Lung water content measurement system and calibration method
A system and method for monitoring lung water content of a patient. The system may include at least two microwave sensors and a processor. The system may transmit one or more microwave signals into the thorax of a patient using one or more of the microwave sensors. The system may then receive one or more of the microwave signals using one or more of the microwave sensors. The one or more received microwave signals may each have at least one associated frequency component with a magnitude and a phase. The system may analyze the phase of one or more received microwave signals to monitor changes in the lung water content. The system may analyze the magnitude of one or more received microwave signals to determine whether the lung water content is increasing or decreasing.
1. A method of monitoring lung water content in a patient, the method comprising:
transmitting a plurality of microwave signals into the thorax of a patient using a plurality of microwave sensors;
using the microwave sensors to receive a plurality of microwave scattering parameter signals in response to the transmitted microwave signals, the microwave scattering parameter signals each comprising a series of magnitude values and a series of phase values, wherein the microwave scattering parameter signals include a heart signal from one or more of the microwave sensors located in proximity to the patient's heart, and a plurality of possible lung water signals from a plurality of the microwave sensors located in proximity to a lung of the patient;
determining a blood pressure indicator using the heart signal;
identifying a change in the water content of the lung based on the phase values of one or more of the possible lung water signals;
selecting the magnitude values of one of the possible lung water signals based on correlation with the blood pressure indicator; and
resolving an ambiguity in the identified change in the water content of the lung by using the selected magnitude values to determine whether the identified change is indicative of increasing or decreasing lung water content.
2. The method of claim 1 , further comprising:
determining that the water content of the lung is increasing if the selected magnitude values are decreasing; and
determining that the water content of the lung is decreasing if the selected magnitude values are increasing.
3. The method of claim 1 , wherein the phase values used to identify the change in the water content of the lung correspond to a first pair of the microwave sensors and the selected magnitude values correspond to a different second pair of the microwave sensors.
4. The method of claim 1 , wherein the phase values used to identify the change in the water content of the lung correspond to a pair of the microwave sensors and the selected magnitude values correspond to the same pair of the microwave sensors.
5. The method of claim 1 , wherein the microwave scattering parameter signals comprise transmission coefficients between pairs of the microwave sensors.
6. The method of claim 5 , wherein the pairs of the microwave sensors consist of adjacent microwave sensors.
7. The method of claim 5 , wherein each pair of the microwave sensors is provided in a side-by-side configuration on a patch.
8. The method of claim 1 , wherein the possible lung water signals correspond to respective pairs of the microwave sensors located laterally or posteriorly on the patient's thorax in a clear viewing area for the lung.
9. The method of claim 1 , wherein the heart signal corresponds to a pair of the microwave sensors located closest to the patient's heart.
10. The method of claim 1 , wherein the heart signal comprises a plurality of systolic peaks.
11. The method of claim 10 , wherein determining the blood pressure indicator comprises analyzing magnitudes of the systolic peaks.
12. The method of claim 1 , wherein the blood pressure indicator comprises mean arterial pressure.
13. The method of claim 1 , wherein the microwave signals comprise different frequencies.
14. A system for monitoring lung water content in a patient, the system comprising:
a plurality of microwave sensors; and
a processor configured to perform a method comprising
transmitting a plurality of microwave signals into the thorax of a patient using the microwave sensors;
using the microwave sensors to receive a plurality of microwave scattering parameter signals in response to the transmitted microwave signals, the microwave scattering parameter signals each comprising a series of magnitude values and a series of phase values, wherein the microwave scattering parameter signals include a heart signal from one or more of the microwave sensors located in proximity to the patient's heart, and a plurality of possible lung water signals from a plurality of the microwave sensors located in proximity to a lung of the patient;
determining a blood pressure indicator using the heart signal;
identifying a change in the water content of the lung based on the phase values of one or more of the possible lung water signals;
selecting the magnitude values of one of the possible lung water signals based on correlation with the blood pressure indicator; and
resolving an ambiguity in the identified change in the water content of the lung by using the selected magnitude values to determine whether the identified change is indicative of increasing or decreasing lung water content.
15. The system of claim 14 , wherein the method performed by the processor further comprises:
determining that the water content of the lung is increasing if the selected magnitude values are decreasing; and
determining that the water content of the lung is decreasing if the selected magnitude values are increasing.
16. The system of claim 14 , wherein the phase values used to identify the change in the water content of the lung correspond to a first pair of the microwave sensors and the selected magnitude values correspond to a different second pair of the microwave sensors.
17. The system of claim 14 , wherein the phase values used to identify the change in the water content of the lung correspond to a pair of the microwave sensors and the selected magnitude values correspond to the same pair of the microwave sensors.
18. The system of claim 14 , wherein the microwave scattering parameter signals comprise transmission coefficients between pairs of the microwave sensors.
19. The system of claim 18 , wherein the pairs of the microwave sensors consist of adjacent microwave sensors.
20. The system of claim 18 , wherein each pair of the microwave sensors is provided in a side-by-side configuration on a patch.
21. The system of claim 14 , wherein the possible lung water signals correspond to respective pairs of the microwave sensors located laterally or posteriorly on the patient's thorax in a clear viewing area for the lung.
22. The system of claim 14 , wherein the heart signal corresponds to a pair of the microwave sensors located closest to the patient's heart.
23. The system of claim 14 , wherein the heart signal comprises a plurality of systolic peaks.
24. The system of claim 23 , wherein determining the blood pressure indicator comprises analyzing magnitudes of the systolic peaks.
25. The system of claim 14 , wherein the blood pressure indicator comprises mean arterial pressure.
26. The system of claim 14 , wherein the microwave signals comprise different frequencies.