in U.S. Pat. No. 4,317,126 assigned to Motorola, Inc., the entire disclosure of which is incorporated herein by this reference. In addition to the sensors disclosed in the U.S. Pat. No. 4,317,126 patent, a particularly preferred silicon pressure sensor is a sensor which includes a temperature compensation circuit for compensating the sensed pressure in the fluid based upon the temperature of the fluid and correcting such sensed pressure. Such a silicon pressure sensor is commercially available from Motorola, Inc. as SPX-1001D pressure sensors.

Covering the pressure sensor 32, as can be more readily seen in the cross-sectional view shown in FIG. 2, is an insulating medium 34. Insulating as used with regard to the insulating medium refers to the nonconductance of electricity. The insulating medium 34 extends over and completely covers the silicon pressure sensor such that there is no electrical connection or electrical pathway between fluid in the first chamber and the silicon pressure sensor. As seen in FIG. 2, the term "covers" is used to mean that the insulating medium and silicon pressure sensor are mechanically contiguous. The insulating medium 34 comprises a material that is sufficiently fluid-like that it transmits the pressure in the fluid to the sensor. The insulating medium is also preferably biocompatible as it is in contact with the fluid being administered to the patient. A particularly preferred insulating medium is a silicone polymer, such as a methyl silicone elastomer. Such an insulating medium prevents electrical shock to the patient through the fluid as any electrical current to the silicon pressure sensor is insulated from the fluid in the first chamber by the insulating medium.

In order for the silicon pressure sensor to accurately measure the pressure of the fluid in the first chamber, the silicon pressure sensor is preferably vented to the atmosphere. The venting of the silicon pressure sensor to the atmosphere is accomplished by providing a first aperture 45 in the base of the electrical connector which coincides and aligns with a second aperture 46 in the housing. The second aperture in the housing opens into the second chamber and coincides and aligns with a third aperture 48 in the insulated body. The third aperture 48 in the insulated body opens to the lower side of the silicon pressure sensor and thereby provides a direct pathway to the atmosphere for the silicon pressure sensor.

A series of electrical pins 36 extend through the insulated body 24 into the first chamber and are in electrical contact with the silicon pressure sensor 32 through suitable circuits 37. The portion of the pins 36 which extend into the first chamber are completely imbedded within the insulating medium 34 and thereby physically separated from fluid in the first chamber by the insulating medium. The electrical pins extend through the insulated body and into the second chamber of the housing of the pressure transducer assembly. The electrical pins extend from the insulated body to provide a male electrical plug which can be inserted into a corresponding female electrical plug on the electrical connector assembly 14 to provide electrical contact between the pressure transducer housing assembly and the electrical connector assembly.

In the preferred embodiment, the second chamber is open and provides a receptor site for the electrical connector assembly. That is, at least a portion of the electrical connector assembly can be inserted into the second chamber to mate with the electrical pins. The view shown in FIG. 3 of the drawing shows a view of the pressure transducer housing assembly looking into the open second chamber 22 wherein the insulated body 24 can be seen with the extending electrical pins 36. In other embodiments, the electrical pins can also extend through the sidewall of the housing to enable connection to an electrical connector assembly.

The electrical connector assembly can be mated to the pressure transducer housing assembly. The electrical connector assembly includes electrical plug receptors 38 which receive the electrical pins 36. The electrical plug receptors are connected through suitable wiring 40 which can carry the electrical impulses generated by the silicon pressure sensor to a suitable display unit or monitor as is shown in FIG. 6. Such wiring can also provide power to the pressure transducer assembly. An end view of the electrical connector assembly 14 is illustrated in FIG. 4. The mating of the pressure transducer housing assembly and the electrical connector assembly is shown in an exploded view in FIG. 5. The electrical connector assembly can include a cavity 44 into which a portion 17 of the housing 16 of the pressure transducer housing assembly can be inserted to mate the electrical pins 36 and electrical plug receptors 38. The electrical connector assembly can include a projecting portion 39 which can insert into the open second chamber of the housing. Such an arrangement provides a relatively snug fit between the pressure transducer housing assembly and the electrical connector assembly to prevent inadvertent separation of the assemblies. In a preferred embodiment of the invention, the pressure transducer housing assembly and the housing 16 thereof can be provided with resilient snap-fitting projections such as the resilient arm portions 42 which can be inserted into and snap-fittingly engage suitable apertures 41 in the body of the electrical connector assembly 14.

The electrical connector assembly provides an electrical conduit between the pressure transducer housing assembly and a display unit. The electrical connector assembly includes the assembly 14 and the associated wiring 40 which leads from the electrical connector assembly to a display unit.

The utility of the pressure transducer assembly herein is schematically illustrated in FIG. 6. In FIG. 6, a patient 50 is catheterized with a catheter which extends into the circulatory system. The catheter is connected at about the exit site from the patient of flexible tubing 52 along which can be positioned a clamp 54 for occluding fluid flow through the tubing. The tubing 52 is connected to the pressure transducer housing assembly 12 at the outlet port. As can be seen by one having skill in the art, the housing of the pressure transducer housing assembly can be positioned in any manner with regard to inlet and outlet flow of fluid as the direction of flow of any fluid through the housing does not influence the pressure reading by the silicon pressure sensor. The terms inlet and outlet, as used herein, are merely arbitrarily assigned to the two ports on the housing to facilitate the description of utility.

The inlet port of the housing is connected through suitable flexible tubing 60 to a source of an I.V. solution such as an I.V. bag and drip chamber 58. A clamp 54 and a fluid-flow restriction device 62 can be positioned along the flexible tubing leading to the pressure transducer housing assembly 12.

The electrical connector assembly 14 is interconnected to the pressure transducer housing assembly. The wiring 40 extending therefrom can be connected to a suitable display unit or monitor 56 can be powered by batteries or by normal alternating current.

In operation, prior to connecting the flexible tubing 52 to the catheter which has been inserted in the patient, fluid from the I.V. bag is permitted to flow through the tubing 60, pressure transducer housing assembly 12, and flexible tubing 52. The connection between the flexible tubing 52 and catheter is then made so as to prevent the formation or inclusion of entrapped air along the fluid-flow path. After connecting the tubing 52 to the catheter, a complete fluid-flow path is .[.obtined.]. .Iadd.obtained .Iaddend.and with the communication of the fluid in the pressure transducer assembly and the patient's circulatory system, any pressure within the circulatory system is correspondingly observed in the fluid present in the first chamber of the pressure transducer assembly. The silicon pressure sensor thereby observes the pressure in the fluid and transforms such sensed pressure into electrical impulses which flow along the wiring 40 to the display unit 56 wherein the pressure readings are displayed for the benefit of the attendant.