Combined flow, pressure and temperature sensor

Abstract

The invention relates to a device for measuring pressure, temperature and/or flow velocity. It includes a sensor ( 6 ) with a sensor support body ( 13 ) provided with a diaphragm ( 15 ) covering a cavity ( 14 ) formed in the support body ( 13 ). A pressure sensitive element ( 41 ) is mounted on the diaphragm, for recording pressure. Furthermore, a temperature sensitive resistor ( 42 ) is mounted in the vicinity of the pressure sensitive resistor and has a known temperature dependence, for recording temperature. It also includes an electrical circuit ( 43, 44, 45, 46 ) selectively outputting signals from either of the pressure sensitive element and the temperature sensitive resistor.

1. A device for determining pressure, temperature and a flow parameter of a flowing fluid, comprising
 i) a sensor support body ( 13 ) mounted for insertion into a vessel of a living body and having a diaphragm ( 15 ) covering a cavity ( 14 ) formed in said support body ( 13 );  
 ii) a pressure sensitive element ( 41 ), having a known temperature dependence, mounted on said diaphragm ( 15 ), and providing an output indicative of a pressure;  
 iii) a temperature sensitive resistor ( 42 ) mounted in the vicinity of said pressure sensitive element ( 41 ) and having a known temperature dependence, providing an output signal indicative of a temperature, said resistor ( 42 ) also functioning as a temperature reference means for said pressure sensitive element ( 41 ); and  
 iv) an electrical circuit ( 43 ,  44 ,  45 ,  46 ), connected to the pressure sensitive element and to the temperature sensitive resistor, for calculation of a flow parameter of said flowing fluid on the basis of the temperature signals.  
 
     
     
       2. The device of  claim 1 , wherein said electrical circuit comprises a double Wheatstone bridge, including a first ( 42 ,  43 ,  44 ,  46 ) and a second ( 41 ,  42 ,  45 ,  46 ) bridge, said two bridges having two resistors in common, whereby the first bridge comprises said temperature sensitive resistor ( 42 ), and the second bridge comprises the pressure sensitive element ( 41 ) and said temperature sensitive resistor ( 42 ). 
     
     
       3. The device as claimed in  claim 1 , comprising a Wheatstone bridge, wherein the output from the bridge is indicative of pressure, and the total impedance of the bridge is indicative of temperature. 
     
     
       4. The device as claimed in  claim 1 , wherein both the pressure sensitive element ( 41 ) and the temperature sensitive resistor ( 42 ) are located on said diaphragm ( 15 ). 
     
     
       5. The device as claimed in  claim 1 , wherein only the pressure sensitive element ( 41 ) is located on said diaphragm ( 15 ) and the temperature sensitive resistor ( 42 ) is located on said sensor support body ( 13 ). 
     
     
       6. The device as claimed in  claim 1 , wherein the temperature sensitive resistor ( 42 ) is mounted on a dummy diaphragm, having essentially the same properties as the diaphragm ( 15 ) on which the pressure sensitive element is located. 
     
     
       7. The device as claimed in  claim 1 , attached at the distal end of a guide wire having a proximal and a distal end. 
     
     
       8. The device as claimed in  claim 1 , further comprising means for temperature compensation in the pressure measurement mode, such that the recorded potential representing a pressure is modified by adding or subtracting from said recorded potential, a known off set potential value depending on temperature. 
     
     
       9. The device as claimed in  claim 1 , wherein the pressure sensitive element ( 41 ) is of a piezoresistive type. 
     
     
       10. The device as claimed in  claim 1 , wherein the pressure sensitive element ( 41 ) is of a capacitive type. 
     
     
       11. The device as claimed in  claim 1 , wherein the pressure sensitive element ( 41 ) is a mechanically resonant sensor. 
     
     
       12. The device of  claim 1 , further including a selective power supply power connected to said temperature sensitive resistor to heat the temperature sensitive resistor to a predetermined temperature, and a temperature deviation determinator. 
     
     
       13. A guide wire and sensor assembly for determining pressure, temperature and a flow parameter of a fluid flowing in a living body, comprising
 i) a guide wire ( 2 ) having a distal and a proximal end;  
 ii) a sensor element ( 6 ) provided at the distal end of said guide wire, said sensor element comprising 
 a) a sensor support body ( 13 ) provided with a diaphragm ( 15 ) covering a cavity ( 14 ) formed in said support body;  
 b) a pressure sensitive element ( 41 ) having a known temperature dependence and mounted on said diaphragm ( 15 ), recording pressure; and  
 c) a temperature sensitive resistor ( 42 ) mounted in the vicinity of said pressure sensitive element ( 41 ) and having a known temperature dependence, recording temperature, said resistor ( 42 ) also functioning as a temperature reference for the pressure sensitive element ( 41 ) and to provide temperature signals for calculation of a flow parameter; and  
 
 iii) an electrical circuit comprising a double Wheatstone bridge, including a first ( 42 ,  43 ,  44 ,  46 ) and a second ( 41 ,  42 ,  45 ,  46 ) bridge, said two bridges together comprising six resistive elements, said double Wheatstone bridge having two resistors in common, whereby the second bridge includes said pressure sensitive element ( 41 ) and said temperature sensitive resistor ( 42 ), and the first bridge includes the temperature sensitive resistor ( 42 ).  
 
     
     
       14. A guide wire and sensor assembly for determining pressure, temperature and a flow parameter of a fluid flowing in a vessel, comprising
 i) a guide wire ( 2 ) having a distal and a proximal end;  
 ii) a sensor element ( 6 ) provided at the distal end of said guide wire, said sensor element comprising 
 a) a sensor support body ( 13 ) provided with a diaphragm ( 15 ) covering a cavity formed in said support body ( 13 );  
 b) a pressure sensitive element ( 41 ) having a known temperature dependence and mounted on said diaphragm ( 15 ), recording pressure; and  
 c) a temperature sensitive resistor ( 42 ) mounted in the vicinity of said pressure sensitive element and having a known temperature dependence, recording temperature, said resistor also functioning as a temperature reference for the pressure sensitive element and to provide temperature signals for calculation of a flow parameter; and  
 
 iii) an electrical circuit selectively recording output signals from either of said pressure sensitive element and said resistor, said circuit comprising a Wheatstone bridge ( 51 ,  52 ,  53 ,  54 ), wherein the output from the bridge is indicative of pressure, and the total impedance of the bridge is indicative of temperature.  
 
     
     
       15. The method of claim  14    19 , wherein the flow of fluid comprises a primary and a secondary fluid, divided up in two sequential flows having different temperatures, the primary flow comprising blood, and the secondary flow being a fluid of substantially lower temperature than the blood. 
     
     
       16. The method of claim  15    19 , wherein a temperature profile is obtained by the continuous measurement of the temperature, and wherein the width at half height of said temperature profile is used as said flow parameter. 
     
     
       17. The method of claim  15    19 , wherein the time for the  cold fluid to pass the sensor element is used as said flow parameter. 
     
     
       18. The method of claim  15    19 , wherein the time of transit of the  cold fluid from the  a time of injection until it reaches said sensor element is used as said flow parameter. 
     
     
       19. A method of determining pressure, temperature and a flow parameter of fluid flowing in vessels, comprising the following steps:
 a) providing a pressure sensitive element and a resistor on a sensor element at a measurement site in a vessel of a living body, said pressure sensitive element and said resistor being part of an electric circuit yielding a pressure indicative output and a temperature indicative output, said pressure sensitive element and said resistor having known temperature dependencies, whereby the resistor is used as a reference for the pressure sensitive element;  
 b) subjecting said sensor element to flowing fluid and monitoring the pressure and temperature of said fluid by continuously recording said pressure indicative output and said temperature indicative output from said electric circuit;  
 c) subjecting said resistor to a changed thermal environment;  
 d) registering the change in said temperature indicative output resulting from said changed thermal environment; and  
 e) calculating a flow parameter from said change in said temperature indicative output.  
 
     
     
       20. The method of  claim 19 , including achieving said changed thermal environment by said fluid causing a temperature drop in said resistor, said flow parameter being a quantity proportional to the volume flow. 
     
     
       21. The method of  claim 20 , wherein the volume flow is calculated by integrating the temperature over time using the equation 
             Q   =       V   /       ∫   t0     t   1       ⁢       (       T   m     /     T   l       )     ⁢           ⁢     ⅆ   t           ∝     V   /       ∫     t   0       t   1       ⁢       (       T   o     -     T   m       )     ⁢           ⁢     ⅆ   t                     (   1   )             
 
       wherein
 V is the volume of injected liquid  
 T m  is the measured temperature  
 T 1  is the temperature of injected liquid  
 T 0  is the temperature of the blood, i.e. 37° C.  
 Q is the volume flow  
 t 0  is the point in time where a temperature change is detected  
 t 1  is the point in time where the temperature is regarded as having reached normal temperature.  
 
     
     
       22. The method of  claim 19 , wherein said changed thermal environment is achieved by said resistor being heated by passing a current through it, whereby said fluid cools said resistor such that the actual temperature of said resistor is lower than the expected temperature, that would have been obtained, had said resistor not been subjected to said flowing fluid, and calculating a flow parameter from said deviation from said expected temperature value, said flow parameter being a quantity proportional to the flow velocity. 
     
     
       23. The method of  claim 22 , wherein the flow velocity is calculated using the equation
   V=(h−C 0 ) 2 /C 1    
 
       wherein
   h=I 2 R w /A(T w −T f )  
 
       wherein
 I=wire current  
 R w =wire resistance  
 T w =wire temperature  
 T f =temperature of a flowing fluid  
 h=film coefficient of heat transfer  
 A=heat transfer area  
 V=flow velocity.  
 
     
     
       24. A method of diagnosing small vessel disease, comprising performing a measurement at a site in a vessel distally of a suspected stricture according to the following steps:
 a) providing a pressure sensitive element and a resistor on a sensor element at a measurement site, said pressure sensitive element and said resistor being part of an electric circuit yielding a pressure indicative output and a temperature indicative output, said pressure sensitive element and said resistor having known temperature dependencies, whereby the resistor is used as a reference for the pressure sensitive element;  
 b) subjecting said sensor element to flowing fluid and monitoring the pressure and temperature of said fluid by continuously recording said pressure indicative output and said temperature indicative output from said electric circuit;  
 c) subjecting said resistor to a changed thermal environment;  
 d) registering the change in said temperature indicative output resulting from said changed thermal environment; and  
 e) calculating a flow parameter from said change in said temperature indicative output; and  
 f) comparing the calculated flow parameter and the measured pressure with corresponding quantities representative of a healthy patient.  
 
     
     
       25. The method of  claim 24 , wherein said comparing step f) comprises comparing a flow parameter in a rest condition with a flow parameter in a work condition, and the pressure distally of a stenosis with the proximal pressure in a work condition. 
     
     
       26. A method of diagnosing small vessel disease, comprising performing measurements at a site in a vessel distally of a suspected stricture according to the following steps:
 a) providing a pressure sensitive element and a resistor on a sensor element at a measurement site, said pressure sensitive element and said resistor being part of an electric circuit yielding a pressure indicative output and a temperature indicative output, said pressure sensitive element and said resistor having known temperature dependencies, whereby the resistor is used as a reference for the pressure sensitive element;  
 b) subjecting said sensor element to flowing fluid and monitoring the temperature of said fluid by continuously recording said temperature indicative output from said electric circuit;  
 c) subjecting said resistor to a changed thermal environment;  
 d) registering the change in said temperature indicative output resulting from said changed thermal environment;  
 e) calculating a flow parameter (Q rest ) from said change in said temperature indicative output;  
 f) injecting a vaso dilating drug in said vessel to simulate a work condition;  
 g) monitoring the pressure (P work,dist ) and temperature of said fluid by continuously recording said pressure indicative output and said temperature indicative output from said electric circuit;  
 h) subjecting said resistor to a changed thermal environment;  
 i) registering the change in said temperature indicative output resulting from said changed thermal environment;  
 j) calculating a flow parameter (Q work ) from said change in said temperature indicative output;  
 k) determining the proximal pressure (P prox,work );  
 l) calculating 
   CFR=Q work /Q rest  and  
   FFR=P dist,work /P prox,work    
 
 j) comparing the calculated CFR and FFR with corresponding quantities representative of a healthy patient.  
 
     
     
       27. A device for biological pressure and temperature measurements, comprising:
 a guide wire;  
 a pressure sensor mounted on the guide wire;  
 a temperature sensor mounted on the guide wire in the vicinity of the pressure sensor; and  
 an electronic circuit to generate and output an indication of temperature based on signals from the temperature sensor.  
 
     
     
       28. A device as set forth in  claim 27 , further comprising a sensor support body and wherein the pressure sensor and the temperature sensor are both mounted to said sensor support body. 
     
     
       29. A device as set forth in  claim 27 , further comprising a chip and wherein the pressure sensor and the temperature sensor are both mounted to said chip. 
     
     
       30. A device as set forth in  claim 27 , further comprising a silicon chip and wherein the pressure sensor and the temperature sensor are both mounted to said silicon chip. 
     
     
       31. A device as set forth in  claim 27 , further comprising a substrate and wherein the pressure sensor and the temperature sensor are both mounted to said substrate. 
     
     
       32. A device as set forth in  claim 27 , wherein the pressure sensor senses pressure at the same time the temperature sensor senses temperature. 
     
     
       33. A device as set forth in  claim 27 , wherein the pressure sensor includes a diaphragm. 
     
     
       34. A device as set forth in  claim 33 , wherein the temperature sensor is located off of the diaphragm. 
     
     
       35. A device as set forth in  claim 27 , wherein the electronic circuit also generates a profile of temperature versus time. 
     
     
       36. A device as set forth in  claim 35 , wherein the electronic circuit also generates flow information based on said profile.