Patent Application
20060099834
The present invention relates to a method and a device for reducing leakage current in a guide wire assembly having conductor members arranged at a connector end of the guide wire to provide electrical contact with electrical leads of the guide wire and to provide signals transferred via the electrical leads to an external device, said conductor members being separated by at least one insulator.
Guide wires are generally known in the art. Their use is, for example, in connection with treatment of coronary disease. As is conventional, a contrast media is used in connection with an x-ray of a blood vessel to show occlusion, however, without showing a cross section of a stenosis. Complicating the diagnosis of the problem is that different patients have different blood flow. Measurement of blood pressure is a way to diagnose the significance of the stenosis. In practice, a distal end of the guide wire is inserted into the body, for example into an opening into the femoral artery, and placed at a desired location. At the distal end of the guide wire is a miniature sensor arranged for measuring pressure. Further, once the guide wire is placed by the physician into the appropriate location, a catheter of appropriate type may be guided onto the guide wire. A balloon dilation may then be performed.
Electrical leads extending along the guide wire carry measurement signals from the sensor via connectors to a monitor for further processing. The guide wire is electrically connected through a male connector arranged at a proximal end of the guide wire, via a female connector, to the monitor. At the male connector, there are one conductor member arranged for each lead extending along, or inside, the guide wire. Insulating spacers are arranged to separate the conductor members. On insertion of the male connector in the female connector, the conductor members are brought into electric contact with corresponding female contact members.
When the physician places the guide wire into the appropriate location in the body, the male connector may be contaminated by, for example, dirt, fat, moist, etc., which is attached to the physician's fingers and deposited onto the male connector. Alternatively, body fluids such as blood may be deposited onto the connector when the guide wire is inserted in the body. In another scenario, to permit replacement or exchange of the catheter, the male connector is disconnected from the female connector and the catheter is removed over the guide wire. At that time, body fluids will be deposited directly onto the male connector and indirectly onto the female connector, via the male connector. Hence, the connectors may be contaminated by blood and other bodily fluids at the time the catheter is changed, and these body fluids will potentially alter the electrical properties of the connector. As a further consequence, the contaminations given above may deteriorate the insulation between the conductor members in the connectors, and measured values may become unreliable due to leakage currents flowing through the insulating spacers. Further, insulation may be deteriorated for other reasons, for example because of manufacturing defects.
A guide wire assembly with connectors is shown, for example, in U.S. Pat. No. 6,663,570, Mott et al. In U.S. Pat. No. 6,663,57, a system is disclosed for connecting a flexible elongate member arranged with an electrically operable sensor to a physiology monitor. The system comprises a flexible cable having an electrical conductor therein and a connector arranged on an end of the flexible cable for receiving an end of the flexible elongate member. A contact member in the connector is electrically connected to the conductor in the flexible cable to transfer data to the physiology monitor.
In this type of prior art guide wire assembly, bodily fluids and other contaminations can clearly cause electrical problems in the connector. Consequently, there remains a need for a connector which can be used with the restricted small size of a guide wire typically having a diameter of 0.35 mm, and which can be used in situations where there might be contamination by human or animal body fluid or contaminations such as dirt, fat or moist.
An object of the present invention is to solve the above given problems, and to provide a device in which leakage currents in the guide wire assembly is reduced, which leakage currents are due to bodily fluids or other contamination that deteriorates insulation capacity in the guide wire assembly. Leakage currents may also be due to general deteriorations in insulating capacity, for example arising from manufacturing defects.
A further object is to provide a more reliable guide wire assembly.
These objects are attained by a method of reducing leakage current in a guide wire assembly having conductor members arranged at a connector end of the guide wire to provide electrical contact with electrical leads of the guide wire and to provide signals transferred via the electrical leads to an external device, said conductor members being separated by at least one insulator, in accordance with claim 1.
These objects are also attained by a device for reducing leakage current in a guide wire assembly having conductor members arranged at a connector end of the guide wire to provide electrical contact with electrical leads of the guide wire and to provide signals transferred via the electrical leads to an external device, said conductor members being separated by at least one insulator, in accordance with claim 13.
According to a first aspect of the present invention, there is provided a method comprising the steps of applying a guard potential to said at least one insulator, which guard potential is arranged to reduce a potential difference across the insulator such that leakage current is reduced.
According to a second aspect of the present invention, there is provided a device comprising an electrode arranged to apply a guard potential to said at least one insulator, which guard potential is arranged to reduce a potential difference across the insulator such that leakage current is reduced.
An idea of the present invention is to minimize leakage current via at least one insulator arranged to separate conductor members in a guide wire assembly. As previously described, when a physician places the guide wire into an appropriate location in the body, the male connector of the guide wire may be contaminated by, for example, dirt, fat, moist, etc., which is attached to the physician's fingers and deposited onto the male connector. Alternatively, body fluids such as blood may be deposited onto the male connector when the guide wire is inserted in the body. When connecting the male and female connector, the contaminations are attached to the insulator of the male connector, and the insulating capacity of the insulator is hence deteriorated, i.e. insulating resistances between conductor members are decreased. As a consequence, leakage current will flow via the insulator and a potential difference is created across the insulator. Clearly, the electrical properties of the connectors will be altered. As a direct consequence, measured physiological values will become unreliable. Therefore, at the insulator, a guard voltage is applied. This guard potential is arranged to reduce the potential difference across the insulator. When this potential difference is reduced, ideally to zero voltage, the leakage current is reduced correspondingly. Note that fluids not necessarily must be deposited onto the insulator for the present invention to be advantageously implemented in a guide wire assembly. Deterioration in insulating capacity of the insulator may be remedied by means of the present invention, even though the deterioration has emerged under other circumstances.
In a guide wire assembly comprising a miniature sensor for measuring physiological variables, leads extending along, or inside, the guide wire carry measurement signals from the sensor via connectors to an external device, such as a monitor, for display and/or further processing. In the following example, it is assumed that a first lead carries a pressure signal and a second lead is set to a reference potential, typically ground. Note that the lead being coupled to a reference voltage, such as ground, is not regarded as a signal lead, as no actual measurement signal is transferred via that particular lead. In case two leads are utilized, there are typically two corresponding conductor members arranged at the connector end of the guide wire for coupling the sensor signal carried by one of the leads to the external monitor, and for connecting the other lead to a common ground. An insulating guide wire sheath extends along the guide wire and ends at a first conductor member, which couples the pressure signal out of the guide wire assembly. Adjacent to the first conductor member is the insulator separating the first conductor member from a second conductor member, which is connected to ground, or some other appropriate reference potential. As previously described, bodily fluids will deteriorate the insulating capacity of the insulator, but by applying the guard potential to the insulator by means of an electrode, the potential difference across the insulator, with respect to the adjacently located conductor member to which the signal carrying lead is connected, is reduced and the corresponding leakage current will be reduced accordingly. This is highly advantageous, as the problem relating to unreliable sensor values due to leakage currents in the connector is eliminated.
According to further embodiments of the present invention, which are advantageous when the guide wire sheath is conductive, an additional guard potential is applied. When the guide wire sheath is conductive, an additional insulator must be used. This additional insulator is located adjacent to the guide wire sheath, i.e. between the guide wire sheath and a conductor member. The insulating capacity of the additional insulator may, for reasons previously described, also deteriorate when bodily fluids, dirt, fat, moist, etc. are disposed on the connector. More general problems causing deterioration, for example manufacturing defects, may also be overcome by the present invention. To reduce a potential difference across the insulator arranged adjacent to the guide wire sheath, such that leakage current is reduced, the additional guard potential is applied to the additional insulator or the guide wire sheath by means of an additional electrode. The application of the guard potential to the guide wire sheath has the further advantage that a potential reducing effect can be utilized at a distal part of the guide wire, towards the sensor. Suppose a deterioration in insulating capacity occurs between an electrical lead and the guide wire sheath; a leakage of current will then occur between the lead and the guide wire sheath. This current will be reduced in the same manner as at the insulator(s) arranged at the guide wire proximal end, by applying the guard potential to the guide wire sheath.
Preferably, the previously described guard potential and the additional guard potential of the present embodiment are set to be the same potential, derived from the same drive element. Said electrode and said additional electrode will hence be driven from the same potential.
According to another embodiment of the invention, a sensor electrode is arranged at a conductor member located adjacent to an insulator across which a potential difference is to be reduced. The voltage of the signal at the conductor member can hence be measured and supplied as guard potential. By measuring the signal voltage level at the conductor member of interest, the voltage level of the guard potential can be set to be identical to the signal voltage level, which has as a result that the potential difference across the insulator(s) can be reduced to a minimum. By means of sensing the signal voltage level and providing a guard potential based on that level via the electrodes arranged to supply the guard potential, a closed loop control system for controlling leakage current is provided.
According to another embodiment of the present invention, which advantageously can be employed in case two or more signals are transferred via respective signal leads and the guide wire has a conductive sheath as previously described, an averaged signal is employed as guard potential via the guard potential electrodes.
In the following, it is assumed that a first lead carries a pressure signal, a second lead carries a temperature signal and a third lead is set to a reference potential, typically ground. In case of three leads, there are typically three corresponding conductor members arranged at the connector end of the guide wire for coupling the sensor signals carried by two of the leads to the external monitor, and for connecting the third lead to a common ground. A conductive guide wire sheath extends along the guide wire and ends at a first insulator, which insulates the sheath from the first conductor member located on the other side of the first insulator, along the guide wire axis. The first insulator couples the pressure signal out of the guide wire assembly. Adjacent to the first conductor member is a second insulator separating the first conductor member from the second conductor member, which couples the temperature signal out of the guide wire assembly. A third insulator insulates the second conductor member from the third, grounded conductor member. In this particular embodiment, two sensor signals (plus a common ground) are transferred along the guide wire, but it should be noted that any other number of sensor signals may be transferred, and the principle of this embodiment may be applied to said any number of sensor signals.
The potentials at the first and second conductor members generally have the same voltage level, which has the effect that no leakage current will flow through the second insulator separating the first and second leads, since no potential difference is present across the second insulator. However, due to bodily fluids there will be a potential difference across the first insulator located between the first conductor member and the guide wire sheath, as well as across the third insulator located between the second conductor member and the third, grounded conductor member. As a consequence, there will be leakage currents via the first and the third insulators, respectively.
By sensing a voltage level of a signal at a conductor member located adjacent to a respective insulator across which a potential difference is to be reduced, i.e. at the first and the second conductor members, by means of a sensing electrode, creating an averaged signal having as a voltage level an average value of the two sensed voltage levels, and supplying said averaged signal as guard potential via a guard potential electrode to the third insulator and either (a) the first insulator or (b) the guide wire sheath, the potential difference across the first and the third insulators is reduced and the corresponding leakage current will be reduced accordingly.
According to yet a further embodiment of the present invention, as an alternative to measuring a voltage level of a signal at a conductor member by means of a sensor electrode, the voltage level in question may be estimated, and the estimated voltage level may be supplied as guard potential for reducing leakage current. Possibly, the voltage level at the contact member is known empirically or by know-how regarding the sensor. In that case, there is no need to measure the signal, and hardware associated with the measurement may be omitted. By means of estimating the signal voltage level and providing a guard potential based on that level via the guard potential electrode(s), an open loop control system for controlling leakage current is provided.
When using the approach of estimating the signal voltage level instead of actually measuring the signal level, it is still possible to use an averaged signal as guard potential, as described above. If two or more signals are transferred via respective signal leads and the guide wire has a conductive sheath, and the estimating approach is employed, the averaged signal is calculated by taking the average value of the estimates of the signal voltage levels at the respective conductor member. Subsequently, the averaged signal is supplied as guard potential.
In still another embodiment of the present invention, the sensed voltage level is low pass filtered, such that a DC voltage level is provided as guard potential. This is advantageous in case the sensor signal, i.e. the signal representing a measured physiological variable, is used to modulate a carrier signal, the modulated signal being received at a corresponding conductor member.
According to still a further embodiment of the present invention, a voltage regulating circuit is arranged for setting and supplying the guard potential to (i) a first insulator across which a potential difference is to be reduced, (ii) a first and a second insulator across which a potential difference is to be reduced, or (iii) a first insulator across which a potential difference is to be reduced and the guide wire sheath arranged adjacent to a second insulator across which a potential difference is to be reduced. Preferably, the voltage regulating circuit for supplying the guard potential acts as a buffer and hence has a (very) high input impedance and a (very) low output impedance. Hence, the sensed signal voltage levels may be connected to the insulators or the sheath via this voltage regulating circuit, creating a closed loop control system. In an embodiment of the invention, the voltage regulating circuit for supplying the guard potential comprises an operational amplifier configuration, such as a voltage follower. In another embodiment of the present invention, the voltage regulating circuit for setting the guard potential comprises a microprocessor having an A/D-converter and a D/A-converter as an interface to the surrounding environment. In case a microprocessor is employed, the previously mentioned averaged signal can be created in the microprocessor by calculating an average value of the concerned signal voltage levels.
In yet another embodiment of the present invention, a sample and hold circuit is arranged at the input of the operational amplifier configuration for repeatedly sampling the voltage level supplied to the operational amplifier. In this embodiment, the guard potential is updated repeatedly by sampling the sensed signal at a particular instance of time and holding the value of the sampled signal by charging a capacitor until the next sample is taken. Sample and hold functionality may alternatively be implemented in the microprocessor. In an alternative embodiment, the guard potential is updated once, after insertion of the male connector into the female connector, by sampling the sensed signal at one instance of time and holding the value of the sampled signal by charging a capacitor.
Typically, the device for reducing leakage current in the guide wire assembly according to the present invention is arranged at a female connector for the guide wire assembly, such that the guard potential is applied to the insulator(s) when the male connector arranged at the connector end of the guide wire is inserted into the female connector to provide signals transferred via the signal leads to an external device.
Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. Those skilled in the art realize that different features of the present invention can be combined to create embodiments other than those described in the following.
Preferred embodiments of the present invention will be described in detail in the following with reference made to accompanying drawings, in which:
In
A distal end of the guide wire (not shown) is inserted into a body, for example into an opening into a femoral artery, and advanced to a desired location. At the distal end of the guide wire is a miniature sensor arranged for measuring physiological parameters such as pressure and temperature. Electrical leads extending inside, or along, the guide wire carry measurement signals from the sensor via the guide wire to the conductor members 104a, b and c. The conductor members are made from any material of high conductivity. Preferably, they are machined of platinum. Other possible materials include stainless steel, gold and copper, etc. The guide wire typically comprises a core wire (not shown), which extends through the guide wire, forming the guide wire center. The core wire is conventionally used to prevent kinks, to provide strength to the guide wire, and to hold the guide wire together. Traditionally, it is made of a high strength material, such as, for example, stainless steel. Other high strength materials (including non-metallic materials) can be used. The core wire therefore should be as large a diameter as possible, while leaving room for the leads and other elements to fit within the catheter within which the guide wire will be used.
With reference to
While the guide wire assembly has been described with reference to a male and a female connector having three contact members, it is to be understood that the number thereof is not critical. Also, said number must not necessarily be the same as the number of conductors in the interface cable, and can thus be higher or lower as appropriate.
In practice, the device for applying the guard potential is arranged at the female connector for the guide wire assembly. As a consequence, the guard potential is applied to an insulator when the male connector of the guide wire is inserted into the female connector to provide signals, which are transferred via the signal leads, to an external device.
Note that it is possible to apply the guard potential Ud to the second insulator 811 instead of applying the voltage to the guide wire sheath 803. This will also reduce the potential difference across the second insulator 811 with respect to the conductor member 808. However, by applying the guard potential Ud to the guide wire sheath 803, a potential reducing effect can be utilized at the distal part of the guide wire, towards the sensor 801. Suppose a deterioration in insulating capacity occurs between any of the electrical leads 805, 806 and the guide wire sheath; a leakage of current will then occur, for example between the first lead 806 and the guide wire sheath 803. This current will be reduced in the same manner as at the insulator(s) arranged at the guide wire proximal end, by applying the guard potential Ud to the guide wire sheath 803. Hence, the concept of applying the guard potential Ud as described in this application may not only be used to reduce leakage currents at the male connector of the guide wire assembly, but along the entire length of the guide wire.
In the embodiments described in detail in connection to
Application of a guard potential Ud to the first insulator 909 by means of an electrode 910 will reduce a potential difference across the first insulator 909 with respect to the first conductor member 908 to which the signal carrying lead is connected. Hence, the corresponding leakage current will be reduced accordingly. Further, application of an additional guard potential, typically being the guard potential Ud applied to the first insulator 909, to the guide wire sheath 903 by means of an additional electrode 912 will reduce a potential difference across the second insulator 911 with respect to the third conductor member 932. Hence, the corresponding leakage current will be reduced accordingly. In this embodiment, two sensing electrodes 933, 934 are arranged to sense a voltage level of a signal at respective conductor members 908, 932 located adjacent to corresponding insulators 909, 911 across which a potential difference is to be reduced and to supply the sensed voltage to a voltage regulating circuit in the form of an operational amplifier 935.
In this particular embodiment, a low pass filter 936 is implemented at the input of the operational amplifier 935. Hence the signals of the electrodes 933, 934 are low pass filtered and added at the input of the amplifier. The output of the operational amplifier (a voltage follower configuration) is supplied as guard potential Ud via the electrodes 910, 912.
In a further embodiment shown in
Even though the invention has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art. The described embodiments are therefore not intended to limit the scope of the invention, as defined by the appended claims.
