Device and method for monitoring body fluid and electrolyte disorders

• US 20060020181A1
• Filed: 09/30/2005
• Published: 01/26/2006
• Est. Priority Date: 03/16/2001
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Covidien LP (Medtronic Plc)
• Inventors: Schmitt, Joseph M.
• Granted Patent: US 8,229,529 B2
• Time in Patent Office: Days
• US Class Current: 600/310
• CPC Class Codes: A61B 5/0053 by applying pressure, e.g. compression, indentation, palpation, grasping, gauging
• CPC Class Codes: A61B 5/0059 using light, e.g. diagnosis by transillumination, diascopy, fluorescence A61B5/0093, A61B5/1455, A61B5/02416 and A61B5/0261 take precedence
• CPC Class Codes: A61B 5/02438 with portable devices, e.g. worn by the patient
• CPC Class Codes: A61B 5/14546 for measuring analytes not otherwise provided for, e.g. ions, cytochromes
• CPC Class Codes: A61B 5/4878 Evaluating oedema
• CPC Class Codes: G01N 21/359 using near infrared light

Abstract

A device and a method for measuring body fluid-related metrics using spectrophotometry to facilitate therapeutic interventions aimed at restoring body fluid balance. The specific body fluid-related metrics include the absolute volume fraction of water in the extravascular and intravascular tissue compartments, as well as the shifts of water between these two compartments. The absolute volume fraction of water is determined using algorithms where received radiation measured at two or more wavelengths are combined to form either a single ratio, a sum of ratios or ratio of ratios of the form log[R(λ₁)/R(λ₂)] in which the received radiation in the numerator depends primarily on the absorbance of water and the received radiation in the denominator depends primarily on the absorbance of water and the sum of the absorbances of non-heme proteins, lipids and water in tissue. The difference between the fraction of water in the intravascular fluid volume (“IFV”) and extravascular fluid volume (“EFV”) compartments are also determined using a differential method that takes advantage of the observation that pulsations caused by expansion of blood vessels in the skin as the heart beats produce changes in the received radiation at a particular wavelength that are proportional to the difference between the effective absorption of light in the blood and the surrounding tissue. This difference, integrated over time, provides a measure of the quantity of the fluid that shifts into and out of the capillaries. A mechanism for mechanically inducing a pulse is built into the device to improve the reliability of measurements of IFV−EFV under weak-pulse conditions.

Claims

1. A sensor comprising:

a probe housing configured to be placed proximate to a tissue location to be monitored;

light emission optics operatively coupled to the housing and configured to direct radiation at the tissue location;

light detection optics operatively coupled to the housing and configured to receive radiation from the tissue location; and

a mechanism connected to the housing and configured to induce a pulse mechanically.

2. The device of claim 1, wherein the mechanism comprises:

a collar configured to encircle the tissue location; and

a linkage configured to decrease and increase the circumference of the collar.

3. The device of claim 2, comprising a rotary solenoid operatively coupled to the linkage to cause the linkage to decrease and increase the circumference of the collar.

4. The device of claim 1, wherein the light emission optics and the light detection optics are arranged to confine the light primarily to a dermis portion of the tissue location.

5. The device of claim 1, wherein the light emission optics and the light detection optics are separated within the range of 1 to 5 mm.

6. A sensor comprising:

a probe housing configured to be placed proximate to a tissue location to be monitored;

light emission optics operatively coupled to the housing and configured to direct radiation at the tissue location;

light detection optics operatively coupled to the housing and configured to receive radiation from the tissue location; and

a mechanism coupled to the housing and configured to apply a force proximate to the tissue location, wherein the mechanism is configured to automatically activate the light emission optics when the force is applied.

7. The device of claim 6, wherein the mechanism comprises a spring-loaded probe head.

8. The device of claim 6, wherein the force is such that a fluid content of the tissue location is not affected to a measurable degree.

9. The device of claim 6, wherein the force exerted by the mechanism is sufficient to push blood out of the tissue location such that the tissue location is substantially extravascular.

10. A sensor comprising:

a housing configured to be placed proximal to a tissue location to be monitored;

an occlusion device coupled to the housing and configured to magnify a fractional change in vascular blood volume to a value greater than a fractional change produced by normal arterial pulsations;

light emission optics operatively coupled to the housing and configured to direct radiation at the tissue location; and

light detection optics operatively coupled to the housing and configured to receive radiation from the tissue location.

11. A device for determining body fluid-related metrics, the device comprising:

a processing device configured to process a signal indicative of radiation received from a tissue location to compute the body fluid-related metrics, wherein the body fluid-related metrics comprise absolute volume fractions of water in extravascular and intravascular bodily tissue compartments and differences between intravascular fluid volume and extravascular fluid volume fractions.

12. The device of claim 11, comprising a display device coupled to the processing device and configured to display the body fluid-related metrics.

13. The device of claim 11, wherein the processing device receives and compares at least two sets of optical measurements, where the at least first set of optical measurements corresponds to the detection of the radiation whose absorption is primarily due to water, lipids and non-heme proteins, and where the at least second set of optical measurements corresponds to the detection of the radiation whose absorption is primarily due to water, and where a comparison of the at least two optical measurements provides a measure of the absolute water fraction within the tissue location.

14. The device of claim 11, wherein the processing device receives and compares at least two sets of optical measurements, where the at least two sets of optical measurements are based on the received radiation from at least two wavelengths and which are combined to form either a single ratio of the received radiation, a sum of ratios of the received radiation, or ratios of ratios of the received radiation.

15. The device of claim 11, wherein the processing device receives and compares at least two sets of optical measurements from at least two different wavelengths, where absorption of light at the at least two different wavelengths is primarily due to water which is in vascular blood and in extravascular tissue, and where a ratio of the at least two measurements provides a measure of a difference between fractions of water in the blood and the tissue location.

16. A device for determining body fluid-related metrics, the device comprising:

a processing device configured to process a signal indicative of radiation received from a tissue location to compute the body fluid-related metrics;

a display device coupled to the processing device and configured to automatically display the body fluid-related metrics in response to receiving a signal from a probe, the signal from the probe being indicative of the probe being pressed against the tissue location.

17. A sensor comprising:

a housing configured to be placed proximal to a tissue location to be monitored;

light emission optics operatively coupled to the housing and configured to direct radiation at the tissue location;

light detection optics operatively coupled to the housing and configured to receive radiation from the tissue location; and

a mechanism coupled to the housing and configured to mechanically inducing a pulse within the tissue location to facilitate measurements of differences between an intravascular fluid volume and an extravascular fluid volume fractions under weak-pulse conditions.

18. A device for determining body fluid-related metrics, the device comprising:

a processing device configured to process a signal indicative of radiation received from a tissue location to compute the body fluid-related metrics, the body fluid-related metrics comprising percent body water and a water balance, where the water balance is an integrated difference between a water fraction in blood and a water fraction in extravascular tissue.

19. A device for determining an absolute volume fraction of water within human tissue, the device comprising:

a processing device configured to process a signal indicative of radiation received from a tissue location to compute the absolute volume fraction of water, wherein the processing device receives and compares at least two sets of optical measurements, where the at least first set of optical measurements corresponds to the detection of the radiation whose absorption is primarily due to water, lipids and non-heme proteins, and where the at least second set of optical measurements corresponds to the detection of the radiation whose absorption is primary due to water, and where a comparison of the at least two optical measurements provides a measure of the absolute volume water fraction within the tissue location.

20. A device for determining a difference between an intravascular fluid volume and an extravascular fluid volume, the device comprising:

a processing device configured to process a signal indicative of radiation received from a tissue location to compute the difference between an intravascular fluid volume and an extravascular fluid volume, wherein the processing device receives and compares at least two sets of optical measurements from at least two different wavelengths, where absorption of light at the at least two different wavelengths is primarily due to water that is in vascular blood and in extravascular tissue, and where a comparison of the at least two measurements provides a measure of a difference between the fractions of water in the blood and the tissue location.

21. A method for determining body fluid-related metrics in a human tissue location, the method comprising:

processing a signal indicative of radiation received from the tissue location to compute the body fluid-related metrics, wherein the body fluid-related metrics comprise absolute volume fractions of water in extravascular and intravascular bodily tissue compartments and differences between intravascular fluid volume and extravascular fluid volume fraction.

22. The method of claim 21, wherein the processing comprises:

measuring at least two sets of optical measurements based on received radiation of at least two wavelengths;

combining the at least two sets of optical measurements to form either a single ratio of the received radiation, a sum of ratios of the received radiation, or ratios of ratios of the received radiation to form combinations of received radiation; and

determining the metrics from the combinations.

23. A device for determining body fluid-related metrics, the device comprising:

a processing device configured to process a signal indicative of radiation received from a tissue location to compute the body fluid-related metrics, wherein the radiation comprises a plurality of spectral wavelengths chosen to be preferentially absorbed by tissue water, non-heme proteins and lipids, where preferentially absorbed wavelengths are wavelengths whose absorption is substantially independent of individual concentrations of non-heme proteins and lipids, and is substantially dependent on a sum of the individual concentrations of non-heme proteins and lipids.

24. The device of claim 23, wherein the wavelengths are chosen to ensure that the received radiation is substantially insensitive to scattering variations and such that the optical path lengths through a dermis portion of the tissue location at the wavelengths are substantially equal.

25. The device of claim 23, wherein the wavelengths are chosen to ensure that the received radiation from the tissue location is insensitive to temperature variations, where the wavelengths are temperature isosbestic in the water absorption spectrum or individual wavelengths of the received radiation are combined in a way that substantially cancels temperature dependencies of the individual wavelengths of the received radiation when computing tissue water fractions.

26. The device of claim 23, wherein the wavelengths are chosen from one of three primary bands of wavelengths of approximately 1100-1350 nm, approximately 1500-1800 nm, and approximately 2000-2300 nm.

27. The device of claim 23, wherein the processing device receives and compares at least two sets of optical measurements, where the at least first set of optical measurements corresponds to the detection of the radiation whose absorption is primarily due to water, lipids and non-heme proteins, and where the at least second set of optical measurements corresponds to the detection of the radiation whose absorption is primarily due to water, and where a comparison of the at least two optical measurements provides a measure of the absolute water fraction within the tissue location.

28. The device of claim 23, wherein the processing device receives and compares at least two sets of optical measurements, where the at least two sets of optical measurements are based on the received radiation from at least two wavelengths and which are combined to form either a single ratio of the received radiation, a sum of ratios of the received radiation, or ratios of ratios of the received radiation.

29. The device of claim 23, wherein the processing device receives and compares at least two sets of optical measurements from at least two different wavelengths, where absorption of light at the at least two different wavelengths is primarily due to water which is in vascular blood and in extravascular tissue, and where a ratio of the at least two measurements provides a measure of a difference between fractions of water in the blood and the tissue location.

30. The device of claim 23, wherein the body fluid-related metrics comprise a tissue water fraction, where the tissue water fraction (f_w) is determined such that

f_w=c₁ log[R(λ

₁)/R(λ

₂)]+c₀, and where;

calibration constants c₀ and c₁ are chosen empirically;

R(λ

₁) is the received radiation at a first wavelength; and

R(λ

₂) is the received radiation at a second wavelength.

31. The device of claim 30, wherein the first and second wavelengths are approximately 1300 nm and approximately 1168 nm, respectively.

32. The device of claim 30, wherein the first and second wavelengths are approximately 1230 nm and approximately 1168 nm, respectively.

33. The device of claim 23, wherein the body fluid-related metrics comprise a tissue water fraction, and where the tissue water fraction (f_w) is determined such that

f_w=c₂ log[R(λ

₁)/R(λ

₂)]+c₁ log[R(λ

₂)/R(λ

₃)]+c₀, and where;

calibration constants c₀, c₁ and c₂ are chosen empirically;

R(λ

₁) is the received radiation at a first wavelength;

R(λ

₂)is the received radiation at a second wavelength; and

R(λ

₃) is the received radiation at a third wavelength.

34. The device of claim 33, wherein the first, second and third wavelengths are approximately 1190 nm, approximately 1170 nm and approximately 1274 nm, respectively.

35. The device of claim 23, wherein the body fluid-related metrics comprise a tissue water fraction, and where the tissue water fraction (f_w) is determined such that

$f_w=c_1$

log ⁡

[ R ⁡

( λ

1 ) / R ⁡

( λ

2 ) ] log ⁡

[ R ⁡

( λ

3 ) / R ⁡

( λ

2 ) ] + c 0 ,

and where;

calibration constants c₀ and c₁ are chosen empirically;

R(λ

₁) is the received radiation at a first wavelength;

R(λ

₂) is the received radiation at a second wavelength; and

R(λ

₃) is the received radiation at a third wavelength.

36. The device of claim 35, wherein the first, second and third wavelengths are approximately 1710 nm, approximately 1730 nm and approximately 1740 nm, respectively.

37. The device of claim 23, wherein the body fluid-related metrics comprise a quantified measure of a difference between a water fraction in blood and a water fraction in extravascular tissue, where the difference is determined such that

$f_w^{\mathrm{blood}}-f_w^{\mathrm{tissue}}={c_1}_{}$

( Δ

⁢

 

⁢

R R ) λ

1 / ( Δ

⁢

 

⁢

R R ) λ

2 + c 0 ,

and where;

f_w^blood is the water fraction in the blood;

f_w^tissue is the water fraction in the extravascular tissue;

calibration constants c₀ and c₁ are chosen empirically; and

${\left(\frac{\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>R}{R}\right)}_{{\mathrm{\lambda <br><br>}}_1}/{\left(\frac{\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>R}{R}\right)}_{{\mathrm{\lambda <br><br>}}_2}$

is a ratio of dc-normalized received radiation changes at a first wavelength, λ

₁ and a second wavelength, λ

₂ respectively, where the received radiation changes are caused by a pulsation caused by expansion of blood vessels in tissue.

38. The device of claim 37, wherein the body fluid-metrics comprise an integral of the difference between the water fraction in the blood and the water fraction in the extravascular tissue to provide a measure of water that shifts into and out of capillaries in the tissue location.

39. The device of claim 37, wherein the first and second wavelengths are approximately 1320 nm and approximately 1160 nm, respectively.

40. A device for determining body fluid-related metrics, the device comprising:

a processing device configured to process a signal indicative of radiation received from a tissue location to compute the body fluid-related metrics, wherein the body fluid-related metrics comprises a tissue water fraction, and where the tissue water fraction (f_w) is determined such that

$f_w=c_1<br><br>\frac{\log <br><br>\left[R<br><br>\left({\mathrm{\lambda <br><br>}}_1\right)/R<br><br>\left({\mathrm{\lambda <br><br>}}_2\right)\right]}{\log <br><br>\left[R<br><br>\left({\mathrm{\lambda <br><br>}}_3\right)/R<br><br>\left({\mathrm{\lambda <br><br>}}_2\right)\right]}+c_0$

and where;

calibration constants c₀ and c₁ are chosen empirically;

R(λ

₁) is the received radiation at a first wavelength;

R(λ

₂) is the received radiation at a second wavelength; and

R(λ

₃) is the received radiation at a third wavelength.

41. The device of claim 40, wherein the wavelengths are chosen to ensure that the received radiation is substantially insensitive to scattering variations and such that the optical path lengths through a dermis portion of the tissue location at the wavelengths are substantially equal.

42. The device of claim 40, wherein the wavelengths are chosen to ensure that the received radiation from the tissue location is substantially insensitive to temperature variations, where the wavelengths of the radiation are temperature isosbestic in the water absorption spectrum or where the wavelengths of the received radiation are combined in a way that substantially cancels temperature dependencies of individual wavelengths of the received radiation when computing tissue water fractions.

43. The device of claim 40, wherein the wavelengths are chosen from one of three primary bands of wavelengths of approximately 1100-1350 nm, approximately 1500-1800 nm, and approximately 2000-2300 nm.

44. The device of claim 40, wherein the processing device receives and compares at least two sets of optical measurements, where the at least first set of optical measurements corresponds to the detection of the received radiation whose absorption is primarily due to water, lipids and non-heme proteins, and where the at least second set of optical measurements corresponds to the detection of the received radiation whose absorption is primarily due to water, and where a comparison of the at least two optical measurements provides a measure of the absolute water fraction within the tissue location.

45. The device of claim 40, wherein said first, second and third wavelengths are approximately 1710 nm, approximately 1730 nm and approximately 1740 nm, respectively.

46. A device for determining body fluid-related metrics, the device comprising:

a processing device configured to process a signal indicative of radiation received from a tissue location to compute the body fluid-related metrics, wherein received radiation comprises a plurality of spectral wavelengths chosen to ensure that the computed body fluid-related metrics are substantially insensitive to scattering variations and such that the optical path lengths through the tissue location at the wavelengths are substantially equal.

47. The device of claim 46, wherein the wavelengths are chosen to ensure that the received radiation from the tissue location is substantially insensitive to temperature variations, where wavelengths of the received radiation are temperature isosbestic in the water absorption spectrum, or where wavelengths of the received radiation are combined in a way that substantially cancel temperature dependencies of any individual wavelength of the received radiation when computing tissue water fractions.

48. The device of claim 46, wherein wavelengths of the received radiation are chosen from one of three primary bands of wavelengths of approximately 1100-1350 nm, approximately 1500-1800 nm, and approximately 2000-2300 nm.

49. The device of claim 46, wherein the processing device receives and compares at least two sets of optical measurements, where the at least first set of optical measurements corresponds to the detection of the received radiation whose absorption is primarily due to water, lipids and non-heme proteins, and where the at least second set of optical measurements corresponds to the detection of the received radiation whose absorption is primarily due to water, and where a comparison of the at least two optical measurements provides a measure of the absolute water fraction within the tissue location.

50. The device of claim 46, wherein the processing device receives and compares at least two sets of optical measurements, where the at least two sets of optical measurements are based on the received radiation from at least two wavelengths and which are combined to form either a single ratio of the received radiation, a sum of ratios of the received radiation, or ratios of ratios of the received radiation.

51. The device of claim 46, wherein the body fluid-related metrics comprise a tissue water fraction, and where the tissue water fraction (f_w) is determined such that

f_w=c₁ log[R(λ

₁)/R(λ

₂)]+c₀, and where;

calibration constants c₀ and c₁ are chosen empirically;

R(λ

₁) is the received radiation at a first wavelength; and

R(λ

₂ ) is the received radiation at a second wavelength.

52. The device of claim 51, wherein the first and second wavelengths are approximately 1300 nm and approximately 1168 nm, respectively.

53. The device of claim 51, wherein the first and second wavelengths are approximately 1230 nm and approximately 1168 nm, respectively.

54. The device of claim 46, wherein the body fluid-related metrics comprise a tissue water fraction, and where the tissue water fraction (f_w) is determined such that

f_w=c₂ log[R(λ

₁)/R(λ

₂)]+c₁ log[R(λ

₂)/R(λ

₃)]+c₀, and where;

calibration constants c₀, c₁ and c₂ are chosen empirically;

R(λ

₁) is the received radiation at a first wavelength;

R(λ

₂) is the received radiation at a second wavelength; and

R(λ

₃) is the received radiation at a third wavelength.

55. The device of claim 54, wherein the first, second and third wavelengths are approximately 1190 nm, approximately 1170 nm, and approximately 1274 nm, respectively.

56. A device for determining body fluid-related metrics, the device comprising:

a processing device configured to process a signal indicative of radiation received from a tissue location compute the body fluid-related metrics, wherein the received radiation comprises a plurality of spectral wavelengths chosen to ensure that the received radiation from the tissue location is substantially insensitive to temperature variations, wherein wavelengths of the received radiation are temperature isosbestic in the water absorption spectrum or wherein the signal is processed in such a way that temperature dependencies of individual wavelengths of the received radiation is substantially cancelled when computing tissue water fractions.

57. The device of claim 56, wherein the wavelengths are chosen from one of three primary bands of wavelengths of approximately 1100-1350 nm, approximately 1500-1800 nm, and approximately 2000-2300 nm.

58. The device of claim 56, wherein the processing device receives and compares at least two sets of optical measurements, where the at least first set of optical measurements corresponds to the detection of radiation whose absorption is primarily due to water, lipids and non-heme proteins, and where the at least second set of optical measurements corresponds to the detection of radiation whose absorption is primarily due to water, and where a comparison of the at least two optical measurements provides a measure of the absolute water fraction within the tissue location.

59. The device of claim 56, wherein the processing device receives and compares at least two sets of optical measurements, where the at least two sets of optical measurements are based on the received radiation from at least two wavelengths and which are combined to form either a single ratio of the received radiation, a sum of ratios of the received radiation, or ratios of ratios of the received radiation.

60. The device of claim 56, wherein the body fluid-related metrics comprise a tissue water fraction, and where the tissue water fraction (f_w) is determined such that

f_w=c₁ log[R(λ

₁)/R(λ

₂)]+c₀, and where;

calibration constants c₀ and c₁ are chosen empirically;

R(λ

₁) is the received radiation at a first wavelength; and

R(λ

₂) is the received radiation at a second wavelength.

61. The device of claim 60, wherein the first and second wavelengths are approximately 1300 nm and approximately 1168 nm, respectively.

62. The device of claim 60, where the first and second wavelengths are approximately 1230 nm and approximately 1168 nm, respectively.

63. The device of claim 56, wherein the body fluid-related metrics comprise a tissue water fraction, and where the tissue water fraction (f_w) is determined such that

f_wc₂ log[R(λ

₁)/R(λ

₂)]+c₁ log[R(λ

₂)/R(λ

₃)]+c₀, and where;

calibration constants c₀, c₁ and c₂ are chosen empirically;

R(λ

₁) is the received radiation at a first wavelength;

R(λ

₂) is the received radiation at a second wavelength; and

R(λ

₃) is the received radiation at a third wavelength.

64. The device of claim 63, wherein the first, second and third wavelengths are approximately 1190 nm, approximately 1170 nm, and approximately 1274 nm, respectively.