Device and method for monitoring body fluid and electrolyte disorders

• US 20060084864A1
• Filed: 09/30/2005
• Published: 04/20/2006
• 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., Debreczeny, Martin
• Granted Patent: US 8,457,722 B2
• Time in Patent Office: Days
• US Class Current: 600/431
• 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: G01N 2021/3181 using LEDs
• CPC Class Codes: G01N 21/3554 for determining moisture content
• CPC Class Codes: G01N 21/359 using near infrared light

Abstract

Devices and methods for measuring body fluid-related metric using spectrophotometry that may be used to facilitate diagnosis and therapeutic interventions aimed at restoring body fluid balance. In one embodiment, the present invention provides a device for measuring a body-tissue water content metric as a fraction of the fat-free tissue content of a patient using optical spectrophotometry. The device includes a probe housing configured to be placed near a tissue location which is being monitored; light emission optics connected to the housing and configured to direct radiation at the tissue location; light detection optics connected to the housing and configured to receive radiation from the tissue location; and a processing device configured to process radiation from the light emission optics and the light detection optics to compute the metric where the metric includes a ratio of the water content of a portion of patient'"'"'s tissue in relation to the lean or fat-free content of a portion of patient'"'"'s tissue.

Claims

1. A device for determining an estimate of whole body water content, comprising:

a processing device configured to process a signal indicative of radiation detected from lean tissue of a patient to compute the estimate of whole body tissue water content, wherein the estimate is correlative to a computed fractional water content of the lean tissue.

2. The device of claim 1, wherein the computation of fractional water content of the lean tissue substantially excludes fat content and bone content of the patient.

3. The device of claim 1, comprising a display device coupled to the processing device to display the estimate of whole body tissue water content.

4. The device of claim 1, wherein the estimate of whole body tissue water content comprises a ratio of the whole body tissue of the patient and the lean tissue of the patient.

5. The device of claim 1, wherein the processing device receives and compares at least a first set and a second set of optical measurements, where the first set of optical measurements corresponds to the detected radiation having an absorption primarily due to water and non-heme proteins, and where the second set of optical measurements corresponds to the detected radiation having an absorption primarily due to water, and where a comparison of the first set and the second set of optical measurements provides a measure of a lean water fraction of the lean tissue.

6. The device of claim 1, 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 detected radiation from at least two wavelengths and which are combined to form a ratio of combinations of the detected radiation.

7. The device of claim 6, wherein the processing device forms a weighted summation of the combinations.

8. The device of claim 1, 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 of the patient and in extravascular tissue of the patient, and where a ratio of the at least two measurements provides a measure proportional to a difference between fractions of water in the blood and a surrounding tissue location.

9. The device of claim 1, wherein the computed fractional water content of the lean tissue (f_w^l) is determined such that

10. The device of claim 9, wherein M and N are both equal to 3, wherein wavelengths indexed by m and n comprise of the same combination of wavelengths, and wherein first, second, third and fourth wavelengths are approximately 1180, 1245, 1275 and 1330 nm respectively.

11. A probe for use in measuring a tissue water fraction of a patient, the probe 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

an occlusion device coupled to the housing and configured to selectively induce a pressure proximal to the tissue location to facilitate measurement of the tissue water fraction.

12. The probe of claim 11, wherein the occlusion device is automatically moveable between a first position in which it induces the pressure proximal to the tissue location and a second position in which it does not induce the pressure proximal to the tissue location.

13. The probe of claim 11, wherein the occlusion device comprises a spring-loaded member configured to automatically activate a monitor coupled to the housing when the spring-loaded member is pressed against the patient proximal to the tissue location.

14. The probe of claim 11, wherein the occlusion device comprises a pressure transducer to measure the compressibility of the patient'"'"'s tissue for use in deriving an index of a fraction of free water within the tissue.

15. The probe of claim 11, wherein the occlusion device is configured to mechanically induce a pulse within the tissue location to facilitate measurements related to differences between an intravascular fluid volume fraction and an extravascular fluid volume fraction under weak-pulse conditions.

16. The probe of claim 11, wherein the occlusion device is configured to mechanically minimize the pressure at the tissue location to facilitate measurements related to unperturbed fluid volume fraction in the tissue location.

17. The probe of claim 11, wherein the occlusion device is configured to mechanically induce pressure proximal to the tissue location to facilitate measurement of an extravascular fluid fraction in the absence of an intravascular fluid fraction.

18. The probe of claim 11, wherein the occlusion device is configured to mechanically vary the pressure proximal to the tissue location to facilitate measurement of an intravascular water fraction and an extravascular water fraction.

19. The probe of claim 11, wherein the light emission optics are tuned to emit radiation at a plurality of narrow spectral wavelengths chosen so that a biological compound of interest in the tissue location will absorb light at the plurality of narrow spectral wavelengths and to affect a minimum absorption by interfering compounds, where a minimum absorption is an absorption by an interfering compound that is less than 10% of the absorption of the biological compound of interest.

20. The probe of claim 11, wherein the light emission optics are tuned to emit radiation at a plurality of narrow 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 the individual concentrations of non-heme proteins and lipids, and is substantially dependent on the sum of the individual concentrations of non-heme proteins and water.

21. The probe of claim 11, wherein the light emission optics are tuned to emit radiation at a plurality of narrow spectral wavelengths chosen to ensure that the received radiation is substantially insensitive to scattering variations and such that optical path lengths through the tissue location at the plurality of narrow spectral wavelengths are substantially equal.

22. The probe of claim 11, wherein the light emission optics are tuned to emit radiation at a plurality of narrow spectral wavelengths chosen to ensure that the received radiation from the tissue location is substantially insensitive to temperature variations, wherein the wavelengths are temperature isosbestic in the water absorption spectrum, or wherein the received radiation is combined in a way that substantially cancels temperature dependencies of the individual wavelengths when computing a tissue water fraction.

23. The probe of claim 11, wherein the light emission optics are tuned to emit radiation at a plurality of narrow spectral wavelengths chosen from one of three primary bands of wavelengths of approximately 950-1400 nm, approximately 1500-1800 nm, and approximately 2000-2300 nm.

24. The probe of claim 11, wherein the light emission optics and the light detection optics are positioned within the housing with appropriate alignment to enable detection in a transmissive mode.

25. The probe of claim 11, wherein the light emission optics and the light detection optics are positioned within the housing with appropriate alignment to enable detection in a reflective mode.

26. The probe of claim 11, wherein the light emission optics and the light detection optics receive the radiation via optical fibers.

27. The probe of claim 11, wherein the light emission optics comprise at least one of a (a) incandescent light source, (b) white light source, and (c) light emitting diode (“

LED”

).

28. A device for measuring a body tissue metric, comprising:

a processing device configured to process a signal indicative of radiation detected from tissue of a patient to compute the body tissue metric, wherein the body tissue metric comprises a measure of a ratio of a difference between a water fraction in blood of the patient and a water fraction in extravascular tissue of the patient over a fractional volume concentration of hemoglobin in the blood.

29. The device of claim 28 wherein the metric comprises a water balance index Q, such that:

30. The device of claim 28 comprising an input device configured to enable a user to input a fractional hemoglobin concentration in blood for use by the processing device.

31. The device of claim 28 wherein the processing device is configured to compute a measure of a change in water content between an intravascular fluid volume (“

IFV”

) and an extravascular fluid volume (“

EFV”

) using the water index.

32. The device of claim 29 wherein the wavelengths λ

₁ and λ

₂ are approximately 1320 nm and approximately 1160 nm, respectively.

33. The device of claim 28 wherein the radiation comprises a plurality of narrow spectral wavelengths chosen from one of three primary bands of wavelengths of approximately 950-1400 nm, approximately 1500-1800 nm, and approximately 2000-2300 nm.

34. The device of claim 28 wherein the body tissue metric comprises an integral of the difference to provide a measure of the water that shifts into and out of capillaries of the patient.

35. A method for determining a body tissue water content metric as a fraction of lean tissue content of a patient, comprising:

processing radiation received from a tissue location of the patient to compute the body tissue water content metric, wherein the body tissue water content metric (f_w^l) is determined such that

$f_w^l=\frac{\left[\underset{n=1}{\overset{N}{\sum <br><br>}}<br><br>p_n<br><br>\text{\hspace{1em}<br><br>}<br><br>\log <br><br>\left\{R<br><br>\left({\mathrm{\lambda <br><br>}}_n\right)\right\}\right]-\left[\underset{n=1}{\overset{N}{\sum <br><br>}}<br><br>p_n\right]<br><br>\text{\hspace{1em}<br><br>}<br><br>\log <br><br>\left\{R<br><br>\left({\mathrm{\lambda <br><br>}}_{N+1}\right)\right\}}{\left[\underset{m=1}{\overset{M}{\sum <br><br>}}<br><br>q_m<br><br>\text{\hspace{1em}<br><br>}<br><br>\log <br><br>\left\{R<br><br>\left({\mathrm{\lambda <br><br>}}_m\right)\right\}\right]-\left[\underset{m=1}{\overset{M}{\sum <br><br>}}<br><br>q_m\right]<br><br>\text{\hspace{1em}<br><br>}<br><br>\log <br><br>\left\{R<br><br>\left({\mathrm{\lambda <br><br>}}_{M+1}\right)\right\}},$

and where;

p_n and q_m are calibration coefficients;

R(λ

) is a measure of the received radiation at a wavelength;

n=1−

and m=1−

M represent indexes for a plurality of wavelengths which may comprise of the same or different combinations of wavelengths.

36. A method for determining a body tissue metric of a patient, comprising:

processing radiation received from a tissue location of the patient to compute the body tissue metric, wherein the body tissue metric comprises a measure of a ratio of a difference between a water fraction in blood of the patient and a water fraction in extravascular tissue of the patient over a fractional volume concentration of hemoglobin in the blood.

37. The method of claim 36 wherein the body tissue metric comprises a water balance index Q, such that:

38. A method of determining a physiological parameter in a human tissue location, comprising:

processing radiation received from the human tissue location to compute the physiological parameter, wherein the physiological parameter is determined such that it is equal to

$\frac{\left[\underset{n=1}{\overset{N}{\sum <br><br>}}<br><br>p_n<br><br>\text{\hspace{1em}<br><br>}<br><br>\log <br><br>\left\{R<br><br>\left({\mathrm{\lambda <br><br>}}_n\right)\right\}\right]-\left[\underset{n=1}{\overset{N}{\sum <br><br>}}<br><br>p_n\right]<br><br>\text{\hspace{1em}<br><br>}<br><br>\log <br><br>\left\{R<br><br>\left({\mathrm{\lambda <br><br>}}_{N+1}\right)\right\}}{\left[\underset{m=1}{\overset{M}{\sum <br><br>}}<br><br>q_m<br><br>\text{\hspace{1em}<br><br>}<br><br>\log <br><br>\left\{R<br><br>\left({\mathrm{\lambda <br><br>}}_m\right)\right\}\right]-\left[\underset{m=1}{\overset{M}{\sum <br><br>}}<br><br>q_m\right]<br><br>\text{\hspace{1em}<br><br>}<br><br>\log <br><br>\left\{R<br><br>\left({\mathrm{\lambda <br><br>}}_{M+1}\right)\right\}},$

and where;

p_n and q_m are calibration coefficients;

R(λ

) is a measure of the received radiation at a wavelength;

n=1−

N and m=1−

M represent indexes for a plurality of wavelengths which may comprise of the same or different combinations of wavelengths.

39. The method of claim 38, wherein the physiological parameter comprises a tissue water fraction of the tissue location.

40. The method of claim 38, wherein the physiological parameter comprises an oxygen saturation value of the tissue location.

41. The method of claim 38, wherein the physiological parameter comprises a fractional hemoglobin concentration of the tissue location.

42. The method of claim 38, wherein the physiological parameter comprises a fractional concentration of hemoglobin in a first set comprised of one or more species of hemoglobin with respect to a concentration of hemoglobin in a second set comprised of one or more hemoglobin species in the tissue location.

43. The method of claim 42 wherein the coefficients, p_n, are chosen to substantially cancel absorbance contributions from all tissue constituents except the hemoglobin species included in the first set, and wherein the coeffients, q_m, are chosen to substantially cancel absorbance contributions from all tissue constituents except the hemoglobin species included in the second set.

44. A method of assessing changes in volume and osmolarity of body fluids in a body tissue, comprising:

processing radiation received from a tissue location to determine a water balance index and a tissue water concentration; and

analyzing the water balance index and the tissue water concentration to assess changes in volume and osmolarity of body fluids proximal the tissue location.

45. The method of claim 44 wherein the water balance index comprises a ratio of a difference between a water fraction in blood and a water fraction in extravascular tissue over a fractional volume concentration of hemoglobin in blood.

46. The method of claim 44 wherein the water balance index comprises a difference between a water fraction in blood and a water fraction in extravascular tissue.