as seen in fig1 a catheter 10 has a catheter body 12 with an elongated axis 15 having at least one sensing site 14 . as will be used in the present description , a catheter 10 is generally an elongated tube or device for either measuring a physiological condition , or sampling a fluid or tissue . in the preferred embodiment , the catheter body 12 is made from a physiologically acceptable material , e . g ., polyvinyl chlorate or silicone rubber . such catheter bodies are available from microvasive , boston , mass . each sensing site 14 is covered by a film 16 that prevents the sensing site 14 from coming into direct contact with a vertebrate body . as will be understood by those skilled in the art , the catheter 10 may be banded with the film 16 covering only the sensing site 14 , or the film 16 may be formed as a sleeve covering the entire catheter body 12 . in the preferred embodiment , the film 16 is made of silicon . in an alternative embodiment ( fig2 a ), the film 16 is permeable to allow conditions such as ph , glucose , temperature , and water to interact with the sensing site 14 . as seen in fig2 the catheter body 12 defines a lumen 18 in fluid communication with a catheter recess 20 defined in the catheter body 12 . a conductive member 22 is carried in the lumen 18 and is approximately coextensive therewith ( fig3 and 4 ). in the preferred embodiment , the conductive member 22 is stranded copper wire , however , those skilled in the art will understand that other conductive members 22 may be carried by the catheter body 12 . in an alternative embodiment , solid core copper wire is used as the conductive member 22 . in another alternative embodiment , copper traces ( not shown ) deposited on a non - conductive polymer strip ( not shown ) are used as the conductive member 22 . the conductive member 22 carries power to and data from a piezoresistive sensor 24 that is acted on by a vertebrate condition . in the preferred embodiment , the sensor 24 is about 1 . 74 to 1 . 76 mm long , about 1 . 74 to 1 . 76 mm wide , and about 0 . 24 to 0 . 26 mm deep . the sensor 24 has a bottom surface 29 and a top surface 26 defining a trough 28 therein . the trough 28 has a trough floor 30 that is deformable according to pressures exerted upon the floor 30 by a mechano - responsive element , i . e ., a fluid 32 or a gel 32 a . as is used in the present description , the term “ mechano - responsive element ” will be understood to mean an element 32 , 32 a that has a measurable physical response in proportion to a condition influencing the element 32 , 32 a . in the preferred embodiment , the sensor 24 is made from piezoresistive material , e . g ., silicon and silicon dioxide . the sensor 24 has at least one bonding pad 34 affixed to the bottom surface 29 . in the preferred embodiment , the bonding pad 34 is a eutectic solder having about a 63 / 37 lead / tin composition . in an alternative embodiment , indium solder is used as for the bonding pad 34 . in another alternative embodiment , a conductive polymer such as silver epoxy is used for the bonding pad 34 . the sensor 24 is bonded to an application specific integrated circuit 36 by a method of low temperature thermal compression bonding known in the art . the sensor 24 is thereby directly electrically coupled to the circuit 36 with the bonding pads 34 . the circuit 36 is directly electrically coupled to the conductive member 22 carried by the catheter body 12 . in the preferred embodiment , the conductive member 22 is comprised of about two to six stranded copper wires bonded to the integrated circuit 36 that are soldered to the circuit 36 . in an alternative embodiment , the conductive member 22 is attached to the circuit 36 by press contacting . in the most preferred embodiment , the conductive member 22 has separate high and low power input wires , separate high and low signal output wires , and a clock wire used as a toggle to step through plural sensing sites 14 . the sensor 24 is positioned within the catheter body 12 so that the trough 28 opens upwardly through the catheter recess 20 . in the preferred embodiment , the catheter 10 has up to about thirty - two sensing sites 14 positioned along the catheter axis 15 . each sensing site 14 has a sensor 24 directly electrically coupled to a circuit 36 by at least one bonding pad 34 . in the preferred embodiment , catheter 10 is connected to a computer based data acquisition system ( not shown ) that supplies power to and receives vertebrate condition data from the sensing site 14 via the conductive member 22 . the circuit 36 is monolithically incorporated with the sensor 24 so the circuit 36 amplifies an electrical signal from the sensor 24 and multiplexes signals received from multiple sensors 24 by a simple count and select scheme known in the art so as to minimize the number of conductive members 22 affixed to the circuit 36 and , thereby , reduce the diameter of the catheter 10 . the mechano - responsive element , i . e ., a fluid 32 or a gel 32 a , is located in the sensor trough 28 so that it substantially fills the trough 28 and the catheter recess 20 . in the preferred embodiment , the fluid 32 is silicon oil , used to measure vertebrate pressures . the fluid 32 rises above the outer surface 38 of the catheter body 12 and is sealed with the film 16 so that the fluid 32 bulges above the surface 38 so that no air bubbles are trapped at the sensing site 14 , thereby substantially eliminating measurement error caused by trapped air bubbles . the catheter 1 0 with the fluid 32 is able to measure pressures in the range of about − 50 to + 300 mmhg exerted upon the sensing site 14 . sensed pressure is transferred via the fluid 32 to the sensor floor 30 , which deforms in proportion to the pressure exerted . in an alternative embodiment , as seen in fig2 a , the gel 32 a , e . g ., a polyester gel , a polyamide gel , or a hydrogel , is responsive to non - pressure vertebrate conditions , e . g ., temperature , water , glucose , ph . the gel 32 a is placed in the sensor trough 28 and catheter recess 20 , and sealed by the catheter film 16 , so it does not bulge above the outer surface 38 of the catheter body 12 . the gel 32 a generally swells or shrinks in volume when acted on by non - pressure conditions , thereby changing pressure the gel 32 a exerts on the sensor floor 30 in proportion to the vertebrate condition . in this embodiment , the catheter film 16 covering the sensing site 14 is permeable to allow the vertebrate condition to interact with the gel 32 a , as shown by directional arrows c ( fig2 a ). each sensing site 14 on a catheter 10 having plural sensing sites 14 can measure a different vertebrate condition by multiplexing signals from different sensing sites 14 and using a simple count and select scheme . for example , temperature may be measured in conjunction with any of the other measurements by interrogation of the circuit elements employed in a temperature circuit . for example , diodes with a negative temperature coefficient are included as part of a constant voltage delivery circuit contained on the circuit 36 . these diodes deliver an increase in voltage with temperature to a bridge network . the diodes can be monitored to measure temperature . other variations of the structure will be apparent to a person of ordinary skill in the art in view of other patents such as u . s . pat . nos . 4 , 274 , 423 and 4 , 722 , 348 , the disclosures of which are incorporated herein by reference . additional advantages and modifications will readily appear to those skilled in the art . the invention in its broader aspects is therefore not limited to the specific detail , representative apparatus and illustrative example shown and described . this has been a description as the present invention is currently known . however , the invention itself should only be defined by the appended claims .
a catheter for sensing vertebrate conditions has plural piezoresistive sensors directly electrically coupled to discrete application specific integrated circuits . a mechano - responsive element is in pressure sensitive relationship with the piezoresistive sensor to act as a transfer medium through which vertebrate conditions such as pressure , temperature , water , glucose , and ph are transferred . each integrated circuit is electrically coupled to a data acquisition system with monolithic circuitry in order to amplify and multiplex signals from multiple sensors .