Method and apparatus for optical detection of mixed venous and arterial blood pulsation in tissue

1. A method of detecting the presence of mixed venous and arterial blood pulsation in tissue, comprising:

receiving first and second electromagnetic radiation signals from a blood perfused tissue portion corresponding to infrared and red wavelengths of light;

obtaining a measure of a persistent phase difference between the first and second electromagnetic radiation signals;

comparing the measure with a threshold;

detecting the presence or absence of venous pulsation using the comparison; and

indicating the presence of venous pulsation to a caregiver if venous pulsation is present.

2. The method of claim 1 , comprising filtering the first and second electromagnetic radiation signals before the obtaining the measure, to pass portions of the first and second electromagnetic radiation signals having frequencies at or near the pulse rate or harmonics of the pulse rate of the blood perfused tissue.

3. The method of claim 1 , wherein the obtaining the measure of the phase difference comprises integrating the measure of the phase difference over a time period.

4. The method of claim 1 , wherein the obtaining the measure of the phase difference comprises obtaining a measure of the openness of an ellipse on a Lissajous plot formed by comparing the first electromagnetic radiation signal against the second electromagnetic radiation signal.

5. The method of claim 1 , wherein the obtaining the measure of the phase difference comprises analyzing a cross-correlation function of the first and second electromagnetic radiation signals, as a function of a delay interval between them.

6. The method of claim 1 , wherein the obtaining the measure of the phase difference comprises a frequency domain analysis and subtracting the phases of the first and second electromagnetic radiation signals at a frequency.

7. The method of claim 6 , wherein the subtracting the phases of the first and second electromagnetic radiation signals comprises taking the complex conjugate of the first and second electromagnetic radiation signals, and dividing the complex conjugate by the product of the magnitudes of the first and second electromagnetic radiation signals.

8. The method of claim 1 , wherein the obtaining the measure of the phase difference comprises obtaining the measure of the phase difference at or near a fundamental pulse rate of the blood perfused tissue.

9. The method of claim 1 , wherein the obtaining the measure of the phase difference comprises obtaining the measure of the phase difference at or near a harmonic of a pulse rate of the blood perfused tissue.

10. The method of claim 1 , wherein the obtaining the measure of the phase difference comprises obtaining the measure of the phase difference at or near a fundamental or at or near a harmonic of a pulse rate of the blood perfused tissue.

11. A device for detecting the presence of mixed venous and arterial blood pulsation in tissue, comprising:

means for receiving first and second electromagnetic radiation signals from a blood perfused tissue portion corresponding to infrared and red wavelengths of light;

means for obtaining a measure of a persistent phase difference between the first and second electromagnetic radiation signals;

means for comparing the measure with a threshold value to form a comparison;

means for detecting the presence or absence of venous pulsation using the comparison; and

means for indicating the presence of venous pulsation to a caregiver when venous pulsation is present.

12. The device of claim 11 , comprising a filter configured for filtering the first and second electromagnetic radiation signals before obtaining the measure, to pass portions of the first and second electromagnetic radiation signals having frequencies at or near the pulse rate or harmonics of the pulse rate of the blood perfused tissue.

13. The device of claim 11 , wherein the means for obtaining the measure of the phase difference comprises means for integrating the measure of the phase difference over a time period.

14. The device of claim 11 , wherein the means for obtaining the measure of the phase difference is configured for obtaining a measure of the openness of an ellipse on a Lissajous plot formed by comparing the first electromagnetic radiation signal against the second electromagnetic radiation signal.

15. The device of claim 11 , wherein the means for obtaining the measure of the phase difference is configured for analyzing a cross-correlation function of the first and second electromagnetic radiation signals, as a function of a delay interval between them.

16. The device of claim 11 , wherein the means for obtaining the measure of the phase difference is configured for a frequency domain analysis and for subtracting the phases of the first and second electromagnetic radiation signals at a frequency.

17. The device of claim 16 , wherein the means for subtracting the phases of the first and second electromagnetic radiation signals is configured for taking the complex conjugate of the first and second electromagnetic radiation signals, and dividing the complex conjugate by the product of the magnitudes of the first and second electromagnetic radiation signals.

18. The device of claim 11 , wherein the means for obtaining the measure of the phase difference is configured for obtaining the measure of the phase difference at or near a fundamental or at or near a harmonic of a pulse rate of the blood perfused tissue.