Method and apparatus for estimating water reserves

• US 20080221406A1
• Filed: 03/09/2007
• Published: 09/11/2008
• Est. Priority Date: 03/09/2007
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Covidien LP (Medtronic Plc)
• Inventors: Baker, Clark R.
• Granted Patent: US 8,357,090 B2
• Time in Patent Office: Days
• US Class Current: 600/306
• 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 5/0075 by spectroscopy, i.e. measuring spectra, e.g. Raman spectroscopy, infrared absorption spectroscopy A61B5/0071 takes precedence
• CPC Class Codes: A61B 5/1075 for measuring dimensions by non-invasive methods, e.g. for determining thickness of tissue layer A61B8/0858 takes precedence
• CPC Class Codes: A61B 5/441 Skin evaluation, e.g. for skin disorder diagnosis
• CPC Class Codes: A61B 5/443 Evaluating skin constituents, e.g. elastin, melanin, water
• CPC Class Codes: A61B 5/4869 Determining body composition
• CPC Class Codes: A61B 8/0858 involving measuring tissue layers, e.g. skin, interfaces

Abstract

A system and method are provided for a water reserve index. The method includes determining a lean water fraction of tissue for at least one tissue site and determining skin thickness for the at least one tissue site. The lean water fraction and skin thickness are combined to produce a water reserve estimate.

Claims

1. A method for determining a water reserve index comprising:

determining a lean water fraction of tissue for at least one tissue site;

determining skin thickness for the at least one tissue site; and

using the lean water fraction and skin thickness to produce a water reserve estimate.

2. The method of claim 1 wherein the lean water fraction is determined spectroscopically.

3. The method of claim 2 wherein the lean water fraction is determined based on spectral absorption bandwidth.

4. The method of claim 1, wherein the skin thickness is determined spectroscopically.

5. The method of claim 1, wherein the skin thickness is determined ultrasonically.

6. The method of claim 1, wherein the skin thickness is determined mechanically.

7. The method of claim 6, comprising using calipers.

8. The method of claim 4, wherein the skin thickness is determined by spectroscopically determining the amplitude of spectral features corresponding to a subcutaneous fat layer relative to spectral features corresponding to water and protein.

9. The method of claim 1 wherein determining the water reserve index comprises adjusting the water index for elevation differences between the heart and the at least one skin site.

10. The method of claim 9, wherein the relative elevation of the skin site is averaged over a period representative of the equilibrium time of the interstitial compartment.

11. A method for determining skin thickness comprising:

emitting electromagnetic radiation from a sensor at an individual'"'"'s skin;

detecting the emitted electromagnetic radiation after it has been scattered and absorbed by constituents of the skin; and

determining the skin thickness based on the amplitude of spectral features corresponding to a subcutaneous fat layer relative to spectral features corresponding to water and protein.

12. The method of claim 11 wherein emitting electromagnetic radiation at skin comprises using multiple discrete light sources operating at wavelengths in the near-infrared spectrum.

13. The method of claim 11 wherein emitting electromagnetic radiation at skin comprises using a continuous spectrum light source.

14. The method of claim 13 wherein using a continuous spectrum light source comprises using a tunable laser.

15. The method of claim 11 wherein detecting the emitted electromagnetic radiation comprises using a photosensitive diode.

16. The method of claim 11 wherein determining the prominence of spectral features corresponding to the subcutaneous layer comprises determining the prominence of peaks at approximately 1210 nm, 1725 nm, and 1765 nm.

17. The method of claim 11 wherein determining the prominence of spectral features comprises performing a spectral analysis on the detected electromagnetic radiation and comparing the detected spectrum with a known spectrum for a euhydrated state.

18. The method of claim 11 comprising performing a calibration based on the location on the individual at which the sensor emits electromagnetic radiation.

19. The method of claim 11 comprising performing a calibration based on the elevation of the sensor relative to a heart.

20. A system for determining a water reserve index comprising:

a sensor, the sensor comprising;

an emitter configured to emit near-infrared light;

a detector located between 1 to 5 mm from the emitter configured to detect the emitted light and generate a signal representative of the detected light, wherein the emitter and the detector are configured to optically couple with an individual'"'"'s skin;

a monitor communicatively coupled to the sensor and configured to receive the generated

signal, the monitor comprising;

a microprocessor configured calculate a lean water fraction based on the received signal, the microprocessor combining the lean water fraction with a skin thickness value to determine a water reserve index; and

a display configured to display the determined water reserve index to the user.

21. The system of claim 20 wherein the microprocessor is configured to compute the skin thickness based on the received signal.

22. The system of claim 20 wherein combining the lean water fraction with skin thickness comprises multiplying the lean water fraction with the skin thickness.

23. The system of claim 20 comprising a keyboard configured to allow a user to input parameters pertinent to the determination of a water reserve index.

24. The system of claim 23 wherein the keyboard is configured to allow a user to input sensor location information.

25. The system of claim 23 wherein keyboard is configured to allow a user to input sensor elevation information.

26. The system of claim 20 wherein the display is configured to allow a user to indicate sensor location information.

27. The system of claim 20 wherein the sensor is configured to the monitor location specific information.

28. The system of claim 20 wherein the emitter is 2.5 mm from the detector.