Abstract:
An electrical device such as a pressure guide wire ( 700 ) which has a resistive pressure sensor, such as a piezoresistive sensor ( 208 ), uses a precision interconnect in order to provide proper pressure measurement readings. The precision interconnect helps avoid the effects of contact and line resistance on the measurement of the pressure sensor&#39;s resistors ( 402  and  404 ). The precision interconnect uses high input impedance device&#39;s such as differential operational amplifiers ( 902, 904 ) in order to overcome the effect of any changes in the contact resistance. Further, an interface switch ( 1110 ) which is responsive to a control signal ( 1106 ) automatically determines what type of pressure guide wire ( 10  or  700 ) is attached to the interface circuit ( 1200 ).

Description:
TECHNICAL FIELD 
     This invention relates in general to electrical devices, and more particularly, to an electrical device such as an intravascular pressure guide wire having a precision interconnect. 
     BACKGROUND 
     Medical guide wires having miniature pressure sensors are well known. Such pressure guide wires typically have a pressure sensor located at the guide wire&#39;s distal end that is used to measure the pressure within a patient&#39;s artery. Electrical conductors which are connected to the pressure sensor are passed through the inside of the guide wire to a set of electrical contacts or sleeves located at the proximal end of the guide wire. The electrical contacts on the guide wire are mated to external monitoring equipment using an interface cable. The external monitoring equipment can provide pressure information to the attending physician that is useful in the diagnosis for example of an arterial occlusion. An example of such a pressure guide wire is described in U.S. Pat. No. 5,715,827, entitled “Ultra Miniature Sensor and Guide Wire Using The Same and Method”. 
     In FIG. 1 there is shown a prior art pressure measuring system  100  comprising a guide wire  10  placed within a patient  12 . The guide wire  10  is used with apparatus  20  that comprises rotary connector assembly  220  and a cable  214  that connects the rotary connector assembly  220  to an interface box  24 . Connector  32  which is part of the rotary connector assembly  220  electrically interconnects with interface box connector  34 . 
     Interface box  24  is connected by cable  26  to a pressure monitoring console  28 , such as a WAVEMAP™ pressure monitoring instrument manufactured by EndoSonics, Inc., Rancho Cordova, Calif. Console  28  can display both proximal and distal pressure measurements as will has controls for calibrating the pressure wire  10  prior to its usage. 
     Referring now to FIG. 2, there is shown a more detailed view of the prior art pressure guide wire  10  coupled to a rotary connector assembly  220 . As shown therein, pressure guide wire  10  can be manufactured utilizing the various constructions as shown and described in U.S. Pat. Nos. 5,163,445, 5,178,159 and 5,240,437. Guide wire  10  comprises a flexible elongate element  202  having a proximal and distal extremities  204  and  206  and which can be formed of suitable material such as stainless steel. The guide wire having an outside diameter for example of 0.018 inch or less and having a suitable wall thickness as for example, 0.001″ to 0.002″ and conventionally called a “hypotube” having a typical length of approximately 150-170 centimeters. A semiconductor pressure sensor  208  is located at the distal extremity of guide wire  10 . 
     The proximal end of guide wire  10  is slid into a rotary connector  210  of the type described in U.S. Pat. Nos. 5,178,159 and 5,348,481 which is part of the rotary connector assembly  220 . A torquer  230  is typically clipped-on by a physician distal to the rotary connector  210 . Rotation of the torquer  230  causes rotation of guide wire  10  when used in connection with a catherization procedure in a manner well known to those skilled in the art. The proximal extremity  204  of the guide wire  10  is removably disposed within housing  212  of the type described in U.S. Pat. Nos. 5,178,159, 5,348,481 and 5,358,409. Located close to the distal extremity of guide wire  10  is a pressure sensor  208  which is used to measure pressure within a patient&#39;s blood vessels. 
     Electrical contacts located within housing  212  make electrical contact with electrically conductive sleeves (not shown in FIG. 2) located on the proximal extremity  204  of guide wire  10 . The electrical contacts located in housing  212  allow for rotation of the guide wire while maintaining electrical contact with the conductive sleeves found in guide wire  10 , these conductive sleeves are electrically coupled to pressure sensor  208 . The electrical contacts in housing  212  are electrically connected to cable  214  that terminates in connector  32 . 
     The connector  32  is connected to another mating connector  34  located on the interface box  24 . Interface box  24  provides signal buffering and voltage level adjustments between guide wire  10  and pressure monitoring console  28 . The electrically conductive sleeves  302 ,  304  and  306 , which are located at the proximal extremity of guide wire  10 , are shown in FIG.  3 . 
     In FIG. 4 there is shown an electrical schematic representation of the pressure sensor  208  which comprises two variable resistors  402  and  404  whose resistance values vary with changes in pressure as is known in the art. Pressure sensor  208  can be a semiconductor having a diaphragm as is well known in the art. The two resistors  402  and  404  are connected to the three electrically conductive sleeves or bands  302 ,  304  and  306  located on the proximal extremity of guide wire  10  as shown. 
     FIG. 5 shows an exploded isometric view of the prior art rotary connector assembly  220  including rotartary connector  210  and housing  212 . In operation, the proximal extremity of the flexible elongate member or pressure guide wire  10  is inserted into bore  501  with one hand while holding the rotary connector with the other hand. The nose piece  503  and the collar  504  are then pulled with fingers in a proximal direction against the force of the spring  508  to release the collet  502  and allow it to open. The guide wire  10  can then enter the bore  501  and pass through the inside of collet  502  and through bearing  510 . The guide wire  10  is then pushed further in until conductive sleeve  302  is making electrical contact with contact member  546 , conductive sleeve  304  is making electrical contact with contact member  544  and conductive sleeve  306  is making electrical contact with contact member  542 . 
     Housing members  514  and  530  retain contacts  542 ,  544  and  546 . A retaining ring  506 , which is inserted through an opening in bearing  510 , engages with and retains collet  502 . Connector  32  provides an interconnection with the interface box  24  through a cable as shown in FIG.  1 . 
     A problem with the above noted design is that sometimes as the guide wire  10  is being rotated, the contact resistance between electrically conductive sleeves  302 ,  304  and  306  located on the guide wire  21  and the corresponding electrical contacts located in housing  212  varies. This contact resistance variation is assumed to be caused by microscopic particles that get lodged between the pressure guide wire&#39;s conductive bands  302 ,  304  and  306  and the corresponding spring contacts  546 ,  544  and  542 . This change in contact resistance causes an error in the pressure measurement as determined by pressure monitoring console  28 , since this change in contact resistance affects the measurement of pressure sensor resistors  402  and  404 . 
     An electrically equivalent circuit showing this change in contact resistance is shown in FIG.  8 . Pressure sensor  208  is shown coupled to sleeve contacts (conductive bands)  302 ,  304  and  306  via electrical conductors. Sleeve contact  302  is shown coupled to contact  546 , sleeve contact  304  is shown coupled to contact  544  and sleeve contact  306  is shown coupled to contact  542 . Variable resistors  802 ,  804  and  806  represent the variable contact resistance caused by the rotating connector interface. The resistance of resistors  802 ,  804  and  806  vary as the pressure guide wire is rotated. As shown, contact resistance  802  is in series with sensor resistor  402  and contact resistance  806  is in series with sensor resistor  404  and thus any change in the contact resistance will affect the measurement of sensor  208 . A need thus exists in the art for a solution that can minimize electrical interconnection problems as the one described above. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features of the present invention, which are believed to be novel, are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in conjunction with the accompanying drawings, in the several figures of which like reference numerals identify like elements, and in which: 
     FIG. 1 is an illustration showing a prior art guide wire in conjunction with a patient undergoing a catheterization procedure for diagnosis or treatment. 
     FIG. 2 shows a more detailed view of the prior art guide wire attached to a rotating connector assembly. 
     FIG. 3 shows the prior art guide wire showing the electrically conductive sleeves located at the proximal extremity of the guide wire. FIG. 4 shows an electrical representation of the prior art pressure sensor attached to the electrically conductive sleeves. 
     FIG. 5 shows an exploded view of the prior art rotary connector and housing used to receive the pressure guide wire. 
     FIG. 6 shows a housing having contacts in accordance with the present invention. 
     FIG. 7 shows a view of a pressure guide wire in accordance with the invention. 
     FIG. 8 shows an electrical representation of the prior art electrical interconnection between the guide wire and the rotary connector. 
     FIG. 9 shows an electrical representation of the electrical interconnection between the guide wire and rotary connector in accordance with the invention. 
     FIGS. 10 and 11 show electrical schematics for the interface circuit in accordance with the present invention. 
     FIG. 12 shows a simplified block diagram of the electrical schematics shown in FIGS. 10 and 11 in accordance with the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     While the specification concludes with claims defining the features of the invention that are regarded as novel, it is believed that the invention will be better understood from a consideration of the following description in conjunction with the drawing figures, in which like reference numerals are carried forward. 
     Referring now to FIG. 6, there is shown an electrical contact assembly  600  in accordance with the invention. Assembly  600  includes first and second housing members  602  and  604  that retain five guide wire spring contacts  606 - 614 . Assembly  600  takes the place of housing members  514  and  530  and contacts  542 ,  544  and  546  in FIG.  5 . In FIG. 7, there is shown a pressure guide wire  700  in accordance with the invention. Similar to guide wire  10 , pressure guide wire  700  includes three conductive sleeves or contacts  702 ,  704  and  706 . However, unlike guide wire  10 , the two outer contacts  702  and  706  are wider than the middle contact  704 . The wider sleeve contact  702  and  706  are designed so that they can make contact with two corresponding contacts each from among contacts  606 - 614 . Guide wire sleeve contact  702  is designed to make an electrical connection with contacts  606  and  608  and sleeve contact  706  makes electrical connection with contacts  612  and  614  when guide wire  700  is placed in assembly  600 . The center guide wire sleeve contact  704  makes electrical connection with center contact  610 . Housing assembly  600  has been designed to be backward compatible and will accept either the newly designed guide wire  700  or the prior art guide wire  10 . When guide wire  10  is inserted into assembly  600 , sleeve contact  306  makes connection with contact  612 , sleeve contact  304  makes connection with contact  610  and sleeve contact  302  makes connection with contact  608 . 
     In FIG. 9, there is shown a simplified electrical representation of the preferred embodiment precision interconnect circuit which solves for the variable contact resistance&#39;s and provides for backward compatibility with both the old pressure guide wire  10  and the new pressure wire  700 . The pressure sensor  208  is coupled to sleeve contacts  702 ,  702 ′,  704 ,  706  and  706 ′ when a new pressure guide wire  700  is being used. When an old pressure guide wire  10  is being used, contacts  702 ′ and  706 ′ are not utilized since the outer sleeve contacts are not as wide as those shown in pressure wire  700 . In FIG. 9, contacts  702 ′ and  706 ′ are simply representing the extra wide sleeve contacts found in contacts  702  and  706  as shown in FIG.  7 . 
     The variable contact resistance problem of the interconnection is highlighted within box  920 . Sleeve contacts  702 ′,  702 ,  704 ,  706  and  706 ′ are coupled to corresponding contacts  614 ,  612 ,  610 ,  608  and  606  in the new design which form the input port for the interconnection circuit. When an old pressure guide wire  10  is attached, contacts  614  and  606  are not utilized. Switches  910  and  912  remain in the open position or first state when a new guide wire  700  is attached and are automatically placed in the closed position or second state when an old guide wire  10  is attached in response to a control signal. The control electronics for switches  910  and  912  will be discussed in detail further below. Switches  910  and  912  allow for the interconnect interface to be backward compatible and support both pressure guide wire  10  and the new pressure guide wire  700 . In the interconnection interface, new pressure guide wire  700  uses a 5-wire interconnection, while the old pressure guide wire uses a 3-wire interconnection. A pair of differential operational amplifiers or precision amplifiers  902  and  904  that have high impedance inputs and are part of the interface circuit allow for three low current paths. These paths take away the effect of changes in the contact resistance ( 924 ,  926  and  928 ) from changes in the sensor resistors  402  and  404 . A reference current is provided to the sensor resistor  402  and  404  as shown in order to generate the appropriate voltage drops used for pressure change detection. 
     Referring now to FIGS. 10 and 11, there is shown a full electrical schematic for the interface circuit which replaces the electronics found in interface box  24 . The circuitry shown in FIGS. 10 and 11 includes not only the circuitry needed to perform the precision interconnection as described above, but also provides the necessary signal conditioning circuitry needed to match the signal from the pressure sensor  208  to the pressure measurement console  28 . The signal conditioning circuitry will not be discussed in detail since it is not needed in the understanding of the present invention. 
     The circuit shown in FIG. 10 is the mother board and the circuit shown in FIG. 11 is a daughter board which in the preferred embodiment comprise two separate printed circuit boards which are coupled together. The two circuit boards are coupled together using jack connectors J 1  and J 2  found in the circuit of FIG. 10 which mate with corresponding plug connectors P 1  and P 2  located on the circuit of FIG.  11 . 
     Connector “JP2”  1002  in FIG. 10 is coupled to the pressure sensor resistors  402  and  404  which are coupled through via connectors  32  and  34  into the interface circuitry. The five sensor contacts are coupled to pins  2 ,  4 ,  6 ,  8  and  10  of connector JP2 as shown in diagram  1014 . Differential amplifiers  902  and  904  as previously shown in FIG. 9 that are part of amplifier stage  1008 , provide a gain of approximately two. The output of these amplifiers are fed into a 2 pole, 250 Hertz low pass filter (LPF) stage  1012  which provides for a gain of approximately twenty. The outputs of the LPF stage  1012  are coupled to connector “JP1”  1010  that in turn couples into the pressure monitoring console  28 . Pins  7  and  9  of connector JP1 are inputs to the pressure monitoring console, while pins  1 ,  2 ,  4 ,  6 ,  8 ,  10 ,  14 ,  15  and  16  are signals coming from the pressure console  28  into the interface circuitry. Although not important to the understanding of the present invention, circuit block  1004 , provides offset voltage correction for the interface between the pressure guide wire  700  and the pressure monitoring console  24 . Box  1016  shows the internal interconnections of connector J 2 . 
     In FIG. 11, operational amplifiers U 5 A, U 1 A and U 1 B form a buffer stage  1108  that provides signal buffering. Block  1104  forms an oscillator circuit that provides a signal of about 10-12 kilohertz. This signal is used to determine whether an old pressure guide wire  10  or a new pressure guide wire  700  is coupled to the interface circuitry in accordance with the present invention. A synchronous demodulator circuit  1102  takes the oscillating signals and provides a control signal  1106  that is used to control switches  910  and  912 . Switches  910  and  912  remain open when pressure sensor  700  is attached and are closed when pressure wire  10  is attached. The output of demodulator circuit  1102  passes through a two pole 30 Hertz low pass filter stage  1112  having a gain of approximately thirty. 
     FIG. 12 shows a simplified block diagram of the electrical schematics of FIGS. 11 and 12 as interface circuit  1200 . Pressure wire  700  is coupled to connector  1002  that is in turn coupled to the interface switch circuit  1110  comprising the two digital switches  910  and  912 . The output of the digital switches is passed through a buffer stage  1108  prior to being sent to the differential amplifier stage  1008  comprising differential amplifiers  902  and  904 . The output of the differential amplifier stage  1008  is sent to the 2 pole 250 Hertz low pass filter stage  1012  before the signals are sent to console  28 . A reference voltage generator stage  1202  provides the necessary voltages to the circuit. 
     As previously mentioned in order to provide for backward compatibility between the old pressure wire  10  and the new pressure wires  700 , an oscillator  1104  and demodulator  1102  are used to provide a control signal  1106  which either closes switches  910  and  912  or leaves them in the open position. When a new pressure wire  700  is detected, the control signal  1106  leaves the switches  910  and  912  in the open state, while if the old pressure wire  10  is detected control signal  1106  causes the switches to go to the closed state. By using a high frequency (10-12 Kilohertz) signal having low amplitude to make the switching determination between the 3-wire and 5-wire guide wires, prevents any stray noise and interference from affecting the control signal. Also, the use of such a low amplitude-oscillating signal prevents the signal from affecting the measurement of pressure sensor resistors  402  and  404 . 
     A large signal at capacitor C 2  causes control signal  1106  at the output of inverter  114  to be logic high closing the switches  910  and  912  indicating a 3-wire pressure wire  10  is connected to the interface circuit. While a low signal at capacitor C 2  caused by the connection of a 5-wire pressure wire  700  causes the control signal  1106  to be at a low logic level leaving switches  910  and  912  in the open position. 
     The present invention with its use of high input impedance differential amplifiers  902  and  904  to measure pressure sensor resistors  402  and  404  avoids the problem caused by changing contact resistance  922 - 930 . Also, the automatic switching technique disclosed above provides for a system which is backward compatible between pressure guide wires  10  and  700 . 
     While the preferred embodiments of the invention have been illustrated and described, it will be clear that the invention is not so limited. Numerous modifications, changes, variations, substitutions and equivalents will occur to those skilled in the art without departing from the spirit and scope of the present invention as defined by the appended claims. For example, although the preferred embodiment has discussed forming a precision interconnect for a rotating connection, the present invention is not so limited and can be used for non-rotating connections. The present invention can be used for not only with a pressure guide wire it can be used with other devices that need proper measurement of electrical parameters from the device. Also, instead of monitoring a pressure sensor  208  utilizing two resistors  402  and  404 , the present invention can be used to provide a precision interconnect for devices having any number of resistors. If the number of resistors that need to be monitored change, a change has also to be made as to the number of monitoring devices such as differential op-amps  902  and  904  need to be used.