Methods and apparatus for real time fluid analysis

• US 6,286,360 B1
• Filed: 02/25/2000
• Issued: 09/11/2001
• Est. Priority Date: 02/25/1999
• Status: Expired due to Fees

• Current Assignee: Metasensors, Inc.
• Original Assignee: Metasensors, Inc.
• Inventors: Drzewiecki, Tadeusz M.
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): CYGAN, MICHAEL T
• Application Number:
  US09/513,315
• Time in Patent Office: 564 Days
• Field of Search: 73/540.2, 73/232, 73/240.1, 73/240.6, 73/240.5, 73/300.3, 73/542.4, 73/614.5, 73/614.7, 73/617.3, 738/616.1, 702/22, 702/23, 702/24, 702/25
• US Class Current: 73/24.01
• CPC Class Codes: A61B 5/083 Measuring rate of metabolism by using breath test, e.g. measuring rate of oxygen consumption
• CPC Class Codes: A61B 5/087 Measuring breath flow
• CPC Class Codes: A61B 5/097 Devices for facilitating collection of breath or for directing breath into or through measuring devices
• CPC Class Codes: G01N 2291/011 Velocity or travel time
• CPC Class Codes: G01N 2291/0215 Mixtures of three or more gases, e.g. air
• CPC Class Codes: G01N 2291/02818 Density, viscosity
• CPC Class Codes: G01N 2291/02836 Flow rate, liquid level
• CPC Class Codes: G01N 2291/02872 Pressure
• CPC Class Codes: G01N 2291/02881 Temperature
• CPC Class Codes: G01N 2291/0423 Surface waves, e.g. Rayleigh waves, Love waves
• CPC Class Codes: G01N 29/022 Fluid sensors based on microsensors, e.g. quartz crystal-microbalance [QCM], surface acoustic wave [SAW] devices, tuning forks, cantilevers, flexural plate wave [FPW] devices microdevices per se B81B
• CPC Class Codes: G01N 29/024 by measuring propagation velocity or propagation time of acoustic waves
• CPC Class Codes: G01N 29/4472 Mathematical theories or simulation

Abstract

A gas analyzer (10) integrated into the main passageway (11) of a breathing circuit includes pressure-drop flow element (12) that measures a pressure drop across an orifice, an acoustic flowmeter (14) measures the speed of sound in the gas mixture, and a SAW device (20) from which the viscosity of the gas mixture is determined. The dielectric constant of the gas mixture is determined from the capacitance of spaced-apart charged plates of a capacitor (22) through which the mixture passes. The gas mixture density is determined from the measured pressure drop and flow rate, while the gas mixture specific heat is determined from the density and speed of sound in accordance with known relationships. The individual concentrations of five constituents of a mixture of gasses can be determined by solving five equations relating the independently measured properties of the gas mixture to the individual constituent concentrations.

Claims

1. An apparatus for determining individual concentrations of at least L fluid constituents and identities of at least M fluid constituents of a mixture of fluids, where L and M are non-negative integers, the apparatus comprising:

a plurality of sensors adapted to measure physical characteristics of the mixture, said sensors including a pressure drop flow element which measures a pressure drop of the mixture across an orifice, an acoustic flowmeter which measures the speed of sound in the mixture and the flow velocity of the mixture, and a surface acoustic wave (SAW) device; and

a processor configured to;

determine values of N−

1 properties of the mixture from the measured physical characteristics, where N is equal to L+M;

establish N−

1 equations relating the individual concentrations of the fluid constituents to the N−

1 properties of the mixture; and

solve the N−

1 equations and a constitutive equation for the individual concentrations of L of the fluid constituents and for identities of M of the fluid constituents.

2. The apparatus of claim 1, wherein:

said processor calculates the viscosity of the mixture from a measured resonance of said SAW device;

said processor calculates the density of the mixture from said pressure drop and the flow velocity; and

said processor calculates the specific heat of the mixture from the density and the speed of sound, wherein said properties of the mixture include the density, viscosity and specific heat.

3. The apparatus of claim 2, wherein:

said sensors further include a capacitor whose capacitance varies in accordance with the dielectric constant of the mixture; and

said processor calculates the dielectric constant of the mixture from the capacitance, the dielectric constant being one of said properties of the mixture.

4. The apparatus of claim 2, wherein:

said sensors further include a refractive index sensor whose output varies in accordance with the refractive index of the mixture; and

said processor calculates the refractive index of the mixture from the output of the refractive index sensor, the refractive index being one of said properties of the mixture.

5. The apparatus of claim 2, wherein said plurality of sensors further includes:

a temperature sensor adapted to measure the ambient temperature of the mixture; and

a pressure sensor adapted to measure ambient pressure of the mixture.

6. The apparatus of claim 1, wherein the mixture of fluids comprises N fluids, and wherein said processor solves the N−

1 equations and the constitutive equation for the individual concentrations of the fluid constituents in real time.

7. The apparatus of claim 1, wherein the fluid constituents of the mixture of fluids are gasses respired during anesthesia administration.

8. The apparatus of claim 1, wherein, said mixture includes an N+1th fluid and said processor determines a combined concentration of two of said fluid constituents, said processor determining the individual concentrations of the two fluid constituents by determining changes in the combined concentration of the two fluid constituents over time.

9. The apparatus of claim 1, wherein:

the identity of one of the fluid constituents is initially unknown;

said processor establishes the N−

1 equations by assuming that the unknown fluid constituent is one of P fluids whose properties are known, where P is a positive integer;

said processor determines that the unknown fluid constituent is said one of the P fluids if the individual concentrations solved for fall within respective predetermined concentration ranges; and

if the individual concentrations solved for do not fall within the respective predetermined concentration ranges, said processor establishes N−

1 equations relating the individual concentrations of the fluid constituents to the N−

1 properties of the mixture by assuming the unknown fluid constituent is different ones of said P fluids and solves the N−

1 equations and a constitutive equation for the individual concentrations of the fluid constituents, until the individual concentrations solved for fall within the respective predetermined concentration ranges or until the unknown fluid constituent has been assumed to be every one of said P fluids.

10. The apparatus of claim 1, wherein:

the identity of one of the fluid constituents is initially unknown;

said processor determines a value of an Nth property of the mixture from the measured physical characteristics;

said processor establishes the N−

1 equations by assuming that the unknown fluid constituent is one of P fluids whose properties are known, where P is a positive integer;

said processor calculates a value of an Nth property of the unknown fluid constituent from an equation relating the Nth property of the mixture to individual concentrations of the constituent components, where the Nth property of the mixture is not used to establish the N−

1 equations;

said processor determines whether the calculated value of the Nth property of the unknown fluid constituent matches, to within a predetermined threshold, a known value of the Nth property of said one of the P fluids;

said processor determines that the unknown fluid constituent is said one of the P fluids if a match is found; and

if a match is not found, said processor establishes N−

1 equations relating the individual concentrations of the fluid constituents to the N−

1 properties of the mixture by assuming the unknown fluid constituent is different ones of said P fluids and solves the N−

1 equations and a constitutive equation for the individual concentrations of the fluid constituents, until a match is found or until a match has been attempted with all of said P fluids.

11. The apparatus of claim 1, wherein:

said mixture comprises P+N fluids, where P is a positive integer;

individual concentrations of P of the fluid constituents are known prior to establishing the N−

1 equations; and

said processor establishes the N−

1 equations relating the individual concentrations of the fluid constituents, including the known individual concentrations of the P fluid constituents, to the N−

1 properties of the mixture.

12. The apparatus of claim 1, wherein said processor determines the individual concentrations of L of the fluid constituents in real time.

13. The apparatus of claim 1, wherein the mixture of fluids comprises inhaled or exhaled gasses, and said processor determines at least one of uptake, consumption and production of inhaled or exhaled gasses.

14. The apparatus of claim 1, wherein said pressure drop flow element, said acoustic flowmeter and said surface acoustic wave (SAW) device are disposed within a main gas flow passage of a breathing circuit.

15. A method of determining individual concentrations of at least L fluid constituents and identities of at least M fluid constituents of a mixture of fluids flowing in a stream, where L and M are non-negative integers, the method comprising the steps of:

(a) measuring a pressure drop of the mixture with a pressure-drop device;

(b) determining mixture flow rate and the speed of sound in the mixture from acoustic flowmeter measurements;

(c) determining mixture viscosity from resonance of a surface acoustic wave (SAW) device;

(d) determining mixture density from the pressure drop, the mixture flow rate and the mixture viscosity;

(e) determining mixture specific heat from the mixture density and the speed of sound in the mixture;

(f) establishing at least three equations relating individual concentrations of the fluid constituents to at least three properties of the mixture, three of the at least three equations respectively relating the individual concentrations of the fluid constituents to the mixture viscosity, the mixture density and the mixture specific heat; and

(g) solving said at least the three equations and a constitutive equation for the individual concentrations of L of the fluid constituents and for identities of M of the fluid constituents.

16. The method of claim 15, wherein the mixture of fluids comprises inhaled or exhaled gasses, the method further comprising:

determining at least one of uptake, consumption and production of inhaled or exhaled gasses.

17. The method of claim 15, further comprising:

(h) determining the dielectric constant of the mixture from capacitance of a capacitor;

wherein;

step (f) includes establishing a fourth equation relating the individual concentrations of the fluid constituents to the dielectric constant of the mixture; and

step (g) includes solving at least four equations and a constitutive equation for the individual concentrations of L of the fluid constituents and for identities of M of the fluid constituents.

18. The method of claim 17, further comprising:

(i) determining the refractive index of the mixture, wherein;

step (f) includes establishing a fifth equation relating the individual concentrations of the fluid constituents to the refractive index of the mixture; and

step (g) includes solving at least five equations and a constitutive equation for the individual concentrations of L of the fluid constituents and for identities of M of the fluid constituents.

19. The method of claim 15, further comprising:

(h) determining the refractive index of the mixture, wherein;

step (f) includes establishing a fourth equation relating the individual concentrations of the fluid constituents to the refractive index of the mixture; and

step (g) includes solving at least four equations and a constitutive equation for the individual concentrations of L of the fluid constituents and for identities of M of the fluid constituents.

20. The method of claim 15, further comprising:

measuring the ambient temperature of the mixture; and

measuring the ambient pressure of the mixture.

21. The method of claim 15, wherein the mixture of fluids comprises N fluids, and step (g) includes solving the N−

1 equations and the constitutive equation for the individual concentrations of the fluid constituents in real time.

22. The method of claim 15, wherein the fluid constituents of the mixture of fluids are gasses respired during anesthesia administration.

23. The method of claim 15, wherein, said mixture includes an N+1th fluid and step (g) includes determining a combined concentration of two of said fluid constituents, the method further comprising:

(h) determining the individual concentrations of the two fluid constituents by determining changes in the combined concentration of the two fluid constituents over time.

24. The method of claim 15, wherein the identity of one of the fluid constituents is initially unknown, and wherein step (f) includes assuming that the unknown fluid constituent is one of P fluids whose properties are known, where P is a positive integer, the method further comprising the steps of:

(h) indicating that the unknown fluid constituent is said one of the P fluids if the individual concentrations solved for in step (g) fall within respective predetermined concentration ranges; and

(i) if the individual concentrations solved for in step (g) do not fall within the respective predetermined concentration ranges, repeating steps (f) through (h) by assuming the unknown fluid constituent is different ones of said P fluids, until the individual concentrations solved for in step (g) fall within the respective predetermined concentration ranges or until the unknown fluid constituent has been assumed to be every one of said P fluids.

25. The method of claim 15, wherein:

the identity of one of the fluid constituents is initially unknown; and

step (f) includes assuming that the unknown fluid constituent is one of P fluids whose properties are known, where P is a positive integer;

the method further comprising the steps of;

(h) determining a value of an additional property of the mixture from measured characteristics;

(i) calculating a value of an additional property of the unknown fluid constituent from an equation relating the additional property of the mixture to individual concentrations of the constituent components, where the additional property of the mixture is not used in step (f);

(j) determining whether the calculated value of the additional property of the unknown fluid constituent matches, to within a predetermined threshold, a known value of the additional property of said one of the P fluids;

(k) if a match is found in step (j), indicating that the unknown fluid constituent is said one of the P fluids; and

(l) if a match is not found in step (j), repeating steps (f), (g), (i), (j) and (k) with different ones of said P fluids until a match is found or until a match has been attempted with all of said P fluids.

26. The method of claim 15, wherein:

said mixture comprises P+N fluids, where P is a positive integer; and

individual concentrations of P of the fluid constituents are known prior to establishing N−

1 equations, the method further comprising;

establishing the N−

1 equations relating the individual concentrations of the fluid constituents, including the known individual concentrations of the P fluid constituents, to the N−

1 properties of the mixture.

27. The method of claim 15, where plural fluids whose ratios of concentrations do not substantially vary over time are treated as a single fluid constituent of the mixture.

28. An apparatus for determining individual concentrations of at least L fluid constituents and identities of at least M fluid constituents of a mixture of fluids, where L and M are non-negative integers, the apparatus comprising:

means for measuring physical characteristics of the mixture, including;

means for measuring a pressure drop of the mixture;

means for acoustically measuring mixture flow rate;

means for measuring the speed of sound in the mixture; and

means for measuring viscosity of the mixture; and

means for determining values of N−

1 properties of the mixture from the measured physical characteristics, where N is equal to L+M;

said means for determining establishing N−

1 equations relating the individual concentrations of the fluid constituents to the N−

1 properties of the mixture, and solving the N−

1 equations and a constitutive equation for the individual concentrations of L of the fluid constituents and for identities of M of the fluid constituents.

29. The apparatus of claim 28, wherein:

said means for determining calculates the density of the mixture from the pressure drop and the flow rate; and

said means for determining calculates the specific heat of the mixture from the density and the speed of sound, wherein said properties of the mixture include the density, viscosity and specific heat.

30. The apparatus of claim 29, wherein:

said means for measuring physical characteristics of the mixture further includes means for determining the dielectric constant of the mixture, the dielectric constant being one of said properties of the mixture.

31. The apparatus of claim 29, wherein:

said means for measuring physical characteristics of the mixture further includes means for determining a refractive index of the mixture, the refractive index being one of said properties of the mixture.

32. The apparatus of claim 29, wherein said means for measuring physical characteristics of the mixture further includes:

means for measuring the ambient temperature of the mixture; and

means for measuring the ambient pressure of the mixture.

33. The apparatus of claim 28, wherein the mixture of fluids comprises N fluids, and wherein said means for determining solves the N−

1 equations and the constitutive equation for the individual concentrations of the fluid constituents in real time.

34. The apparatus of claim 28, wherein the fluid constituents of the mixture of fluids are gasses respired during anesthesia administration.

35. The apparatus of claim 28, wherein, said mixture includes an N+1th fluid and said means for determining determines a combined concentration of two of said fluid constituents and determines the individual concentrations of the two fluid constituents by determining changes in the combined concentration of the two fluid constituents over time.

36. The apparatus of claim 28, wherein:

the identity of one of the fluid constituents is initially unknown;

said means for determining establishes the N−

1 equations by assuming that the unknown fluid constituent is one of P fluids whose properties arc known, where P is a positive integer;

said means for determining determines that the unknown fluid constituent is said one of the P fluids if the individual concentrations solved for fall within respective predetermined concentration ranges; and

if the individual concentrations solved for do not fall within the respective predetermined concentration ranges, said means for determining establishes N−

1 equations relating the individual concentrations of the fluid constituents to the N−

1 properties of the mixture by assuming the unknown fluid constituent is different ones of said P fluids and solves the N−

1 equations and a constitutive equation for the individual concentrations of the fluid constituents, until the individual concentrations solved for fall within the respective predetermined concentration ranges or until the unknown fluid constituent has been assumed to be every one of said P fluids.

37. The apparatus of claim 28, wherein:

the identity of one of the fluid constituents is initially unknown;

said means for determining determines a value of an Nth property of the mixture from the measured physical characteristics;

said means for determining establishes the N−

1 equations;

by assuming that the unknown fluid constituent is one of P fluids whose properties are known, where P is a positive integer;

said means for determining calculates a value of an Nth property of the unknown fluid constituent from an equation relating the Nth property of the mixture to individual concentrations of the constituent components, where the Nth property of the mixture is not used to establish the N−

1 equations;

said means for determining determines whether the calculated value of the Nth property of the unknown fluid constituent matches, to within a predetermined threshold, a known value of the Nth property of said one of the P fluids;

said means for determining determines that the unknown fluid constituent is said one of the P fluids if a match is found; and

if a match is not found, said means for determining establishes N−

1 equations relating the individual concentrations of the fluid constituents to the N−

1 properties of the mixture by assuming the unknown fluid constituent is different ones of said P fluids and solves the N−

1 equations and a constitutive equation for the individual concentrations of the fluid constituents, until a match is found or until a match has been attempted with all of said P fluids.

38. The apparatus of claim 28, wherein:

said mixture comprises P+N fluids, where P is a positive integer;

individual concentrations of P of the fluid constituents are known prior to establishing the N−

1 equations; and

said means for determining establishes the N−

1 equations relating the individual concentrations of the fluid constituents, including the known individual concentrations of the P fluid constituents, to the N−

1 properties of the mixture.

39. The apparatus of claim 28, wherein said means for determining determines the individual concentrations of L of the fluid constituents in real time.

40. The apparatus of claim 28, wherein the mixture of fluids comprises inhaled or exhaled gasses, and said means for determining determines at least one of uptake, consumption and production of inhaled or exhaled gasses.

41. The apparatus of claim 28, wherein said means for measuring physical characteristics of the mixture are disposed within a main gas flow passage of a breathing circuit.