Methods for determining the relative spatial change in subsurface resistivities across frequencies in tissue

• US 9,149,225 B2
• Filed: 12/14/2012
• Issued: 10/06/2015
• Est. Priority Date: 12/14/2011
• Status: Active Grant

• Current Assignee: ImpediMed Limited
• Original Assignee: Intersection Medical, Inc.
• Inventors: De Limon, Alfonso L., Chetham, Scott M., Erlinger, Paul J.
• Primary Examiner(s): EISEMAN, ADAM JARED
• Application Number:
  US13/715,788
• Publication Number:
  US 20130165761A1
• Time in Patent Office: 1,026 Days
• Field of Search: 600/547
• US Class Current: 1/1
• CPC Class Codes: A61B 2562/0215 Silver or silver chloride containing
• CPC Class Codes: A61B 2562/04 Arrangements of multiple sensors of the same type
• CPC Class Codes: A61B 2562/043 in a linear array
• CPC Class Codes: A61B 2562/164 the sensor is mounted in or on a conformable substrate or carrier
• CPC Class Codes: A61B 5/0537 Measuring body composition by impedance, e.g. tissue hydration or fat content
• CPC Class Codes: A61B 5/08 Detecting, measuring or recording devices for evaluating the respiratory organs A61B5/0205 takes precedence
• CPC Class Codes: A61B 5/4875 Hydration status, fluid retention of the body
• CPC Class Codes: A61B 5/4878 Evaluating oedema
• CPC Class Codes: A61B 5/6823 Trunk, e.g., chest, back, abdomen, hip
• CPC Class Codes: A61B 5/6833 Adhesive patches
• CPC Class Codes: A61B 5/68335 including release sheets or liners
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7225 Details of analog processing, e.g. isolation amplifier, gain or sensitivity adjustment, filtering, baseline or drift compensation A61B5/30, A61B5/316 take precedence; transformers for specific applications H01F38/00; amplifiers H03F
• CPC Class Codes: A61B 5/7271 Specific aspects of physiological measurement analysis A61B5/316, A61B5/349 and A61B5/374 take precedence
• CPC Class Codes: A61B 5/7278 Artificial waveform generation or derivation, e.g. synthesising signals from measured signals A61B5/327 takes precedence

Abstract

Non-invasive devices and systems to determine tissue wetness/hydration based on relative changes in subsurface resistivities in tissue below an electrode array applied to a human body across different frequencies. For example, these a sensor including arrays of current-injecting and voltage-sensing electrodes may be placed on a subject'"'"'s back to determine lung wetness. Systems and methods for determining tissue water content, systems and methods for determining lung wetness, sensors for determining relative changes in subsurface resistivities across frequencies and systems and methods to determine which arrays of electrodes in a sensor to use to determine relative changes in subsurface resistivities across frequencies are all described.

Claims

1. A method of non-invasively determining lung wetness, the method comprising:

placing a sensor comprising a plurality of electrodes arranged in a proximal to distal active region on the subject'"'"'s back so that the proximal to distal axis of the sensor extends cranially to caudally along the subject'"'"'s back, and wherein the active region of the sensor is positioned lateral to the subject'"'"'s spine;

using the sensor to determine a relative spatial change in subsurface resistivities across frequencies (RSCSRAF) based on applied currents and detected voltages, wherein determining the RSCSRAF comprises normalizing a resistivity at a first frequency within a first subsurface region by a resistivity at a second frequency within the first subsurface region; and

indicating if the lung is wet based on the relative spatial change in subsurface resistivities across frequencies,

wherein the relative spatial change in subsurface resistivities across frequencies is determined using an inverse problem to solve for the spatial distribution of subsurface resistivities by minimizing the error between detected values and those produced by a forward model calculating a change in subsurface resistivities.

2. The method of claim 1, wherein placing the sensor comprises positioning the active region of the sensor offset from the midline of the subject'"'"'s back lateral to the spine.

3. The method of claim 1, wherein the sensor comprises a plurality of elongate electrodes arranged in parallel and oriented transverse to the proximal to distal axis of the sensor to form the active region.

4. The method of claim 1, wherein placing comprises placing the proximal portion of the active region of the sensor in line with the top of the subject'"'"'s scapula.

5. The method of claim 1, wherein placing comprises placing a middle portion of the sensor in line with the subject'"'"'s lung.

6. The method of claim 1, further comprising applying a plurality of currents between pairs of at least some of the electrodes, wherein current is applied to pairs of electrodes while detecting voltage with other pairs of electrodes, further wherein a plurality of current frequencies are applied.

7. The method of claim 1, wherein using the sensor to determine a relative spatial change in subsurface resistivities across frequencies comprises determining a spatial distribution of relative percent differences of apparent resistivities at a low frequency of 20 kHz or lower and a higher second frequency.

8. The method of claim 1, further comprising presenting a representation of lung wetness based on the relative spatial change in subsurface resistivities across frequencies.

9. The method of claim 1, wherein placing the sensor comprises placing the active region of the sensor offset from the midline of the subject'"'"'s back lateral to the subject'"'"'s spine by an inch +/−

10% of an inch.

10. The method of claim 1, wherein placing the sensor comprises placing the active region of the sensor along the subject'"'"'s back from a region in line with the top of the subject'"'"'s scapula and extending caudally for 8 or more inches.

11. The method of claim 1, wherein placing the sensor comprises placing the center of the active region of the sensor along the subject'"'"'s back from a region in line with the subject'"'"'s lung.

12. The method of claim 1, wherein placing the sensor comprises positioning a lateral edge of the active region of the sensor offset by an inch +/−

10% of an inch from the midline of the subject'"'"'s back.

13. The method of claim 1, wherein placing the sensor comprises placing the sensor so that the active region of the sensor extends laterally from an inch +/−

10% of an inch from the midline of the subject'"'"'s back to 3 inches +/−

10% of 3 inches from the midline of the subject'"'"'s back.

14. The method of claim 1, wherein each electrode of the active region extends laterally from an inch +/−

10% of an inch from the midline of the subject'"'"'s back to 3 inches +/−

10% of 3 inches from the midline of the subject'"'"'s back.

15. The method of claim 1, further comprising conforming the sensor the subject'"'"'s skin as it extends along the length of the back.

19. The method of claim 1, wherein indicating if the lung is wet comprises indicating without producing an image.

16. A method of non-invasively determining lung wetness, the method comprising:

applying currents at a plurality of frequencies from a sensor on a region of a subject'"'"'s back;

determining a spatial distribution of relative spatial change in subsurface resistivities (RSCSRAF) across frequencies across the region of the subject'"'"'s back, wherein the RSCSRAF is determined at last in part by normalizing a resistivity at a first frequency within a first subsurface region by a resistivity at a second frequency within the first subsurface region; and

comparing an average of at least some of the values from the relative spatial change in subsurface resistivities across frequencies to a threshold value, and indicating if the lung is dry or wet based on this comparison,

wherein the relative spatial change in subsurface resistivities across frequencies is determined using an inverse problem to solve for the spatial distribution of subsurface resistivities by minimizing the error between detected values and those produced by a forward model calculating a change in subsurface resistivities.

17. The method of claim 16, wherein comparing an average comprises comparing an average of values from the relative spatial change in subsurface resistivities across frequencies from a central subsurface region beneath the sensor to the threshold value.

18. The method of claim 16, wherein comparing comprises indicating if the lung is dry or wet based on the comparison and based on a depth of a peak relative spatial change in subsurface resistivities across frequencies value.