Measuring and testing – Fluid pressure gauge – Mounting and connection
Utility Patent
2000-04-12
2001-01-02
Oen, William (Department: 2855)
Measuring and testing
Fluid pressure gauge
Mounting and connection
Utility Patent
active
06167763
ABSTRACT:
The present invention relates to pressure measurements inside a living body, and in particular to a sensor/guide device having 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, in a sensor/guide device.
For the purposes of this patent specification 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 the 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 an 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 European Publication EP-0 387 453.
All of these prior devices have 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 a pressure sensitive membrane and atmospheric pressure.
There are several advantages of 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 in fact 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 device by applying a negative pressure in the ventilation channel.
In Swedish Patent SE-86 03304-0 the ventilation channel is located inside thin tubes. This solution gives problems with the mechanical properties when the device is used as a guide wire, because the tubes are more easily deformed than solid wires.
In Swedish Patent 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 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 artifact 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 stiff. Such a solution is presented in SE-8603304-0, corresponding to U.S. Pat. No. 4,941,473.
However, the solution according to said patent requires that the sensing element allows a certain deformation/deflection in relation to the bending resistance of the reinforced/-ing part and the surrounding proximal and distal portions, since the overall mechanical behaviour of the guide wire limits this relation. In the pressure sensor devices previously developed by the present applicants, primarily based on optical transducers, where the pressure signal is based on deflection of a silicon beam, the mentioned requirements are satisfactorily met, since the deflection is about 30 &mgr;m/300 mmHg. However, in sensors depending on smaller mechanical deflection, about 1 &mgr;m/300 mmHg or less, it is very difficult to achieve enough mechanical difference in the bending resistances between the reinforced portion and the surrounding, distal and proximal structure.
Conventional guide wires are commonly comprised of a long solid wire (e.g. 1.75 m) the distal portion (approx. 30 cm) having a reduced diameter to increase flexibility. Guide wires having sensors mounted at the tip on the other hand commonly require tubes for accommodating optical fibres and/or electrical leads to/from the sensors, and also for use as a ventilation channel as indicated above.
On the distal end of all types of guides there is normally provided a spiral or helix, in order to maintain the same diameter over the entire length of the guide. It also enables the distal wire portion inside the spiral or helix to be turned while the spiral remains at rest against the vessel wall or interior wall of a catheter.
It would be desirable to have a guide having the advantageous properties of a conventional type guide, and having an absolute pressure sensor integrated therewith. A prerequisite for this would be to provide an absolute pressure sensor/transducer, without need for a ventilation channel.
SUMMARY OF THE INVENTION
The inventors have now discovered that it is possible to make a sensor/guide device provided with an absolute pressure transducer, that still meets the same requirements as those of prior art differential pressure type devices, and in addition eliminates the bending artifact problems.
This is achieved according to the invention with a micro pressure sensor arrangement, by arranging the sensor element such that it protrudes in a cantilevering fashion, preferably without any contact with surrounding structures of the guide wire, and by a sensor/guide device incorporating such a sensor arrangement.
In a preferred embodiment, the sensor is an electrical sensor of piezoresistive type. A suitable sensor is disclosed in our Swedish patent application 9600334-8, filed Jan. 30, 1996.
In a still further embodiment the electrical cabling needed for connection to a recording apparatus is integrated in the distal portion of the guide wire.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention are given for illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given for illustration only, and thus are not limitative of the present invention.
REFERENCES:
patent: Re. 35648 (1997-11-01), Tenerz et al.
patent: 4712566 (1987-12-01), Hoek et al.
patent: 4941473 (1990-07-01), Tenerz et al.
patent: 4957110 (1990-09-01), Vogel et al.
patent: 4967753 (1990-11-01), Haase et al.
patent: 5018529 (1991-05-01), Tenerz et al.
patent: 5085223 (1992-02-01), Lars et al.
patent: 5113868 (1992-05-01), Wise et al.
patent: 5125058 (19
Hammarstrom Ola
Smith Leif
Tenerz Lars
Foley & Lardner
Oen William
Radi Medical Systems AB
LandOfFree
Pressure sensor and guide wire assembly for biological... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Pressure sensor and guide wire assembly for biological..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pressure sensor and guide wire assembly for biological... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2458858