Methods and systems for determining fluid content of tissue

1. A method for diagnosis, comprising:

directing radio frequency (RF) electromagnetic waves from one or more antennas disposed on a thorax of a body of a patient so that the RF electromagnetic waves pass through or reflect off a lung in the body;

outputting signals responsively to the RF electromagnetic waves that have passed through the lung;

processing the signals over time so as to measure a path characteristic of the RF electromagnetic waves;

comparing the measured path characteristic to one or more benchmark path characteristic values corresponding to identified levels of fluid content of lungs; and

determining fluid content of the lung based on the comparison.

2. The method of claim 1 , wherein processing the signals comprises measuring a change in the path characteristic over one or more respiratory cycles of the lung, and determining the fluid content responsively to the change.

3. The method of claim 1 , wherein the path characteristic comprises an effective RF path length of the RF electromagnetic waves through the body.

4. The method of claim 1 , wherein the benchmark path characteristic values comprise a physical distance traversed by the RF electromagnetic waves through the thorax of the body.

5. The method of claim 4 , wherein:

directing RF electromagnetic waves comprises transmitting the RF electromagnetic waves through the lung by a transmitting antenna at a first location on a first side of the thorax, and further comprising:

receiving, by a receiving antenna, the waves that have passed through the lung at a second location on a second side of the thorax, opposite the first side, and wherein the physical distance is measured between the first and second locations.

6. The method of claim 4 , wherein

directing RF electromagnetic waves comprises the RF electromagnetic waves through the lung toward a heart in the body, and further comprising:

outputting the RF signals responsively to the RF electromagnetic waves reflected from the heart.

7. The method of claim 6 , further comprising:

directing, via an ultrasonic transducer located adjacent to the at least one antenna, ultrasonic waves toward the heart, and

receiving the ultrasonic waves reflected from the heart so as to provide a measure of the physical distance.

8. The method of claim 1 , wherein the path characteristic comprises an amplitude of the RF electromagnetic waves.

9. The method of claim 1 , wherein the path characteristic comprises a phase of the RF electromagnetic waves.

10. A method, comprising:

directing radio frequency (RF) electromagnetic waves from one or more antennas disposed on a body of a patient so that the RF electromagnetic waves pass through a first tissue of the body;

outputting signals responsively to the RF electromagnetic waves that have passed through the first tissue;

processing the signals at a plurality of different points over a period of time so as to determine a path characteristic of the RF electromagnetic waves relative to the first tissue at the different points;

comparing the determined path characteristic at the plurality of different points over the period of time; and

determining a change in fluid content of the first tissue over the period of time based on the comparison.

11. The method of claim 10 , wherein the path characteristic includes an amplitude of the RF electromagnetic waves.

12. The method of claim 10 , wherein the path characteristic includes a phase of the RF electromagnetic waves.

13. The method of claim 10 , wherein the path characteristic includes an effective RF path length of the RF electromagnetic waves that have passed through the first tissue.

14. The method of claim 13 , wherein comparing the determined path characteristic includes comparing the effective RF path length of the RF electromagnetic waves to a physical distance traversed by the RF electromagnetic at the plurality of different points over the period of time.

15. The method of claim 14 , wherein an ultrasonic transducer is used to obtain a measurement of the physical distance.

16. The method of claim 14 , wherein:

the one or more antennas comprises a transmitting antenna and a receiving antenna located across the first tissue, the transmitting antenna and the receiving antenna each including a position sensor for measuring a first location and a second location of the transmitting antenna and the receiving antenna, respectively, and

the physical distance is a distance between the first location and the second location.

17. The method of claim 10 , further comprising determining attachment level of the one or more antennas disposed on the body to skin of the body based on analysis of characteristics of the RF electromagnetic waves.

18. The method of claim 10 , further comprising performing an impedance measurement between the one or more antennas disposed on the body and skin of the body so as to determine an attachment level of the one or more antennas to the skin.

19. The method of claim 10 , further comprising adjusting a pacing of an electrode configured to apply a pacing signal into the body based on the change in the fluid content.

20. The method of claim 10 , wherein processing the signals includes processing physiological data of the patient in conjunction with the signals.

21. The method of claim 20 , wherein the physiological data include information on one or more of patient weight, blood pressure, posture and breathing.