PULMONARY PULSE OXIMETRY METHOD FOR THE MEASUREMENT OF OXYGEN SATURATION IN THE MIXED VENOUS BLOOD

• US 20130310669A1
• Filed: 05/20/2012
• Published: 11/21/2013
• Est. Priority Date: 05/20/2012
• Status: Abandoned Application

• Current Assignee: Jerusalem College Of Technology, Kerry Kreutz
• Original Assignee: Jerusalem College Of Technology
• Inventors: Nitzan, Meir
• Application Number:
  US13/475,988
• Publication Number:
  US 20130310669A1
• Time in Patent Office: Days
• US Class Current: 600/339
• CPC Class Codes: A61B 5/0059 using light, e.g. diagnosis by transillumination, diascopy, fluorescence A61B5/0093, A61B5/1455, A61B5/02416 and A61B5/0261 take precedence
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/1459 invasive, e.g. introduced into the body by a catheter A61B5/1464 takes precedence
• CPC Class Codes: A61B 5/6823 Trunk, e.g., chest, back, abdomen, hip
• CPC Class Codes: G01N 2021/3144 for oxymetry
• CPC Class Codes: G01N 2021/3181 using LEDs
• CPC Class Codes: G01N 21/3151 using two sources of radiation of different wavelengths G01N21/33 - G01N21/39 take precedence
• CPC Class Codes: G01N 21/359 using near infrared light
• CPC Class Codes: G01N 2201/08 Optical fibres; light guides
• CPC Class Codes: G01N 33/4925 measuring blood gas content, e.g. O2, CO2 , HCO3

Abstract

A method for obtaining diagnostic information relating to the lungs of a subject includes directing into tissue of the lungs of the subject light of a first wavelength and detecting part of the light that has passed primarily through microcirculatory tissue of the lungs and generating a signal which is a function of intensity of the detected light. The signal is then processed to derive a PPG curve for pulmonary microcirculatory arteries. The method is implemented using various locations for a light source and a detector, including various combinations of positioning on the thoracic wall, insertion into the esophagus, and in some cases, insertion of a probe through the thoracic wall to a position adjacent to the pulmonary pleura. Use of two different wavelengths allows derivation of mixed venous blood oxygen saturation.

Claims

1. A method for obtaining diagnostic information relating to the lungs of a subject, the method comprising the steps of:

(a) directing into tissue of the lungs of the subject light of a first wavelength;

(b) detecting part of said light that has passed primarily through microcirculatory tissue of the lungs and generating a signal which is a function of intensity of the detected light; and

(c) processing said signal to derive a PPG curve for pulmonary microcirculatory arteries.

2. The method of claim 1, wherein said directing and said detecting are performed without breaching any layer of tissue.

3. The method of claim 2 wherein said light is in the infrared region.

4. The method of claim 1, wherein said directing of said light and said detecting part of said light are performed using a light delivering element and a light receiving element positioned in adjacent relation to the pulmonary pleura.

5. The method of claim 1, wherein said directing and said detecting are performed using a light source and a detector deployed so as to detect light that has passed primarily through microcirculatory tissue of the lungs primarily avoiding major blood vessels in the thorax.

6. The method of claim 1, further comprising directing into the tissue of the lungs infrared light of a second wavelength different from said first wavelength, and wherein said processing is performed so as to derive a PPG curve for pulmonary microcirculatory arteries for each of said first and second wavelengths.

7. The method of claim 6, wherein said directing and said detecting are performed without breaching any layer of tissue, using light sources and a detector deployed so as to detect light that has passed primarily through microcirculatory tissue of the lungs primarily avoiding major blood vessels.

8. The method of claim 6, wherein intensities of the light at said first and second wavelengths are modulated at two different frequencies.

9. The method of claim 6, wherein delivery of light at said first and second wavelengths is time-multiplexed.

10. The method of claim 6, further comprising deriving from said PPG curves a ratio R between values of a parameter related to relative changes in light transmission for said first and second wavelengths, and determining from said ratio R the oxygen saturation in the blood of the pulmonary microcirculatory arteries.

11. The method of claim 10, wherein oxygen saturation SvO₂ in the blood of the pulmonary microcirculatory arteries is determined from R based on a relationship derived experimentally from invasive measurements of oxygen saturation in the pulmonary artery and R from PPG curves of the pulmonary microcirculatory arteries using said first and second wavelengths.

12. The method of claim 11, wherein said relationship is expressed by the formula:

13. The method of claim 10, wherein said light of said first wavelength is the peak of an emission spectrum of a first infrared light source and said infrared light of said second wavelength is a peak of an emission spectrum of a second infrared light source, wherein oxygen saturation SvO₂ in the blood of the pulmonary microcirculatory arteries is determined from R based on a relationship including the mean value of the extinction coefficient for each of the two emission spectra of the two light sources, for oxygenated blood ε

_o and for deoxygenated blood ε

_d.

14. The method of claim 13, wherein the relationship between oxygen saturation in the blood of the pulmonary microcirculatory arteries SvO₂ and said ratio R which includes the mean value of the extinction coefficient for each of the two wavelength spectra for oxygenated blood ε

_o and for deoxygenated blood ε

_d, is

15. The method of claim 13, wherein the relationship between oxygen saturation in the blood of the pulmonary microcirculatory arteries SvO₂ and said ratio R also includes the mean optical path-lengths l₁ and l₂ for each of the two wavelengths.

16. The method of claim 15, wherein the relationship between oxygen saturation in the blood of the pulmonary microcirculatory arteries SvO₂ and said ratio R which includes the mean value of the extinction coefficient for each of the two wavelength spectra for oxygenated blood ε

_o and for deoxygenated blood ε

_d and the mean optical path-lengths l₁ and l₂ for each of the two wavelengths, is

17. The method of claim 10, wherein said parameter related to the relative change in light transmission is selected from the group comprising:

(a) (I_D−

I_S)/I_S, where I_D is the maximal light transmission and I_S is the minimal light transmission;

(b) [I(t₁)−

I(t₂)]/I(t₂), where I(t₁) and I(t₂) are light transmission values at two time points, t₁ and t₂, along the rise-time of the PPG pulse;

(c) ln(I_D/I_S);

(d) ln[I(t₁)/I(t₂)], where t₁ and t₂ are two time points along the rise-time of the PPG pulse;

(e) (dI(t)/dt)/I(t) at some point along the rise-time of the PPG pulse; and

(f) mean of the values of (dI(t)/dt)/I(t) at some points along the rise-time of the PPG pulse.

18. The method of claim 1, wherein said light is directed into the tissue of the lungs by a light source in contact with a first location on the thoracic wall of the subject, and said detecting is performed by a detector in contact with a second location on the thoracic wall of the subject.

19. The method of claim 6, wherein said light for each of said first and second wavelengths is directed into the tissue of the lungs by light sources in contact with a first location on the thoracic wall of the subject, and said detecting is performed by a detector in contact with a second location on the thoracic wall of the subject.

20. The method of claim 19, wherein said second location is at least 15 millimeters from said first location.

21. The method of claim 6, wherein said light for each of said first and second wavelengths is directed into the tissue of the lungs by light sources in contact with a first location on the inner surface of the esophagus of the subject, and said detecting is performed by a detector in contact with a second location on the inner surface of the esophagus of the subject.

22. The method of claim 21, wherein said second location is at least 10 millimeters from said first location.

23. The method of claim 6, wherein said light is directed into the tissue of the lungs by at least one light source in contact with the thoracic wall of the subject, and said detecting is performed by a detector in contact with the inner surface of the esophagus of the subject.

24. The method of claim 6, wherein said directing of said light of said first and second wavelengths and said detecting part of said light are performed using a light delivering element and a light receiving element positioned in adjacent relation to the pulmonary pleura.

25. The method of claim 6, wherein said light for each of said first and second wavelengths is directed into the tissue of the lungs by light sources in contact with a first location on an anatomical wall and wherein said detecting is performed by a detector in contact with a second location on the anatomical wall, said first and second locations being spaced apart by a first spacing, the method further comprising:

(a) sampling additional measurements using one of;

(i) a second detector in contact with a third location on the anatomical wall spaced from said first location by a distance less than said first spacing, and

(ii) a second light source in contact with a third location on the anatomical wall spaced from said second location by a distance less than said first spacing, and

(b) employing said additional measurements to assess a contribution to said PPG curve due to the blood in the tissue of said anatomical wall.

26. The method of claim 6, where the signal-to-noise ratio of the shape of the pulmonary PPG curve is increased by adding together several pulmonary PPG curves, where the time-segments of these pulmonary PPG curves are determined by corresponding PPG signals curves from the systemic circulation, obtained simultaneously with the PPG curves of the pulmonary microcirculatory arteries.

27. The method of claim 26, where said adding together several pulmonary PPG curves is performed separately for pulmonary PPG curves sampled during different phases of the respiration.

28. The method of claim 27, where the different phases of the respiration include one of the group:

end inspiration, end expiration, end inspiration and end expiration.

29. The method of claim 1, where the PPG curve for pulmonary microcirculatory arteries is obtained during a specific phase of the respiration.

30. The method of claim 29, where the specific phase of the respiration includes one of the group:

end inspiration, end expiration, end inspiration and end expiration.

31. A device for determining oxygen saturation SvO₂ in the blood of the pulmonary microcirculatory arteries of a subject, the device comprising the components:

(a) a first light source of a first wavelength in the infrared;

(b) a second light source of a second wavelength in the infrared, different from said first wavelength;

(c) a light delivering element configured to direct the light of the two wavelengths into the same tissue of the lungs;

(d) a detector configured to detect part of the light for each of said first and second wavelengths that has passed through microcirculatory tissue of the lungs and to generate two signals which are functions of intensities of the detected light for each of said first and second wavelengths; and

(e) a processing system configured to process said signals to derive PPG curves for pulmonary microcirculatory arteries and to process said PPG curves for deriving a ratio R between values of a parameter related to relative changes in light transmission for said first and second wavelengths, and determining from said ratio R the oxygen saturation in the blood of the pulmonary microcirculatory arteries;

wherein said first and second light source are in contact with a first location on the thoracic wall of the subject, and said detector is in contact with a second location on the thoracic wall of the subject wherein said second location is at least 15 millimeters from said first location.

32. The device of claim 31, wherein said light of said first wavelength is the peak of an emission spectrum of a first infrared light source and said infrared light of said second wavelength is a peak of an emission spectrum of a second infrared light source, and wherein said processing system determines said oxygen saturation SvO₂ in the blood of the pulmonary microcirculatory arteries from R based on a relationship including the mean value of the extinction coefficient for each of the two emission spectra of the two light sources, for oxygenated blood ε

_o and for deoxygenated blood ε

_d.

33. The device of claim 32, wherein the relationship between oxygen saturation in the blood of the pulmonary microcirculatory arteries SvO₂ and said ratio R which includes the mean value of the extinction coefficient for each of the two wavelength spectra for oxygenated blood ε

_o and for deoxygenated blood ε

_d, is