Device and method for monitoring body fluid and electrolyte disorders

• US 20020161287A1
• Filed: 03/16/2001
• Published: 10/31/2002
• Est. Priority Date: 03/16/2001
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Nellcor Puritan Bennett Incorporated (Medtronic Plc)
• Inventors: Schmitt, Joseph M.
• Granted Patent: US 6,591,122 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 device for measuring body fluid-related metrics using optical spectrophotometry comprising:

a probe housing configured to be placed proximal to a tissue location which is being monitored;

light emission optics connected to said housing and configured to direct radiation at said tissue location;

light detection optics connected to said housing and configured to receive radiation from said tissue location; and

a processing device configured to process radiation from said light emission optics and said light detection optics to compute said body fluid-related metrics.

2. The device of claim 1, further comprising a display device connected to said probe housing and configured to display said body fluid-related metrics.

3. The device of claim 1, wherein said body fluid-related metrics comprise absolute volume fractions of water in the extravascular and intravascular bodily tissue compartments and differences between the intravascular fluid volume and extravascular fluid volume fractions.

4. The device of claim 1, wherein said body-fluid metrics are monitored intermittently.

5. The device of claim 1, wherein said body-fluid metrics are monitored continuously.

6. The probe housing of the device of claim 1 further comprising a spring-loaded probe configured to automatically activate a display device connected to said probe housing when said spring-loaded probe is pressed against a tissue location which is being monitored.

7. The probe housing of the device of claim 1 further comprising a pressure transducer to measure the compressibility of tissue for deriving an index of a fraction of free water within said tissue.

8. The probe housing of the device of claim 1 further comprising a mechanism for mechanically inducing a pulse within said tissue location to permit measurements of differences between an intravascular fluid volume and an extravascular fluid volume fractions under weak-pulse conditions.

9. The device of claim 1, wherein said light emission optics are tuned to emit radiation at a plurality of narrow spectral wavelengths chosen so that the biological compound of interest will absorb light at said plurality of narrow spectral wavelengths and so that absorption by interfering species will be at a minimum, where a minimum absorption is an absorption by an interfering species which is less than 10% of the absorption of the biological compound of interest.

10. The device of claim 1, wherein said 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 lipids.

11. The device of claim 1, wherein said light emission optics are tuned to emit radiation at a plurality of narrow spectral wavelengths chosen to ensure that measured received radiation are substantially insensitive to scattering variations and such that the optical path lengths through the dermis at said wavelengths are substantially equal.

12. The device of claim 1, wherein said light emission optics are tuned to emit radiation at a plurality of narrow spectral wavelengths chosen to ensure that measured received radiation from said tissue location are insensitive to temperature variations, where said wavelengths are temperature isosbestic in the water absorption spectrum or said received radiation are combined in a way that substantially cancel temperature dependencies of said individual received radiation when computing tissue water fractions.

13. The device of claim 1, wherein said 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 1100-1350 nm, approximately 1500-1800 nm and approximately 2000-2300 nm.

14. The device of claim 1, wherein said light emission optics and said light detection optics are mounted within said probe housing and positioned with appropriate alignment to enable detection in a transmissive mode.

15. The device of claim 1, wherein said light emission optics and said light detection optics are mounted within said probe housing and positioned with appropriate alignment to enable detection in a reflective mode.

16. The device of claim 1, wherein said light emission optics and said light detection optics are placed within a remote unit and which deliver light to and receive light from said probe housing via optical fibers.

17. The device of claim 1, wherein said light emission optics comprise at least one of a (a) incandescent light source, (b) white light source, and (c) light emitting diode (“

LED”

).

18. The device of claim 1, wherein said 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 light 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 light whose absorption is primary due to water, and where a comparison of said at least two optical measurements provides a measure of the absolute water fraction within said tissue location.

19. The device of claim 1, wherein said processing device receives and compares at least two sets of optical measurements, where said at least two sets of optical measurements are based on received radiation from at least two wavelengths and which are combined to form either a single ratio of said received radiation, a sum of ratios of said received radiation or ratios of ratios of said received radiation.

20. The device of claim 1, wherein said processing device receives and compares at least two sets of optical measurements from at least two different wavelengths, where absorption of light at said at least two different wavelengths is primarily due to water which is in the vascular blood and in the extravascular tissue, and where a ratio of said at least two measurements provides a measure of a difference between the fractions of water in the blood and surrounding tissue location.

21. The device of claim 1, wherein said body fluid-related metrics comprise tissue water fraction, and where said tissue water fraction, ƒ

_w is determined such that ƒ

_w=c₁ log [R(λ

₁)/R(λ

₂)]+c₀, and where;

calibration constants c₀ and c₁ are chosen empirically;

R(λ

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

R(λ

₂) is a received radiation at a second wavelength.

22. The tissue water fraction as determined in claim 21,wherein said first and second wavelengths are approximately 1300 nm and approximately 1168 nm respectively.

23. The tissue water fraction as determined in claim 21, wherein said first and second wavelengths are approximately 1230 nm and approximately 1168 nm respectively.

24. The device of claim 1, wherein said body fluid-related metrics comprise tissue water fraction, and where said tissue water fraction, ƒ

_w is determined such that ƒ

_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 a received radiation at a first wavelength;

R(λ

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

R(λ

₃) is a received radiation at a third wavelength.

25. The tissue water fraction as determined in claim 24, wherein said first, second and third wavelengths are approximately 1190 nm, approximately 1170 nm and approximately 1274 nm respectively.

26. The device of claim 1, wherein said body fluid-related metrics comprises tissue water fraction, and where said tissue water fraction, ƒ

_w is determined such that

27. The tissue water fraction as determined in claim 26, wherein said first, second and third wavelengths are approximately 1710 nm, approximately 1730 nm and approximately 1740 nm respectively.

28. The device of claim 1, wherein said body fluid-related metrics comprises a quantified measure of a difference between the water fraction in the blood and the water fraction in the extravascular tissue, where said difference is determined such that

29. The body fluid-metric as determined in accordance to claim 28, further comprising an integral of said difference between the water fraction in the blood and the water fraction in the extravascular tissue to provide a measure of the water that shifts into and out of the capillaries.

30. The bodily fluid-metrics as determined in claim 29, wherein said first and second wavelengths are approximately 1320 nm and approximately 1160 nm respectively.

31. The device of claim 1, further comprising a display device configured to display body fluid-related metrics comprising percent body water and a water balance, where a water balance is the integrated difference between a water fraction in the blood and a water fraction in the extravascular tissue.

32. A device for measuring the absolute volume fraction of water within human tissue using optical spectrophotometry comprising:

a probe housing configured to be placed proximal to a tissue location which is being monitored;

light emission optics configured to direct radiation at said tissue location, wherein said light emission optics comprises one of a (a) incandescent light sources, (b) white light sources and (c) light emitting diodes (“

LEDs”

) which 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;

a photodiode configured to receive radiation from said tissue location;

a processing device configured to process radiation from said light emission optics and said light detection optics to compute said absolute volume fraction of water, wherein said 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 light 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 light whose absorption is primary due to water, and where a comparison of said at least two optical measurements provides a measure of the absolute water fraction within said tissue location; and

a display device connected to said probe housing and configured to display said absolute volume fraction of water.

33. The probe housing of the device of claim 32 further comprising a spring-loaded probe configured to automatically activate said display device when said spring-loaded probe is pressed against a tissue location which is being monitored.

34. The device of claim 32 where said absolute volume fraction of water within human tissue is determined using said processing device which receives and compares at least two sets of optical measurements, where said at least two sets of optical measurements are based on received radiation from at least two wavelengths and which are combined to form either a single ratio of said received radiation, a sum of ratios of said received radiation or ratios of ratios of said received radiation.

35. The tissue water fraction as determined in claim 34, wherein said 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 1100-1350 nm, approximately 1500-1800 nm and approximately 2000-2300 nm.

38. The device of claim 36, where said difference between an intravascular fluid volume and an extravascular fluid volume is determined such that

39. The body fluid-metric as determined in accordance to claim 38 further comprising an integral of said difference between an intravascular fluid volume and an extravascular fluid volume to provide a measure of the water that shifts into and out of the capillaries.

40. The bodily fluid-metrics as determined in claim 38, wherein said first and second wavelengths are 1320 nm and 1160 nm respectively.

36. A device for measuring a difference between an intravascular fluid volume and an extravascular fluid volume using optical spectrophotometry comprising:

a probe housing configured to be placed proximal to a tissue location which is being monitored;

light emission optics configured to direct radiation at said tissue location, wherein said light emission optics comprises one of a (a) incandescent light sources, (b) white light sources or (c) light emitting diodes (“

LEDs”

) which are tuned to emit radiation at a plurality of narrow spectral wavelengths chosen so that the biological compound of interest will absorb light at said plurality of narrow spectral wavelengths and so that absorption by interfering species will be at a minimum;

a photodiode configured to receive radiation from said tissue location;

a processing device configured to process radiation from said light emission optics and said light detection optics to compute said difference between an intravascular fluid volume and an extravascular fluid volume, wherein said processing device receives and compares at least two sets of optical measurements from at least two different wavelengths, where absorption of light at said at least two different wavelengths is primarily due to water which is in the vascular blood and in the extravascular tissue, and where a comparison of said at least two measurements provides a measure of a difference between the fractions of water in the blood and surrounding tissue location; and

a display device connected to said probe housing and configured to display said difference between an intravascular fluid volume and an extravascular fluid volume.

41. A method for measuring a volume fraction of water in a human tissue location using optical spectrophotometry comprising:

placing a probe housing proximal to said tissue location;

emitting radiation at at least two wavelengths using light emission optics configured to direct radiation at said tissue location;

detecting radiation using light detection optics configured to receive radiation from said tissue location;

processing said radiation from said light emission optics and said light detection optics;

computing said volume fraction of water, where said volume fraction determined by;

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

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

determining said volume fraction of water and from said combinations; and

displaying said volume fraction of water on a display device connected to said probe housing.

42. A method for measuring a difference between an intravascular fluid volume and an extravascular fluid volume in a human tissue location using optical spectrophotometry comprising:

placing a probe housing proximal to said tissue location;

emitting radiation using light emission optics configured to direct radiation at said tissue location;

detecting radiation using light detection optics configured to receive radiation from said tissue location;

processing said radiation from said light emission optics and said light detection optics;

computing said difference between an intravascular fluid volume and an extravascular fluid volume, and where said difference between an intravascular fluid volume and an extravascular fluid volume is determined such that

$f_w^{\mathrm{blood}}-f_w^{\mathrm{tissue}}={c_1<br><br>\left(\frac{\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>R}{R}\right)}_{{\mathrm{\lambda <br><br>}}_1}/{\left(\frac{\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>R}{R}\right)}_{{\mathrm{\lambda <br><br>}}_2}+c_0,$

and where;

ƒ

_w^blood is the water fraction in the blood;

ƒ

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

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

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

₁ and a second wavelength, λ

₂ respectively, where said received radiation changes are caused by a pulsation caused by expansion of blood vessels in tissue in response to a heart beat;

calibration constants c₀ and c₁ are chosen empirically; and

displaying said difference between an intravascular fluid volume and an extravascular fluid volume on a display device.