Surgery – Diagnostic testing – Cardiovascular
Reexamination Certificate
2001-06-26
2003-10-21
Walton, George L. (Department: 3736)
Surgery
Diagnostic testing
Cardiovascular
C073S001570, C073S721000, C073S756000, C116S200000, C116S283000, C116S284000, C600S486000, C600S487000, C600S561000
Reexamination Certificate
active
06635020
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a transducer system for the measurement of blood pressure or other fluid pressure. In particular, the present invention relates to a fluid pressure transducer apparatus that incorporates reusable sensor components with disposable fluid path components, and which is easily calibrated for accurate fluid pressure monitoring.
2. Background Technology
For many medical applications, it is important to monitor bodily fluid pressures such as blood pressure. There are generally two types of methods used for measuring and/or monitoring blood pressure, namely indirect and direct methods. Indirect measurements are based on non-invasive procedures such as using a pressure cuff and a stethoscope. Direct pressure measurements are, in contrast, made by using invasive techniques that have the advantages of providing more accurate, more continuous, and if desired, more localized pressure monitoring.
For direct blood pressure measurement and monitoring, typically a catheter is inserted into a blood vessel and is connected to tubing that in turn is connected to a pressure transducer. The transducer includes a sensor that senses the pressure of the fluid path and converts the pressure therein to electrical signals which correspond to the quantity of pressure. The electrical signals are transmitted to a monitor and/or other output devices that display the patient's blood pressure.
With rising health care costs there has been a drive towards developing more cost-effective devices for measuring blood pressure. This has led to the development of disposable blood pressure transducers. Disposable systems typically include a pressure sensor, cable, plastic housing, stopcock, flush device, and associated tubing which are assembled together and provided to the hospital or medical care provider in a sterile package. Such a system is intended for a single patient use, following which the entire assembly is disposed of. The average manufacturing cost of this type of system is fairly high, with the pressure sensor and cable representing the two most costly components. Therefore, any improvements in this type of system with the aim of reduced costs will tend to focus on these two components, specifically evaluating the necessity of disposing this portion of the system following each use.
Reusable transducer systems have been developed that comprise a two-component system in which the relatively expensive sensor on a faceplate is reusable, while the other component with the patient-contacting fluid path is disposable. In these types of systems, each component is provided with a diaphragm that closes off access to the fluid path and the sensor, respectively. In order to measure pressure in the fluid path, the disposable component is attached to the reusable faceplate component with the diaphragms in a confronting and pressure communicating relationship to thereby communicate pressure from the fluid path to the sensor. These two-component transducer systems typically have the disposable fluid path component, usually referred to as the fluid dome, rotatably coupled to the reusable sensor portion. The components are typically secured together by threaded interaction to bring the diaphragms into confronting and pressure communicating relationship by relative rotation between the dome and the reusable component and their respective diaphragms. After use, the disposable unit is removed from the reusable part and discarded, and may be replaced with a new and sterile unit.
Examples of blood pressure measuring devices that are reusable are described in U.S. Pat. Nos. 5,752,918; 5,868,678; 4,920,972; 5,993,395; and 6,117,086. There are also commercially available reusable blood pressure measuring devices such as the LogiCal™ transducer system manufactured by Medex, and the BioTrans™ transducer system manufactured by Biosensors International. These systems have addressed the problems of cost containment through reuse of the sensor and cable; however, all of these systems generally exhibit the following problems: (1) unpredictable failure time due to an unspecified life cycle of the reusable faceplate; (2) inventory level management problems as a result of the unspecified reusable life cycle; (3) sensor inaccuracy and calibration costs; (4) lack of a convenient calibration method for the end user; and (5) obstructed fluid path visibility in the region of the disposable/reusable diaphragm interface.
More specifically, regarding the first problem described above, there are limitations to the expected lifetime of the reusable faceplate component which are caused by wear associated with multiple disposable dome attachments to the reusable faceplate, particularly in the location of the disposable dome interface with the reusable sensor. The lifetime of the device is also limited by the effects of material degradation from alcohol or detergent cleansing of the reusable faceplate and sensor diaphragm surface following each use. Unpredictable failure of the reusable component is a serious problem in medical applications where a patients' lives are frequently in jeopardy.
The second problem described above concerns the inventory management problems that can arise from a blood transducer device having an unknown reusable component lifetime. A hospital or medical care provider may overstock the replacement faceplates to ensure the availability of these components. This approach, however, counteracts the cost advantages of using a reusable system due to the need to carry excessive inventory. Alternatively, the possibility of not carrying sufficient inventory may result in the loss of a critical device in an emergency situation.
The third problem described above is associated with sensor accuracy and calibration costs. Current iterations of the two component reusable systems use a sensor module identical to those used in traditional disposable systems, which have been pre-calibrated to meet the performance specifications of the disposable systems. A shift in sensor performance is typically observed following assembly of the sensor into the reusable package. The reusable system manufacturer is able to correct for some of the performance shifts that occur following packaging, but usually does not have the expertise required to adjust all of the affected parameters. As a result, these manufacturers are frequently confronted with yield losses associated with out of specification performance and/or non-optimized performance. Furthermore, each sensor must be re-calibrated on an individual basis after packaging into the device housing, which greatly increases costs and time required for individual testing of each assembled device.
The fourth problem with prior systems concerns the difficulties in calibration or functionality tests for an end user. The traditional calibration methods have usually been either (1) front side pressure application; (2) back side pressure application; or (3) electronic calibration. Front side calibration typically consists of attaching a pressure generating device such as a syringe to the fluid filled side of the transducer and monitoring the transducer output for proper response. The disadvantages of front side calibration are that the system must be primed with fluid prior to the test, and that the pressure mechanism must interact with the sterile fluid pathway, which requires significant effort to ensure that the fluid pathway is not contaminated. Back side calibration differs from front side calibration by applying pressure to the non-sterile side of the transducer, which avoids the problems of sterility violation and is the method currently utilized by several manufacturers.
Electronic calibration and functionality testing are performed without the use of a pressure source. A resistive network is interconnected with the electronic circuitry of the sensor and/or cable via a user operated switch which creates a predictable change in the sensor's output. This method has the advantage of eliminating any n
Christensen Mark A.
Simon Eric
Tripp, Jr. Carl F.
Thermometrics
Walton George L.
Workman & Nydegger & Seeley
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