Surgery – Truss – Pad
Patent
1990-03-28
1992-02-04
Pellegrino, Stephen C.
Surgery
Truss
Pad
128637, 128748, 73715, 73706, A61B 502
Patent
active
050852230
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a miniaturized pressure transducer used to measure in vivo physical pressure. An example of such a use is the insertion of the transducer into the vena cava to obtain a bloodless measurement of the pressure in the coronary vessel.
Pressure transducers of the kind mentioned above are known from our International Patent Application WO 88/00023. Such a known transducer is illustrated in FIG. 1, and includes an inner tube 1 within which a pressure transducer element comprising a silicon wafer 2 and an light conductor 3 is inserted. The lumen 4 of the tube is in communication with the atmospheric pressure. The distal part of the inner tube 1 is completely surrounded by a diaphragm 5. The inner tube has an opening 6 covered by the diaphragm. The diaphragm is mechanically affected by the physical pressure which is to be measured, and its movements are transferred to the light conductor 3. The amount of light reflected from the flat surface 7 of the silicon wafer 2 and picked up by the light conductor 3 is proportional to the physical pressure which is to be measured.
A disadvantage of the known structure is that the diaphragm is unprotected and is subject to the risk of damage including the possibility that the diaphragm material could be torn away from the tip of the transducer.
The risk of damage to the diaphragm is particularly likely to occur in the case where the transducer, which has an outer diameter in the order of magnitude 0.5 mm, is inserted in a catheter which is used to perforate the tissue in which the pressure is to be measured.
The present invention has the object of providing a solution to the above-mentioned problem.
The diaphragm must meet certain mechanical requirements. It must be impermeable, flexible and not dependent on temperature. As the flexibility of the diaphragm material increases the resolution of the pressure signals will be better. Thus, in the known pressure transducer, a compromise must be made between the mechanical flexibility and the mechanical tearing strength of the diaphragm material.
The pressure transducer itself is subject to certain demands regarding its exterior dimensions. Its outside diameter should, therefore not exceed about 0.46 mm, and its axial length should be short, hardly longer than about 4 mm.
The above mentioned problem is solved, in accordance with the invention, with mechanically protecting the diaphragm by an outer tube. The outer tube is placed over the inner tube and has a wall opening situated directly opposite the wall opening of the inner tube. The diaphragm, the thickness of which can be then reduced considerably, is fixed between the outer and inner tubes, and only the part of which is exposed by the opening of the outer tube can be subjected to damage. This exposed diaphragm surface is considerably less than the exposed diaphragm surface in the embodiment shown in FIG. 1.
The arrangement of an outer tube having an outside diameter not greater than 0.46 mm has been enabled by the miniaturization of the silicon wafer 2 and by a reduction of the diameter of the light conductor 3, as compared to the pressure transducer described in WO 88/00023.
Since the exposed diaphragm surface is considerably reduced, the tearing strength requirement for the diaphragm material is also considerably reduced, thereby making, for use in the pressure transducer considerably more types of diaphragm material than was previously the case. Thus it will be possible to use diaphragm material which is soft and which gives rise to high-resolution signals.
Different embodiments of the invention will now be described from the following detailed description, and in connection with the accompanying drawings, wherein
FIG. 1 is a longitudinal section of a known miniaturized pressure transducer,
FIG. 2 is a longitudinal section of a first embodiment of the pressure transducer in accordance with the invention,
FIG. 3 is a longitudinal section of a second embodiment of the pressure transducer in accordance with the invention,
FIG. 4 is a longitudinal
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Bertil Hok
Lars Tenerz
Ola Hammarstrom
Roman Lonc
Tomas Engstrom
Longo Robin R.
Pellegrino Stephen C.
Radi Medical Systems AB
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