Methods and systems for photoacoustic monitoring using indicator dilution

• US 8,886,294 B2
• Filed: 11/30/2011
• Issued: 11/11/2014
• Est. Priority Date: 11/30/2011
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Covidien LP (Medtronic Plc)
• Inventors: Lisogurski, Daniel, Li, Youzhi, Chen, Bo
• Primary Examiner(s): Le, Long V.
• Assistant Examiner(s): BOR, HELENE CATHERINE
• Application Number:
  US13/308,086
• Publication Number:
  US 20130137959A1
• Time in Patent Office: 1,077 Days
• Field of Search: 600/473, 600/480, 600/465, 600/526, 600/342
• US Class Current: 600/473
• CPC Class Codes: A61B 5/0095 by applying light and detecting acoustic waves, i.e. photoacoustic measurements
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/0261 using optical means, e.g. infrared light
• CPC Class Codes: A61B 5/0275 using tracers, e.g. dye dilution
• CPC Class Codes: A61B 5/029 Measuring or recording blood output from the heart, e.g. minute volume A61B8/065 takes precedence
• CPC Class Codes: A61B 5/1455 using optical sensors, e.g. spectral photometrical oximeters
• CPC Class Codes: A61B 5/6867 specially adapted to be attached or implanted in a specific body part A61B5/6847 takes precedence

Abstract

A patient monitoring system may provide photoacoustic sensing based on an indicator dilution to determine one or more physiological parameters of a subject. The system may detect an acoustic pressure signal, which may include one or more thermo-dilution responses, one or more hemo-dilution responses, or a combination thereof, using one or more sensor units. The system may use multiple light sources and/or detectors to diagnose and/or improve signal to noise ratio, distinguish between arterial and venous signals, prevent under-sampling, and separate the effects of hemo-dilution and thermo-dilution.

Claims

1. A method for determining a physiological parameter of a subject, the method comprising:

detecting a first acoustic pressure signal and a second acoustic pressure signal using one or more acoustic detectors, wherein the first acoustic pressure signal and the second acoustic pressure signal are caused by absorption of at least some of one or more photonic signals by one or more constituents in a first blood vessel and in a second blood vessel, respectively, and wherein the first acoustic pressure signal and the second acoustic pressure signal comprise dilution responses corresponding to an indicator;

deriving a first photoacoustic signal from the first acoustic pressure signal and a second photoacoustic signal from the second acoustic pressure signal;

comparing the first photoacoustic signal to the second photoacoustic signal to determine a shape difference or a time difference between the first and second photoacoustic signals;

determining whether the first blood vessel or the second blood vessel is an artery or a vein based at least in part on the shape difference or the time difference;

selecting the first photoacoustic signal or the second photoacoustic signal based at least in part on the determination of whether the first blood vessel or the second blood vessel is the artery or the vein; and

determining the physiological parameter based at least in part on the selected first photoacoustic signal or the second photoacoustic signal.

2. The method of claim 1, wherein determining the physiological parameter is based at least in part on the time difference between the dilution response of the first acoustic pressure signal and the dilution response of the second acoustic pressure signal.

3. The method of claim 2, wherein the first blood vessel and the second blood vessel comprise respective vessels of at least one of a carotid artery and a jugular vein, a radial artery and a cephalic vein, and an ulnar artery and an ulnar vein.

4. The method of claim 2, wherein the physiological parameter is a flow rate of blood through an organ located between the first vessel and the second vessel.

5. The method of claim 1, wherein a first photonic signal of the one or more photonic signals is out of phase relative to a second photonic signal of the one or more photonic signals.

6. The method of claim 1, wherein the physiological parameter is one of cardiac output, intrathoracic blood volume, intrathoracic circulatory volume, global end-diastolic volume, pulmonary circulatory volume, and extravascular lung water.

7. The method of claim 1, wherein the first acoustic pressure signal comprises a first response to a first thermo-dilution indicator and a second response to a second thermo-dilution indicator, and wherein the second acoustic pressure signal comprises a first response to the first thermo-dilution indicator and a second response to the second thermo-dilution indicator, and wherein the first and the second thermo-dilution indicators are introduced to the subject at different temperatures.

8. The method of claim 1, further comprising determining a value indicative of signal confidence based on at least one of the first acoustic pressure signal and the second acoustic pressure signal, and wherein the determining the physiological parameter is further based on the value indicative of signal confidence.

9. The method of claim 1, wherein determining the time difference or the shape difference comprises cross-correlating the first and the second photoacoustic signals.

10. The method of claim 1, wherein the shape difference is based at least in part on a peak or trough height, peak or trough width, an integrated area of peak or trough, or a peak or trough skewness.

11. The method of claim 1, wherein the constituent is hemoglobin.

12. A system for determining a physiological parameter of a subject, the system comprising:

one or more light sources configured to provide one or more photonic signals to one or more monitoring sites of the subject;

one or more acoustic detectors configured to detect a first acoustic pressure signal and a second acoustic pressure signal from the one or more monitoring sites, wherein the first acoustic pressure signal and the second acoustic pressure signal are caused by the absorption of at least some of the one or more photonic signals by one or more constituents in a first blood vessel and a second blood vessel, respectively, and wherein the first acoustic pressure signal and the second acoustic pressure signal comprise a responses corresponding to an indicator; and

processing equipment configured to;

derive a first photoacoustic signal from the first acoustic pressure signal and a second photoacoustic signal from the second acoustic pressure signal;

compare the first photoacoustic signal to the second photoacoustic signal to determine a shape difference or a time difference between the first and second photoacoustic signals;

determine whether the first blood vessel or the second blood vessel is an artery or a vein based at least in part on the shape difference or the time difference;

select the first photoacoustic signal or the second photoacoustic signal based at least in part on the determination of whether the first blood vessel or the second blood vessel is the artery or the vein; and

determine the physiological parameter based at least in part on the selected first photoacoustic signal or the second photoacoustic signal.

13. The system of claim 12, wherein the processing equipment is configured to determine the physiological parameter based at least in part on the time difference between the first response of the first acoustic pressure signal and the second response of the second acoustic pressure signal.

14. The system of claim 13, wherein the first blood vessel and the second blood vessel comprise respective vessels of at least one of a carotid artery and a jugular vein, a radial artery and a cephalic vein, and an ulnar artery and an ulnar vein.

15. The system of claim 12, wherein a first photonic signal of the one or more photonic signals provided to the one or more monitoring sites is out of phase relative to a second photonic signal of the one or more photonic signals provided to the one or more monitoring sites.

16. The system of claim 12, wherein the processing equipment is further configured to determine one of cardiac output, intrathoracic blood volume, intrathoracic circulatory volume, global end-diastolic volume, pulmonary circulatory volume, and extravascular lung water.

17. The system of claim 12, wherein the first acoustic pressure signal comprises a first response to a first thermo-dilution indicator and a second response to a second thermo-dilution indicator, and wherein the second acoustic pressure signal comprises a first response to the first thermo-dilution indicator a second response to the second thermo-dilution indicator, and wherein the first and the second thermo-dilution indicators are introduced to the subject at different temperatures.

18. The system of claim 12, wherein the processing equipment is further configured to determine a value indicative of signal confidence based on at least one of the first photoacoustic signal and the second photoacoustic signal, and wherein the determining the physiological parameter is further based on the value indicative of signal confidence.

19. The system of claim 12, comprising at least one sensor unit having a sensor body comprising at least one light source and at least one acoustic detector.

20. The system of claim 19, wherein the sensor body comprises multiple acoustic detectors.

21. The system of claim 19, wherein the sensor unit comprises an encoder storing information related to whether the at least one light source is configured to emit pulsed or continuous wave light.