Measuring and testing – Fluid pressure gauge – Mounting and connection
Reexamination Certificate
2000-11-15
2004-04-27
Raevis, Robert (Department: 2856)
Measuring and testing
Fluid pressure gauge
Mounting and connection
Reexamination Certificate
active
06725726
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a connecting element for connecting a transducer to a sealed fluid system, comprising at least one inlet channel, at least one outlet channel and a measuring chamber connected at least to at least one inlet channel and at least one outlet channel in such a way as to allow a flow to pass through, the measuring chamber being formed in a housing and part of the wall of the measuring chamber being formed by a membrane which is significantly more compliant than the remaining part of the wall of the measuring chamber.
Such connecting elements are known in medical technology by the colloquial term “dome” or “pressure dome”, which originates from the dome-shaped design of the measuring chamber. They serve the purpose of permitting the measurement of pressures in fluids during the examination and treatment of people and animals, preferably by means of electronic equipment.
2. Description of the Prior Art
For pressure monitoring during the flushing of body cavities, in DE 42 19 888 A1, for example, there is described a flow pressure transducer with such a connecting element, which is designed for a large volume throughput in accordance with the intended area of use.
For monitoring hemodynamic parameters of a patient, in particular intensive-care patients, it is customary nowadays in addition to the recording of an ECG also to record the invasive pressures into the [sic] patient monitoring, that is to say keeping a check on the state of the vital bodily functions of the patient. Depending on the degree of monitoring, between one and four pressures (arterial, pulmonary-arterial, LAP and venous) are measured.
For this purpose, a catheter with an integrated monitoring set is used. The positioning of the end opening of the catheter defines the measuring point in the patient's body. A monitoring set refers to a compilation of those parts which establish the connections between the patient and the so-called monitor and, usually for reasons of hygiene, are intended for once-only use. A monitor refers to the electronic monitoring and recording system with which the corresponding measured data are evaluated and displayed, and which in case of need emits corresponding alarm signals if measured data leave prescribed set ranges.
A general description of this, relating to the example of examination by a flow-directed catheter, is found in Buchwalsky, Rainer: Einschwemmkatheter: Technik, Auswertung u. prakti. Konsequenzen [flow-directed catheters: technology, evaluation and practical consequences] (Beiträge zur Kardiologie [articles on cardiology], Vol. 29); Erlangen: perimed Fachbuch-Verlagsgesellschaft, 1985, pages 106-109.
The monitoring set to be fastened to the catheter comprises an unventilated infusion apparatus for feeding infusion solutions to the patient, a flushing system, which ensures a continuous flushing rate of customarily 3 ml/h at the catheter tip to avoid occlusion being caused by thrombi, if appropriate with a quick flushing function for special cases, and a pressure dome. The pressure dome transmits the pressure signal via its flexible membrane to a reusable transducer (pressure sensor). Such a pressure dome has in the past been fastened on such a transducer by a screw or bayonet connection (see in this respect DE 42 19 888 A1, column 3, lines 28 to 30).
Examples of such pressure domes are to be found on information sheet “Disposable Transducer Domes” of the company SMP Specialty Medical Products, Dallas, Tex., US, with reference to the models 078 to 082. A typical transducer (pressure sensor) is described, for example, in a leaflet of the company SensoNor a.s, Horten, NO, Edition 1/95, on the product SensoNor 840.
Further elements of a monitoring set are the pressure hoses (marked in color) and possibly a three-way cock, to allow medicaments to be fed in, or a blood removal system for taking blood for further investigations.
A special problem is that of venting the parts of the monitoring set in connection with the blood system. The problems involved in venting such systems are generally known to the users. During the filling of the system (usually with physiological saline solution) air bubbles become trapped particularly easily in the dome, i.e. in its dome-like measuring chamber above the membrane. On account of the great elasticity inherent in gases, by contrast with the virtually incompressible fluids, the air bubbles trapped there represent a barrier in the transmission of pressure frequencies of more than a few Hertz. This has the effect of significantly falsifying the transmission of the change in pressure to the membrane, and consequently to the transducer lying thereunder, and as a result the representation of the pressure curves on the monitor.
A connecting element of the type mentioned at the beginning is known from prior public use by SMP Specialty Medical Products, Dallas, Tex., US, under the type designation 081. This “dome” is intended to fit the Hewlett Packard 1290 Quartz transducer and allow itself to be fastened on the latter by means of a bayonet connection. Lockable Luer-lock connections with a loose threaded part, or with an external full thread, as are specified for example in DIN 13 090 Part 2, serve for connecting the inlet channel and outlet channel to the hoses of a monitoring set.
The known connecting element is produced from a crystal-clear plastic. The measuring chamber of this connecting element is very large and has, in particular, a large diameter of approximately 23 mm. In this case, the ceiling of the measuring chamber is at the same time the upper side of the housing. This ceiling and upper side of the housing is formed in a plane-convex manner as a magnifying lens. This is intended to achieve the effect that even small bubbles in the measuring chamber are detected as reliably as possible by the medical care personnel.
Disposable transducers which contain the pressure-measuring sensor in a flow housing are therefore designed in the form of a simple tube in the flow chamber in order to avoid this very trapping of air bubbles. However, they have the disadvantage that the valuable electronics are integrated in the disposable article and therefore are thrown away each time the monitoring set is changed and have to be disposed of along with it. To comply with hygiene requirements, such an exchange must take place at the latest every second day. This entails not only the disadvantage that the still serviceable electronics are replaced with every change, accompanied by corresponding costs, but also that the presence of electronic components requires additional special, and consequently cost-intensive, treatment as electronic scrap during disposable.
For this reason, dome systems which can be used repeatedly are becoming more popular, at least in Europe. The valuable electronics, in particular the pressure sensor, are located in a special housing. Such a part is usually referred to as the transducer. One or more transducers are integrated in a special retaining plate. The retaining plate is fastened, for example on an infusion stand, by means of a clamping or screwing device. The measured pressure data are transmitted from the transducers in the retaining plate to the monitor via one or more cables.
When in the past it was necessary to mount a twin or even triple monitoring set on a number of transducers with the screw or bayonet connection usually encountered in the case of repeatedly reusable transducers, the turning movements necessary for this were possible to a restricted extend only in the case of the first transducer. When mounting on the second transducer, the presence of the structure mounted on the first transducer was already a hindrance. Mounting a second dome onto the second transducer was not possible without removing the transducer from a common retaining plate.
This complicated handling is not only troublesome, it also represents an absolute obstacle to designing retaining plates with permanently fitted transducers and rea
Adolfs Manfred
Glocker Raymond
Memscap AS
Paul A. Beck & Assoc.
Raevis Robert
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