Measuring and testing – Fluid pressure gauge – Mounting and connection
Patent
1997-12-04
2000-09-05
Oen, William
Measuring and testing
Fluid pressure gauge
Mounting and connection
G01L 700
Patent
active
061125989
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to pressure measurements in situ, and in particular to a sensor/guide device comprising a guide wire and a distal sensor for pressure measurements in stenotic vessels of atherosclerotic vessels.
In a particular aspect the present invention relates to a sensor arrangement for minimizing bending artifacts, such as those referred to as catheter-whip, suitable for use with the sensor/guide device.
For the purposes of this application the term "guide wire" means a device for guiding and placing e.g. catheters in vessels in a living body.
The term "fluid" means gaseous, such as air, nitrogen, noble gases etc, or liquid, such as blood, other body fluids, water, silicone oil etc.
The term "cantilevering" means that one end of a structure is rigidly mounted, and the opposite end of said structure protrudes from the site of mounting into a medium that is substantially less rigid than that at the mounting site.
The term "rigidly mounted" means that mechanical stress in the structure to which the element is mounted will be carried over to the element at the point of attachment.
BACKGROUND OF THE INVENTION
Devices of the above identified type are known from e.g. Swedish Patents SE-85 00104-8, 86 02836-2, 86 03304-0, 88 02765-1, 90 02415-9, and EP-0 387 453.
All said devices comprise a differential type pressure transducer/sensor, i.e. the pressure is measured as a differential between the applied pressure and atmospheric pressure. Such systems require a ventilation channel for levelling or equalizing the pressure difference between the backside of the pressure sensitive membrane and atmospheric pressure.
There are several advantages with a pressure measurement device for biological pressure measurements having a differential type pressure transducing system, as opposed to an absolute measurement technique. First, the pressure value of interest is de facto a pressure differential between e.g. the pressure inside an organ and atmospheric pressure. Secondly, there is no need for compensation for atmospheric pressure fluctuations. Thirdly, it is advantageous to use an effective pressure measurement range of 0-300 mm Hg, rather than 760-1060 mm Hg, the latter prevailing when atmospheric pressure is part of the measured value. Fourthly, there is no vacuum required in the reference chamber, and the ventilation channel will equalize the pressure changes occurring in the reference cavity due to e.g. temperature fluctuations. Finally, it is possible to calibrate by applying a negative pressure in the ventilation channel.
In SE-86 03304-0 the ventilation channel is located inside thin tubes. This solution gives problems with the mechanical properties when the device according to said patent is used as a guide wire, because the tubes are more easily deformed than solid wires.
In SE-90 02416-7 another solution is disclosed having a solid core and an outer plastic tubing.
The devices of the prior art mentioned above suffer all from manufacturing problems in that the sensor elements can only be tested after a substantial assembly work has been carried out.
However, despite all the advantages of the prior art devices of the differential pressure measurement type over absolute pressure measurements, there are some disadvantages too. The disadvantages become more pronounced when dimensions become smaller, and are mainly related to the presence of the ventilation channel.
For example, the flow resistance of the channel is a function of the limiting frequency response, and therefor the channel must have a certain cross section, i.e. there is a lower limit with respect to the usable dimensions.
A general problem with guide wire micro pressure transducers for in vivo measurements is the occurrence of bending artifacts when the sensor element is subjected to mechanical stress. One such artefact is referred to as catheter-whip, meaning a shift in the signal when the sensor element passes a sharp turn. A solution to such problems is to reinforce the region near the sensing element, so that this region becomes s
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Simultaneous Measurement of Flow Velocity and Trans-stenotic Pressure Gradient, (1994) (no mo.).
Textbook "Interventional Cardiology" 2nd Ed. W.B. Saunders Company (no date).
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Hammarstrom Ola
Smith Leif
Tenerz Lars
Oen William
Radi Medical Systems AB
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