VENOUS OXYGEN SATURATION SYSTEMS AND METHODS

• US 20130066173A1
• Filed: 09/09/2011
• Published: 03/14/2013
• Est. Priority Date: 09/09/2011
• Status: Abandoned Application

• Current Assignee: Nellcor Puritan Bennett Ireland
• Original Assignee: Nellcor Puritan Bennett Ireland
• Inventors: Addison, Paul, Watson, James, Mannheimer, Paul
• Application Number:
  US13/229,490
• Publication Number:
  US 20130066173A1
• Time in Patent Office: Days
• US Class Current: 600/323
• 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 5/0816 Measuring devices for examining respiratory frequency measuring frequency of electric signals G01R23/00
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives

Abstract

Methods and systems are discussed for determining venous oxygen saturation by calculating a ratio of ratios from respiration-induced baseline modulations. A calculated venous ratio of ratios may be compared with a look-up table value to estimate venous oxygen saturation. A calculated venous ratio of ratios is compared with an arterial ratio of ratios to determine whether baseline modulations are the result of a subject'"'"'s respiration or movement. Such a determination is also made by deriving a venous ratio of ratios using a transform technique, such as a continuous wavelet transform. Derived venous and arterial saturation values are used to non-invasively determine a cardiac output of the subject.

Claims

1. A non-invasive method for determining physiological information about a subject, the method comprising:

obtaining a first non-invasive physiological signal that includes a component indicative of arterial blood in the subject;

obtaining a second non-invasive physiological signal that includes a component indicative of venous blood in the subject;

determining an arterial blood oxygen content based at least in part on a first set of components derived from the first physiological signal;

determining a venous blood oxygen content based at least in part on a second set of components derived from the second physiological signal; and

determining a cardiac output based at least in part on the arterial blood oxygen content and the venous blood oxygen content.

2. The method of claim 1, further comprising:

measuring a respiration rate, and

filtering the second physiological signal at or around the respiration rate.

3. The method of claim 2, wherein the first physiological signal and second physiological signal are photoplethysmograph signals.

4. The method of claim 3, further comprising measuring an oxygen consumption rate of the subject.

5. The method of claim 4, wherein determining the cardiac output comprises:

determining a concentration of oxygen consumption by subtracting the venous blood oxygen content from the arterial blood oxygen content; and

determining cardiac output by dividing the oxygen consumption rate by the concentration of oxygen consumption.

6. The method of claim 2, wherein the first set of components includes a factor indicative of blood oxygen concentration and a ratio of ratios derived from components of the first physiological signal.

7. The method of claim 2, wherein the second set of components includes a factor indicative of blood oxygen concentration and a ratio of ratios derived from components of the second physiological signal.

8. The method of claim 2, further comprising correcting the cardiac output to account for dissolved gases in blood by:

adding a term indicative of partial pressure of a first gas in arterial blood; and

subtracting a term indicative of partial pressure of a second gas in venous blood.

9. A system for determining physiological information about a subject, the system comprising:

a first input configured to receive a first non-invasive physiological signal that includes a component indicative of arterial blood;

a second input configured to receive a second non-invasive physiological signal that includes a component indicative of venous blood; and

processing equipment configured to;

determine an arterial blood oxygen content based at least in part on a first set of components derived from the first physiological signal;

determine a venous blood oxygen content based at least in part on a second set of components derived from the second physiological signal; and

determine a cardiac output based at least in part on the arterial blood oxygen content and the venous blood oxygen content.

10. The system of claim 9, the system further comprising:

a third input configured to receive a measured respiration rate; and

wherein the processing circuitry is further configured to filter the second physiological signal at or around the respiration rate.

11. The system of claim 10, wherein the first physiological signal and the second physiological signal are photoplethysmograph signals.

12. The system of claim 10, further comprising an input configured to receive a signal that measures an oxygen consumption rate of the subject.

13. The method of claim 12, wherein the processing equipment is further configured to:

determine a concentration of oxygen consumption by subtracting the venous blood oxygen content from the arterial blood oxygen content; and

determine cardiac output as a flow rate by dividing the oxygen consumption rate by the concentration of oxygen consumption.

14. The system of claim 10, wherein the first set of components includes at least a factor indicative of blood oxygen concentration and a ratio of ratios derived from components of the first physiological signal.

15. The system of claim 10, wherein the second set of components includes at least a factor indicative of blood oxygen concentration and a ratio of ratios derived from components of the second physiological signal.

16. The system of claim 10, wherein the processing equipment is further configured to correct the cardiac output to account for dissolved gases in blood by adding a term indicative of partial pressure of a first gas in arterial blood;

and subtracting a term indicative of partial pressure of a second gas in venous blood.

17. A computer readable medium having stored instructions that when executed directs:

a first input port to receive a first non-invasive physiological signal that includes a component indicative of arterial blood;

a second input port to receive a second non-invasive physiological signal that includes a component indicative of venous blood return; and

processing equipment to;

determine an arterial blood oxygen content based at least in part on a first set of components derived from the first physiological signal;

determine a venous blood oxygen content based at least in part on a second set of components derived from the second physiological signal; and

determine a cardiac output based at least in part on the oxygen consumption rate, the arterial blood oxygen content and the venous blood oxygen content.

18. The computer readable medium of claim 17, that when executed further directs:

a third input port to receive a signal that measures a respiration rate;

wherein determining the venous blood oxygen content comprises filtering the second physiological signal around the respiration rate.

19. The computer readable medium of claim 18 that when executed further directs:

a fourth input port to receive a signal that measures an oxygen consumption rate of the subject.

20. The computer readable medium of claim 18 that when executed further directs:

processing equipment to;

determine a concentration of oxygen consumption by subtracting the venous blood oxygen content from the arterial blood oxygen content; and

determine cardiac output as a flow rate by dividing the oxygen consumption rate by the concentration of oxygen consumption.