Bioimpedance methods and apparatus

• US 7,945,317 B2
• Filed: 09/10/2004
• Issued: 05/17/2011
• Est. Priority Date: 09/12/2003
• Status: Expired due to Fees

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.), Renal Research Institute LLC
• Original Assignee: Renal Research Institute LLC
• Inventors: Zhu, Fansan, Levin, Nathan W.
• Primary Examiner(s): Hindenburg; Max
• Assistant Examiner(s): Henson; Devin
• Application Number:
  US10/570,368
• Publication Number:
  US 20070027402A1
• Time in Patent Office: 2,440 Days
• Field of Search: 600/547, 600/587, 324/600
• US Class Current: 600/547
• CPC Class Codes: A61B 2560/0223 of calibration, e.g. protocols for calibrating sensors
• CPC Class Codes: A61B 5/0537 Measuring body composition by impedance, e.g. tissue hydration or fat content
• CPC Class Codes: A61B 5/055 involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
• CPC Class Codes: A61B 5/4872 Body fat
• CPC Class Codes: A61B 5/4881 Determining interstitial fluid distribution or content within body tissue measuring analytes in interstitial fluid in-vivo A61B5/1451

Abstract

Methods and apparatus for providing bioimpedance analysis are provided. In certain aspects, equivalent circuit frequency response models are provided which lead to improved correlations with MRI data. The frequency response models take account of body composition, including the fat component of a body segment. Data obtained by performing bioimpedance spectroscopy (BIS) and MRI on the calves of subjects illustrates the improved correlations achieved compared to single frequency analyses at 50 kilohertz and analyses performed using the conventional Cole-Cole model.

Claims

1. A method for analyzing bioimpedance data for a body segment of a subject, said body segment having an external skin surface, said method comprising:

(a) applying alternating current at a plurality of frequencies to at least two points on the external skin surface so as to cause current to pass through the segment;

(b) for each frequency, recording the voltage difference between at least two other points on the external skin surface, said recorded voltage differences comprising both magnitude and phase information; and

(c) using the recorded voltage differences at the plurality of frequencies to determine at least one numerical value indicative of the muscle, fat, and/or extracellular fluid content of the segment, said numerical value being determined using an impedance model for the segment which at least comprises three parallel paths, one of which consists of a capacitor C_M and a resistor R_I in series which represent primarily the muscle component of the segment, one of which consists of a capacitor C_F and a resistor R_F in series which represent primarily the fat component of the segment, and one of which consists of a resistor;

wherein the three parallel path impedance model is used at least one frequency less than or equal to 10 kilohertz and at least one frequency greater than 10 kilohertz.

2. The method of claim 1 wherein the at least one numerical value is indicative of the muscle content of the segment and is obtained from a correlation equation which transforms an R_I value to a muscle content value for the segment.

3. The method of claim 2 wherein the correlation equation is obtained by:

(i) performing steps (a), (b), and (c) on a plurality of calibration subjects to obtain an R_I value for each of said subjects;

(ii) performing magnetic resonance imaging of the segment for the plurality of calibration subjects to obtain a value for the muscle content of the segment for each of said subjects; and

(iii) performing a regression analysis on the values obtained in steps (i) and (ii) to obtain the correlation equation.

4. The method of claim 3 wherein the regression analysis yields an R² value of at least 0.5 for the correlation equation.

5. The method of claim 4 wherein the plurality of calibration subjects includes at least one calibration subject having a body mass index less than 20 and at least one calibration subject having a body mass index greater than 35.

6. The method of claim 1 wherein the at least one numerical value is indicative of the fat content of the segment and is obtained from a correlation equation which transforms an R_F value to a fat content value for the segment.

7. The method of claim 6 wherein the correlation equation is obtained by:

(i) performing steps (a), (b), and (c) on a plurality of calibration subjects to obtain an R_F value for each of said subjects;

(ii) performing magnetic resonance imaging of the segment for the plurality of calibration subjects to obtain a value for the fat content of the segment for each of said subjects; and

(iii) performing a regression analysis on the values obtained in steps (i) and (ii) to obtain the correlation equation.

8. The method of claim 7 wherein the regression analysis yields an R² value of at least 0.5 for the correlation equation.

9. The method of claim 8 wherein the plurality of calibration subjects includes at least one calibration subject having a body mass index less than 20 and at least one calibration subject having a body mass index greater than 35.

10. The method of claim 1 wherein the parallel path which consists of a resistor represents primarily the extracellular fluid component of the segment.

11. The method of claim 1 wherein the parallel path which consists of a resistor represents primarily a parallel combination of the extracellular fluid and the bone components of the segment.

12. The method of claim 1 wherein the impedance model further comprises a capacitor in series with the three parallel paths.

13. The method of claim 1 wherein the plurality of frequencies comprises frequencies greater than or equal to 5 kilohertz and less than or equal to 1000 kilohertz.

14. The method of claim 1 wherein the applied alternating currents of step (a) and the recorded voltage differences of step (b) are used to calculate impedance values at the plurality of frequencies and step (c) comprises curve fitting to those impedance values.

15. The method of claim 14 wherein:

(i) the curve fitting employs an equation of the type;

16. The method of claim 1 wherein in step (a), said at least two points on the external skin surface comprise:

(i) two points on the subject'"'"'s leg;

(ii) two points on the subject'"'"'s calf;

(iii) two points on the subject'"'"'s arm;

(iv) two points on the subject'"'"'s biceps;

(v) two points on the subject'"'"'s abdomen;

(vi) one point on the subject'"'"'s left hand and one point on the subject'"'"'s right hand;

(vii) one point on the subject'"'"'s left foot and one point on the subject'"'"'s right foot;

or

(viii) one point on one of the subject'"'"'s hands or one of the subject'"'"'s arms and one point on one of the subject'"'"'s legs or one of the subject'"'"'s feet.

17. The method of claim 1 further comprising displaying the at least one numerical value indicative of the muscle, fat, and/or extracellular fluid content of the segment to a user.

18. The method of claim 1 wherein the method is performed on the same subject at two or more points in time.

19. The method of claim 18 wherein the method is performed in connection with:

(i) a dialysis procedure;

(ii) an exercise program;

(iii) a rehabilitation program; and

/or

(iv) a weight control program.

20. Apparatus for analyzing bioimpedance data comprising a programmed computer for performing the method of claim 1.