Bio-impedance apparatus and method

• US 20060064029A1
• Filed: 09/13/2005
• Published: 03/23/2006
• Est. Priority Date: 07/03/2002
• Status: Active Grant

• Current Assignee: Tel Aviv University Future Technology Development L.P. (Tel Aviv University)
• Original Assignee: Tel Aviv University Future Technology Development L.P. (Tel Aviv University)
• Inventors: Arad (Abboud), Shimon
• Granted Patent: US 7,907,998 B2
• Time in Patent Office: Days
• US Class Current: 600/547
• CPC Class Codes: A61B 5/053 Measuring electrical impedance or conductance of a portion of the body
• CPC Class Codes: A61B 5/0537 Measuring body composition by impedance, e.g. tissue hydration or fat content
• CPC Class Codes: A61B 5/0538 invasively, e.g. using a catheter
• CPC Class Codes: A61B 5/4878 Evaluating oedema
• CPC Class Codes: A61N 1/37 Monitoring; Protecting

Abstract

A method of determining an impedance of at least one lung of a patient having an implanted pacemaker that comprises first and second leads and a case, the method comprising: a) using the leads and the case to acquire at least a first and a second impedance measurement responsive to impedance of the patient'"'"'s chest that are at least partially independent; and b) using the impedance measurements to determine the impedance of at least one of the lungs substantially independently of impedance of the other lung.

Claims

1. A method of determining an impedance of at least one lung of a patient having an implanted pacemaker that comprises first and second leads and a case, the method comprising:

a) using the leads and the case to acquire at least a first and a second impedance measurement responsive to impedance of the patient'"'"'s chest that are at least partially independent; and

b) using the impedance measurements to determine the impedance of at least one of the lungs substantially independently of impedance of the other lung.

2. A method according to claim 1, wherein using the measurements to determine the impedance of at least one of the lungs comprises determining the impedance of said lung such that Poisson'"'"'s equation for a model of the chest has a solution consistent with the at least two impedance measurements.

3. A method according to claim 2, wherein the model of the chest treats the impedances of the two lungs as two independent variables.

4. A method according to claim 1, wherein acquiring the impedance measurements comprises, for each impedance measurement:

a) generating a current between at least one of the leads and the case; and

b) measuring a voltage involving a potential difference between at least one of the leads and the case;

wherein, for each impedance measurement, a different configuration of the first and second leads is used than is used for any other of the impedance measurements, for generating the current or for measuring the voltage or for both.

5. A method according to claim 4, wherein, for the first and second impedance measurements, the current is generated only between the case and one of the leads, the same lead for both the first and second impedance measurements, and the voltage involves only a potential difference between the case and one of the leads, a different one for the first impedance measurement than for the second impedance measurement.

6. A method according to claim 1, wherein determining the impedance of at least one lung comprises determining the impedances of both lungs.

7. A method according to claim 6, wherein the impedance measurements also comprise a third impedance measurement.

8. A method according to claim 7, also including determining a third parameter of the thorax, in addition to the two lung impedances.

9. A method according to claim 8, wherein the third parameter comprises an intravascular volume of the thorax.

10. A method according to claim 8, wherein at least one of the lung impedances pertains only to a portion of said lung, and the third parameter comprises an impedance of another portion of said lung.

11. A method according to claim 7, wherein a least squares method is used to find a fit of the two lung impedances to the at least three impedance measurements.

12. A method according to claim 6, wherein determining the lung impedances comprises:

a) making an initial guess for the values of the lung impedances;

b) calculating the expected impedance measurements for said values of the lung impedances;

c) correcting the values of the impedances according to a difference between the measured and expected values for the impedance measurements; and

d) repeating (b) and (c) until a convergence criterion is satisfied.

13. A method according to claim 12, wherein calculating the expected impedance measurements comprises using one or more of the finite element method, the finite difference method, the finite boundary element method, and the finite volume method.

14. A method according to claim 1, wherein one of the leads is implanted in the right ventricle.

15. A method according to claim 1, wherein one of the leads is implanted in the right atrium.

16. A method according to claim 1, wherein one of the leads is implanted in the left ventricle coronary vein.

17. A method according to claim 1, wherein the case is implanted in the left pre-pectoral position.

18. A method according to claim 1, wherein the case is implanted in the right pre-pectoral position.

19. A method of determining the impedance of at least one lung, comprising:

a) generating a first current between a pacemaker case implanted in the chest, and at least one of a first lead and a second lead implanted at different locations in the heart;

b) measuring a first voltage involving a potential difference between at least one of the leads and the case, due at least in part to at least a portion of the current which is generated between the other lead and the case; and

c) calculating the impedance of at least one lung from the first current and the first voltage.

20. A pacemaker for bio-impedance measurements, comprising:

a) a case adapted for implanting in the chest;

b) a first lead adapted for implanting at a location in the heart;

c) a second lead adapted for implanting at a different location in the heart;

d) a bio-impedance system, adapted to make impedance measurements comprising at least a first and a second impedance measurement, using the case and the first and second leads; and

e) a data analyzer, adapted to determine an impedance of at least one of the lungs, substantially independently of impedance of the other lung.